slMBMd Platinum Craftsmanship is
REPORT FOR ANALYSTS identification fully comparable to the fingerprint system of the Federal Bureau of Investigation. T h e possibilities of crystals of two different compounds having all three indices of refraction identical are no greater t h a n the possibility of two people in t h e United States having identically t h e same fingerprints. Of course, this method is available only for those compounds which can be formed into stable crystals. Chromatography. A n o t h e r r a p i d l y a d v a n c i n g research tool is c h r o m a t o g r a p h y . A l t h o u g h k n o w n t o t h e biochemical researcher for m a n y y e a r s , it has been only d u r i n g t h e p a s t 10 years t h a t chromatography has assumed a position of s t a t u r e in t h e analytical field. Research work on synthetic penicillins and the characterization of the various penicillins would have been almost impossible without t h e analytical separation step carried out on chromatographic columns. Analytical separation of amino acids has also been greatly facilitated b y t h e use of chromatographic columns.
Important to you
W i t h 114 years of quality craftsmanship behind it every BISHOP Platinum product is your assurance of perfect performance, to your standards, in the laboratory . . . in industry. BISHOP Platinum apparatus meets the rigid specifications of the nation's research and control chemists. Time proven designs assure speed and accuracy in routine work. You can depend on all BISHOP products:
Bimetals Electrodes Foil Laboratory Apparatus Precious Metal Catalysts Noble Metal Salts & Solutions Tubing Wire
J. BISHOP & CO. PLATINUM WORKS Malvern, Pennsylvania Circle No. 28 A on Readers' Service Card, page 73 A
28 A
·
ANALYTICAL CHEMISTRY
More recently development of paper strip chromatography has brought about significant advances in analytical methods. This technique provides the analytical chemists with an invaluable method for p u r i t y determination. T h e first knowledge of t h e presence of deserpidine in a fine chemical t h o u g h t to be pure reserpine came about when t h e chemical was chromatogramed on a paper strip. A small difference in t h e R; value led to t h e suspicion of a cont a m i n a n t having t h e same chemical characteristics as reserpine. Chemists tried other solvent systems until one was established which definitely and finally separated deserpidine from reserpine. As described earlier, t h e presence of three impurities in U S P diethylstilbestrol was discovered b y the use of paper strip chromatography. After detecting and isolating these impurities, the analytical research group t h e n was able to develop precise identity and p u r i t y tests utilizing ultraviolet spectrophotometry, x-ray spectrometry, and paper strip chromatography. A proposal for a revised monograph on diethylstilbestrol which embodies the above tests has been prepared for t h e Committee of Revision of the U.S. Pharmacopeia. Paper strip chromatography has also been adapted to q u a n t i t a t i v e work through development of a scanning device a t t a c h m e n t for the ultraviolet spectrophotometer (#). AVith this device t h e paper can be scanned over t h e entire length of t h e strip, t h e desired constituent located, and identified from the spectrophotometric curve produced.
Frequently, measurements of the area occupied by the desired constituent on the paper strip chromatogram can be used for q u a n t i t a t i v e estimation of t h e a m o u n t present. One of the most recent developments in t h e analytical field has been t h a t of gas phase chromatography and instrumentation for this method. Basically, the method depends upon converting organic liquid mixtures to the vapor phase and chromatographing the vapor through a temperatured gradient. One of t h e first assays carried out by this method in our own experience has been t h e assay on 2-bromopentane, a raw material used in the synthesis of a pharmaceutical product. C o n t a m i n a n t s in t h e starting material were believed responsible for low yields. B y gas phase chromatography we were able to show the presence of other isomers of bromopentane, along with a small percentage of pentenes. A knowledge of t h e contaminants present permitted a process change which increased yields significantly. Radioactive Tracers. A n o t h e r newa n a l y t i c a l tool d e p e n d s on r a d i o a c t i v e tracer materials. Through the addition of small a m o u n t s of such t r a c e r s in an a s s a y t h e q u a n t i t a t i o n of s e p a r a tion t e c h n i q u e s h a s been achieved, t h u s establishing a m e a n s of increasing t h e precision of p u r i t y measurements. T h e recently issued first supplement to U S P X V carries a modified assay for vitamin Bi 2 utilizing tracer methods. Other Tools. N o r e p o r t on tools of recent origin for use b y t h e a n a l y t i cal chemist would be complete w i t h o u t a t least m e n t i o n i n g n o n a q u e o u s t i t r a tion, polarography, voltammetry, fluorometry, a n d m a n y o t h e r instrum e n t a l m e t h o d s . Space a n d t i m e d o n o t p e r m i t a complete discussion of t h e possibilities of t h e use of each of these tools. Physical Appearance Important One final point m u s t be m a d e with relation t o t h e specificity of an assay, and t h a t is "pharmaceutical elegance." T h e physical appearance of a p h a r m a ceutical which is to be used b y h u m a n patients is of far greater importance t h a n t h e appearance of m a n y industrial chemical products. I n years past probably every supplier has been faced with t h e situation wherein a customer has referred back to him a shipment with a s t a t e m e n t t h a t "it contains too m u c h dirt and extraneous material." T h e only criterion for t h e evaluation of t h e degree of extraneous material present was t h e eye of the inspecting chemist. If t h e examination happened to m a d e in a brightly lighted place the chemical might be rejected because of the presence of small black
