Anal. Chem. 1992, 6 4 , 824-827 REFERENCES Tornes, J. Aa.; Johnsen, B. A. J. Chromatogr. 1888, 467, 129-138. Bossie, P. C.; Reutter, D. J.; Sarver, E. W. J. Chromatogr. 1987, 407, Bossle, P. C.; Martin, J. I.; Sarver, E. W.; Sommer, H. Z. J. Chroma- togr. 1983, 267, 209-212. Verweij, A.; Degenhardt, C. E. A. M.; Boter, H. L. Chemosohere 1979, Verweij. A.; Boter, H. L.; Degenhardt, C. E. A. M. Science 1979, 204, Hahey, D. J.; Horning, M. G. J. Chromatogr. 1873, 79, 65. Purdon, J. G.; Pagotto, J. G.: Miller, R. K. Report DREO-936; Defence Research Establishment: Ottawa, 1985. Andersson, G.; Fredriksson, S. A,; Lindberg, G., Olofsson, B, FOA 4 Report; Forsvatels Forskningsantstalt Huvudavdeining 4, S901 82 llmen - . . . __, Sweden Tripathi, D. N.; Kaushik, M. P.; Bhattacharya. A. J.-Can. Soc. For- ensic Sci. 1987, 20 (4), 151-153. Report on identification of potential organophosphorus warfare agents; Ministry for Foreign Affairs of Finland: Helsinki, 1979 [ISBN 951-46- (1 1) Yao, C. C. D.; Zlatkis, A. Chromatographia 1987, 23 (9, 370-72. Durgesh N. Tripathi* Karuna S. Pandey Arabinda Bhattacharya Ramamoorthy Vaidyanathaswamy Analytical Services Wing Defence Research & Development Establishment T~~~~~ Road Gwalior-474 002 (MP), India RECEIVED for review August 23, 1991. Accepted January 6, TECHNICAL NOTES Recovery of Submilligram Quantities of Carbon Dioxide from Gas Streams by Molecular Sieve for Subsequent Determination of Isotopic ( 13C and 14C) Natural Abundances James E. Bauer* Department of Oceanography, Florida State University, Tallahassee, Florida 32306 Peter M. Williams Scripps Institution of Oceanography, Marine Research Division, University of California, S a n Diego, La Jolla, California 92093-0218 Ellen R. M. Druffel Woods Hole Oceanographic Institution, Department of Chemistry, Woods Hole, Massachusetts 02543 INTRODUCTION Quantitative recovery and isotopic analysis of COP generated from organic and inorganic carbon is important for a variety of natural sample types. For example, the two mast commonly used techniques for the oxidation of organic carbon to COz are the sealed-tube method' and various modifications of the flow-through combustion method., While both methods ul- timately depend upon the presence of 0, for the oxidation process, the sealed-tube method has been the method of choice for the subsequent recovery and isotopic analysis of COP This is due to the relative ease with which COz (sublimation point = -78.5 C at 760 mmHg pressure) can be cryogenically re- moved from an otherwise noncondensible, static (i.e,, non- flowing) gas mixture under vacuum. This concept has been improved upon through the use of variable-temperature cryogenic traps (VTTS)~** which allow gas components having different melting points to be sequentially frozen out and distilled off for collection of essentially pure product. In contrast, COz contained in carrier gas streams is generally difficult to collect at atmospheric pressure following organic carbon combustion since this usually entails using 0, as both the oxidant and the carrier gas. Cryogenic collection of C 0 2 at liquid nitrogen temperature (bp -195.8 C) from an 0, stream results in the condensation of liquid 0, (bp -183.OoC), a potentially hazardous situation, and possibly in incomplete C02 recovery. Pumping the liquified 0, away under vacuum, or trapping the CO, from the 0, stream at temperatures below * Corresponding author. the boiling point of 0, using VWs, can also result in incom- plete recovery and isotopic fractionation of CO,. In fact, even when N, is used as the carrier gas at atmospheric pressure and liquid nitrogen temperature, intermittent condensation of the N2 stream may O C C U ~ though this is much less severe than for 0,. Finally, systems which are designed to collect CO, from gas streams (especially 0,) cryogenically or using partial vacuums can attain considerable complexity. A method is therefore needed which allows CO, to be quantitatively recovered from 0, and N2 gas streams at at- mospheric pressure. For isotope studies, a further requirement is that no fractionation of the carbon isotopes in the CO, occurs. This led us to develop a simple, convenient method which is based on the highly selective absorptive properties of aluminosilicate molecular sieves for different gases. While molecular sieves have been employed to a limited extent in some commercial organic carbon analyzers, in some cases for 613C determinations (e.g., see ref 61, a thorough assessment of the analytical capabilities of sieves has, to our knowledge, not been made. The method presented here has a low asso- ciated blank (<0.02 pmol of C), is robust over a wide range of 0, and N2 carrier gas flows (at least 100-2000 cm3.min-l) and quantities of CO, (at least 0.3-50 wmol of C), and is nonfractionating with respect to carbon isotopic (13C and 14C) natural abundances. Molecular sieves should have a variety of applications for C 0 2 quantification and isotopic analysis. EXPERIMENTAL SECTION The specific molecular sieve used in these studies was a syn- thetic sodium aluminosilicate zeolite having the molecular formula 0 1992 American Chemical Society
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Bauer et al. (1992) studied this question.