Trace-element analysis of water samples using 700-keV protons

We have evaluated the trace-element sensitivty of ion-induced x-ray analysis on residues from water samples using 700-keV protons. We find that most elements of interest can be detected in quantities below one part per billion in running times of about 3 min. We discuss in detail the necessary steps for absolute calibration of the analysis system, and the process of sample preparation in countries where high-purity substrates are difficult to obtain.