A Nier-type mass spectrometer and its associated electronic units have been constructed for the purpose of measuring small variations in the abundances of oxygen of mass 18 and of carbon of mass 13 in carbon dioxide, and of oxygen of mass 18 in oxygen gas, to an accuracy of ±0.01 percent of the abundance of these isotopes. The electronic units of the necessary stability for this degree of accuracy are described. A gas feed system is described which permits fast alternate introduction of the sample of gas to be analyzed and a standard gas into the mass spectrometer. All measurements of the variation in the abundance of the oxygen and carbon isotopes are made with reference to a standard.

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Liquid chromatography has, in recent years, found increasingly wide acceptance as a tool in the analysis of a broad range of compounds and mixtures. Much of the resurgence of interest in liquid chromatography is the result of an increasing number of chemicals which are either too thermally labile and unsuited for gas chromatographic analysis or have volatility characteristics which require alternate methods of analysis. For example, high speed liquid partition chromatography has been used extensively for the analyses of a number of biochemicals, such as nucleotides (1), nucleic acid bases (1), steroids (2), analgesics (3), fat soluble vitamiqes (4), natural products (4), and antibiotics (4), as well as for the analysis of such environmental hazards as polychlorinated biphenyls (5), nonionic surfactants (6), and various other herbicides and pesticides (5).Because of the increasing utility of liquid chromatogra-

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