US3469789A - Sample introducing device for spectro-chemical analysis - Google Patents

Description

Sept. 30, 1969 E. c. SIMMONS SAMPLE INTRODUCING DEVICE FOR SPECTRO-CHEMICAL ANALYSIS Filed June 7. 1967 DETECTOR INVENTOR. EUGENE c. SIMMONS ATTORNEY United States Patent 3,469,789 SAMPLE INTRODUCING DEVICE FOR SPECTRO-CHEMICAL ANALYSIS Eugene C. Simmons, Woodbury, Conn., assignor to Corning Glass Works, Corning, N.Y., a corporation of New York Filed June 7, 1967, Ser. No. 644,342

Int. Cl. A61m 11/06 US. Cl. 239-338 Claims ABSTRACT OF THE DISCLOSURE An atomizer is disclosed for introducing a sample into a flame or 'a similar atom disassociating means for analysis of the sample constituents. A very fine uniform mist or fog is produced by directing an atomized spray of the sample solution or suspension against an obstruction such as a sphere. The fog leaves the atomized chamber via an output tube whereas larger droplets tend to strike the chamber walls and are collected in the chamber.

Spectro-chemical analysis of an unknown sample to determine the presence of a particular element therein requires that the atoms of that particular element be disassociated from the parent compound. In such analytical techniques as atomic absorption spectrophotometry (AAS) the sample is almsot exclusively examined as a solution. This solution is atomized to a fine mist and is introduced into a flame. In the flame the solvent first evaporates, followed by the solid, which thereby disassociates either wholly or partially into its component atoms. Depending on the technique utilized, a majority of the atoms are excited and then emit light (emission spectroscopy) or a majority of the atoms remain in the ground state and absorb light (AAS). These two procedures generally differ only in the method of measuring atomic-vapor concentrations in the flame. The intensity of the light emitted or absorbed is proportional to the concentration in the solution of the element concerned provided that certain conditions such as flame temperature and amount of liquid atomized remain constant.

Atomization of the liquid, i.e., the production of a mist in a stream of air or other supporting gas of the flame, may be achieved by utilizing a combined atomizerburner or a separate atomizing system. This invention relates to an indirect atomizer wherein the sample is initially mixed with an air stream, the air-mist mixture or aerosol next being well mixed with a fuel gas and passed upward through the burner tube. The indirect atomizer is usually preferred for AAS because it permits a greater flexibility in flame characteristics, e.g., shape and gas composition.

Conventional indirect atomizers generally operate as follows. The air necessary for combustion is forced through a nozzle. During the subsequent expansion, a region of reduced pressure is produced and the liquid sample is sucked through a tube to the low pressure region and atomized by the current of air. The larger drops in the mist precipitate against the walls of the chamber and are removed so that mainly the smaller drops are carried along to the flame. Screens or baflies may be used to promote the precipitation of the larger drops. Although only a small percentage of the originally atomized liquid reaches the burner, the indirect atomizer is generally preferred since it produces a fine, uniform mist and results in a laminar, non-turbulent, noiseless flame.

There is presently a need for an atomizer which can provide even smaller droplets than can be obtained from the above described conventional atomizers. The reason for this will become evident from a discussion of the changes which take place after the aerosol mist reaches the flame. First, droplets of the solvent evaporate and a solid particle remains. The clotlet of solid material may undergo the following changes: the elimination of a more volatile constituent, chemical interaction between the various inorganic substances present, including the flame gases, melting of the product, and finally, partial or complete volatilization of the residue. These various changes must occur very rapidly since it is estimated that less than ten milliseconds are taken for a particle to pass through one cm. of a typical flame. Therefore, the conversion of droplets into vapor must take only a very short time if atomic vapor is to be efliciently produced.

Interferences such as the suppression effect are thought to be related to the droplet size. It has been found that suppression can be reduced or eliminated in several ways, including the use of more efficient atomizers to produce smaller droplets. Since the evaporation of droplets and the later disassociation of the vapor takes place rapidly, but the intermediate process of vaporization of the dry residue must be considered in relation to certain physical parameters, it is the rate of vaporization, compared with the transit time of the particle through the flame, which determines the extent at which the residue is vaporized. The most important variables controlling this 'are probably boiling point, vapor pressure and particle size. Since the use of a more eflicient atomizer results in much smaller clotlets which have a larger surface area per unit volume, there is a greater rate of vaporization and hence more atoms are produced.

The rate of vaporization of clotlets is important, not only from an interference point of view, but also as a means for increasing sensitivity. A greater number of atoms in the flame produced by the more eificient volatilization of droplets enhances the percent absorption by an atomic absorption spectrophotometer.

Furthermore, conventional atomizers are inoperative on relatively high viscosity liquids. Engine oil, for example, must be diluted before a conventional vaporizer could deliver an acceptable amount of aerosol mist to a burner. It is, however, desirable to directly vaporize a high viscosity liquid sample and thereby increase the number of atoms present in the flame.

Probably a more important use for a device capable of atomizing oil is in the area of solid sampling. Heretofore, most samples were introduced in a liquid state since most atomizers can introduce a liquid sample into a flame at a uniform rate. Attempts at introducing a solid in a finely pulverized state have not met with success due to the nonuniform rate at which a venturi device can draw in the powdered sample. However, it has been found that when a finely pulverized sample is mixed with an oil having a sufliciently high viscosity, the resulting homogenous suspension remains for a period of time which is suflicient for it to be atomized and fed to a burner. Since the atomizer of this invention can atomize oil having a relatively high viscosity, a pulverized solid sample suspended in the oil is delivered to the flame at a uniform rate.

It is therefore an object of this invention to provide an atomizer for spectro-chemical analysis which will create an aerosol mist directly from a high viscosity liquid such as engine oil or the like.

A further object of this invention is to provide an atomizer for spectre-chemical analysis which will convert the sample solution into an extremely fine mist or fog.

A further object of this invention is to provide a universal sampling device which may be utilized for introducing a gas (smokestack materials, airborne dust and the like), a liquid, or a solid (finely pulverized solid material in an oil suspension) into the flame of a spectro-chemical analysis instrument.

Still another object of this invention is to provide an atomizer which will produce an extremely fine aerosol mist and thereby increase the percentage absorption of an atomic absorption spectrophotometer which is used in conjunction therewith.

Briefly, this invention comprises an atomizer having means to draw a small stream of a sample solution or suspension from a pool and thrust it against an obstruction, thereby creating a very fine mist or fog along with larger undesirable particles of sample solution. Means are provided for precipitating these undesirable droplets against the atomizer chamber and thereby precluding their entry into the exit port and thereafter into the flame.

Other objects and advantages will become apparent from the following detailed description and explanation of the invention wherein reference is made to the drawings in which:

Fig. 1 is a partially schematic diagram showing the manner in which the atomizer is used in conjunction with an atomic absorption spectrophotometer;

FIG. 2 is a top view in section of the preferred embodiment of this invention;

FIG. 3 is a side elevation view in section of the preferred embodiment; and

FIG. 4 is a view taken along lines 1VIV of FIG- URE 3.

FIG. 1 schematically represents a basic atomic absorption system, and the manner in which an atomizer is utilized in such a system. An atomizer 10, the details of which are shown in FIGS. 2 and 3, is supplied with a liquid sample which is fed to the input pipe 11 by a hose 12 to which a funnel 13 may be attached. A compressed air supply hose 14 is connected to the compressed air input pipe 15 while a fuel supply hose 18 is connected to the fuel input pipe 19. The atomizer output port 21 is connected to a linear burner 23 by an L-shaped coupling tube 22.

A hollow-cathode lamp 25 generates a light beam 26 which passes through the flame directly above the burner 23, after which the resonance wave length is isolated by a monocromator or filter 28. The filtered light beam is detected by the detector 29 which may consist of a photo detector, amplifier and display or recording device.

Referring now to FIGS. 2 and 3, the atomizer, which may be constructed of a material such as glass, stainless steel or the like, comprises a cylindrical body 31. The output port 21 is axially aligned with one end of the cylindrical housing 31 and a portion 24 thereof extends a short distance into the housing 31. An auxiliary air supply tube 32 is axially aligned with the opposite end of the cylindrical housing and also extends a short distance therein. The compressed air pipe 15 is aligned centrally within the auxiliary air tube 32 by a plurality of supports 33. The end of the compressed air pipe 15 which extends into the housing 31 is tapered to form a nozzle 34. A capillary tube 36, which is mounted on a support 35, extends from the bottom portion of the housing 31 to a point adjacent the orifice of nozzle 34. A spherical obstruction 38, which is mounted on a support 39, has its center located on the axis of the compressed air pipe 15, the upper end of the capillary tube 36 being situated between the nozzle 34 and the spherical obstruction 38.

Since the compressed air pipe 15 does not supply suflicient air to feed the burner, an auxiliary air source is made available. The auxiliary source consists of a cap 41 which is rigidly mounted to the end of the input air port 32, and a second cap 42 which is mounted adjacent the cap 41 and is free to rotate with respect thereto. A pair of slots 43 which are located in the cap 41 are located the same radial distance from the axis of the pipe 15 as a pair of slots 44 which are located in the cap 42. As shown in FIG. 4, the cap 42 may be rotated to provide various degrees of alignment between the slots 43 and 44 to control the amount of auxiliary air entering the cylindrical housing.

During operation the sample solution is added to the atomizer through the sample input tube 11. This may be simply accomplished by adding the solution to a tube which is attached to the input pipe 11 as is shown in FIG. 1. When the level of the sample solution has reached the bottom of the capillary tube 36, the solution will be drawn up the capillary tube and thrust against the spherical obstruction 38 to produce a fine mist or fog. The fine mist is carried with the exiting or discharging air through the output port 21 along with the fuel which has been supplied through the pipe 19. Larger undesirable particles which are also produced are not able to exit with the fine mist but instead strike the walls of the cylindrical housing and return to the pool in the bottom thereof. The extension of the output port 21 into the housing insures that only the finest mist is discharged from the atomizer. As is illustrated in FIG. 1 the atomizer is usually operated with its longitudinal axis slightly off horizontal so that any mist which has condensed inside the output port 21 will return to the cylindrical housing. This can be accomplished by utilizing a connecting tube 22 which has an elbow having an angle 0 which is slightly greater than Tests for determining droplet size have shown that the atomizer of this invention produces an aerosol mist of particles which are finer than those produced by conventional atomizers. The use of this atomizer with an AAS has provided readings of percent absorption which are considerably higher than those obtained by conventional atomizers.

Furthermore, when high viscosity liquids such as undiluted engine oil containing wear metal or a suspension of a pulverized solid mixed in oil have been used in this atomizer, it has provided a fine mist of oil in the flame. The amount of wear metal or other solid particles present in the oil can therefore be easily and accurately determined. In addition, samples such as whole blood or dried, powdered animal tissue in a silicone oil can be atomized by the atomizer of this invention.

Various modifications may be made to the embodiment disclosed hereinabove without departing from this invention. For example, means other than the tube 11 may be used for supplying a sample solution to the chamber 31. An inlet opening or tube in the side or top of the chamber 31 could be used for supplying the sample solution. Moreover, means such as a syringe could be used to inject a specific amount of sample solution into an inlet opening or tube.

The atomizer could also include a drain pipe fixed to the bottom thereof and having a valve affixed thereto for draining any unused solution prior to the addition of another sample to the reservoir. In addition to draining the unused solution from the reservoir, it is advantageous to run distilled water through the vaporizer prior to running a new sample solution through the atomizer.

What is claimed is:

1. An atomizer for use in spectro-chemical analysis comprising:

an atomizer chamber,

means for directing a stream of high velocity gas into said chamber,

means for retaining a quantity of a sample solution which is to be analyzed,

an obstruction located in the path of said gas stream,

means located in said gas stream adjacent said obstruction for supplying a constant rate of solution from said retaining means to said gas stream, said solution being carried by said stream to said obstruction whereby at least a portion of said solution is dispersed into an aerosol mist of extremely fine particles,

an output port in said chamber,

means for preventing droplets of undesirably large size from exiting from said output port, and

means for supplying a combustible gas to said chamher.

2. An atomizer for use in spectro-chemical analysis comprising:

an atomizer chamber having first and second ends,

an air supply tube connected to said first end and extending a short distance into said atomizer chamber,

a compressed gas supply tube located centrally within said air supply tube and extending into said atomizer chamber,

means for retaining a volume of sample fluid,

a capillary tube extending from said volume of sample fluid to a point adjacent the orifice of said compressed gas tube,

an obstruction situated adjacent said capillary tube at the downstream side thereof and in the path of said compressed gas, so that the low pressure region created by the compressed gas exiting from the orifice in said compressed gas tube draws said sample solution from said retaining means, said solution being directed against said obstruction at a high velocity suflicient to disperse the same into an aerosol mist, a portion of which consists of extremely fine particles,

an output tube connected to said second end of said atomizer chamber and extending a distance therein which is suflicient to obstruct the outward flow of larger particles in said aerosol mist while permitting said extremely fine particles to exit therethrough, and

a fuel input pipe communicating with said chamber through one side thereof, whereby a mixture of fuel, .air, and said aerosol mist are permitted to simultaneously emanate from said output tube.

3. An atomizer as described in claim 2 wherein said means for retaining a volume of sample fluid comprises the bottom portion of said chamber, and further including means for supplying said sample fluid to said chamber.

4. An atomizer as described in claim 2 which further comprises means connected to said air supply tube for varying the amount of air flowing therethrough.

5. An atomizer as described in claim 2 wherein said obstruction is a sphere.

6. An atomizer as described in claim 3 wherein said means for supplying said sample fluid comprises a pipe protruding through the bottom of said chamber and projecting a short distance therein.

7. An atomizer as described in claim 2 wherein said fuel input pipe is disposed adjacent said air supply tube at an angle thereto so that fuel supplied thereby is mixed with air and said aerosol mist prior to flowing through said output tube.

8. A spectro-chemical analysis system including an atomizer for feeding an atomized sample to a burner which produces a flame containing atoms of said sample, said system being of the type wherein a light beam is passed through said flame and is thereafter analyzed, said system being characterized in that said atomizer comprises an atomizer chamber,

means for directing a stream of high velocity gas into said chamber,

means for retaining a quantity of sample solution which is to be analyzed,

an obstruction located in the path of said gas stream,

means located in said gas stream adjacent said obstruc tion for supplying a constant rate of solution from said retaining means to said gas stream, said solution being carried by said stream to said obstruction whereby at least a portion of said solution is dispersed into an aerosol mist of extremely fine particles,

an output port in said chamber, and

means for preventing droplets of undesirable large size from exiting from said output port.

9. A spectro-chemical analysis system in accordance with claim 8 wherein said atomizer further comprises a fuel input pipe communicating vw'th said chamber through one side thereof, whereby a mixture of fuel, air and aerosol mist are permitted to simultaneously emanate from said output tube.

10. A spectro-chemical analysis system in accordance with claim 9 wherein said fuel input pipe is disposed adjacent said air supply tube at an angle thereto so that fuel supplied thereby is mixed with air and said aerosol mist prior to flowing through said output tube.

References Cited UNITED STATES PATENTS 2,562,874 7/1951 Weichselbaum 88-145 3,018,971 1/1962 Cheney 239338 3,172,406 3/1965 Bird et al. 238-338 3,269,665 8/1966 Cheney 239-338 FOREIGN PATENTS 616,089 1/1949 Great Britain.

EVERETT W. KIRBY, Primary Examiner

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