INSTRUMENTATION iliiS
Automatic colorimetric analyzer eliminates need for many analytical procedures
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.TJTOMATION continues t o invade t h e analytical laboratory. W h e r e a large number of essentially repetitive deter minations a r e t o be made, i t can p r o vide great savings in time a n d money. It is almost equally useful in pure r e search, as evidenced b y use of such instruments as recording spectropho tometers, polarographs, a n d "vapor phase chromatographs. A fine ex ample in t h e field of colorimetric analy sis has been brought t o o u r attention. Through t h e courtesy of Andres F e r rari, director of t h e research labora tories of t h e Technicon I n s t r u m e n t s Corp., Chauncey, Ν . Υ., we a r e able to present details of t h e Autoanalyzer. A paper on this topic was presented b y Ferrari before t h e Division of Ana lytical Chemistry a t t h e recent national m e e t i n g of
the AMERICAN
CHEMICAL
SOCIETY in N e w Y o r k .
T h e Autoanalyzer is a completely automatic system which records t h e level of concentration of a given com ponent in t h e test solution against a known concentration of t h a t compo nent in a standard control solution. No gravimetric or volumetric measure ment is involved : R a t h e r it is a m a t t e r of continuous plotting of ratios ( t h e concentration of t h e sought material in the unknown against i t s known con centration ratio in t h e s t a n d a r d con
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T h e p u m p consists of t w o parallel stainless steel roller chains with spaced roller t h w a r t s t h a t bear continuously against a spring-loaded p u m p platen. Across this platen lies a manifold—a set of flexible tubes whose different
Mutter
lumens determine t h e rate of flow through each. T h u s t h e volume deliv ery of each material entering into t h e test can be varied b y passing i t t h r o u g h a t u b e of specified lumen. As t h e chain travels across t h e platen, t h e rollers advance t h e various liquids into t h e system i n t h e exact proportions r e quired b y t h e particular test. T h e separate tubes a r e uniformly, simul taneously, a n d completely occluded in concert, so t h a t proportioned delivery is accurate a n d reproducible from test to test. T h e system is readily flushed a n d cleaned. Preassembled manifolds for new techniques can be substituted with ease a n d precision. The unit t o t h e left of t h e p u m p is a dialyzer. I t s function is t h e compos ite equivalent of t h e m a n y single or associated procedures (precipitation, filtration, centrifugation, etc.) neces sary t o arrive a t a " p u r e " sample. I n this unit, sample a n d control are treated identically. T h e thermostated heat ing b a t h , which is shown immediately behind t h e dialyzer, provides a n y d e sired heating required t o develop t h e particular color reaction. Again, sam ple a n d controls are heated for exactly the same length of time. A t this point it m a y be useful t o point o u t t h a t suc cessive samples, a s well as control solu tions a r e separated from each other
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t r o l ) . F o r t h a t reason i t is never nec essary t o bring a reaction t o comple tion. T h e complete system m a y e m ploy colorimetry, conductance, p H , flame spectrometry, or t h e use of t e m perature-sensitive elements as criteria of concentration. T h e present descrip tion is confined t o colorimetry. T h e complete system is illustrated in Figure 1. A t t h e rear right is t h e sampler plate. Samples a r e placed in plastic sample cups. T h e sample cups m a y be likened t o conventional test tubes holding samples t o be analyzed, with this i m p o r t a n t exception: Vol umes m a y be random ; they do n o t have to be measured or weighed out. I m mediately in front of this unit, a t t h e right, is t h e proportioning p u m p a n d mixing coil. This performs all t h e functions ordinarily requiring manual pipetting, weighing, measuring, a n d pouring of reagents, diluents, etc. T h e proportioning p u m p can p u m p con tinuously u p t o eight separate fluids (and air or various gases) simultane ously, while varying their individual delivered o u t p u t in any ratio u p t o 8 : 1 .
by Ralph H.
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Figure I . Complete Autoanalyzer
Figure 2. Sampler
plate
ΙΙβββΙΙΙFigure 3. Proportioning pump and dialyzer
Figure 4 . Heating bath
Figure 5. Differential colorimeter VOL. 30, NO. 1, JANUARY 1958 ·
53 A
INSTRUMENTATION
6tf/M£
instrument abstracts
Applied Physics Corp./362 W. Colorado
Street/Pasadena/California
at the Richfield Laboratories
Cary Model 14 Spectrophotometer enables determination of lead concentrations to one part per billion
The destructive effect of lead on the activity of costly catalysts makes accurate determinations of even minute amounts extremely important. With improved techniques now in use at the new Research Laboratories of the Richfield Oil Corporation, Anaheim, California, chemists can determine lead concentrations in naptha charge stocks within one part per billion. The conventional dithizone colorimetric procedures can be used to estimate the lead concentration to an accuracy of approximately 10 parts per billion. A refinement of this procedure, employing the Cary Model 14 Recording Spectrophotometer, is used to more precisely determine the concentration. The color intensity of the lead dithizone solution is measured at 5100 Angstroms for the unknown sample and for two standard solutions whose concentrations are respectively a little more and a
little less than the estimated concentration of the unknown. By interpolating, the analyst can then determine the lead concentration of the unknown to an accuracy of one part per billion or better. In this procedure, the high photometric accuracy of the Model 14 is of primary importance in reliably recording the minute differences in absorbance values between the sample and standards. This high photometric accuracy is one of several performance features provided in each Cary Recording Spectrophotometer to a degree not found in any other similar instruments. Perhaps these advantages can lead to new breakthroughs in your analytical techniques. Complete information on both Cary Spectrophotometers, Model 11 and Model 14, is contained in a bulletin which is available upon request. Ask for Data File A10-18.
BRIEF SPECIFICATIONS OF CARY MODEL 11
SPECTROPHOTOMETERS MODEL 14
RANGE
2100A to 8000)5
1860Â to 2.6 microns.
STRAY LIGHT
Less than 0.0001% at 1860A and 2.6 microns.
Less than 0.0001% between 2100A1 and 1.8 microns: less than 0 . 1 % at 1860Â and 2.6 microns.
SCANNING SPEEDS
From l.oS/sec. to 125Â7sec.
From 0.5Â7sec to 500Â7sec.
RESOLUTION
Better than 1.0A throughout range.
Better than 1.0A U.V.-visible region and 3.0Â near-infrared.
WAVELENGTH ACCURACY
Better than 5.0Â U.V. region and 10.( visible region.
Better than 4.0À throughout range.
REPRODUCIBILITY
Β
. 6 " 7 t h a n °-5Â visible region.
UV
·
regi
°"
and 3
°
S
0.5» throughout range,
PHOTOMETRIC 0.002 in absorbance. 0.004 in absorbance. REPRODUCIBILITY For further information, circle number 54 A on Readers' Service Card, page 73 A
54A
·
ANALYTICAL CHEMISTRY
by the original sampler plate. The latter, in sucking up samples or control solutions, is intermittently exposed to the air, so that the feed line is spaced with air bubbles and thus very effectively separates the various batches. Adequate tests have established the fact that this intermittent spacing and purging introduces negligible contamination from preceding samples. The next unit, to the left, is the photoelectric colorimeter which compares sample and control. These are measured through interference filters from a common light source. At the extreme left is the recorder, which plots the ratio of colorimetric readings. In its simplest form, the record presents the ratio of transmittancies. An optional form of the recorder is fitted with a logarithmic slide-wire with which all readings are directly proportional to concentration for systems which obey Beer's law. Still other optional equipment permits the direct printing out on tape of the relative absorbances. Figure 2 is a detailed view of the sampler plate. The loaded plate rotates at a choice of speeds representing 20, 40, or 60 analyses per hour. A hinged pickup crook dips into each cup in succession, aspirating its contents for a given interval and feeding it into the system. At the proper instant, the pickup crook automatically lifts up, while the sampling plate rotates and then dips into the next cup, and so on until all samples are transferred to the instrument. During the periodic intervals between dips the aspirating crook draws in air, which acts as an insulating barrier between successive samples as they flow along the analyzing route. The time ratio of drawing sample vs. drawing air is roughly 2 to 1. A more detailed view of the proportioning pump and dialyzer is shown in Figure 3. The autodialyzer consists of a matching pair of transparent plastic plates whose mating surfaces are mirror-grooved to provide a continuous channel when the plates are brought into contact. With a cellophane membrane sandwiched between them the plates are clamped together, leaving the continuous pathway separated only by the semipermeable membrane. The dialyzer path is 87 inches long, affording a large surface to the dialyzing membrane. Nondialyzable constituents are voided to waste. Figure 4 shows the heating bath, maintained to ± 0.1° C. at any desired temperature. The analyzing stream flows through a glass helix, immersed in the bath, some 40 feet long with an inside bore of 1.6 mm. and 1-mm. walls. The bath medium is nonevaporating diethylene glycol. Transit time is about
INSTRUMENTATION
BURRELL
For Scientists Everywhere
LABORATORY FURNACE variable temperature range to 2"750°f
5 minutes. For enzymatic reactions and bacterial activity tests, a bath set at 37° ± 0.1° C. is available. The differential colorimeter shown in Figure 5 is conventional, but the sampling cell, with rectangular eompactment, is of the siphon type with a feed from the analyzing stream which permits the escape of the spacing air bubbles.
Applications A versatile laboratory fur nace for reliable operation from the lowest to the high est temperatures. From 600° F. to 2000° F., use for ashing, drawing, ig niting and tempering, above 2000° F., for sintering, melt ing, clinkering, fusing and high-speed hardening.
BURRELL BOX-MUFFLE TYPE FURNACE, Model 30 Heating chamber 7" wide χ %ι/χ" deep χ 4" high. For use with 230 volt, 50-60 cycle, single phase power supply, or with automatic controller for 115 volt, 50-60 cycle, single phase. Burrell Cat. No. 37-442 . . . . $1500. F.O.B. Pittsburgh, Pa.
Asie for Bulletin No. 375
BURRELL
CORPORATION
Scientific Instruments and Laboratory Supplies 2223 FIFTH AVENUE, PITTSBURGH 19, PA.
For further information, circle number 56 A on Readers' Service Card, page 73 A 56 A
·
ANALYTICAL CHEMISTRY
Several important clinical proce dures have been worked out; methods for blood urea and glucose may be mentioned. In the former, samples are placed in the cups. The air-spaced samples pass into a flowing stream of diluent, through a mixing coil, and then into the dialyzer. While in the dialyzer, urea diffuses across the mem brane into a parallel flowing stream of reagent (diacetylmonoxime) also seg mented by air. After leaving the dialyzer, the diacetylmonoxime is joined by a stream of sulfuric-arsenic acid reagent. It then passes through a mix ing coil and into a thermostatically heated bath, where the final color reac tion is developed. The fluid, on leaving the heating bath, passes into the flowcell colorimeter, where changes in absorbances proportional to the concen tration of urea are recorded on a stripchart recorder. A similar procedure is used for blood sugar in which the samples, after di alysis, react with alkaline potassium ferricyanide. During the subsequent heating cycle, the ferricyanide is re duced to ferrocyanide, the absorbance of which is recorded. A blood calcium technique has also been worked out based upon the reaction of calcium ion with ammonium purpurate in alkaline diethylamine-HCl buffer. A complete study has been made by Ferrari in collaboration with RussoAlesi and Kelley of the Squibb Institute for Medical Research on the completely automated system for the chemical de termination of streptomycin and peni cillin in fermentation media. Full de tails were presented at the New York meeting and will be published else where. In this careful study, the anal yses were punched on paper tape using a Flexowriter tape-punching typewriter. The tapes were then fed to a computer for complete statistical treatment of the data. The over-all precision was estimated to be to ± 2%. It may be expected that this equip ment will have a profound influence on control-laboratory practice. Researchwise, it offers means of continuous sam pling from reacting systems and sup plies accurate and more voluminous data than manual methods.
