Calculation of intensities of molecular interferences in GD-MS: Application to analysis of aluminium alloys

A method for calculating the concentration of molecular ions in GD-MS is reported. The method is based on measurements of effective stability factors (ESF) of molecular ions. ESPs have been measured for various types of molecular ions: combination of Ar with gases and components of the sample; components with each other and gases. An investigation was carried out, by using a cryo-cooled pin-cell, on 5 aluminium standard materials. It is shown that ESFs for different types of molecular ions lie in the small range 1 x 10(-9)-10(-8) ppm(-1), except for ArH+, hydrides, oxides and nitrides of metals. Comparison with reaction rate constants show that polarization grip of an atom by an ion is mainly responsible for more or less uniform values of ESFs. With use of this method a program for mathematical simulation of mass-spectra was developed. The relative errors of calculated intensities of interferences do not exceed the 15% level. The method provides a way for more accurate estimations of unresolved interferences and gives a comprehensive idea of the spectrum in a given region.