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Publication numberUS3684452 A
Publication typeGrant
Publication dateAug 15, 1972
Filing dateFeb 27, 1970
Priority dateFeb 27, 1970
Publication numberUS 3684452 A, US 3684452A, US-A-3684452, US3684452 A, US3684452A
InventorsBessman Samuel P
Original AssigneeBessman Samuel P
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Automatic digestion and dry ashing apparatus
US 3684452 A
Abstract  available in
Previous page
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Claims  available in
Description  (OCR text may contain errors)

AUTOMATIC DIGESTION AND DRY ASHING APPARATUS Filed Feb. 27, 1970 Aug. 15, 1972 s. P. BESSMAN 3 Sheets-Sheet l W- 1972 s. P. BESSMAN 3,684,452

AUTOMATIC DIGESTION AND DRY ASHING APPARATUS 3 Sheets-Sneet 2 Filed Feb. 27, 1970 AUTOMATIC DIGESTION AND DRY ASHING APPARATUS Filed Feb. 27, 1970 Aug. 15, 1972 s. P. BESSMAN 3 Sheets-Sneet 5 W F/G.o

3,684,452 AUTOMATIC DIGESTION AND DRY ASHING APPARATUS Samuel P. Bessman, Department of Pharmacology, University of Southern California, 2025 Zonal Ave., Los

Angeles, Calif. 90033 Filed Feb. 27, 1970, Ser. No. 15,045 Int. Cl. G01n 33/16 U.S. Cl. 23-253 R 10 Claims ABSTRACT OF THE DISCLOSURE Apparatus for performing analytical procedures wherein a multiplicity of test tubes are mounted on a turntable or endless belt and the sample inside each tube is evaporated and dry or wet ashed. A U-shaped heating channel through which the turntable mounted tubes pass has a multiplicity of heating coils mounted in the channel walls. A coil in each side wall of the channel is just above the liquid level in the tube so as to heat the tube and contents to progressively more elevated temperatures without causing boiling and bumping. The distal half of the channel contains at the bottom thereof an additional heating element further to heat the tubes and contents. A special sample removal and sample inlet structure forming part of the invention involves a multiplicity of suction outlet and inlet connections which provide for a staged tube wash and rinse sequence. In each wash and rinse substation a liquid inlet line and a suction outlet line dip into the tube with wash water flowing from inlet into the tube then out the suction outlet. The suction outlet tube in each successive substation are set at a higher level, so that the next to final wash and rinse substation leaves the tube full of liquid and the final wash substation removes it ahnost completely.

The present invention relates to improvements in apparatus for performing analytical procedures and more specifically for performing ashing procedures.

Automatic analyzing systems adapted to the multitudinously repetitive chemical analysis of the sort commonly encountered in hospital laboratories and in biochemical experimentation olfer material advantages to the analyst, and are virtually mandatory for conducting the many clinical tests now desired by physicians. The need has been recognized and an established body of art exists on automatic laboratory equipment and analytical procedures adopted thereto. Characteristically, such equipment involves an apertured turntable with test tubes disposed in the apertures, and electric motors and switching controls to intermittently rotate the turntable through an arc corresponding to center-to-center distance be tween adjacent tubes per movement. As each tube moves on the turntable it travels through a predetermined sequence, e.g. sample entry, reaction and sample removal, according to whatever analytical procedure has been set up for the equipment. Sometimes the measurement is made directly on the liquid material which is in the tube, e.g. by colorimetric techniques. At other times the sample is withdrawn and tested elsewhere. In any event, the tube itself stays on the turntable and must be washed clean before repeating the test cycle. Otherwise, preloading the equipment with a fresh set of clean tubes would be required every cycle.

Instead of a turntable, an endless belt or chain carrier may support the tubes in their course through an analysis sequence.

The apparatus of the present invention involves adaptation of conventional turntable or endless belt analytical equipment to carrying out ashing tests on aliquots. Many United States Patent difierent types of solutions containing different organic compounds may be evaporated and wet or dry ashed in the system. For example, organic phosphates, sulfates, iodides and metal chelates may be ashed, using, of course, appropriate reagents.

The structural adaptation involved is not complicated. The intermittently rotated turntable mounting or endless belt mounting is modified only to whatever extent is required to provide space under the turntable or belt for the heating channel. In practice, a turntable, apertured at the periphery thereof for holding test tubes has a stationary arcuate heating channel placed beneath the apertures, so that the test tubes depending from the apertures will travel the length of the channel as the turntable rotates. The contents of each tube is evaporated and ashed. The ancillary structure, e.g. motor, switches, etc. are not afiected and may be the same as in prior-art intermittent systems. A straight-run heating channel can be employed with the endless belt or chain carrier equipment.

Presence of dry ashed residue in the test tubes can cause contamination of subsequent analyses in the same tube or make difficult the sample removal and test tube cleaning operations which occur at the end of each cycle. Accordingly, a special washing and rinsing accessory structure is provided as part of this invention.

Basically, the special washing and rinsing station involves a multiplicity of substations in which the digested sample (now redissolved as part of the chemical analysis test procedure) is first removed by a suction line. Thereafter, at each wash and rinse substation, a wash solution inlet and suction outlet line enter the test tube. All of the wash solution inlet lines extend to near the bottom of the test tube. However, the various suction outlet lines terminate successively at everhigher height levels inside the test tube. At the first wash and rinse substation the suction outlet line extends to near the bottom of the test tube. At the second, the suction line terminates at a somewhat higher level in the tube; at the third, still a higher level, etc. until in the last wash and rinse substation the suction outlet line terminates just below the top of the test tube leaving the test tube essentially full of wash water. Thereafter, at the last wash outlet substation a suction outlet extending to the bottom of the test tube draws out all of the wash solution. The test tube (or other form of tubular test receptacle) is now clean and available for reintroduction of sample.

The purpose of providing a multiplicity of washing inlet and suction outlet substations with the suction outlet substations at progressively higher elevation relative to the tubular receptacle is to ensure maximum cleanliness. Initial removal of the dissolved sample nonetheless leaves a film and crust of sample material on the side and bottom surfaces of the test tube. Introduction of washing solution is, of course, intended to dissolve all of this residue material, multi-stage washing is intended to dilute the dissolved material in the wash water and to further dissolve any undissolved material, until, ultimately, only pure water is present in the test tube. Unfortunately, actual solution of all of the material in the original residual film takes time and a tendency exists because of surface tension and other physiochemical effects for undissolved material to remain in the tube and be collected as a ring on the tube at the level of the air-liquid interface corresponding to the position of the suction outlet. Provision then of the present multi-stage washing system with the outlet liquid level being ever higher in the tube stage to stage disturbs this situation. More of the residue is dissolved and washed away and, most importantly, any final undissolved residue remaining after the washing operation is concentrated at the very top of the test tube at a level far above the liquid level of the initial sample and that achieved during the course of the chemical analysis. This multiple stage graded elevation washing system permits crusts which form to fall ofr at each stage and be suctioned out through the outlet rather than drive all crusts to the top which would occur if the heights of the Wash outlet tubes were the same. Accordingly, the washing procedure removes any possibility of contamination of the test tube occasioned by its use on successive test samples and in a real sense is related to the ashing procedure because it means that one test does not leave a residue which affects tests subsequently made on samples in the same test tube. This arrangement also permits dilferent wash solutions to be added in sequence and finally removed in a last rinse to the top of the tube.

For further understanding of the invention, reference is now made to the attached drawing wherein the equipment of the present invention is diagrammatically illustrated:

FIG. 1 is a top view of the turntable;

FIG. 2 is a section taken along line 22 of FIG. 1;

FIG. 3 is a partial section taken along lines 3-3 of FIG. 1 and illustrates the test tube washing and rinsing operation;

FIG. 4 is a top view of the heating channel;

FIG. 5 is a top view of a chain drive system;

FIG. 6 is an enlarged view taken along line 6-6 of FIG. 5 showing the spatial relation of test tubes, bracket holders, sprocket chain and heating channel; and

FIG. 7 is an enlarged partial view of the chain and test tube holders.

Referring now to the drawings it may be seen that the structure of the present invention comprises in one mode thereof a turntable 12 containing a multiplicity, e.g. 50 circular apertures 14. A test tube 16 is disposed in each aperture being supported therein by the out-turned lip of the test tube. Turntable 12 is driven by a shaft 18 which in turn is intermittently rotated by intermittent drive means 20 powered by an electric motor 22. The intermittent drive means 20 is shown illustratively because intermittent drive mechanisms (e.g. Dayton M 8 brake gear motor and Geneva mechanism) are well-known to the art per se and may be routinely purchased in the open market, for use in the aliquot ashing structure of the present invention.

Also driven oif motor 22 is a cam 24 which causes an overarm structure 26 to ride between the lower position illustrated in the drawing where the various inlet and outlet lines are inserted into the test tubes 16 and an upper position wherein these lines are fully withdrawn therefrom, and turntable 12 is free to rotate without interference. Overarm assembly 26 is comprised of an upstanding bar 27 which rides on cam 24, a guide bearing 29 and an apertured plate 28 atop bar 27 which serves as mount for the many inlet and outlet lines. A friction fit of the glass or plastic tubing in the individual apertures 30 holds these lines in place. If desired, the vertical motion of the overarm structure can be brought about by rack and pinion, lever and solenoid, or other well-known device.

FIGS. 1 and 3 show how the multiplicity of inlet and outlet lines are associated with overarm structure 26. In the illustrated embodiment six substations are shown, a sample removal station 41, four wash and rinse removal station 50. As turntable 12 rotates (clockwise) in the direction shown by the arrow, the test tube containing dissolved sample reaches the removal substation 41 under plate 28, then while turntable 12 is stationary, cam 24 causes overarm 26 to descend, dropping tubes 31-40 into their corresponding test tubes. Sample withdrawal line 31 is a suction tube which extends virtually to the bottom of the tube at station 41 when the overarm assembly is at the bottom of its cycle. This suction line removes all of the sample liquid from the test tube for testing or discard depending upon the individual analytical test procedure involved. Although the sample has been withdrawn, a

liquid film remains on the wall inside the test tube and sometimes undissolved residues are also present in the test tube, usually on the side wall thereof. Suction through line 31 is adjusted to allow essentially all of the sample to be withdrawn from the test tube through sample withdrawal line 31 during the stationary part of the cycle of turntable 12. Then the cam 24 acts to raise overarm assembly 26 and its associated inlet and outlet lines clear of the test tubes, and, thereafter, turntable 12 moves the test tubes one tube position. The test tube from which sample has just been withdrawn passes to the first washing and rinsing substation 42 and the next test tube in line moves into the sample withdrawal substation 41. In each of the washing and rinsing substations a wash solution inlet 32, 34, 36 and 38 extends nearly to the bottom of the test tube 16. In each of the wash and rinse substations 42, 44, 46 and 48 a suction outlet line 33, 35, 37, and 39 is positioned inside the test tube at an ever-higher level, with outlet line 33 in the first washing and rinsing substation 42 being positioned quite far down in the tube, e.g. about up from the bottom, the outlet line 35 in substation 44 being about half way up from the bottom, the outlet line 37 in the next substation 46 being up from the bottom, and outlet line 39 in the last washing and rinsing substation 48 terminating very near to the top of the test tube. In the first of the washing and rinsing substations 42, wash solution entering from line 32 is drawn out by suction in line 33. Any solids or liquid residue not drawn out line 33 during the rinse tends to concentrate on the walls of the test tube at about the meniscus level of the outlet line 33. The washing action is terminated by stopping flow by a timed valve just prior to the upward movement of overarm structure 26, then turntable 12 rotates the test tubes to the next succeeding position and overarm 26 drops wash solution line 34 and wash solution outlet line 35 into the same tube for the next washing and rinsing of substation 44. Wash solution again rinses out any remaining solution, and in so doing tends to lift any residual solid material from the former meniscus level (about up the tube). Any redeposit of solids would be at the higher meniscus level in the second washing stage. In like fashion the test tube 16 passes through the third washing and rinsing substation 46, then through the fourth washing and rinsing substation 48 wherein the lines 37, then 39 raise the deposition point of any undissolved material successively higher until in the last washing stage 48 the position of outlet line 39 is very near the top of the test tube, far above the expected level of sample solutions employed in the analytical test procedure. In substation 50 suction outlet line 40 is positioned by the action of overarm 26 at the bottom of the test tube to remove the wash solution left in the test tube after passage through wash and rinse station 48. I

Experience with models constructed according to the practice of the present invention has shown that in the ashing of organic phosphate, four or five wash and rinse substations will diminish contamination in the test tubes, cycle to cycle, by a factor of over 1,000-fold.

For simplicity, the sample addition and reagent additional substations have been omitted from the drawing. The sample introduction may, of course, be made part of the overarm structure 26 by provision of an additional substation on plate 28. Generally, plate 28 is lengthened or other like plates are connected to bar 27 so that additional inlet lines, as needed, introduce sample, reagents, diluents, etc. according to whatever analytical procedure is involved. Thus, it should be understood that after the tube 16 passes the washing station, new sample can be introduced and reacted as desired in each test tube 16 during its travel around turntable 12 towards the arrangement for ashing the samples (reacted or otherwise) inside tubes 16. Conventional sample addition, reagent addition, stirring and like structure is contemplated in association with the ashing arrangement and the washing station structure- In any event the samples inside the test tubes 16 approaching heating channel 60 are prepared as necessary for ashing in their passage through channel 60. Also, after departure of test tubes 16 from heating channel 60 diluent and reagents may be added, and if desired, additional procedures appropriate to the tests being conducted may be carried out while the test tubes progress on turntable 12. For example, the sample may be stirred by a vibrating reed, a rotating magnet, or wire actuated by a reactance coil, or it may be mixed by agitation by a vibrating bar applied externally to test tube 16. Such reagent addition and test procedures per se form no part of the present invention and have been omitted so that the inventive features present here may be emphasized. Again, the diluent and reagent addition lines, even stirring rods or vibrators, are carried by an overarm structure like overarm 26, being, if desired, an arcuate extension of plate member 28.

The detailed construction of heating channel 60* is important to controlled ashing. Thus, as may be seen in FIGS. 2, 3 and 4, heating channel 60 is a semicircular refractory-lined open member resting on the housing 70'. Turntable 12 is disposed above channel 60 and is related thereto so that test tubes 16 may pass between the channel walls 72, 74. A heating coil 73, 75 is disposed in each side wall 72, 74 of the channel 60 at a level thereon which is at or above the meniscus of the liquid sample being ashed in test tubes '16. The reason for disposing heating coils 7 3, 75 at this level is to avoid bumping and spattering of the liquid. Such phenomena can occur when the bottom of a (liquid filled) test tube is strongly heated. Positioning the heaters at the side of the tube at or slightly above the meniscus level heats the liquid from the top down. Vaporization and gentle boiling starts at the top. In a variation of this apparatus, air or nitrogen may be blown in a fine stream into the tubes from nozzles positioned above them while they are in the heating channel to accelerate evaporation and prevent boiling. Once the liquid has been diminished appropriately, heat may be applied to the bottom. A third heating coil 77 extends about the distal half of heating channel 60 at the bottom of the channel, directly beneath the test tubes 16. In practcie, an advantageous expedient is to employ coiled resistance wire for heating coils 73, 7S and 77. The pitch of the coils in the resistance wires is varied, being greater at the proximal end, i.e. the channel entrance, and becoming less or tighter towards the distal end, so that as a test tube 16 traverses the channel length the concentration of heat thereon increases. The heating coils 73 and 75, and later 77 as well, gradually heat the liquid sample then vaporize away the liquid and finally ash the residue to whatever extent is desired. Rheostats or other electrical controls on heating coils 73, 75, 77 may be present to adjust the degree of heating which occurs at various stages in channel 60. The heating elements can be coils as in the present model or rod, plate, hot air blast or flame so disposed to produce the heat distribution described.

In an exemplary instance 50 tubes 16 are provided all around the periphery of turntable 12, and the turntable is intermittently rotated the distance of one tube position at intervals of about one minute. Suitable, the heating channel 60 constitutes an arcuate segment equivalent to 20 tubes, which is about an arc of 145 around the circumference of turntable 12. This structural relationship allows 20 minutes for any one tube to traverse channel 60 and for the contents therein to be ashed. The actual length of channel, the heat distribution, the timing of the turntable, the number of tubes thereon, etc. are all variable and can be predetermined in light of the analytical procedures to be carried out by the apparatus.

After the ashing has taken place in channel 60, test tubes 16 move along on turntable 12 as it rotates, and

at appropriate points (not shown) between heating channel 60 and the washing stations, reagents and diluents are added; and if the equipment is so set up, the tests are run on the ashed material. No illustration thereof has been included in the drawing since the actual testing procedure is outside the scope of the present invention and means for addition of diluents and reagents to turntable or endless chain-mounted test tubes is known to the art. It may be noted, however, for exemplary purposes that addition of reagents and diluents can be accomplished with a separate rocker arm structure like that already described, or alternatively, by extending the length of plate 28 appropriately and placing inlet tubing thereon.

The apparatus of the present invention can receive a continuous flowing stream of solution from an ion exchange column, for example, and deposit same within the test tubes 16 in small fractions. For this purpose, the tube containing the flowing stream may be provided with a valve operated in synchronization with movement of turntable 12 or chain 102 and of the overarm. Solenoid operated valves adapted to permit liquid flows in synchronization with analyzer apparatus are in common usage in equipment of this nature and per se form no part of the present invention have not therefore been illustrated in the drawing.

In any event, in the use of the present apparatus to handle analytic tests on aliquots from an ion exchange column, testing for phosphates, the redissolved digested material removed by suction tube 31 of overarm 26 is transferred to, and tested in, a colorimetric device. In this phosphate test the heating coils 73, 75, 77 in heating channel 60 or those in heating channel 122 are adjusted so that the finally attained temperature of test tubes '16 and their contents reaches, but does not exceed, 200 C., so that the phosphate esters are ashed to inorganic phosphate, yet the phosphate ash is not heated to the point of forming volatile pyrophosphates.

The description made above has been almost entirely with regard to a turntable mode of analyzer, with some allusion to use of the heating channel and washing stations with other analyzer structure such as endless belts. FIGS. 5, 6, 7 illustrate an endless chain version of the invention, employing, for example, a Boston Gear Roller Chain #41 for the carrier 102, driven by a drive sprocket gear 104. Idler gears 106, 108, guide carrier 102 through a circuitous endless path. An overarm structure 112 in this instance linear, is otherwise the same as overarm structure 26 and its associated tubing and operating structure. The individual rollers 114 each carry a depending flange 1)16 to which an L-shaped bracket 118 is attached. A digestion test tube 16 is suspended by its lip in a central aperture 120 on the face of bracket 118 as is best shown in FIG. 6.

The relationship of the endless belt or roller chain analyzer to the heating channel 122 is the same as exits with the turntable mode. Tube 16 passes between channel side walls 124, 126 with heating elements 128, 130 positioned above or at the liquid level inside tube 16 and a distal end heating element 132 directly beneath the tube bottom. A stationary support serves to guide and support the bracket 3118, preventing sag.

Some further modifications such as presence of multiple heating channels with cooling and/ or alternatively reagent addition between channels may be easier to incorporate in the endless belt or chain type of analyzers,

The actual operation of the apparatus in this instance is to permit addition of an aliquot through an inlet line then at a separate inlet line (the overarm being extended one position to include such inlet line) add a one-tenth of a milliliter of 1% magnesium nitrate solution. Thereafter, the sample in each test tube 16 traverses the heating channel being heated therein, dried and ashed to 200 C. to convert the phosphate esters to inorganic phosphate. (The ashing procedure from start of heating until departure from the heating channel takes 20 minutes.) Two test tube positions are allowed for cooling the tube and ash content (2 minutes), then at the next position acid solution is added. Five positions later the tubes ride upon a vibrating mixing bar. At the very next position the suction tube 31 removes the digested, ashed, now dissolved sample for further processing elsewhere or for a colorimetric measurement of the sample. In the next four positions 42, 44, 46, 48 the paired inlet and outlet lines wash and rinse the test tubes and ultimtately, at the end of this washing sequence, wash water is removed by suction line 40, to complete the cycle. The importance of tube cleanliness cannot be over emphasized. The analytic apparatus turntable or chain, normally is used for many hundreds, perhaps thousands, of ashings in a single run. If at some point in the run a very high concentration of the element or compoud of interest, e.g. phosphorus, occurs, the possibility always exists that small residues from this high concentration point will remain in the tubes to contaminate the test tubes involved causing spurious assays for subsequent aliquots 50 tubes later or in the next complete cycle of the turntable or chain. That is why the present washing and rinsing arrangement which causes each meniscus in the multistage washing sequence to be higher and more dilute than the previous meniscus not only enhances the probability for removing all residues but tends to ensure that any small residue unremoved by the washing sequence will be positioned far up in the test tube at a level which does not interfere with ashing and testing of samples introduced on subsequent cycles of the analyzer turntable or chain.

In the exemplary mode described above the test tubes are three centimeters deep by millimeters in diameter holding a sample of about 1.0 milliliter of aqueous solution. Approximately 15 micromoles of organic phosphate compounds such as adenosine triphosphate or glucose-6- phosphate can be ashed completely in each tube at 200 C.. and the tube washed with no contamination apparent in subsequent cycles of the apparatus. If contaminating residues remain from a sample of reltaively large phosphate content digested in one particular tube, then every subsequent 50th tube would analyze for a significant amount of phosphate. Special tests were run (using colorimetric readings) with high phosphate samples followed by blank samples. No change was seen from the base line reading in blanks run in the same tubes on subsequent cycles, demonstrating that large amounts of phosphates can be completely digested, and any undissolved residue washed away without contaminating the test tube. With equal facility organic sulfur compounds, organic iodides and metal chelates in aqueous solution can be ashed, and the residues cleaned from the tubes.

In passing it may be mentioned that the normal ashing temperatures for the analytic tests contemplated for equipment of this nature e.g. ZOO-400 C. is sufliciently low to permit using conventional materials of construction, e.g. aluminum for the turntable, or Teflon coated metal, and fabrication of heating channel 60 as a U-shaped or step-shaped trough made of ceramic and conventional coiled resistance wire for heating coils 73, 75, 77.

What is claimed is:

1. An apparatus for automatically conducting analytical procedures comprising a plurality of test tubes mounted in an endless arrangement; means for intermittently advancing the test tubes one tube position at a time; means at one tube position operating in timed relation to tube movement for introducing sample to the test tube at that position while said tubes are stationary; means for removing sample solution from each tube at a terminal tube position; and means intermediate the terminal position and the sample introduction position for Washing the test tubes; said apparatus including an open heating channel in association with the endless tube arrangement beneath a portion thereof and related thereto so that the test tubes traverse the length of said heating channel, said heating channel further having a pair of heating elements disposed at each side Wall thereof positioned at at least the normal elevation of the meniscus of the liquid sample inside the test tubes entering said heating channel, where by the sample heats from the top down.

2. The apparatus of claim 1 wherein a third heating element is provided in the underside of the heating channel to heat the bottom of the test tubes passing thereover said heating element extending only about the distal half of said channel.

3. The apparatus of claim 1 wherein said heating elements are formed of coiled resistance wire, the coils thereof being progressively tighter from the channel entrance to the channel exit whereby the test tubes traversing said heating channel are subjected to a progressively higher degree of heat from said heating elements as they traverse the channel length.

4. The apparatus of claim 1 wherein said test tubes are mounted on a turntable.

5. The apparatus of claim 1 wherein said test tubes are mounted on an endless chain.

6. In an apparatus for automatically conducting analytical procedures comprising a plurality of test tubes mounted in an endless arrangement; means for intermittently advancing the test tubes one tube position at a time; means at one tube position operating in timed relation to tube movement for introducing sample to the test tube at that position while said test tubes are stationary; means for removing sample solution from each tube at a terminal tube position; and means intermediate the terminal position and the sample introduction position for washing the test tubes, said washing station including a multiplicity of washing substations, with means at each substation for introducing wash solution and for removing wash solution, the wash solution removal means in each substation being a suction outlet line, the suction outlet lines terminating substation to substation at progressively higher elevations in the test tube with the final outlet suction line terminating at above the normal sample level, and a final wash solution removal substation comprising a suction outlet line for removing all the wash solution remaining in the tube after leaving the final washing substation.

7. The apparatus of claim 6 wherein said test tubes are mounted on a turntable.

8. The apparatus of claim 6 wherein said test tubes are mounted on an endless chain.

9. The apparatus of claim 6 wherein an open heating channel is associated with the endless tube arrangement beneath a portion thereof and related thereto so that the test tubes are heated from heat applied at at least the normal elevation of the meniscus of the liquid sample inside the test tubes entering said heating channel.

10. The apparatus of claim 9 wherein said heating channel includes a pair of heating elements disposed one along each side wall thereof and a heating element extending along the underside of the heating channel for about the distal half of said channel.

References Qited UNITED STATES PATENTS 2,249,098 7/1941 Van Sant l4l65 X 3,188,181 6/1965 Peterson et al. l4l13-0 X 3,192,968 7/1965 Baruch et al. l4l82 3,525,591 8/1970 Iungner et al. 23-253 R MORRIS O. WOLK, Primary Examiner R. M. REESE, Assistant Examiner US. Cl. X.R.

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U.S. Classification422/64, 141/82, 141/130, 141/65, 141/91
International ClassificationG01N35/00, G01N35/02, B01L7/00
Cooperative ClassificationG01N35/025, G01N2035/00386, B01L7/00
European ClassificationB01L7/00, G01N35/02C