P-E Analytical N e w s • •
Vertical sampling accessory for Model Infrared analysis for heavy water
•
Crime detection
OUT-SIZED CELL NO PROBLEM Analytical chemists who use infrared keep coming up with unique approaches to infrared problems old and new. We try to help by building equipment that makes these approaches practical. For example, there was the customer who wanted to mount two heated sample cells, each 10 inches long by 4 inches in diameter, on his Model 21 for a particular analysis, but he still wanted to be able to use the instrument for normal operations. These cells couldn't be fitted into the regular sample space by any of the conventional means at our disposal, so we did what comes naturally to our Application Engineering Group — devised a special accessory.
Vertical Sampling Accessory on P-E Model 21.
This special vertical sampling accessory, illustrated above, consists of a tailor-made optical system, a vertical stand to which the sample cells are attached, and an external globar source. The complete unit is placed in the Model 21's sample area using existing mounting provisions. T h e rest of the instrument remains entirely unchanged. Here is another example of the Model 21's versatility, of its ability to accommodate almost any kind of accessory. We welcome customer requests which put this versatility to work.
aided by Model
27 IR spectrometer
154-B Vapor
Fractometer
are much the same as those in any chemical facility, and are being tackled via familiar channels. Heavy water production is a case in point. The analytical problem here is to set up a series of instruments which can both monitor the product from the various stages of the process, and also serve as controllers. Such instruments must be sensitive, accurate, and rapid in response, and for this reason infrared techniques are being applied. In a paper entitled "The Analysis of Heavy Water by Infrared Spectrometry" 1 , Dr. J. Gaunt of the United Kingdom's Atomic Energy Research Establishment at Harwell reports that the deuterium content of heavy water can be estimated with speed and accuracy by infrared analysis. Dr. Gaunt's work was carried out to provide laboratory analytical techniques, but he always kept in mind their possible extension to plant control. In all cases, samples of heavy water were used in the form in which they would be available from the plant. Cells were made as thick as possible, anticipating difficulties in continuously flowing representative samples from a bypass through very thin cells. Dr. G a u n t confirms T r e n n e r a n d Walker's 2 findings on the effect of temperature on the absorption coefficients. This effect can be ignored only if samples and i n s t r u m e n t s a r e t h e r m o s t a t i c a l l y controlled, and it decreases as deuterium content increases. In the analysis of heavy water a calibration curve must be drawn up from known standards. This involves observing changes in the absorption of a band characteristic of the material. The choice of a suitable band is complicated to some extent in heavy water by the equilibrium which is rapidly established when pure D 2 0 and pure H 2 0 are mixed: HoO + D 2 0 ± 5 2HOD When the D 2 0 content is less than 3 % , the solution contains essentially only H 2 0 and H O D ; when greater than 97%, only D 2 0 and HOD. Therefore, measurements based on an H O D absorption band gives the greatest sensitivity in the 99-100% range, and also in the 3 % , 0.2% and natural concentration ranges. The H O D absorption band is useless in the 48-56% range since here the H O D concentration is practically constant. However, both the H 2 0 and D 2 0 concentrations vary quite markedly over this range and measurements on either should give the desired results. Dr. Gaunt's report goes on to describe in detail his methods in measuring deuterium content in the 50%, 3 % , 0.2% and natural ranges. iSpectrochimica Acta, 1956, Vol. 8, pp. 57-65. ^Trenner N. R. and Walker R. W., Perkin-Elmer Instrument News, 1952, Vol. 4, No. 1.
ALCOHOL, CRIME AND VAPOR FRACT0METRY At a r e c e n t m e e t i n g of t h e F o r e n s i c Society of Canada, a P-E engineer discussed the "Application of Vapor Fract o m e t r y to C r i m i n a l I n v e s t i g a t i o n , " particularly to the analysis of alcohol in blood, breath and liquor. The society is a relatively young organization composed of members of Canadian Forensic Laboratories, lawyers and medical men and those who are interested in the enforcement of federal and provincial statutes. The objects of the Society are to promote better understanding between members of the legal, medical, police and scientific organizations and to organize and disseminate information on modern scientific methods used in the aid of justice.
They learned that gas chromatography shows promise as a basis for the rapid and accurate measurement of quantities of alcohol in blood, liquor or exhaled gas. The use of the same equipment for detection of adulterants and poisons was also demonstrated. An application of wide interest in crime detection work is the proof of exact similarity of two volatile mixtures using a gas chromatogram "fingerprint" to show the exact qualitative and quantitative identity of two materials.
IR LOOKS AT HEAVY WATER Atomic energy research is getting to be almost routine these days. For the analytical chemist, the quantitative and qualitative problems in an atomic energy plant
I N S T R U M E N T
D I V I S I O N
Perkin-Elmer Corporation
800
MAIN AVE., NORWALK,
CONNECTICUT
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ANALYTICAL CHEMISTRY
