SIMULTANEOUS MEASUREMENT OF ISOTOPE RATIOS IN SOLIDS BY LASER-ABLATION WITH A TWIN QUADRUPOLE INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETER

A twin quadrupole inductively coupled plasma mass spectrometer is used with laser ablation sample introduction in both the steady state (10 Hz) and single pulse modes. The twin quadrupole instrument allows the measurement of ions at two m/z values simultaneously. A 10 Hz laser produces a noisy, steady-state ion signal in both channels. The signals are highly correlated and the majority of flicker noise cancels when the ratio is calculated. Isotope ratios for copper are measured with an RSD of 0.26%. Transient signals for single laser pulses are also obtained. The integrated peak area of the transient signals is correlated even when flicker noise on the transient is present. Copper isotope ratio measurements for several laser pulses are measured with an RSD of 0.85%. For a single pulse the RSD is 1.6%.