As methylmercury will not be quantitatively volatilized by the atomic absorption procedure above, it appears that the rather drastic and very rapid oxidation of the sample oxidizes methylmercury to inorganic mercury. As the recoveries obtained using the respective radioactive and stable mercury compounds are identical, the tracer method can be utilized to obtain an accurate analysis of submicrogram amounts of both inorganic mercury and methylmercury in combustible samples. As used in this laboratory, the method consists of adding a known amount of mercury-203 t o the sample, oxidizing the sample in the bomb, determining the recovery of
mercury-203 by gamma counting, determining the stable mercury content by Atomic Absorption Spectroscopy (AAS), and correcting the AAS result with the mercury203 recovery. If the amount of organic mercury in the sample is desired, a separation of organic from inorganic fractions should be performed on the original sample. Fbceived for review August 7, 1973. Accepted October 23, '1973. Mention of commercial products used in connection with work reported in this article does not constitute an endorsement by the Environmental Protection Agency:
Identification of Polyisoprene Rubbers M. L. Bahrani,' N. K. Chakravarty, and A. K. Saxena Texfiles and Stores Research and Development Establishment, Post Box No. 86, Kanpur 208001, India
The Weber color test ( I ) has been used for identification of natural rubber-vulcanized or unvulcanizedsince 1902. An attempt has been made to modify the test procedure by taking a pyrolyzate of the polymeric material instead of the substance itself in order to simplify the test and save time. Nearly half a gram of the polymeric substance to be identified, shredded into small pieces, is taken in a test tube (15 mm X 100 mm) fitted with a delivery tube through quick-fit joints. The test tube is put inside a drilled hole of size in a copper block 10 cm X 5 cm X 10 cm high. This copper block is capable of being maintained at temperatures from 400 to 470 "C electrically by means of a bimetal thermostatic control and embedded heating coil. As soon as the decomposition products start issuing, say after about 1 minute, the delivery arm is dipped in 10 ml of 10% bromine solution in carbon tetrachloride. Collection of pyrolyzate emanating for about 3 or 4 minutes is quite sufficient for this test. The carbon tetrachloride sol
Correspondence to be addressed to this author.
(1) W. C Wake, "The Analysis of Rubber and Rubber-like Polymers," McLaren, London, 1968, p 48.
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lution of the pyrolyzate is heated in a water bath to boil off excess carbon tetrachloride and bromine. Appearance of violet-red to violet-blue color on heating with a few drops of phenol, is a positive test for polyisoprene rubbers, both natural and synthetic. Polymers containing butadiene as a constituent, also give this test if the temperature of pyrolysis mounts to 500 "C. The main advantage of this new method is that it does not call for a long swelling and bromination period as required in Weber's method where the material under investigation takes a considerably long time for the process because of slow swelling of vulcanizates in carbon tetrachloride, apart from the elimination of the acetone extraction operation. Hence, it is very quick; the entire test takes about 10 to 15 minutes. The color developed is also very prominent and unambiguous-red-violet to blue-violet. Yet another advantage, though not so significant, is the complete absence of colored fillers which a t times tend to mask the violet color of the test. Received for review June 25, 1973. Accepted November 5 , 1973.
A N A L Y T I C A L C H E M I S T R Y , VOL. 46, NO. 3, M A R C H 1974
