US3486836A - Heated chamber burners - Google Patents

Description

Dec. 30, 1969 A- A. VENGHIATTIS HEATED CHAMBER BURNE'RS 3 Sheets-Sheet 1 Filed May 27, 1968 INVENIOR. 1916 745 19. Vengiwaih Xi t 5 E NM W Dec. 30, 1969 A. A. VENGHIATTIS HEATED CHAMBER BURNER'S- 3 Sheets-Sheet 2 Filed May 27, .1968

United States Patent U.S. Cl. 431-126 5 Claims ABSTRACT OF THE DISCLOSURE For atomizing a sample solution in, for example, atomic absorption spectroscopy, a nebulizer introduces to a burner head a relatively fine mist of sample solution, and the burner evaporates the solvent and reduces the (metallic) tested-for sample elements to their atomic state. Typically the larger drops of sample solution mist are eliminated between the nebulizer and the burner, so that the majority of the sample solution literally goes down the drain. In the present assembly a relatively long heated chamber is positioned between the nebulizer and the burner, so as to form a heated sample solution vapor (i.e., steam); and an optionally used condenser is positioned between the remote end of this heated chamber and the burner, so that most of the solvent (e.g., water) may be removed before the now concentrated sample reaches the burner. It has been found that for certain tested-for sample (metallic) elements and certain fuel-oxidant mixtures, disabling (as by removal) of the cooling element of the condenser actually improves the effective sensitivity. An improvement of approximately ten times is typically obtained in both sensitivity and ultimate detection limit relative to conventional nebulizer-burner assemblies.

DESCRIPTION This invention relates to a system for introducing a liquid sample solution in a vaporized state into a radiant energy beam of, say, an atomic absorption spectrometer; More particularly the invention concerns a liquid sampling burner assembly in which a liquid sample is first nebulized to a liquid aerosol, is then more completely vaporized by a heater chamber, followed by optional condensation of a major part of the solvent, before it is introduced into the actual burner which completely vaporizes the sample aerosol and causes the tested-for atomic elements to be reduced to their atomic state.

In, for example, atomic absorption spectroscopy the typical known sample introduction system (for liquid samples in the form of a, say, aqueous solution) comprises a nebulizer operated by the oxidant gas for aspirating the sample solution from a capillary tube for converting it into a relatively fine aerosol or mist into an expansion chamber. Fuel is mixed with the aerosol sample in the chamber, which chamber is usually long enough to allow settling of the larger droplets of the aerosol. A spoiler (a generally spiral shaped deflection plate) may be placed in the spray path within the chamber to assist in separating out these larger drops. The so filtered out larger droplets are usually eliminated. through a drain at the bottom of the expansion chamber. Typically about 90% of the total sample solution utilized goes down this drain rather than being presented to the flame. The expansion chamber also performs a premixing of the fuel with the sample aerosol and the oxidant (which typically is the gas forming the driving gas stream in the nebulizer). The resulting mixture of fuel-oxidizer and (the remaining 10% of) the sample aerosol is then passed through the burner slot (which may Vary in shape and particularly in width depending on the combination of 3,486,836 Patented Dec. 30, 1969 ice fuel-oxidizer utilized); for this reason the burner head is typically made as an interchangeable element.

Broadly speaking, the invention eliminates the loss of sample solution (thus providing ten times as much sample to the flame) by converting the larger drops (rather than eliminating them) to smaller droplets. In particular this conversion is elfected by utilizing a relatively large, long heated spray chamber between the nebulizer and the burner head. In addition a condensing column may be introduced between the heated chamber and the burner head so as to remove most of the inert solvent (e.g., water) so as to allow only practically dry sample particles to reach the flame. This condensing column is preferably so constructed that it may be easily disabled, since it has been found that its use is actually detrimental to some analyses of certain materials (utilizing particular fuel-oxidizer combinations). In its more specific aspects, the invention includes the provision of a sufficiently long heated chamber and a sufficiently large heating energy supply as to insure substantially complete evaporation of relatively large quantities of sample solution. In fact it has been found that failure to provide sufiicient heating capacity will cause the attendant larger droplets carried by the sample steam to raise the noise level of the flame, thereby substantially reducing the eifective detection limit (i.e., that concentration of sample giving an absorption signal twice as great as the noise signal).

An object of the invention is the provision of a liquid sample vaporizing system for use with an analytical instrument, which system yields an improvement in both the sensitivity and the detection limit in the analysis being performed.

A similar object is the provision of a system as just described, which includes a heating chamber between the initial liquid sample nebulizing means and the final flame producing means. 7

A further object is the provision of a system as just described, which also includes a condensing means between the heating chamber and the final flame, so as to remove a substantial portion of the solvent of the liquid sample, thereby increasing the concentration of the testedfor elements so as to allow greater total quantities of tested-for sample to be introduced into the flame without causing excessive noise.

A related object is the provision of a system as just described, in which the condensing means can be effectively disabled in a relatively simple manner, for those combinations of tested-for sample, fuel and oxidant which yield higher effective sensitivity and/or detection limit when the solvent is not so removed before introduction to the flame.

Further objects, features and advantages of the invention will become obvious to one skilled in the art on reading the following detailed specification of a single preferred embodiment of the invention, in conjunction with the accompanying drawings, in which:

FIGURE 1 is a side elevation with parts broken away, showing the entire liquid sample atomizing system, including an initial sample nebulizer, a large heating chamber, a partially removable condensing column, and the final flame-producing burner;

FIGURE 2 is a vertical lateral section, taken on the line 22 in FIGURE 1;

FIGURE 3 is a vertical longitudinal sectional view of the condensing column and final burner portions of the FIGURE 1 system, as taken on line 3-3 in FIGURE 2;

FIGURE 4 is a horizontal longitudinal sectional view of the condensing column portion, taken on the line 44 in FIGURE 2;

FIGURE 5 is a graphical representation of the improvement in absorption signal when using a nitrous oxides and acetylene mixture and a, small orifice burner head (e.g., for silicon analysis), obtained by using the condensing element to eliminate most of the water vapor; and

FIGURE 6 is a similar representation of how disabling of the condenser improves the absorption signal when an air and acetylene mixture and a large orifice area burner head are used (e.g., for copper analysis).

In FIGURE 1 the pneumatic nebulizer 10 (sometimes referred to as an atomizer) of the type conventionally used to nebulize the liquid sample in atomic absorption spectroscopy (see, for example, the D. A. Davies, R. Venn and J. B. Willis article, entitled, An Adjustable Atomizer for Atomic Absorption Spectroscopy, in the Journal of Scientific Instruments, vol. 42 (1965), pages 816 and 817) is attached to the left-hand end of a heated chamber 12, to the right-hand end of which is attached a condensing assembly 14, to which in turn is attached a burner 16. The burner 16 may be similar to that conventionally utilized in for example atomic absorption spectroscopy except that the fuel is introduced directly into the burner, as will appear subsequently.

The nebulizer 10 receives in a well known manner a continuous supply of liquid sample solution through a capillary tube 20, as well as a continuous supply of a gaseous oxidizer (for example, air) through a larger tube 22. The relatively fast flowing oxidant introduced through tube 22 acts to aspirate and nebulize the liquid sample in a well-known manner so that an aerosol of varying size droplets of sample leave the nebulizer through its discharge port 24. The nebulizer is mounted on an end cap 26 (as by screws 28), which end cap sealingly closes (as by screw threads 30 and sealing gasket 32) the large hollow cylinder 34 forming the main housing of heated chamber 12. Cylinder 34 may be of any suitable metal (for example, stainless steel) and is preferably heat insulated as by a somewhat larger cylindrical shield (of for example a glass cloth and silicone laminate), coaxially mounted about cylinder 34 as by studs 38 and insulating (say, ceramic) spacers 40. End cap 26 also supports a large coil heater 42 (of for example Calrod) the two ends (one of which is seen at 44) being passed through cap 26 and tightly and sealingly held in an aperture therein, as by a threaded nut 46 and a sealing metallic O-ring 48. The two ends of the double coiled heater 42 are supplied with electrical energy through leads, one of which is seen at 50. Coil heater 42 should be of sufiicient capacity to carry up to about 1500 watts of electrical energy, for reasons that will be explained hereinafter. The liquid sample aerosol leaving the discharge port 24 of the nebulizer 10 will thus be completely vaporized within the chamber formed by cylinder 34 by the relatively large capacity heater coil 42.

The right-hand end of cylinder 34 carries mounting stud or post 56, which in turn is supported in a base 58, which is preferably of such construction as to allow vertical adjustment of the post 56 and therefore the entire nebulizer, heated chamber, condenser and burner system. The righthand end 34' of tube 34 has a reduced portion which is sealingly attached (as by sliding fit at 62) to a part cylindrical, part frusto-conical hollow tube 64, forming the main housing of the condenser assembly 14. Rigidly attached to the interior wall of the frusto-conical portion of tube 64 is a relatively thick-walled tubular member 66. The outer surface of member 66 is configured as a relatively deep spiral so as to form a continuous spiral groove or chamber 68 between member 66 and tube 64. Additionally, a generally horizontal channel has been cut through the lower part of the outer surface of tubular member 66, as at 70, so as to act as a drainage passage for condensed liquid (see also FIGURE 3). A drainage tube 72 is attached through a hole in the lower part of tube 64 adjacent the left-hand end of this drainage channel 70. The left-hand generally frusto-conical end 74 of member 66 acts as a deflector to guide the sample (and solvent) vapor into the large spiral groove 68.

A readily removable condensing element 76 (see FIG- URES 3 and 4) is positioned within the interior of tubular member 66 and secured by the means of screw 78 to the member 66. The outer wall of condensing element 76 is relieved as at 80 so as to define a continuous annular space 82 between member 66 and element 76. Sealing means such as O-rings 84, 86 are provided between the two contiguous surfaces of elements 66 and 76 at both ends of annular space 82. Near one end, cylindrical annular space 82 communicates as by short radial passage 88 (see FIG- URE 4) with an axial bore 90 formed within the condensing element 76. Axial bore 90 contains a hollow connecting tube 92, which is engaged therein in a fluid-tight manner, as by annular sealing ring 94. Connecting tube 92 sealingly engages (as by annular ring 96) a short bore 98 formed in a removable end cap 100. A reduced diameter axial bore 102 and a reduced short vertical bore 104 (see FIGURE 2) communicate connecting tube 92 and bore 98 with a larger vertical bore 106, which sealingly engages (as at 108) a fluid connection pipe 110. Thus, a cooling fluid (e.g., water) may be introduced (or withdrawn) through pipe 110 so as to circulate through bores 106, 104, 102 and 98, through connecting tube 92, axial bore 90, and radial passage 88 to the annular space 82 between element 76 and member 66.

A similar connection (see FIGURE 2) at a diametrically opposite point on the circumference of end cap 100 is provided as the outlet (or inlet) for the circulating cooling fluid. These elements 198-210 may be identical to the other, just described connection involving corresponding elements identified by reference numerals exactly one hundred (100) lower. A relatively long connecting tube 192 (see FIGURE 4) preferably is used to connect this other fluid (cooling) connection pipe 210 (through bores 206, 204, 202, and 198) to a short axial bore 190 near the lefthand end of the oxidenser in FIGURE 4. Sealing rings 194 and 196 are also preferably provided for tube 192. A short radial passage 188 then connects bore 190 to the annular space 82 at a point near the left-hand end of this space. Such effective connection of the fluid inlet and outlet flow paths to opposite longitudinal (i.e., horizontal in FIGURE 4) ends of annular space 82 helps to insure better circulation of the cooling fluid.

End cap 100 sealingly engages (as at 112) with the right-hand end of hollow tube 64. The major part of the interior surface of cap 100 at 114 is generally conical so as to be of mating shape to the generally conical outer surface 116 at the right-hand end of condensing element 76. Since surfaces 114 and 116 are spaced at a substantial distance apart, a generally conical annular passage 118 is formed therebetween. At its left-hand edge, conical passage 118 communicates with the right-hand end of the spiral passageway 68 at 120. At its right-hand or apex side, conical passage 118 joins at 122 so as to form a horizontal central passage 124 (extending as a bore through the right-hand end of cap 100). A plurality of readily disengageable attaching means, such as screws 126, releasably attach cap 100 to condensing element 76. This in sures the proper spacing and alignment of condensing element 76 and end cap 100, the end cap being also supported by its engagement with the right-hand end of hollow tube 64, as previously noted.

A reduced external diameter tubular portion 128 of end cap 100 is connected to the burner 16 as by connecting collar 130 provided with a suitable sealing ring 132. The burner itself comprises a generally cylindrical main tubular housing 134 having a relatively large aperture near its center for receiving connecting collar 130 and tubular portion 128, through which the sample plus oxidizer gaseous mixture is introduced at 136 into the mixing chamber 138 of the burner. The fuel (for example acetylene) is introduced into the chamber 138 through nozzle 140 at the end of vertical pipe 142, to the lower end of which may be supplied the gaseous fuel, as by plastic tubing 144. The fuel supply assembly may be supported in the burner by a relief plug 146 held within the lower part of tubular housing 134 and sealingly engaged (as at 148) therewith.

A silencing assembly may optionally be provided at the lower end of housing 134. This assembly may comprise an extension or lower tail 152 of housing 134, containing a series of apertures as at 154, and a catcher nut 156, which is provided with a series of apertures at 158, not directly aligned with apertures 154. In case of a flash back, the relief plug 146 is pushed downwards; instead of allowing the burning mixture to escape through the large bottom hole of the burner with a loud bang, the silencer compels the gases of the combustion to follow an intricate path 154, 158 which results in a softer noise.

The upper end 160 of tubular housing 134 is preferably designed so as to allow a series of interchangeable different burner heads to be attached in a simple manner. For example, upper end 160 may have a somewhat enlarged internal diameter, as indicated at 162, so as to slidably receive a tubular portion of such interchangeable burner heads. Additionally a small manually operable (i.e., thumbscrew) screw or the like is preferably provided, and a groove is preferably provided in surface 162 for an O-ring or similar sealing means 166 which will not interfere with the removal of the burner head 170. Such interchangeability is advantageous, since for certain fuel oxidizer mixtures (for example, an air-acetylene mixture) a relatively large orifice area may be preferred (for example, a burner head which has three slots, each of which are approximately 108 mm. long and approximately 0.5 mm. in width). On the other hand for other fuel-oxidant combinations (for example the hotter burner nitrous oxide and acetylene mixtures), a much smaller orifice.- area burner head would be used (for example a single slot of approximately 50 mm. length by 0.5 mm. width).

OPERATION AND EXAMPLES Y A continuous supply of liquid sample is aspirated through capillary tube by the venturi and/or Pitot effect of the relatively rapid gas flow of the oxidizer (e.g., air or nitrous oxide) introduced through tube 22 into nebulizer 10. Because of the nebulizing or atomizing action of the nebulizer 10, the liquid sample and oxidizer mixture will leave the discharge port 24 as a relatively fine aerosol containing small sample liquid droplets. The relatively great length (about 12 inches in a prototype) of the heated chamber defined by hollow cylinder 34 and the large energy capacity of heater 42 (a 1500 watt, 110- volt Calrod heater controlled through a variable transformer was used in the same prototype) assures that all of the relatively large droplets are completely vaporized. For dilute aqueous sample solution, slighty more than 600 calories per minute (i.e., 10 calories'per second) or approximately 42 watts will be required to vaporize the solution (assumed to be at room temperature of about 20 C. initially) for an aspiration at a rate of one milliliter per minute. Thus, for an aspiration rate of 8 ml. of sample solution per minute, the theoretical heating power required would be about 340 watts. It has been found that the optimum heating power (for 8 milliliters per minute, of a 1 microgram of sample material per milliliter of aqueous solution) is around 500 watts, somewhat higher than the theoretical minimum required because of the fact that the resulting steam is super heated (to about 200 C.) and because of some losses.

Surprisingly it has been found that, for atomic absorption spectroscopy, the curve of heating power vs. absorbance of the sample (in the flame of the final burner head) of the radiation is a curve that resembles a skewed bell or gauss distribution type curve, having a relatively fast rise in absorbance as the heater power goes from 0 to near the optimum value, a relatively gentle. convex top to the curve, and a more gradual drop as the heater power goes beyond the optimum range. For example, a 1 microgram per millimeter aqueous solution of copper, aspirated by nebulizer 10 at approximately 8 millimeters per minute exhibited such a variation in absorbance with the instrument settings unchanged (a Model 303 Perkin-Elmer Atomic Absorption Spectrophotometer being used) as follows. At approximately watts heating power the absorbance was about 0.05; at 200 watts the absorbance had increased sharply to about 0.41; at about 350 watts it reached about 0.53; at 500 watts it reached a maximum value of approximately 0.56; at about 700 watts it was back down to 0.53; and back down to 0.42 at about 950 watts. The decrease gradually continued so that the absorbance was only about 0.27'-at approximately 1200 watts, only about 0.16 at a little over 1400 watts, and down to about 0.10 at just under 1800 watts of power. Thus, for these conditions, the optimum heating power is approximately 500 watts, but excellent results are obtained at between approximately 350 and 700 watts and good ones at least between about 200 and 1,000 watts. Additional experiments with manganese (in the same concentrations and at the same aspiration rate) yielded a generally similar type of curve, exhibiting a sharp rise to a relatively gentle maximum area, then followed by an even more gentle (than the copper) slow fall off of absorbance with too much heating power.

Condensation of at least the majority of the water vapor by the condensing assembly 1 4 is desirable where a large quantity of sample solution is presented to a relatively small orifice area of the final burner head. Where a relatively large area burner head (for example, a multiple slot burner head) is utilized, typically with air as the oxidant and acetylene as the fuel, the burner head can properly handle up to about 8 mm. per minute of aqueous solution (representing about 17 liters of steam per minute, at 200 C. and 760 torr). On the other hand, a small orifice area burner head (typically a single slot of approximately one-half the length of a multipe slot burner head) cannot handle more than about 2 milliliters per minute of sample solution without causing excessive noise in the flame (and even flame extinction) by the large original sample solution quantities are to be presented to the burner. The circulation of a coolant (e.g., water) through the annular space 82 in the condensing assembly 14 maintains all of the metal parts of this assembly at a relatively low temperature (at least approximating room temperature), so as to condense substantially more than the majority of steam as water vapor. This condensed water will of course tend to run along the bottom of the spiral grooves 68, passing through the horizontal channel 70, and ultimately through the drainage tube 72.

The value of using the condenser with a small orifice burner (with nitrous oxide and acetylene being the combustion reactants) can be seen from FIGURE 5. In that figure a relatively noise low absorbance signal is obtained without the condenser at an original sample solution aspiration rate of 2 milliliters per minute of an analyzed silicon solution at A. The much greater and less noisy absorption signal at B was obtained for the same silicon solution (and the same setting of the same atomic absorption spectrometer) but utilizing a six ml. per minute original sample solution aspiration rate and the condenser (as shown in FIGURES 1, 3 and 4). It can be shown that the data of FIGURE 5 represents an improvement of useful sensitivity of at least four times.

On the other hand, where a large area orifice burner head is utilized, it is not only feasible but preferable to avoid condensing most of the steam formed in the heated chamber 12 from the final flame of the burner. With such large area orifice burner heads (typically using air and acetylene as the combustion mixture), relatively large quantities of steam may be handled as noted before. In fact, it has been found that elimination of this steam actually reduces the sensitivity of the atomic absorption measurement being made. Thus, FIGURE 6 shows the absorption signal obtained at C with the condenser and an 8.5 milliliter per minute original sample solution aspiration rate of an aqueous copper solution while using the condenser; and the right-hand signal at D represents a slightly lower sample introduction rate (namely, 7.5 milliliters per minute) of the same (copper) solution in the same atomic absorption spectrophotometer at the same instrument settings. As may be seen from FIGURE 6, removal of the condensing element 76 (and of course disconnection of any cooling fluid) actually increases the sensitivity of the atomic absorption spectrophotometer under these conditions by about 1.8 times. An analogous experiment with a lead solution yielded similar if not quite as definite results (namely a 1.6 times increase in chart are relatively unrefractory (i.e., are relatively easily vaporized and do not form refractory oxides); while the last thee elements on the chart are the type requiring the hotter flame provided by a nitrous oxide acetylene combustion mixture. As will be noted from the following chart, there is substantial improvement in both sensitivity and detection limit for both types of analysis, (namely, the easily vaporized elements using air and acetylene without the condenser element 76; and the more refractory elements, using a nitrous oxide, acetylene combustion mixture with the condenser 76, and of course a supply of cooling fluid through annular channel 82).

Sample rate Sensitivity gjml. for Detection limit g/ml.

present 1% absorption) Approx. imfor S/N of 2:1 Approx. 1m-

burner provement provement Element (ml/mm.) Present Old factor Present Old factor Using air, acetylene (no condenser) Using N20, Acetylene (with condenser) sensitivity without the condenser). Thus, the ease with 30 which the condensing assembly may be disabled by removal of the condensing element 76 provides an appreciable improvement in sensitivity when the operator wishes to change from a large orifice burner head for airacetylene mixtures to small orifice burner heads (for nitrous oxide and acetylene mixtures) and back again.

The small particles of sample material carried by the oxidizer gas (with or without a substantial additional amount of wtaer vapor as steam, depending on whether the condenser is disabled or utilized) will, after passage through the spiral groove 68' ultimately pass through conical annular passage 118, through the horizontal central passage 124 through opening 136 into the burner chamber 138 proper. The sample and oxidizer (and steam) mixture will then be thoroughly mixed with the rapidly flowing gaseous fuel (for example, acetylene) exiting from nozzle 140 (being fed therethrough by tube 144 and pipe 142). The highly combustible resulting mixture will leave the upper end 160 of burner housing 134, and pass through an appropriate burner head, shown generally at 170. Depending on the type of oxidizer (e.g., nitrous oxide or air, respectively), a burner head having a single narrow (about one-half millimeter) moderately long (e.g., 50 mm.) slot or a large orifice burner head (for example, one with three slots, each of which are one-half mm. in width and over one hundred mm. in length) will normally be used. The appropriate burner head may be interchanged, in more or less conventional manner, as by thumb screw 164.

A heated chamber total consumption burner substantially conforming to the preferred embodiment hereinbefore described yielded substantial improvement both in sensitivity (i.e., as measured by the micrograms of tested-for metal elements per milliliter of original sample solution to obtain a 1% absorption reading in the atomic absorption spectrophotometer) and in detection limit (i.e., the number of micrograms of element per milliliter of sample solution necessary to obtain a signalto-noise ratio of 2:1). The following chart shows the improved sensitivity and detection limits obtained with the present improved chamber burner and the corresponding sensitivity and detection limits obtained with a conventional unheated burner, as well as the improvement factor in both sensitivity and detection limit (obtained merely by dividing the old figure by the presently obtained one). The first group of elements given in the As may be seen from the above partial experimental results, the relatively large heating chamber and relatively high energy heater provide substantial improvement in both sensitivity and detection limit for both types of analysis. The adaptability of the present heated chamber burner to use with either air-acetylene (or similar oxidant fuel combinations) or the higher temperature nitrous oxide and acetylene (or other high temperature oxidizer and fuel combinations) by simple removal and replacement of condensing element 76 (coupled with conventional interchange of burner heads) makes the heater chamber burner of the invention particularly versatile for atomic absorption spectroscopy in general. It should also be noted that in the heated chamber and burner combination of the invention, the acetylene (or other gaseous fuel) cannot back up from the burner (i.e., the chamber 138 defined by housing 134) because a constant forward movement of the sample and oxidizer mixture is always occurring through channels 122, 124 and 136. Thus, no large volume (and in particular the interior of condenser assembly 14 and of the heated chamber 12) can be filled with the highly combustible mixture of fuel plus oxidizer. The heater chamber burner according to the invention yields improved sensitivity and detection limits in atomic absorption spectroscopy (or other similar uses), increased versatility as to optional condensing of the liquid (e.g., water) of the sample solution, and relative safety. Since various changes may be made in the constructional details of the disclosed preferred embodiment, the invention is not limited to any such details; rather the invention is defined solely by the scope of the appended claims.

What is claimed is:

1. A heated chamber burner for forming a flame containing atomized particles of a sample material originally introduced as a sample solution, comprising:

nebulizer means, supplied with an original sample solution and an oxidizer gas, for aspirating said original sample solution and for forming therefrom an aerosol containing sample solution droplets in said 0xidizer gas;

an elongated heated chamber containing a high-capacity heater, connected to the discharge outlet of said nebulizer for receiving said oxidizer gas and sample aerosol and for bringing said aerosol to a state of super heated steam so as to form a mixture of oxidizer gas and solvent super heated vapor containing essentially a molecular dispersion of the solid sample material;

extensive channel means, connected to the exit end of said heated chamber, for carrying said samplecontaining oxidizer gas and solvent vapor mixture over a long path;

burner means connected to the exit end of said channel means, including gaseous-fuel introduction means and a mixing chamber for mixing the gaseous fuel with said oxidizer and sample-containing vapor mixture, and a burner head including an orifice at which combustion of the final mixture occurs;

and readily disengageable condenser means, releasably connected in heat-exchanging proximity of said extensive channel means, for optionally causing at least the major portion of said solvent vapor to be liquefied and therefore removed from said oxidizer and sample-containing vapor mixture before introduction into said burner means;

whereby, when said condenser means is operating, a relatively large amount of original sample solution can be mixed with a moderate amount of oxidizer gas without causing extinguishing or undesirable flickering of the ultimate flame at said burner head orifice.

2. A heated chamber burner according to claim 1, in

which:

said high-capacity heater is a large electric heater, to which a variable amount of electrical energy may be supplied;

whereby the appropriate amount of electrical heating energy may be supplied at diflerent sample-solution nebulizing rates, caused by varying oxidizer-gas introduction rates. 3. A heated chamber burner according to claim 2, in which:

said large electric heafer has an electrical energy capacity of over 1000 watts. 4. A heated chamber burner according to claim 1, in which:

said extensive channel means comprises means forming a generally hollow coil-shaped spiral chamber; and said readily disengageable condenser means comprises a condensing element removably positioned within said hollow coil-shaped spiral chamber so as to be in heat-exchanging relationship therewith. 1 5. A heated chamber burner according to claim 4, in

which:

said readily disengageable condenser means further comprises means for circulating a cooling fluid in heat-exchanging relationship with said condensing element and said extensive channel means;

whereby continual cooling of said condenser means and said extensive channel means is effected.

References Cited 25 UNITED STATES PATENTS 2,858,729 11/1958 Keyes. 3,163,699 12/1964 Stauntom.

3O EDWARD G. FAVORS, Primary Examiner

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