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Regeneration of Used Molecular Separator for the Gas Chromatograph-Mass Spectrometer Method by Microwave Plasma Shozo Toda, Kazuyuiki Aizawa, Nobutaka Takahashi, arid Keiichiro Fuwa Deparirneni of Agrlculiura1 Chernisiry, Faculty of Agriculture, University of Tokyo, Tokyo, Japan
The qualitative and quantitative analytical technique for organic matters by use of the mass spectrometer after the separation of sample components by gas cbmmatograph, the GC-MS method, has been quite prevalent for the past several years, especially for the analysis of minute .amount of samples. For the hest operation of this combined method, the carrier gas of the gas chromatograph which flows a t atmospheric pressure in the column must be removed immediately after chromatography, and the pressure in the mass spectrometer must be down to less than lW Torr. Therefore, several kinds of molecular separators have been invented to remove the carrier gas, such as those made by Ryhage (I), Watson and Biemann (2), Lipsky, Horvath, and McMurray (3), Llewellyn and Littlejohn (41, and Cree (5). Binks, MacMillan, and Pryce (6) have reported that this GC-MS method was invaluable for the analysis of the methyl ester of gibberellins AI to AX and of the trimethylsilyl ether methyl ester of hydroxylated gibberellins. We have studied the methyl ester of gibberellins in plant extract by the same method, and found it was most useful. It was also found; however, that our molecular separator, one of the Watson and Biemann type, had lost its capacity to separate the carrier gas after a certain period of separating samples of large molecular weight of the methyl ester of gibberellins. The amount of material condensed on the fritted glass tube increases because of the high boiling point of the methyl ester of gibberellins, and the flow rate of helium carrier gas through the fritted glass decreases. As a result, the separation yield of the molecular separator is reduced, the residual material on the fritted glass is apt to he mixed with the fresh sample flowing from gas chromatograph, and, consequently, the final analytical results hecome poorer and contaminated. Gleit and Holland (7)have shown that the ultra-shortwave discharge plasma of oxygen could he used to decompose organic substances. Recently some instruments utilizing this principle went on the market for ashing (8). In this paper, we have attempted to use the ultra-shortwave discharge plasma of oxygen to remove organic material condensed on the fritted glass of the molecular separator of GC-MS.
EXPERIMENTAL Instruments. The GC-MS spectrometer was a Hitachi Model L type gas chromatograph connected to a Hitaehi RMU-6 type mass spectrometer with a Watson-Biemann type molecular separator made of glass (Daw Coming '20.).The molecular separator (1) R. Ryhage. Anal. Chem., 36,759 (1964) (2) J. T. Watson and K. Biemann. Anal. Chem., 36, 1135 (1964): 37, 8446 (1965). (3) S. R. Lipsky, C. G. Harvath. and W.J. McMurray, Anal. Chem., 38, 15% (19RRI ~
(4)
P. M.
Llewellyn and D. P. Littiejohn. Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, February 1966. (5) R. F. Cree, Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy. March 1967. (6) R. Binks, J. MacMillan. and R. J. Pryce. Phytochemistry, 8, 271 (1969). (7) C. E. Gleit and W.D. Holland. Anal. Chem., 34, 1454 (1962). (8) Tracerlab. Low Temperalure Asher LTA-600 Catalog (1968): International Plasma Corporation. IPC Plasma Machine Catalog (1968)
