CA2605416A1 - System and method for spectrophotometric measurement of total alkalinity using a liquid core waveguide - Google Patents
System and method for spectrophotometric measurement of total alkalinity using a liquid core waveguide Download PDFInfo
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- CA2605416A1 CA2605416A1 CA002605416A CA2605416A CA2605416A1 CA 2605416 A1 CA2605416 A1 CA 2605416A1 CA 002605416 A CA002605416 A CA 002605416A CA 2605416 A CA2605416 A CA 2605416A CA 2605416 A1 CA2605416 A1 CA 2605416A1
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- 239000007788 liquid Substances 0.000 title claims abstract description 81
- 238000000034 method Methods 0.000 title claims abstract description 35
- 238000002798 spectrophotometry method Methods 0.000 title description 5
- 238000011067 equilibration Methods 0.000 claims abstract description 45
- 238000002835 absorbance Methods 0.000 claims abstract description 30
- 239000012528 membrane Substances 0.000 claims abstract description 12
- 239000004809 Teflon Substances 0.000 claims abstract description 9
- 229920006362 Teflon® Polymers 0.000 claims abstract description 9
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims description 48
- 239000007793 ph indicator Substances 0.000 claims description 27
- XJRPTMORGOIMMI-UHFFFAOYSA-N ethyl 2-amino-4-(trifluoromethyl)-1,3-thiazole-5-carboxylate Chemical group CCOC(=O)C=1SC(N)=NC=1C(F)(F)F XJRPTMORGOIMMI-UHFFFAOYSA-N 0.000 claims description 14
- 238000010494 dissociation reaction Methods 0.000 claims description 13
- 230000005593 dissociations Effects 0.000 claims description 13
- UIIMBOGNXHQVGW-UHFFFAOYSA-M Sodium bicarbonate Chemical compound [Na+].OC([O-])=O UIIMBOGNXHQVGW-UHFFFAOYSA-M 0.000 claims description 10
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 8
- 235000017557 sodium bicarbonate Nutrition 0.000 claims description 5
- 229910000030 sodium bicarbonate Inorganic materials 0.000 claims description 5
- 238000007789 sealing Methods 0.000 claims description 2
- BVKZGUZCCUSVTD-UHFFFAOYSA-N carbonic acid Chemical compound OC(O)=O BVKZGUZCCUSVTD-UHFFFAOYSA-N 0.000 claims 2
- 239000000523 sample Substances 0.000 abstract description 32
- 238000005259 measurement Methods 0.000 abstract description 24
- 238000001139 pH measurement Methods 0.000 abstract description 5
- 239000012488 sample solution Substances 0.000 abstract description 3
- 230000003287 optical effect Effects 0.000 abstract description 2
- 239000007789 gas Substances 0.000 description 37
- 229910002092 carbon dioxide Inorganic materials 0.000 description 28
- 239000013535 sea water Substances 0.000 description 20
- 239000000243 solution Substances 0.000 description 15
- BVKZGUZCCUSVTD-UHFFFAOYSA-M Bicarbonate Chemical compound OC([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-M 0.000 description 6
- 238000004448 titration Methods 0.000 description 5
- 239000002253 acid Substances 0.000 description 4
- 238000010521 absorption reaction Methods 0.000 description 3
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 229910052802 copper Inorganic materials 0.000 description 2
- 239000010949 copper Substances 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 239000013505 freshwater Substances 0.000 description 2
- 238000010249 in-situ analysis Methods 0.000 description 2
- 230000002572 peristaltic effect Effects 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 239000012925 reference material Substances 0.000 description 2
- 238000003221 volumetric titration Methods 0.000 description 2
- 101100243025 Arabidopsis thaliana PCO2 gene Proteins 0.000 description 1
- 238000013494 PH determination Methods 0.000 description 1
- 239000000370 acceptor Substances 0.000 description 1
- 150000007513 acids Chemical class 0.000 description 1
- 230000004071 biological effect Effects 0.000 description 1
- 229910000019 calcium carbonate Inorganic materials 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 230000001351 cycling effect Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000000835 fiber Substances 0.000 description 1
- 239000007792 gaseous phase Substances 0.000 description 1
- 238000011545 laboratory measurement Methods 0.000 description 1
- 239000004973 liquid crystal related substance Substances 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 230000020477 pH reduction Effects 0.000 description 1
- 230000035699 permeability Effects 0.000 description 1
- 239000012071 phase Substances 0.000 description 1
- 238000010926 purge Methods 0.000 description 1
- 238000011002 quantification Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 230000004044 response Effects 0.000 description 1
- 238000005070 sampling Methods 0.000 description 1
- 235000017550 sodium carbonate Nutrition 0.000 description 1
- 229910000029 sodium carbonate Inorganic materials 0.000 description 1
- 159000000000 sodium salts Chemical class 0.000 description 1
- 238000010561 standard procedure Methods 0.000 description 1
- 239000012086 standard solution Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 239000003643 water by type Substances 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
- G01N21/77—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator
- G01N21/78—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator producing a change of colour
- G01N21/80—Indicating pH value
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/01—Arrangements or apparatus for facilitating the optical investigation
- G01N21/03—Cuvette constructions
- G01N21/0303—Optical path conditioning in cuvettes, e.g. windows; adapted optical elements or systems; path modifying or adjustment
Abstract
A system and method for spectrophotometrically measuring the total alkalinity of a liquid sample. In a particular aspect, the method involves equilibration of a CO2 gas with a sample solution across the permeable walls of a Teflon AF
2400 liquid core waveguide. The waveguide acts as both an equilibration membrane and an optical cell in which spectrophotometric pH measurements are obtained via measurements of absorbance ratios.
2400 liquid core waveguide. The waveguide acts as both an equilibration membrane and an optical cell in which spectrophotometric pH measurements are obtained via measurements of absorbance ratios.
Description
System and Method for Spectrophotometric Measurement of Total Alkalinity Using a Liquid Core Waveguide CROSS REFERENCE TO RELATED APLICATIONS
This application claims priority to currently pending U.S. Provisional Patent Application 60/672,474, entitled, "Alkalinity Sensor", filed April 18, 2005 and U.S.
1o Non-Provisional Patent Application 11/279,971 entitled "System and Method for Spectrophotometric Measurement of Total Alkalinity Using a Liquid Core Waveguide", filed April 17, 2006.
BACKGROUND OF INVENTION
Seawater alkalinity (AT), defined as a difference between the excess concentrations of proton acceptors over proton donors in 1 kg of seawater, is one of the important parameters in carbon dioxide systems. Due to its invariance during CO2 gas exchange and biological activity, Ai- is considered to be a cornerstone in analytical assessments of oceanic CO2 cycling. Anomalies of AT normalized to salinity have been contributed to water mass movement and/or dissolution of calcium carbonate.
Conventional systems and method for measuring seawater A-r usually involve acid titration of the bases to carbonic acid end point by either a single step addition or sequential stepwise addition. The multi-step titration method is widely used on shipboard measurements due to its high precision and automated operation. The combined speed and simplicity of single-step titration with spectrophotometric pH
determinations for measurement of end point excess acid has been shown. Such methods have greatly improved the precision of alkalinity measurements.
However, these end point detections require accurate knowledge of end point pH without the influence of CO2 generated in titration steps and thus usually involve a purge step.
Such step makes the automation of an online instrument difficult. The multipoint volumetric titration remains the standard procedure for discrete sampling.
Accordingly, what is needed in the art is an improved system and method for measuring the total alkalinity of a sample liquid which overcomes the limitations of the prior art systems.
SUMMARY OF INVENTION
In accordance with the present invention, a method for measuring the total alkalinity 1o of a sample liquid using a liquid core waveguide having a gas permeable membrane and an equilibration cell is provided. In accordance with the method of the present invention, the liquid core waveguide is positioned in an interior cavity of an equilibration chamber. A flow of gas is then introduced into the interior cavity of the equilibration chamber. The sample liquid is treated with a pH indicator and introduced into the interior of the liquid core waveguide. The interior of the liquid core waveguide is then sealed and the gas is allowed to equilibrate across the gas permeable membrane of the liquid core waveguide. After equilibration is obtained, the absorbance ratio of the sample liquid is measured at a plurality of wavelengths using the liquid core waveguide. The total alkalinity (AT)of the sample liquid is then calculated from the measured absorbance ratios, according to the equation:
log(AT + [H+~~ =1og(Kl (K0 )i (pCO2 )/ K1 )+ E + log((R(25)- e1 )/(e2 -R(25)e3 )) where;
[H+] 10-"H , Ko is the Henry's law constant, K; is the dissociation constant of carbonic acid, the subscripti refers to the sample liquid within the waveguide, E is an empirical derived constant, K, is an indicator dye dissociation constant, R(25)is a ratio of the pH indicator absorbance at 589 and 432 nm, and e, and e2and e3are molar absorptivity ratios appropriate to the pH indicator.
In one embodiment, the pH indicator is a sulfonephthalein pH indicator, such as bromocresol purple.
Additionally, the method of the present invention may include passing the flow of gas though a thermostated water bath prior to introducing the flow of gas into the interior cavity of the equilibration chamber. The equilibration chamber may further be housed in a thermostated water bath.
To establish a reference point for the absorbance ratio measurements, the absorbance ratio of the liquid sample without the pH indicator is measured.
The gas is introduced at a controlled rate into the interior of the equilibration 1o chamber. The gas may be any of a variety of gases, but more specifically the gas is C02 or NaHCO3. In a specific embodiment, the gas is 30% CO2.
Liquid core waveguides (LCW) constrain light propagation within a liquid medium when the liquid has a higher index of refraction (RI) than the surrounding tubing of the LCW. In a particular embodiment of the invention, the liquid core waveguide is a Teflon AF 2400 liquid core waveguide.
According to the present invention, a system for measuring the total alkalinity of a sample liquid is provided. In one embodiment, the system includes an equilibration chamber having an interior cavity and a liquid core waveguide having a gas permeable membrane. A gas supply is provided to supply gas to the interior cavity of the equilibration chamber.and a sample liquid supply is provided to supply a sample liquid including a pH indicator into the interior of the liquid core waveguide.
The liquid core waveguide is positioned within the interior cavity of the equilibration chamber and the liquid core waveguide is used to measure the absorbance ratio of the sample liquid at a plurality of wavelengths. Means are also provided for calculating the total alkalinity(A,.) of the sample liquid from the measured absorbance ratios according to the equation:
log(Ar + [H+]) =1og(K; (Ko )t (pCO, )/ K1 )+ E + log((R(25)- e, )/(e, -R(25)e3 )) where;
[H} ]=10-PH , Ko is the Henry's law constant, K; is the dissociation constant of carbonic acid, the subscripti refers to the sample liquid within the waveguide, E is 3o an empirical derived constant, K, is an indicator dye dissociation constant, R(25) is a ratio of the pH indicator absorbance at 589 and 432 nm, and e, and ez and e3 are molar absorptivity ratios appropriate to the pH indicator.
Accordingly, the present invention provides a novel AT methodology involving spectrophotometric pH measurements with Liquid Core Waveguide techniques.
Liquid core waveguides (LCW) constrain light propagation within a liquid medium when the liquid has a higher index of refraction (RI) than the surrounding tubing of the LCW. The procedure of the present invention obviates the use of strong acids in 1o volumetric titration, provides rapid sample throughput using very small samples, and achieves measurement precisions comparable to multipoint titrations.
Additionally, the method is amenable to autonomous operation and in-situ analysis of the surface ocean.
BRIEF DESCRIPTION OF THE DRAWINGS
For a fuller understanding of the invention, reference should be made to the following detailed description, taken in connection with the accompanying drawings, in which:
FIG. 1 is flow diagram illustrating a method in accordance with an embodiment of the invention;
2o FIG. 2 is an illustration of an embodiment of the system configuration used for spectrophotometric measurements of total alkalinity in accordance with the present invention;
FIG. 3 is an illustration of an AT measurement obtained using a 0.8mm OD/ 0.76 mm ID LCW in accordance with an embodiment of the invention;
FIG. 4 illustrates the absorbance ratio measurements in accordance with an embodiment of the invention;
FIG. 5 includes a table which illustrates the constant E in Eq.14 as measured with certified reference material (CRM) provided by Dr. Andrew Dickson with known AT.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
3o Fig. 1 is a flow diagram illustrating a method for measuring total alkalinity in accordance with the present invention. In accordance with the present invention, a method for measuring the total alkalinity of a sample liquid using a liquid core waveguide having a gas permeable membrane and an equilibration chamber is provided. The liquid core waveguide is positioned within the interior cavity of the equilibration chamber 10. A flow of gas is introduced into the interior cavity of the equilibration chamber 15, such that the gas surrounds the liquid core waveguide positioned within the chamber. The sample liquid is treated with a pH
indicator and then introduced into the interior of the liquid core waveguide 20. The interior of the liquid core waveguide is then sealed and the gas is allowed to equilibrate across the gas permeable membrane of the liquid core waveguide 25. After equilibration is obtained, the absorbance ratio of the sample liquid is measured at a plurality of wavelengths using the liquid core waveguide 30. The total alkalinity (A,)of the sample liquid is then calculated from the measured absorbance ratios 35, according to the equation:
1og(AT+ [H+])=1og(K1(Ko VpCO2)I Kj+ E + 1og((R(25)- el MeZ - R(25)e3 )) where;
[H+] =1O-pH , Ko is the Henry's law constant, Ki is the dissociation constant of carbonic acid, the subscripti refers to the sample liquid within the waveguide, E is an empirical derived constant, K, is an indicator dye dissociation constant, R(25) is a ratio of the pH indicator absorbance at 589 and 432 nm, and el and e2 and e3 are molar absorptivity ratios appropriate to the pH indicator.
In accordance with one embodiment of the present invention, pH measurements within a Teflon AF 2400 liquid core waveguide are used for robust measurements of total alkalinity (AT). Teflon AF 2400 liquid core waveguides are well suited to CO2 system measurements due to high gas permeability coefficients of Teflon AF
2400, and the simplicity of measurements in which Teflon AF 2400 serves as both the optical cell and CO2 equilibration membrane.
Fig. 2 an embodiment of the system 50 used for spectrophotometric measurements of total alkalinity in accordance with the present invention. The solution within the liquid crystal waveguide 40 contains a sulfonephthalein pH indicator and seawater as the sample to be measured. In one embodiment, the pH indicator is about 2 pM.
In a specific embodiment, the outer solution within the cavity of the equilibrate chamber 45 and surrounding the waveguide 40 is a C02 gas mixture (30% C02).
Upon equilibration, the pH of the inner sample solution becomes constant.
Since the fugacity of the CO2 (fCO2) of the inner and outer solutions are identical at equilibrium, the total alkalinity of samples inside of the LCW can then be calculated from known thermodynamic relationships.
The alkalinity of seawater is defined as:
AT = 2[C032 ]T+[HC03 ] T +[B(OH) 4 ] T +[OH ]+ [HP042 ]+2[PO43 ] -[H+]... (1) In one embodiment utilizing 30% of C02 as equilibration gas, the pH upon equilibration is below 5.7 over a wide range of AT normally encountered in natural waters. Under this condition, all other species X(=[C032 ] T, [B(OH) 4] T, ...) are converted to protonated species and equal amount of HC03 is formed according to this reaction:
C02* +H20 +X- = HC03 + HX (2) The only important species is [HCO3 ]T and [H+] between pH 5 to 6.
The dissociation constant of carbonic acid is expressed in terms of the concentrations ([ ]) of H+, HC03 and CO2* as K, = [H+][ HC03 ] T /[ COz ] (3) where [ COz ] is the sum solution concentration of COZ and H2CO3 ([ CO; ]=C02]
+
[H2C03]). [COz] can also be expressed in terms of the Henry's law constant (Ko) and the fugacity of C02 (i.e. fCO2) in solution:
[ COz ] =Ko fC02. (4) Combining Eqs. (1) and (2), the [HCO3 ] of the solution inside a liquid core waveguide is given as, [ HCO3 ]j= K; (Ko)j(fCO2)j/[H+]i (5) where the subscript "i" refers to the solution inside the LCW.
As such, for an equilibrated sample (pH <5.5 for AT is about 2000 pmol/kg and 30%
CO2 as equilibrating gas), Eq. (4) could be simplified to:
AT = [ HCO3 ] - [H+] (6) Thus the seawater alkalinity can be conveniently obtained by measurement of solution pH after equilibrated with pCO2 by:
log(AT+[H+]eq) =1og[ HCO3 ] = log( K', (Ko)#C02)) +pH (7) The pH of the LCW's internal solution is measured with a sulfonephthalein indicator.
In one embodiment, the sulfonephthalein indicator used for AT measurements is bromocresol purple (BCP). This indicator has been used for laboratory measurements of seawater alkalinity with a precision better than 1 mol kg-1. The absorbance characteristics and dissociation behavior of BCP has been measured in both freshwater and seawater media. With an indicator pKi near 5.8 in seawater media, BCP is ideally suited for pH measurements between 5 and 6.
It is known that solution pH can be calculated from absorbance ratios (R =,zZ
A/,z,A ) with the following equation:
pH = pKi + log((R-el)/(e2-Re3)) (8) where Ki is the indicator dissociation constant (Ki =[H+][12 ]/[HI-]) and pK, =-IogKi.
Absorption maxima of HI- and 12- for bromocresol purple (BCP) are ki = 432 nm and k2 = 589 nm. The symbols el, e2 and e3 in Eq. (6) refer to indicator molar absorbance ratios at wavelengths k, and k2 e1 = 589EH1 / 432EH1, e2 = 589E1 / 432EH1, e3 = 432G 1 / 432EH1 (9) where xe-i is the molar absorption coefficient of 12- at wavelength 2~ and a,EHi is the molar absorption coefficient of HI- at wavelength k. Using BCP, the solution pH is given as:
P HT =5.8182 + 0.00129+ log((R(25)-0.00381)/(2.8729-0.05104R(25)) (10) and R(25) =R(t)(1+0.01869(25-t)) (11) 1o The fugacity is related to partial pressure of CO2 gas by:
fC02 =c' pCO2. (12) Combined equation, log(AT+[H+]eq) =log[ HCO3 ]= log( K' (Ko)i(PCO2)/Ki) + E+
log((R(25)-ej)/(e2-R(25)e3)) (13) where E is conceptually related to activity coefficient of CO2 gas and can be treated as an empirical constant which depends on flow rate and the pressure of the gas; Ko is calculated from the known dependence of Henry's law (gas solubility) constants on temperature and ionic strength. CO2 solubility constants in freshwater and seawater can be expressed as:
In Ko = 93.4517 (100/T) - 60.2409 + 23.3585 In(T/100) +
S (0.023517 - 0.023655 (T/100) + 0.0047036 (T/100)2) (14) K, is calculated from the known dependence on temperature and ionic strength based on Roy et al's quantification.
In(Kj)=-2307.1266/T +2.83655-1.5529413InT +(-4.0484/T-0.20760841)S1/2 +0.08468345S -0.00654208S3/2 + In(1-0.001005S) (15) In an exemplary embodiment of the invention, bromocresol purple (BCP) sodium salt was obtained from Eastman Kodak Company. Ultrapure grade Na2CO3 (J.T.
Baker) was dried in an 110 C oven overnight and kept in a desiccator before use.
This application claims priority to currently pending U.S. Provisional Patent Application 60/672,474, entitled, "Alkalinity Sensor", filed April 18, 2005 and U.S.
1o Non-Provisional Patent Application 11/279,971 entitled "System and Method for Spectrophotometric Measurement of Total Alkalinity Using a Liquid Core Waveguide", filed April 17, 2006.
BACKGROUND OF INVENTION
Seawater alkalinity (AT), defined as a difference between the excess concentrations of proton acceptors over proton donors in 1 kg of seawater, is one of the important parameters in carbon dioxide systems. Due to its invariance during CO2 gas exchange and biological activity, Ai- is considered to be a cornerstone in analytical assessments of oceanic CO2 cycling. Anomalies of AT normalized to salinity have been contributed to water mass movement and/or dissolution of calcium carbonate.
Conventional systems and method for measuring seawater A-r usually involve acid titration of the bases to carbonic acid end point by either a single step addition or sequential stepwise addition. The multi-step titration method is widely used on shipboard measurements due to its high precision and automated operation. The combined speed and simplicity of single-step titration with spectrophotometric pH
determinations for measurement of end point excess acid has been shown. Such methods have greatly improved the precision of alkalinity measurements.
However, these end point detections require accurate knowledge of end point pH without the influence of CO2 generated in titration steps and thus usually involve a purge step.
Such step makes the automation of an online instrument difficult. The multipoint volumetric titration remains the standard procedure for discrete sampling.
Accordingly, what is needed in the art is an improved system and method for measuring the total alkalinity of a sample liquid which overcomes the limitations of the prior art systems.
SUMMARY OF INVENTION
In accordance with the present invention, a method for measuring the total alkalinity 1o of a sample liquid using a liquid core waveguide having a gas permeable membrane and an equilibration cell is provided. In accordance with the method of the present invention, the liquid core waveguide is positioned in an interior cavity of an equilibration chamber. A flow of gas is then introduced into the interior cavity of the equilibration chamber. The sample liquid is treated with a pH indicator and introduced into the interior of the liquid core waveguide. The interior of the liquid core waveguide is then sealed and the gas is allowed to equilibrate across the gas permeable membrane of the liquid core waveguide. After equilibration is obtained, the absorbance ratio of the sample liquid is measured at a plurality of wavelengths using the liquid core waveguide. The total alkalinity (AT)of the sample liquid is then calculated from the measured absorbance ratios, according to the equation:
log(AT + [H+~~ =1og(Kl (K0 )i (pCO2 )/ K1 )+ E + log((R(25)- e1 )/(e2 -R(25)e3 )) where;
[H+] 10-"H , Ko is the Henry's law constant, K; is the dissociation constant of carbonic acid, the subscripti refers to the sample liquid within the waveguide, E is an empirical derived constant, K, is an indicator dye dissociation constant, R(25)is a ratio of the pH indicator absorbance at 589 and 432 nm, and e, and e2and e3are molar absorptivity ratios appropriate to the pH indicator.
In one embodiment, the pH indicator is a sulfonephthalein pH indicator, such as bromocresol purple.
Additionally, the method of the present invention may include passing the flow of gas though a thermostated water bath prior to introducing the flow of gas into the interior cavity of the equilibration chamber. The equilibration chamber may further be housed in a thermostated water bath.
To establish a reference point for the absorbance ratio measurements, the absorbance ratio of the liquid sample without the pH indicator is measured.
The gas is introduced at a controlled rate into the interior of the equilibration 1o chamber. The gas may be any of a variety of gases, but more specifically the gas is C02 or NaHCO3. In a specific embodiment, the gas is 30% CO2.
Liquid core waveguides (LCW) constrain light propagation within a liquid medium when the liquid has a higher index of refraction (RI) than the surrounding tubing of the LCW. In a particular embodiment of the invention, the liquid core waveguide is a Teflon AF 2400 liquid core waveguide.
According to the present invention, a system for measuring the total alkalinity of a sample liquid is provided. In one embodiment, the system includes an equilibration chamber having an interior cavity and a liquid core waveguide having a gas permeable membrane. A gas supply is provided to supply gas to the interior cavity of the equilibration chamber.and a sample liquid supply is provided to supply a sample liquid including a pH indicator into the interior of the liquid core waveguide.
The liquid core waveguide is positioned within the interior cavity of the equilibration chamber and the liquid core waveguide is used to measure the absorbance ratio of the sample liquid at a plurality of wavelengths. Means are also provided for calculating the total alkalinity(A,.) of the sample liquid from the measured absorbance ratios according to the equation:
log(Ar + [H+]) =1og(K; (Ko )t (pCO, )/ K1 )+ E + log((R(25)- e, )/(e, -R(25)e3 )) where;
[H} ]=10-PH , Ko is the Henry's law constant, K; is the dissociation constant of carbonic acid, the subscripti refers to the sample liquid within the waveguide, E is 3o an empirical derived constant, K, is an indicator dye dissociation constant, R(25) is a ratio of the pH indicator absorbance at 589 and 432 nm, and e, and ez and e3 are molar absorptivity ratios appropriate to the pH indicator.
Accordingly, the present invention provides a novel AT methodology involving spectrophotometric pH measurements with Liquid Core Waveguide techniques.
Liquid core waveguides (LCW) constrain light propagation within a liquid medium when the liquid has a higher index of refraction (RI) than the surrounding tubing of the LCW. The procedure of the present invention obviates the use of strong acids in 1o volumetric titration, provides rapid sample throughput using very small samples, and achieves measurement precisions comparable to multipoint titrations.
Additionally, the method is amenable to autonomous operation and in-situ analysis of the surface ocean.
BRIEF DESCRIPTION OF THE DRAWINGS
For a fuller understanding of the invention, reference should be made to the following detailed description, taken in connection with the accompanying drawings, in which:
FIG. 1 is flow diagram illustrating a method in accordance with an embodiment of the invention;
2o FIG. 2 is an illustration of an embodiment of the system configuration used for spectrophotometric measurements of total alkalinity in accordance with the present invention;
FIG. 3 is an illustration of an AT measurement obtained using a 0.8mm OD/ 0.76 mm ID LCW in accordance with an embodiment of the invention;
FIG. 4 illustrates the absorbance ratio measurements in accordance with an embodiment of the invention;
FIG. 5 includes a table which illustrates the constant E in Eq.14 as measured with certified reference material (CRM) provided by Dr. Andrew Dickson with known AT.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
3o Fig. 1 is a flow diagram illustrating a method for measuring total alkalinity in accordance with the present invention. In accordance with the present invention, a method for measuring the total alkalinity of a sample liquid using a liquid core waveguide having a gas permeable membrane and an equilibration chamber is provided. The liquid core waveguide is positioned within the interior cavity of the equilibration chamber 10. A flow of gas is introduced into the interior cavity of the equilibration chamber 15, such that the gas surrounds the liquid core waveguide positioned within the chamber. The sample liquid is treated with a pH
indicator and then introduced into the interior of the liquid core waveguide 20. The interior of the liquid core waveguide is then sealed and the gas is allowed to equilibrate across the gas permeable membrane of the liquid core waveguide 25. After equilibration is obtained, the absorbance ratio of the sample liquid is measured at a plurality of wavelengths using the liquid core waveguide 30. The total alkalinity (A,)of the sample liquid is then calculated from the measured absorbance ratios 35, according to the equation:
1og(AT+ [H+])=1og(K1(Ko VpCO2)I Kj+ E + 1og((R(25)- el MeZ - R(25)e3 )) where;
[H+] =1O-pH , Ko is the Henry's law constant, Ki is the dissociation constant of carbonic acid, the subscripti refers to the sample liquid within the waveguide, E is an empirical derived constant, K, is an indicator dye dissociation constant, R(25) is a ratio of the pH indicator absorbance at 589 and 432 nm, and el and e2 and e3 are molar absorptivity ratios appropriate to the pH indicator.
In accordance with one embodiment of the present invention, pH measurements within a Teflon AF 2400 liquid core waveguide are used for robust measurements of total alkalinity (AT). Teflon AF 2400 liquid core waveguides are well suited to CO2 system measurements due to high gas permeability coefficients of Teflon AF
2400, and the simplicity of measurements in which Teflon AF 2400 serves as both the optical cell and CO2 equilibration membrane.
Fig. 2 an embodiment of the system 50 used for spectrophotometric measurements of total alkalinity in accordance with the present invention. The solution within the liquid crystal waveguide 40 contains a sulfonephthalein pH indicator and seawater as the sample to be measured. In one embodiment, the pH indicator is about 2 pM.
In a specific embodiment, the outer solution within the cavity of the equilibrate chamber 45 and surrounding the waveguide 40 is a C02 gas mixture (30% C02).
Upon equilibration, the pH of the inner sample solution becomes constant.
Since the fugacity of the CO2 (fCO2) of the inner and outer solutions are identical at equilibrium, the total alkalinity of samples inside of the LCW can then be calculated from known thermodynamic relationships.
The alkalinity of seawater is defined as:
AT = 2[C032 ]T+[HC03 ] T +[B(OH) 4 ] T +[OH ]+ [HP042 ]+2[PO43 ] -[H+]... (1) In one embodiment utilizing 30% of C02 as equilibration gas, the pH upon equilibration is below 5.7 over a wide range of AT normally encountered in natural waters. Under this condition, all other species X(=[C032 ] T, [B(OH) 4] T, ...) are converted to protonated species and equal amount of HC03 is formed according to this reaction:
C02* +H20 +X- = HC03 + HX (2) The only important species is [HCO3 ]T and [H+] between pH 5 to 6.
The dissociation constant of carbonic acid is expressed in terms of the concentrations ([ ]) of H+, HC03 and CO2* as K, = [H+][ HC03 ] T /[ COz ] (3) where [ COz ] is the sum solution concentration of COZ and H2CO3 ([ CO; ]=C02]
+
[H2C03]). [COz] can also be expressed in terms of the Henry's law constant (Ko) and the fugacity of C02 (i.e. fCO2) in solution:
[ COz ] =Ko fC02. (4) Combining Eqs. (1) and (2), the [HCO3 ] of the solution inside a liquid core waveguide is given as, [ HCO3 ]j= K; (Ko)j(fCO2)j/[H+]i (5) where the subscript "i" refers to the solution inside the LCW.
As such, for an equilibrated sample (pH <5.5 for AT is about 2000 pmol/kg and 30%
CO2 as equilibrating gas), Eq. (4) could be simplified to:
AT = [ HCO3 ] - [H+] (6) Thus the seawater alkalinity can be conveniently obtained by measurement of solution pH after equilibrated with pCO2 by:
log(AT+[H+]eq) =1og[ HCO3 ] = log( K', (Ko)#C02)) +pH (7) The pH of the LCW's internal solution is measured with a sulfonephthalein indicator.
In one embodiment, the sulfonephthalein indicator used for AT measurements is bromocresol purple (BCP). This indicator has been used for laboratory measurements of seawater alkalinity with a precision better than 1 mol kg-1. The absorbance characteristics and dissociation behavior of BCP has been measured in both freshwater and seawater media. With an indicator pKi near 5.8 in seawater media, BCP is ideally suited for pH measurements between 5 and 6.
It is known that solution pH can be calculated from absorbance ratios (R =,zZ
A/,z,A ) with the following equation:
pH = pKi + log((R-el)/(e2-Re3)) (8) where Ki is the indicator dissociation constant (Ki =[H+][12 ]/[HI-]) and pK, =-IogKi.
Absorption maxima of HI- and 12- for bromocresol purple (BCP) are ki = 432 nm and k2 = 589 nm. The symbols el, e2 and e3 in Eq. (6) refer to indicator molar absorbance ratios at wavelengths k, and k2 e1 = 589EH1 / 432EH1, e2 = 589E1 / 432EH1, e3 = 432G 1 / 432EH1 (9) where xe-i is the molar absorption coefficient of 12- at wavelength 2~ and a,EHi is the molar absorption coefficient of HI- at wavelength k. Using BCP, the solution pH is given as:
P HT =5.8182 + 0.00129+ log((R(25)-0.00381)/(2.8729-0.05104R(25)) (10) and R(25) =R(t)(1+0.01869(25-t)) (11) 1o The fugacity is related to partial pressure of CO2 gas by:
fC02 =c' pCO2. (12) Combined equation, log(AT+[H+]eq) =log[ HCO3 ]= log( K' (Ko)i(PCO2)/Ki) + E+
log((R(25)-ej)/(e2-R(25)e3)) (13) where E is conceptually related to activity coefficient of CO2 gas and can be treated as an empirical constant which depends on flow rate and the pressure of the gas; Ko is calculated from the known dependence of Henry's law (gas solubility) constants on temperature and ionic strength. CO2 solubility constants in freshwater and seawater can be expressed as:
In Ko = 93.4517 (100/T) - 60.2409 + 23.3585 In(T/100) +
S (0.023517 - 0.023655 (T/100) + 0.0047036 (T/100)2) (14) K, is calculated from the known dependence on temperature and ionic strength based on Roy et al's quantification.
In(Kj)=-2307.1266/T +2.83655-1.5529413InT +(-4.0484/T-0.20760841)S1/2 +0.08468345S -0.00654208S3/2 + In(1-0.001005S) (15) In an exemplary embodiment of the invention, bromocresol purple (BCP) sodium salt was obtained from Eastman Kodak Company. Ultrapure grade Na2CO3 (J.T.
Baker) was dried in an 110 C oven overnight and kept in a desiccator before use.
Sodium bicarbonate (Ultra grade, 99.5% minimum) and hydrochloric acid (IN) were obtained from Sigma Chemical.
The absorbance of the indicator dye was measured with Cary 400 spectrophotometer with a fiber optic coupling. The liquid core waveguide (LCW) composed of Teflon AF 2400 tubing was obtained from Biogeneral. Equilibration 1o temperatures were measured using a Model 1521 Hart Scientific thermometer with a calibrated thermistor probe.
With reference again to Fig. 2, in an exemplary embodiment, the main body of the equilibrate chamber 45 is cylindrical with a 2 cm outer diameter (OD) and a 0.5 cm inner diameter (ID). A 15 cm section of LCW 40 is housed in the equilibration chamber 45. The seawater/indicator solution is introduced to the LCW through a T-connector 55 using a peristaltic pump 60. Fiber-optical leads within the LCW
extend into the area where solutions are equilibrated. 30% CO2 gas passes through the outside channel 65. Additionally, the gas may be passed through a two meter long copper coil immersed in thermostated water bath prior to entering the outside channel 65. The LCW 40 has an inner volume smaller than 0.1 cm3 whereas the equilibration chamber 45 has a volume on the order of 3 cm3.
In one embodiment, the equilibration cell 50 is housed in a water bath controlled to 0.05 C. Measurements were obtained as follows:
At the beginning of each measurement a reference is taken with seawater without indicator dye.
CO2 (30%) is then passed from the outer chamber after having been thermostated through a long copper coil. In one embodiment, the gas flow rate is monitored with flow meter and controlled to be 15 cm3 per minute.
The LCW is then filled with the sample with indicator added.
The peristaltic pump is then turned off (sealing the sample solution within the LCW) while CO2 gas is constantly flowing outside LCW.
The absorbance of the indicator dye was measured with Cary 400 spectrophotometer with a fiber optic coupling. The liquid core waveguide (LCW) composed of Teflon AF 2400 tubing was obtained from Biogeneral. Equilibration 1o temperatures were measured using a Model 1521 Hart Scientific thermometer with a calibrated thermistor probe.
With reference again to Fig. 2, in an exemplary embodiment, the main body of the equilibrate chamber 45 is cylindrical with a 2 cm outer diameter (OD) and a 0.5 cm inner diameter (ID). A 15 cm section of LCW 40 is housed in the equilibration chamber 45. The seawater/indicator solution is introduced to the LCW through a T-connector 55 using a peristaltic pump 60. Fiber-optical leads within the LCW
extend into the area where solutions are equilibrated. 30% CO2 gas passes through the outside channel 65. Additionally, the gas may be passed through a two meter long copper coil immersed in thermostated water bath prior to entering the outside channel 65. The LCW 40 has an inner volume smaller than 0.1 cm3 whereas the equilibration chamber 45 has a volume on the order of 3 cm3.
In one embodiment, the equilibration cell 50 is housed in a water bath controlled to 0.05 C. Measurements were obtained as follows:
At the beginning of each measurement a reference is taken with seawater without indicator dye.
CO2 (30%) is then passed from the outer chamber after having been thermostated through a long copper coil. In one embodiment, the gas flow rate is monitored with flow meter and controlled to be 15 cm3 per minute.
The LCW is then filled with the sample with indicator added.
The peristaltic pump is then turned off (sealing the sample solution within the LCW) while CO2 gas is constantly flowing outside LCW.
The pCO2 levels across LCW are allowed to equilibrate while absorbances are continuously monitored at 589nm and 432 nm, as well as a non-absorbing wavelength, 730nm. These wavelengths are exemplary in nature and other wavelengths are within the scope of the invention.
Eq. (13) can then be used to relate AT and BCP absorbance ratios.
In determining the calibration constant, "c" for determination of the Eq. (13) standard solution is introduced to the LCW and then following the procedures above, equilibration was achieved. Absorbance ratio measurements were obtained at 589, 432 and 730 nm and the constants in Eq. 13 are calculated based on Eq. 14 and 15. [H+] concentration is calculated based on equilibration R ratio. The constant c is calculated as:
E= log(A-r+[H+]eq) - Iog( K; (Ko);(pCO2)/Ki) - log((R(25)-ej)/(e2-R(25)e3)) (16) In an exemplary embodiment, a seawater sample collected from 600 m deep is used to demonstrate the application of the present invention for AT
measurement.
The salinity of the sample was measured to be 34.750 with a Portsal salinometer.
2o The alkalinity of this seawater sample was measured by LCW technique described above.
Fig. 3 shows the A-r measurement obtained in accordance with the present invention using a 0.8mm OD/ 0.76 mm ID LCW. Observations of both 589A and 432A indicate that 5 min is usually sufficient for system equilibration. Subsequent to system equilibration, Fig. 4 shows that absorbances at each wavelength are quite stable.
The constant E in Eq.14 is measured with certified reference material (CRM) provided by Dr. Andrew Dickson with known AT and summarized in the table of Fig.
5. Average of 9 measurements gives E=0.05404. Thus, natural seawater alkalinity can be measured using Iog(A-r +[H+]eq) =log( K; (Ko);(pC02)/Ki) + 0.05404+ Iog((R(25)-ej)/(e2-R(25)e3)) (17) for a wide range of salinity and temperature for the batch of standard prepared.
Spectrophotometric procedures using liquid core waveguides provide simple and robust AT measurement of natural samples. Spectrophotometric AT measurements are field portable and are easily adapted to in-situ analysis. The time required for system equilibration is influenced somewhat by temperature but is generally less than 10 minutes. Compared with equilibration time in total CO2 measurement where lo acidified seawater sample is passed through outside chamber of LCW, the equilibration time is dramatically reduced when CO2 gas is used as equilibration gas. The response of the inner sample pH to the diffusion is almost instantaneous when the sample flow is stopped and the equilibration process is initiated.
Most of the kinetic process completes in first two minutes. Tests show that when thin wail and small diameter LCW is used, the equilibration time could be shortened even further.
In a particular embodiment of the invention, 30% C02 was chosen as equilibration gas. Such concentration is chosen so that for seawater AT analyses, the absorbance ratio of acid and base form of the indicator are close to one at normal seawater AT and over wide range of AT values the pH of the equilibrated sample is well within the indicating range of BCP.
Fig. 3 demonstrates that over wide AT range, the pH changes in the seawater sample are proportional to the AT levels and thus just one standard gas allow wide range of AT to be measured. It is noticed that Eq. 16 is only applicable to 0.7 m NaCi solution. For seawater analyses Eq. 17 is used. Similar to the pH measurement, when pCO2 level is fixed the calibration constant c should be constant at fixed temperature and salinity and not instrument dependent.
As an alternative to CO2 gas as equilibration phase, a NaHCO3 solution could be used to provide the equilibration gaseous phase upon acidification.
3o The precision of A-r measurements depends principally on the precision of instrumental absorbance ratio measurements. Variations in R on the order of 0.001 correspond to variations in AT on the order of 0.1 %.
References:
G.M. Robert-Baldo, J. Morris R.H. Byrne, Ana. Chem. 57 (1985) 2564 R.H. Byrne, J.A. Breland, Deep-sea research. Part A 36 (1989) 803.
T.D. Clayton, R.H. Byrne, Deep-sea research. Part A 40 (1993) 2115.
S. McElligott, R.H. Byrne, R.A. Feely, Marine Chemistry 60 (1998) 63.
R. H. Byrne, S. McElligott, F. J. Millero, Deep-sea research. Part A, 46 (1999) 1985.
1 o R.H. Byrne Anal. Chem. 59 (1987) 1479 M.D. DeGrandpre, M.M. Baehr, T.R. Hammar, Anal. Chem. 71 (1999) 1152.
R.D.Waterbury, W. Yao, R.H. Byrne, Analytica chimica acta. 357 (1997) 99 E. Kaltenbacker, E.T. Steimle, R.H. Byrne, Underwater Technology, Proceedings of the 2000 International Symposium, (2000) 41.
A.Yu Alentiev, Yu.P. Yampolskii, V.P.Shantarovich, S.M. Nemser, N.A. Plate, J.
Membrane Sci. 126 (1997) 123.
1. Pinnay, L.G. Toy, J. Membrane Sci. 109, (1996) 125.
W. Yao, R.H. Byrne, Deep-sea research. Part A 45 (1998) 1383 W. Yao, R.H. Byrne, Environ. Sci. Technol. 35 (2001) 1197.
2o H. Zhang, R.H. Byrne, Mar. Chem. 52 (1996) 17.
R.F. Weiss, Mar. Chem. 2 (1974) 203.
F.J. Millero, Geochim. Cosmochim. Acta, 59 (1995) 661 The disclosure of all publications cited above are expressly incorporated herein by reference, each in its entirety, to the same extent as if each were incorporated by reference individually.
It will be seen that the advantages set forth above, and those made apparent from the foregoing description, are efficiently attained and since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matters contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
It is also to be understood that the following claims are intended to cover all of the 1o generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween. Now that the invention has been described,
Eq. (13) can then be used to relate AT and BCP absorbance ratios.
In determining the calibration constant, "c" for determination of the Eq. (13) standard solution is introduced to the LCW and then following the procedures above, equilibration was achieved. Absorbance ratio measurements were obtained at 589, 432 and 730 nm and the constants in Eq. 13 are calculated based on Eq. 14 and 15. [H+] concentration is calculated based on equilibration R ratio. The constant c is calculated as:
E= log(A-r+[H+]eq) - Iog( K; (Ko);(pCO2)/Ki) - log((R(25)-ej)/(e2-R(25)e3)) (16) In an exemplary embodiment, a seawater sample collected from 600 m deep is used to demonstrate the application of the present invention for AT
measurement.
The salinity of the sample was measured to be 34.750 with a Portsal salinometer.
2o The alkalinity of this seawater sample was measured by LCW technique described above.
Fig. 3 shows the A-r measurement obtained in accordance with the present invention using a 0.8mm OD/ 0.76 mm ID LCW. Observations of both 589A and 432A indicate that 5 min is usually sufficient for system equilibration. Subsequent to system equilibration, Fig. 4 shows that absorbances at each wavelength are quite stable.
The constant E in Eq.14 is measured with certified reference material (CRM) provided by Dr. Andrew Dickson with known AT and summarized in the table of Fig.
5. Average of 9 measurements gives E=0.05404. Thus, natural seawater alkalinity can be measured using Iog(A-r +[H+]eq) =log( K; (Ko);(pC02)/Ki) + 0.05404+ Iog((R(25)-ej)/(e2-R(25)e3)) (17) for a wide range of salinity and temperature for the batch of standard prepared.
Spectrophotometric procedures using liquid core waveguides provide simple and robust AT measurement of natural samples. Spectrophotometric AT measurements are field portable and are easily adapted to in-situ analysis. The time required for system equilibration is influenced somewhat by temperature but is generally less than 10 minutes. Compared with equilibration time in total CO2 measurement where lo acidified seawater sample is passed through outside chamber of LCW, the equilibration time is dramatically reduced when CO2 gas is used as equilibration gas. The response of the inner sample pH to the diffusion is almost instantaneous when the sample flow is stopped and the equilibration process is initiated.
Most of the kinetic process completes in first two minutes. Tests show that when thin wail and small diameter LCW is used, the equilibration time could be shortened even further.
In a particular embodiment of the invention, 30% C02 was chosen as equilibration gas. Such concentration is chosen so that for seawater AT analyses, the absorbance ratio of acid and base form of the indicator are close to one at normal seawater AT and over wide range of AT values the pH of the equilibrated sample is well within the indicating range of BCP.
Fig. 3 demonstrates that over wide AT range, the pH changes in the seawater sample are proportional to the AT levels and thus just one standard gas allow wide range of AT to be measured. It is noticed that Eq. 16 is only applicable to 0.7 m NaCi solution. For seawater analyses Eq. 17 is used. Similar to the pH measurement, when pCO2 level is fixed the calibration constant c should be constant at fixed temperature and salinity and not instrument dependent.
As an alternative to CO2 gas as equilibration phase, a NaHCO3 solution could be used to provide the equilibration gaseous phase upon acidification.
3o The precision of A-r measurements depends principally on the precision of instrumental absorbance ratio measurements. Variations in R on the order of 0.001 correspond to variations in AT on the order of 0.1 %.
References:
G.M. Robert-Baldo, J. Morris R.H. Byrne, Ana. Chem. 57 (1985) 2564 R.H. Byrne, J.A. Breland, Deep-sea research. Part A 36 (1989) 803.
T.D. Clayton, R.H. Byrne, Deep-sea research. Part A 40 (1993) 2115.
S. McElligott, R.H. Byrne, R.A. Feely, Marine Chemistry 60 (1998) 63.
R. H. Byrne, S. McElligott, F. J. Millero, Deep-sea research. Part A, 46 (1999) 1985.
1 o R.H. Byrne Anal. Chem. 59 (1987) 1479 M.D. DeGrandpre, M.M. Baehr, T.R. Hammar, Anal. Chem. 71 (1999) 1152.
R.D.Waterbury, W. Yao, R.H. Byrne, Analytica chimica acta. 357 (1997) 99 E. Kaltenbacker, E.T. Steimle, R.H. Byrne, Underwater Technology, Proceedings of the 2000 International Symposium, (2000) 41.
A.Yu Alentiev, Yu.P. Yampolskii, V.P.Shantarovich, S.M. Nemser, N.A. Plate, J.
Membrane Sci. 126 (1997) 123.
1. Pinnay, L.G. Toy, J. Membrane Sci. 109, (1996) 125.
W. Yao, R.H. Byrne, Deep-sea research. Part A 45 (1998) 1383 W. Yao, R.H. Byrne, Environ. Sci. Technol. 35 (2001) 1197.
2o H. Zhang, R.H. Byrne, Mar. Chem. 52 (1996) 17.
R.F. Weiss, Mar. Chem. 2 (1974) 203.
F.J. Millero, Geochim. Cosmochim. Acta, 59 (1995) 661 The disclosure of all publications cited above are expressly incorporated herein by reference, each in its entirety, to the same extent as if each were incorporated by reference individually.
It will be seen that the advantages set forth above, and those made apparent from the foregoing description, are efficiently attained and since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matters contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
It is also to be understood that the following claims are intended to cover all of the 1o generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween. Now that the invention has been described,
Claims (20)
1. A method of measuring the total alkalinity of a sample liquid using a liquid core waveguide having a gas permeable membrane, the liquid core waveguide positioned in an interior cavity of an equilibration chamber, the method comprising the steps of:
introducing a flow of gas into the interior cavity of the equilibration chamber;
introducing a sample liquid including a pH indicator into the interior of the liquid core waveguide;
allowing the gas to equilibrate across the gas permeable membrane of the liquid core waveguide;
measuring the absorbance ratio of the sample liquid at a plurality of wavelengths using the liquid core waveguide; and calculating the total alkalinity of the sample liquid from the measured absorbance ratios.
introducing a flow of gas into the interior cavity of the equilibration chamber;
introducing a sample liquid including a pH indicator into the interior of the liquid core waveguide;
allowing the gas to equilibrate across the gas permeable membrane of the liquid core waveguide;
measuring the absorbance ratio of the sample liquid at a plurality of wavelengths using the liquid core waveguide; and calculating the total alkalinity of the sample liquid from the measured absorbance ratios.
2. The method of claim 1, wherein the total alkalinity (A T) is calculated according to the equation:
log(A T + [H+])=log(K1(K0)i(p CO2)i K1)+ E + log((R(25)- e1)/(e2 - R(25)e3 )) where;
[H+] =10-p H, K0 is the Henry's law constant, K~ is the dissociation constant of carbonic acid, the subscripti refers to the sample liquid within the waveguide, E is an empirical derived constant, K1 is an indicator dye dissociation constant, R(25) is a ratio of the pH indicator absorbance at 589 and 432 nm, and e1 and e2 and e3 are molar absorptivity ratios appropriate to the pH indicator.
log(A T + [H+])=log(K1(K0)i(p CO2)i K1)+ E + log((R(25)- e1)/(e2 - R(25)e3 )) where;
[H+] =10-p H, K0 is the Henry's law constant, K~ is the dissociation constant of carbonic acid, the subscripti refers to the sample liquid within the waveguide, E is an empirical derived constant, K1 is an indicator dye dissociation constant, R(25) is a ratio of the pH indicator absorbance at 589 and 432 nm, and e1 and e2 and e3 are molar absorptivity ratios appropriate to the pH indicator.
3. The method of claim 1, wherein the pH indicator is a sulfonephthalein pH
indicator.
indicator.
4. The method of claim 1, wherein the pH indicator is bromocresol purple
5. The method of claim 1, further comprising the step of passing the flow of gas though a thermostated water bath prior to introducing the flow of gas into the interior cavity of the equilibration chamber.
6. The method of claim 1, further comprising the step of housing the equilibration chamber in a thermostated water bath.
7. The method of claim 1, further comprising the step of measuring the absorbance ratio of the liquid sample without the pH indicator to establish a reference.
8. The method of claim 1, wherein the flow of gas is introduced at a controlled rate.
9. The method of claim 1, further comprising the step of sealing the interior of the liquid core waveguide after the sample liquid has been introduced.
10. The method of claim 1, wherein the gas is selected from the group consisting of CO2, NaHCO3 and 30% CO2.
11. The method of claim 1, wherein the liquid core waveguide is a Teflon AF
2400 liquid core waveguide.
2400 liquid core waveguide.
12. A system for measuring the total alkalinity of a sample liquid, the system comprising:
a equilibration chamber having an interior cavity;
a liquid core waveguide having a gas permeable membrane, the liquid core waveguide positioned within the interior cavity of the equilibration chamber, the liquid core waveguide for measuring the absorbance ratio of the sample liquid at a plurality of wavelengths;
a gas flow introduced into the interior cavity of the equilibration chamber;
a sample liquid including a pH indicator introduced into the interior of the liquid core waveguide; and means for calculating the total alkalinity of the sample liquid from the measured absorbance ratios.
a equilibration chamber having an interior cavity;
a liquid core waveguide having a gas permeable membrane, the liquid core waveguide positioned within the interior cavity of the equilibration chamber, the liquid core waveguide for measuring the absorbance ratio of the sample liquid at a plurality of wavelengths;
a gas flow introduced into the interior cavity of the equilibration chamber;
a sample liquid including a pH indicator introduced into the interior of the liquid core waveguide; and means for calculating the total alkalinity of the sample liquid from the measured absorbance ratios.
13. The system of claim 12, wherein the total alkalinity (A T) is calculated according to the equation:
log(A T + [H+])=log(K~(K0)/(pCO2)/ K1)+ E + log((R(25)- e1)/(e2 - R(25)e3)) where;
[H+]=10 -pH , K0 is the Henry's law constant, K~ is the dissociation constant of carbonic acid, the subscripti refers to the sample liquid within the waveguide, E is an empirical derived constant, K1 is an indicator dye dissociation constant, R(25) is a ratio of the pH indicator absorbance at 589 and 432 nm, and e1 and e2 and e3 are molar absorptivity ratios appropriate to the pH indicator.
log(A T + [H+])=log(K~(K0)/(pCO2)/ K1)+ E + log((R(25)- e1)/(e2 - R(25)e3)) where;
[H+]=10 -pH , K0 is the Henry's law constant, K~ is the dissociation constant of carbonic acid, the subscripti refers to the sample liquid within the waveguide, E is an empirical derived constant, K1 is an indicator dye dissociation constant, R(25) is a ratio of the pH indicator absorbance at 589 and 432 nm, and e1 and e2 and e3 are molar absorptivity ratios appropriate to the pH indicator.
14. The system of claim 1, wherein the pH indicator is a sulfonephthalein pH
indicator.
indicator.
15. The system of claim 1, wherein the pH indicator is bromocresol purple
16. The system of claim 1, further comprising a thermostated water bath positioned between the gas flow and the interior cavity of the equilibration chamber.
17. The system of claim 1, further comprising a flow controller for controlling the flow rate of the gas.
18. The sytem of claim 1, wherein the interior of the liquid core waveguide is sealable.
19. The system of claim 1, wherein the gas is selected from the group consisting of CO2, NaHCO3 and 30% CO2.
20. The system of claim 1, wherein the liquid core waveguide is a Teflon AF
2400 liquid core waveguide.
2400 liquid core waveguide.
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| US60/672,474 | 2005-04-18 | ||
| US11/279,971 US7727770B2 (en) | 2005-04-18 | 2006-04-17 | System and method for spectrophotometric measurement of total alkalinity using a liquid core waveguide |
| US11/279,971 | 2006-04-17 | ||
| PCT/US2006/014474 WO2006113663A2 (en) | 2005-04-18 | 2006-04-18 | System and method for spectrophotometric measurement of total alkalinity using a liquid core waveguide |
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| US8785207B2 (en) * | 2008-09-12 | 2014-07-22 | Sri International | Method and apparatus for measuring multiple parameters in-situ of a sample collected from environmental systems |
| NO333632B1 (en) * | 2011-05-11 | 2013-07-29 | Inst Energiteknik | Method and apparatus for analyzing alkalinity conditions in aqueous liquids |
| US10060891B1 (en) * | 2016-02-19 | 2018-08-28 | University Of South Florida | Continuous acid-free measurements of total alkalinity |
| US10620129B1 (en) * | 2016-10-13 | 2020-04-14 | University Of South Florida | Systems and methods for determining carbon system parameters of water |
| US10018610B1 (en) * | 2017-02-21 | 2018-07-10 | Becs Technology, Inc. | Measuring total alkalinity in a recirculating fluid system |
| US10041923B1 (en) | 2017-04-12 | 2018-08-07 | Swift Engineering, Inc. | Spectrophotometric system for measuring water quality |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4209299A (en) * | 1978-02-21 | 1980-06-24 | The Regents Of The University Of California | Method and apparatus for determination of volatile electrolytes |
| US4318709A (en) * | 1979-11-08 | 1982-03-09 | Miles Laboratories, Inc. | Test means, test device and method for determining the ionic strength or specific gravity of a liquid sample |
| US4526755A (en) * | 1982-02-22 | 1985-07-02 | International Telephone & Telegraph Corporation | Gas analyzer or the like |
| US5416879A (en) * | 1993-03-29 | 1995-05-16 | World Precision Instruments, Inc. | Apparatus and method for measuring light absorption in small aqueous fluid samples |
| US5660790A (en) * | 1996-08-13 | 1997-08-26 | Litmus Concepts, Inc. | PH and amine test elements |
| US6016372A (en) * | 1997-10-16 | 2000-01-18 | World Precision Instruments, Inc. | Chemical sensing techniques employing liquid-core optical fibers |
| US6011882A (en) * | 1997-10-16 | 2000-01-04 | World Precision Instruments, Inc. | Chemical sensing techniques employing liquid-core optical fibers |
| US6436717B1 (en) * | 1998-05-13 | 2002-08-20 | Yellow Springs Optical Sensor Co. Pll | System and method for optical chemical sensing |
-
2006
- 2006-04-17 US US11/279,971 patent/US7727770B2/en not_active Expired - Fee Related
- 2006-04-18 CA CA002605416A patent/CA2605416A1/en not_active Abandoned
- 2006-04-18 EP EP06750502A patent/EP1872113A2/en not_active Withdrawn
- 2006-04-18 WO PCT/US2006/014474 patent/WO2006113663A2/en active Application Filing
Also Published As
| Publication number | Publication date |
|---|---|
| WO2006113663A3 (en) | 2007-11-08 |
| WO2006113663A2 (en) | 2006-10-26 |
| US7727770B2 (en) | 2010-06-01 |
| EP1872113A2 (en) | 2008-01-02 |
| US20060234389A1 (en) | 2006-10-19 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Discontinued |
Effective date: 20130418 |