I N.ST R U M E N T A T I 0 N Infrared absorption spectrum techniques are ideal in medical research, criminological investigation, or forensic tests
by Ralph H. methods and tecb0 niques . several for the identification of F THE
substances, few are as direct and conJ
We had the opportunity of seeing striking examples of this technique a t Kodak Park last fall, and through the courtesy of Don H. Anderson of the Industrial Laboratory of the Eastman Kodak Co., we are able to present some of the principal features of the method. A beam-condensing lens system for handling microspecimens was developed several years ago [Anderson, D. If., and Miller, 0. E., J . Opt. Soc. Amer. 43,777 (1953)l. This system employed planoconvex silver chloride lenses. The high index of refraction of silver chloride makes it easy to attain a high relative
Mirl/er
aperture system with a reasonable degree of correction for spherical aberration. The Special Products Sales Division of Eastman Kodak can supply a set of infrared mirrosample optics for this purpose, consisting of an unmounted pair of plano-convex silver chloride lenses of 24-mm. diameter and 22-mm. focal length, coated with a black silver sulfide smoke that cuts out
Figure 1. Typieal silver chloride lens
vincing as an infrared absorption spectrum, and wherever the nature of the substance permits, such characterisation leaves little to be desired. I n medical or biochemical research, criminological investigations, or forensic tests those methods are ideal, provided one can extend the techniques to extremely small specimens. A combination of techniques has made this possible, so that 10 to 50 y of material will suffice for quantitative spectra and simple identification can be made in the fractional microgram range.
V O L U M E 28, NO. 4, A P R I L 1 9 5 6
Figure 2. Typical spectrograms 41 A
instrument abstracts Applied Physics Corporation/Pasadena/CaZifornia
Double Monochromator Provides Low Stray Light, High Resolving Power Spectrophotometer Users c a n measure high absorbance values with the same speed, accuracy and Miabilrty a s ,,ther measurrm&ts by using a (:3ry Recordrng Spectrophotomlodel3l Vihmting Reed F:lectromatrr. It is orefwred . for .. menssuring ion currents in work where extreme response speed is not required, such as isotope determinations. Sensitivity of the Model31 is 10- amprres. and like the 36 i t has h i e h s t a h h t v - less l h 8 n 5 x 110- ' agperes zerddrift. Write for bulletin ~
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ACA-12.
RAMAN SPECTROGRAPH INFRARED ANALYZERS
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. ~fL€CTROMf1ERS UllRAVIOLET ANALYZERS
362 WEST COLORADO SIREEI / PASADENA 1 / CALIFORNIA
For further IltOrmlliol, circle numbers 42 A.1, 12 A d 01 Readers' Senirl Card. p a b 61 A
42 A
INSTRUMENTATION radiation helow 1 mirron. The silver rliloride itself is transparent well beyond 17 microns. Still more convenient, for those who wish a completely mounted assembly, are commercial beam-condensing units supplied by both Raird Associates and Beckman Instruments, Inc. These can be placed in position in standard twin-beam instruments in a matter of a few seconds. They are patterned after the design of Anderson and Miller. A typical silver chloride lens is illustrated in Figure 1. The the pinhead is ahout 20 times larger than that required for infrared analysis. Sample preparation involves a simplified potassium hromide pellet technique. Anderson and Woodall have described a complete procedure for the preparation of round and rectangular pellets weighing only 5 mg. and eontaining as little as 10 y of the compound under test. These are mounted very easily in the silver chloride beam-condensing system of cross-sectional area less than 4 sq. mm. [Anderson. D. H., and Woodall, iY.B., ANAL. CHICK2 5 , 1906 (1953)l. Further details of L: simple die for preparing potassium bromide pellets under vacuum are given by Anderson and Smith [ANAL.CHEM. 26, 1674 (1954)l. Kxtensive experience with the pellet tevliniquen has led these authors to shanclon the mineral oil mull almost completely, a n exprrience no doubt s h r e d Iiy mist workers in recent years. Sunie typical spectrograms obtained with this inicroproceilure are shown in Fignre 2. Although we have quoted concentration ranges above, the designations applying to Figure 2 have been quoted in soruewhat more striking fashion by Anderson, when he states, "If one twentieth of a grain of sugar could be split off, this \voulil be enough tu give a recognizal,le infrared curve for SIII'I'OR~. IRSS than one thous:m
