SIMULTANEOUS MEASUREMENT OF ION RATIOS BY INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY WITH A TWIN-QUADRUPOLE INSTRUMENT

The ion beam from the inductively coupled plasma (ICP) is split into t wo parts by a device comprised of two electrostatic analyzers in a bac k-to-back arrangement. Each ion beam is then monitored by a separate q uadrupole mass analyzer and electron multiplier. Thus, ion ratios can be measured simultaneously without scanning. Isotope ratios for copper are measured with a precision of 0.14% relative standard deviation (R SD). Internal standard ratios for Co+/La+ are measured with a precisio n of 1% RSD. Ion signals in the two channels are highly correlated, an d the magnitude of flicker noise is reduced in the resulting ratios. B ias in the measured isotope ratios is substantial but can be corrected by calibration.