The feasibility of using a low pressure glow discharge as an ion source for the mass spectrometric determination of trace elements in aqueous media was investigated. A cryogenically cooled hollow cathode ion source was developed to analyze aqueous samples without external preconcentration. Aqueous solutions containing seventy elements were analyzed and the detection limits, sensitivity factors, and linear regression correlation coefficients were determined. A standard test solution of trace elements in water was analyzed and the concentrations of trace elements were calculated using the sensitivity factors determined previously. The results compared favorably within the error limits predicted by the semiquantitative survey methods used. Tap water and natural lake water samples were examined and minimal interference effects due to organic compounds and biological compounds were noted;In conjunction with the feasibility study of a glow discharge using the cryogenic hollow cathode ion source, a research ion optical system (RIOS) was developed as a flexible mass analyzer for the development of new ion sources. The RIOS is a double focussing mass analyzer designed utilizing the "Mattauch-Herzog" geometry with externally adjustable slit assemblies. The RIOS can be adapted to a variety of ion detection systems and ion sources;('1)DOE Report IS-T-931. This work was performed under contractW-7405-3ng-82 with the Department of Energy.