US3525476A

US3525476A - Fluid diffuser with fluid pressure discharge means and atomizing of material in holder

Info

Publication number: US3525476A
Application number: US716458A
Authority: US
Inventors: Eldon A Boling; Stanley B Smith Jr; Jerrold Zindler
Original assignee: Instrumentation Laboratory Co
Current assignee: THERMO JARRELL ASH Corp WALTHAM MA A CORP OF
Priority date: 1968-03-27
Filing date: 1968-03-27
Publication date: 1970-08-25
Anticipated expiration: 1987-08-25

Description

970 E. A. BOLING ET AL 3,525,476

FLUID DIFFUSER WITH FLUID PRESSURE DISCHARGE MEANS AND ATOMIZING OF MATERIAL IV HOLDER Filed March 27, 1968 2 SheetsSheet 1 Aug. 25, 1970 E. A. BOLING ET AL 3,525,476

FLUID DIFFUSER WITH FLUID PRESSURE DISCHARGE MEANS AND ATOMIZING OF MATERIAL IN HOLDER Filed March 27, 1968 2 Sheets-Sheet 2 560 480 l 4 88 1 40 l i L 82 g Hg 42 1 R FIG 4 United States Patent FLUID DIFFUSER WITH FLUID PRESSURE DISCHARGE MEANS AND ATOMIZING 0F MATERIAL IN HOLDER Eldon A. Boling, Brookline, Stanley B. Smith, Jr., l lexington, and Jerrold Zindler, Cambridge, Mass.,'ass1gnors to Instrumentation Laboratory, Inc., Watertown, Mass., a corporation of Massachusetts Filed Mar. 27, 1968, Ser. No. 716,458 Int. Cl. A61m 11/06 US. Cl. 239-338 8 Claims ABSTRACT OF THE DISCLOSURE A pneumatic nebulizer includes a plenum chamber, a capillary tube that extends through the plenum chamber and a nozzle section that has a series of five coaxial steps. The end of the capillary tube is disposed in the smallest step section of the nozzle section and air at a pressure of 40 p.s.i.g. aspirates a sample through the capillary tube into the nozzle to produce a primary stream of nebulized sample. In one embodiment a secondary stream of fuel and air is supplied in a counter stream from an 0.050 inch orifice spaced 0.375 inch from the outlet plane of the nozzle. This secondary stream impinges on the primary sample stream and further reduces the size of the nebulized sample particles. In a second embodiment, a secondary stream is provided from an annular orifice 0.020 inch in width which impinges on the primary stream from a 45 angle within the nozzle section. A baflle in the form of a 0.375 inch diameter ball is placed in front of the nozzle and the mixed streams impinge on that surface.

SUMMARY OF INVENTION This invention relates to pneumatic nebulizers and more particularly to nebulizer systems especially although not exclusively useful with spectroanalytical systems of the atomic absorption and emission types.

In an analysis of a sample, uniform distribution of the sample in a carrier is desirable as output signal variation arises if the distribution is non-uniform. It is also desirable to increase the magnitude of output signal which may be increased by increasing the proportion of sample in the carrier.

In an atomic absorption type of spectroanalytical instrument, for example, a light beam is passed through a population of atoms representative of the particular sample being analyzed, the wavelength of the light beam corresponding to an atomic resonance line of the particular element under analysis. The atomic population for use in this analysis is normally produced by nebulizing a liquid containing sample into a flame where the molecules are broken down into atoms. Atoms of the element of interest absorb light of its corresponding wavelength, and the ratio of the intensity of the resonance line light beam passed through the flame to that of an equivalent light beam not passed through the flame under ideal circumstances closely follows Beers laW. However, atomic absorption analyses frequently deviate from Beers law as the concentration of atoms in the flame is a function not only of the concentration of the element in the liquid sample but also of a variety of other factors including: (1) the rate at which the nebulizer converts sample containing liquid into droplets small enough to be swept through a spray chamber and into the flame (termed hereafter the fog rate); (2) the mean size of droplets and the range of droplets sizes in the fog; (3) characteristics of the fuel and oxidant employed; (4) the fuel oxidant ratio; (5) the ratio of fog to fuel and oxidant; (6) the chemical matrix of the sample. While the present 3,525,475 Patented Aug. 25, 1970 "ice invention was developed primarily for nebulization of samples for spectroanalysis, the invention also has utility in other fields that involve atomization of materials.

It is a particular object of this invention to provide an improved nebulizer for use with spectroanalytical instruments.

Another object of the invention is to provide a novel and improved nebulizer that has an increased fog rate.

Still another object of the invention is to provide a nebulizer which increases the efliciency of conversion of aspirated sample to fog.

A further object of the invention is to provide a neb-' ulizer which substantially increases the rate at which fog can be generated and concurrently reduces the size of fog droplets to a degree that the fog stream will not wet plane surfaces placed in the stream path.

A further object of the invention is to reduce the variations in the flame employed in a spectroanalytical instrument.

Another object of the invention is to provide a novel and improved nebulizer-spray chamber burner combination in which the instrument variations (noise) due to variations in the flame are significantly reduced.

Another object of the invention is to provide an improved source of fuel oxidant and sample which provides improved mixing of the constituents supplied to the burner structure.

Still another object of the invention is to materially increase the sensitivity of and stability of spectroanalytical instruments that employ flames.

In accordance with the invention there is provided a nebulizer that includes a nozzle structure having an aspirator orifice and a sample orifice disposed adjacent the aspirator orifice so that the sample may be aspirated into the nozzle structure by fluid flow through the aspirator orifice to form a primary stream. The nebulizer further includes an auxiliary orifice for directing a second fluid stream to impinge on the primary stream in an interaction zone in the immediate vicinity, that is within approximately one inch of the nebulizer nozzle. The interaction of the primary and secondary streams produces a. fog having droplets of smaller dimension than the droplets in the aspirated primary stream. In nebulizers con structed in accordance with the invention, fog droplets of sufficiently small size such that the fog does not wet a plane surface placed in the flow path of the fog may be produced. The second fluid stream should impinge on the primary stream at a substantial angle, i.e.., greater than about 15, to the direction of flow of the primary stream; in one embodiment an angle of 45 is employed and in another particular embodiment an angle of is employed. In a particular embodiment, the secondary stream is produced from an annular orifice located within the nebulizer nozzle so that the interaction zone is at least partly within the nebulizer nozzle itself. Further, it is preferred to employ a nebulizer nozzle formed in a series of steps of increasing cross-sectional area that are coaxial with one another and with the primary stream. In particular'embodiments the use of a supplemental baffle structure fixedly positioned in front of the nebulizer nozzle directly in the path of the primary stream is desirable.

The invention is particularly useful in spectroanalytical apparatus in combination with a spray chamber in which a fog of sample material is transmitted to an analysis station. In an atomic absorption type of spectroanalytical instrument, the invention increases the amount of sample converted to fog, and reduces the size of the particles of the fog; thus increasing the sensitivity of the analysis both from the standpoint of increasing the amount of material available per unit time for analysis and reducing instrument output signal noise due to variations in the flame.

Other objects, features and advantages of the invention will be seen as the following description of particular embodiments thereof progresses, in conjunction with the drawings, in which:

FIG. 1 is a diagrammatic sectional view of an atomizerburner structure constructed in accordance with the invention for use in an atomic absorption spectrometer;

FIG. 2 is a sectional view of the nebulizer structure employed in the structure shown in FIG. 1;

FIG. 3 is a diagrammatic view of the flow patterns employed in the nebulizer shown in FIG. 2;

FIG. 4 is a sectional view of a second form of nebulizer constructed in accordance with the invention;

FIG. 5 is a diagrammatic view of the flow patterns produced by the nebulizer shown in FIG. 4;

FIG. 6 is a diagrammatic view of a second form of nebulizer-spray chamber system constructed in accordance with the invention; and

FIG. 7 is a diagrammatic view of still another form of nebulizer-spray chamber system constructed in accordance with the invention.

DESCRIPTION OF PARTICULAR EMBODIMENTS With reference to FIG. 1 spray chamber 10 has mounted on it a burner head 12 which is connected to the spray (premix) chamber 10 by means of conduit 14. The chamber is supported by brackets 16. At the end of the spray chamber 10 remote from the burner head 12 is secured an end cap that supports a nebulizer structure generally indicated at 18. This nebulizer structure includes a capillary to which is connected 22, the end of which is disposed in a liquid sample 24 held in container 26. Coupled to the nebulizer structure 18 is oxidant inlet conduit 28 and extending through the end cap is a fuel inlet conduit 30. Conduit 30 is connected to tube 32 that has an outlet orifice 34 disposed in coaxial opposition to the outlet orifice 36 of the nebulizer. A drain 38 is provided in the base of spray chamber 10.

Details of the nebulizer structure may be seen with reference to FIG. 2. The nebulizer body 10 includes a nozzle section that has a series of coaxial steps 41-44 dimensioned as indicated in the following table:

Length Diameter (inch) Disposed within nebulizer body is an insert 46 which defines a further coaxial nozzle step 48, 0.035 inch in diameter and 0.093 inch long, and a plenum chamber 50; and a sample tube holder 52 which supports the capillary tube 20. Holder 52 is threadedly connected to body 40 so that rotation of the knurled head 54 adjusts the position of the end 56 of the capillary tube 20 relative to the entrance of the nozzle step 48. A housing 58, to which is secured oxidant entrance conduit 28, is disposed over nebulizer body 40 and O-rings 60, carried by the nebulized body 40, provide a seal between the housing and the body to define a chamber 62 into which the oxidant is introduced. The body further includes passages 64 which are aligned with corresponding passages 66 in insert 46 to provide flow of oxidant into plenum chamber 50 and from that chamber through the narrow space between the end of capillary 20 and the entrance to passage 48, the flow of oxidant past the end of the capillary aspirating sample from container 26 for flow into the nebulizer nozzle section. An O-ring 68 mounted on holder 52 provides a seal between holder 52 and body 40.

Capillary tube 20 has an CD. of 0.028 inch and an ID. of 0.018 inch. The orifice 34 of the fuel supply tube 32 has a diameter of 0.050 inch. In this particular embodiment satisfactory operation has been obtained where orifice 34 is spaced over a range of positions from A inch to 1 inch from the outlet plane 64 of the nebulizer nozzle, a preferred spacing being inch.

In a particular operation, air at a pressure of 40 p.s.i.g. is supplied through inlet 28 to plenum chamber 50 to aspirate a sample from container 26 through capillary 20. A fuel-air mixture of acetylene at a pressure in the order of 6-8 p.s.i.g. through a 0.036 inch throttling orifice and air at a pressure of 5 p.s.i.g. through a 0.032 inch throttling orifice is supplied through tube 32, producing a flow interaction as diagrammatically indicated in FIG. 3. The sample-oxidant stream 70 from the primary nebulizer flares out slightly and the fuel-oxidant stream 72 from conduit 32 impinges directly on the sample stream, producing an interaction zone 74 closely adjacent the exit plane 74 of the nebulizer nozzle. (Auxiliary stream 72 should have substantial velocity. In this system, for example, satisfactory results were not obtained with a /s inch conduit orifice 34.) With this device, fluid samples are converted to fog, at rates up to 2.0 ml./min., which fog does not wet a large plane surface placed in the path of the fog stream. Aqueous samples containing copper in a concentration of 10 parts per million, nebulized with this apparatus, produce atomic absorption instrumental readings up to 1.6 absorbance units while the same copper solution nebulized with a conventional nebulizer structure (without the auxiliary stream from conduit 32) was converted to fog at a rate 1.0 milliliter per minute or less and produced instrumental readings of 0.7 absorbance units maximum.

A second form of nebulizer structure is shown in FIG. 4. This nebulizer structure also employs a series of nozzle steps 41a-44a. The base orifice 48a and capillary 20a are also of the same dimensions as the corresponding elements of the nebulizer shown in FIG. 2. An adjustable annular orifice (a suitable width being 0.020 inch) communicates via conical passage 82 with plenum chamber 84. Passage 82 is inclined at an angle of 45 to the nebulizer axis and is formed between threadedly connected nebulizer nozzle components 86 and 88 which are sealed by O-ring 90. In addition, a baflle in the form of a ball 92, 0.375 inch in diameter is located 0.1875 inch from plane 64a of the nebulizer nozzle.

In operation, oxygen supplied through orifice 48a aspirates a sample from container 26 through capillary 20a and produces a fog stream. Fuel (or a fuel oxidant mixture) is supplied to orifice 80 through passage 82, producing a total air fuel ratio in the range of 8-1 to 12-1. With reference to the diagrammatic representation in FIG. 5, the primary flow from the nebulizer orifices 20a and 48a form stream 94 and the secondary flow from orifice 80 forms stream 96. These two streams impinge on one another and produce an interaction zone 98 inside the nozzle (in an area of sub-atmospheric pressure). The interaction products from zone 98 impinge on bafile surface of ball 92 and the resultant fog produced then flows through the spray chamber to the burner head.

With this nebulizer arrangement, the baflle surface can be placed substantially closer to the exit of the nebulizer than if the secondary stream is not used and the nebulizer efiiciency is greater, a larger fraction of the aspirated sample being converted to fog. Further, the mixing of the fuel, oxidant and sample is more thorough and the variation in the flame and its effect on the analysis is thus significantly reduced. For most analyses, the absorbance readings for a given sample are steadier and mode precise, thus enabling the analyses to be completed more quickly. Also instrumental variations (noise) due to variations in the flame are reduced, particularly in the deep ultraviolet. For example, near the resonance line for lead (2170 Angstroms) absorption of light by the flame becomes significant and that absorption is markedly affected by the fuel oxidant ratio in the flame. With the nebulizer shown in FIG. 4, the variation in output signal base line in this region is one-quarter to one-half that obtained using a conventional nebulizer improving both the precision and the detection limit of elements with resonance lines in this region of the spectrum. A device of the type shown in FIG. 4 can reliably generate fog of reduced droplet size at a rate of 2 milliliters per minute, the fog stream not wetting a large plane surface placed in its path.

In certain applications the arrangement of nebulizer and spray chamber indicated in FIG. 6 is particularly advantageous. In that arrangement a nebulizer of configuration shown and described in connection with FIG. 4 is applied, which neutralizer is mounted vertically in a fog forming chamber 100 that has a drain section 102 in its base. The fog chamber 100 has, in its side wall, a connection to mixing chamber b. This configuration results in quieter overall operation of the nebulizer-spray chamber system and reduced analytical noise. Still another modification of nebulizer-spray chamber system is indicated in FIG. 7 in which a nebulizer of the type detailed in FIG. 2 is used, with supplemental secondary

counter flow jets

104 and 106 directed at an angle of 120 to the primary flow from nebulizer 180, the primary nebulizer stream being directed vertically downwardly in fog forming chamber 100, which chamber is connected to mixing chamber 100 via an aperture in its side wall.

While particular embodiments of the invention and modification thereof having been shown and described, other modifications will be apparent to those skilled in the art and therefore it is not intended that the invention be limited to the disclosed embodiments or to details thereof and departures may be made therefrom within the spirit and scope of the invention.

What is claimed is:

1. A nebulizer comprising a nozzle structure having an aspirator orifice, a sample orifice disposed adjacent said aspirator orifice so that a sample may be aspirated through said sample orifice by fluid flow through said aspirator orifice to form a primary stream, and an auxiliary orifice for directing a second fluid stream for flow directly counter to the flow of said primary stream to impinge on said primary stream in an interaction zone in the immediate vicinity of the nebulizernozzle, the interaction of said primary and secondary streams producing a fog having droplets of smaller dimension than the droplets in said primary stream.

2. Apparatus for use in a spectroanalytical instrument comprising a burner structure, a spray chamber for supplying a fuel-oxidant mixture to said burner structure, and a nebulizer for furnishing said fuel-oxidant mixture in fog form to said spray chamber comprising a nozzle structure having an aspirator orifice, a sample orifice disposed adjacent said aspirator orifice so that a sample may be aspirated through said sample orifice by fluid flow through said aspirator orifice to form a primary stream, and an auxiliary orifice for directing a second fluid stream for flow directly counter to the flow of said primary stream to impinge on said primary stream in an interaction zone in the immediate vicinity of the nebulizer nozzle, the interaction of said primary and secondary streams producing a fog having droplets of smaller dimension than the droplets in said primary stream for flow through said spray chamber to said burner structure.

3. The apparatus as claimed in claim 2 and further including additional orifices for directing supplementary secondary fluid streams for impingement on said primary stream at said interaction zone.

4. Apparatus for use in a spectroanalytical instrument comprising a burner structure, a spray chamber for sup- :plying a fuel-oxidant mixture to said burner structure, a fog forming chamber connected to said spray chamber, and a nebulizer for furnishing said fuel-oxidant mixture in fog form to said spray chamber comprising a nozzle structure having an aspirator orifice, a sample orifice disposed adjacent said aspirator orifice so that a sample may be aspirated through said sample orifice by fluid flow through said aspirator orifice to form a primary stream, said nebulizer nozzle being mounted on said fog forming chamber to direct said primary stream downwardly through said fog forming chamber and the fog flow from said fog forming chamber through spray chamber to said burner structure being generally horizontal, and an aux iliary orifice for directing a second fluid stream to im pinge and on said primary stream in an interaction zone in the immediate vicinity of the nebulizer nozzle, the interaction of said primary and secondary streams producing a fog having droplets of smaller dimension than the droplets in said primary stream for flow through said spray chamber to said burner structure.

5. The apparatus as claimed in claim 4 wherein said nebulizer nozzle includes a nozzle outlet defining wall that includes a series of steps defining a series of openings of increasing cross-sectional area coaxial with said primary stream, said auxiliary orifice directs said secondary stream for impingement on said primary stream at said interaction zone at an angle greater than 15 to the direction of flow of said primary stream, and said interaction zone is within one inch of said nebulizer nozzle.

6. The apparatus as claimed in claim 5 wherein said auxiliary orifice directs said secondary stream for flow directly counter to the flow of said primary stream.

7. The apparatus as claimed in claim 6 and further including additional orifices for directing supplementary secondary fluid streams for impingement on said primary stream at said interaction zone.

8. The apparatus as claimed in claim 5 wherein said auxiliary orifice is an annular orifice formed within said nebulizer nozzle and further including a convex surface fixed in position in front of said nebulizer nozzle directly in the path of said primary stream.

References Cited .UNITED STATES PATENTS 2,571,871 10/1951 Hayes 239348 X 2,840,417 6/1958 Dorsak et a1. 239-338 X 2,857,801 10/1958 Murray 239338 X 2,890,765 6/1959 Friedell 239-438 X 3,138,330 6/1964 Gilbert 239-346 X FOREIGN PATENTS 1,312,057 11/1962 France.

SAMUEL F. COLEMAN, Primary Examiner