Determination of Submicrogram Amounts of Mercury by the Oxygen Bomb Combustion Method Erich W. Bretthauer, A. Alan Moghissi,l Susan S. Snyder, and Neil W. Mathews U S . Environmental Protection Agency, National Environmental Research Center, Las Vegas, P. 0. Box 15027, Las Vegas, Nev. 891 14
Organic and inorganic mercury compounds are widely distributed in the environment. Owing to this wide distribution and the toxicity of these compounds, interest in their detection and determination has been of long standing. Recent advances in flameless atomic absorption techniques have lowered detection limits for aqueous inorganic mercury in environmental samples. The unpredictable and unreproducible losses of mercury using conventional digestion and analysis techniques, however, continues to result in unreliable analysis for many types of environmental samples ( I , 2 ) . In the method developed in this Laboratory, oxidation of the sample containing inorganic and/or organic mercury was conducted in an oxygen-filled bomb. Using this technique and utilizing a radiotracer of mercury to quantitate any losses during the oxidation, an accurate method was developed to determine environmental levels of mercury in combustible samples. The method was tested by determining the recovery of both stable and radioactive mercury, added in either an organic or inorganic form, from vegetation samples.
Table I. Recovery of Inorganic Mercury Added to
Sample No.
1 2
3 4
Alfalfa Samples Added mercury, ng
Added mercury-203, cpm
11,000 11,000 540 550
28,473 33,210 29,691 30,059
Recovery mercury in water and wash,
Recovery mercury-203 in water and wash,
70
70
81.8 81.8 78.3 90.9
81.9 78.8 77.5 89.5
Table 11. Recovery of Organic Mercury Added t o Alfalfa Samples
Sample No.
1 2 3
Added mercury, ng
600 600 600
Added mercury-203, cpm
11,073 10,565 10,592
Recovery mercury in water and wash,
Recovery mercury-203 in water and wash,
70
70
86.6 87.5 82 .O
83.5 88 . O 85.6
EXPERIMENTAL Apparatus. Sample oxidations were conducted in a 1800-ml oxygen bomb manufactured by the Parr Instrument Company, Moline, Ill. Mercury-203 analyses were performed using a 400channel gamma spectrometer which was manufactured by the Technical Measurement Corporation, North Haven, Conn. The gamma spectrometer was used in conjunction with a 4-inch thallium activated sodium-iodide detector manufactured by the Harshaw Chemical Company, Cleveland, Ohio. Stable mercury analyses were performed with a Model 353 atomic absorption spectrometer equipped with a mercury flameless reduction and absorption cell manufactured by the Instrumentation Laboratories, Inc., Lexington, Mass. Reagents. Stannous chloride dihydrate, sulfuric acid, sodium hydroxide, nitric acid, mercuric oxide, and ethanol (95%) were all obtained in reagent grade from J. T . Baker Chemical Co., Phillipsburg, N . J . Matheson, Coleman and Bell, Norwood, Ohio, supplied the L ( + ) cysteine hydrochloride monohydrate. Argon gas was obtained from Union Carbide Company, New York, N. Y. Mercury203 nitrate (2 to 10 Ci/g Hg) and methylmercuric-203chloride (0.5 to 5 Ci/g Hg) were obtained from ICN, Irvine, Calif. Polycarbonate screw cap bottles (250 ml) were obtained from Nalgene Labware, Rochester, N.Y. The bottles were graduated in the laboratory so that 100 5 ml could be easily added. Procedure. Ten grams of combustible material are placed in the stainless steel sample cup. One-tenth ml of mercury-203 standard containing approximately 1 X lo5 dpm/ml is then added to the sample. The sample cup is carefully placed in the head of the Parr Bomb. A 10-cm length of nichrome fuse wire is placed between the two electrodes. The head is placed in the bomb, 17 atmospheres of oxygen are added, the bomb is checked for leaks and the sample combusted. The pressure is released into the air a t the rate of two liters per minute until ambient pressure is reached. The bomb and bomb head are washed with 3 N H K 0 3 into a 250-ml screw cap polycarbonate container. Polycarbonate,
*
Present address, Office of Interdisciplinary Programs, Georgia Institute Technology, 255 No. Avenue NW, Atlanta, Ga. 30322. (1) Analytical Methods Committee, Analyst (London), 90, 505 (1965) (2) T. Toribara e f a l . , Talanta, 17, 1025 (1970).
Pyrex (Corning Glass Works) glass or Teflon (Du Pont) containers should always be used to avoid losses of mercury ( 3 ) .The volume is made t o 100 ml with 3 N "03. One-tenth ml of the mercury203 standard is added into a second 250-ml screw cap polycarbonate container. The volume is made to 100 ml with 3 N "03. The bomb wash and standard are counted using a thallium activated NaI crystal in conjunction with a 400-channel gamma spectrometer. The bomb wash is analyzed for stable mercury using a flameless atomic absorption technique similar to that of Magos and Cernik (4).Appropriate standards were prepared from mercuric oxide. All dilutions were made with 3 N "03 prepared in distilled, deionized water. All standards were prepared in screw cap polycarbonate containers. Stable mercury was determined according to the following procedure: Two ml of sample are added to the reaction cell which is attached to the atomic absorption spectrometer. Two ml of 1%L(+) cysteine hydrochloride solution are added to the sample which is being continuously agitated with a magnetic stirrer. Approximately 0.1 gram of SnC12 is added t o the mixture and the system is closed and mixed for 30 seconds. Two ml of 30% NaOH are then rapidly added using a syringe, the s y s t e p is closed, and the sample mixed for 2' minutes. The mercury is then released from the reaction cell into the absorption cell using 5 scf/h of argon as a carrier gas and the height of the absorption peak determined.
RESULTS AND DISCUSSION A known amount of mercuric-203 chloride and stable mercuric chloride was added to four alfalfa samples, the samples were combusted, and the recoveries determined. The results are shown in Table I. A known amount of methylmercuric-203 chloride and stable methylmercuric chloride was then added to three alfalfa samples, the samples were combusted, and the recoveries determined. The results are shown in Table 11. (3) M . Greenwood and T. W. Clarkson, Arner. Ind. Hyg. Ass. J , , 31, 250 (1970). ( 4 ) L. Magosand A. A . Cernik, Brit. J . Ind. Med., 26, 114 (1965).
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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:
Identificationof 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.
446
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.
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