CALIBRATION METHOD FOR THE QUANTITATIVE-ANALYSIS OF GAS-MIXTURES BY MEANS OF MULTIPHOTON IONIZATION MASS-SPECTROMETRY

A technique for quantitative analysis of gas mixtures in a laser mass spectrometer is presented. It is based on the addition of two calibrat ion gases with different orders of multiphoton ionization process to t he sample gas. The ratio of the signals of these two internal standard s serves as a sensor for the laser intensity within the ionization vol ume. Thus strongly fluctuating signals due to higher-order multiphoton ionization can be normalized for every single laser shot. In addition , for such a relative measurement, effects of long-term drifts of the apparatus are eliminated. Concentrations varying from a few ppm to sev eral percent could be determined with an accuracy better than 10% at e very single laser shot. Therefore this technique allows high time reso lution.