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A systematic procedure for establishing elemental composition from a concerted high-resolution precise mass analysis of the monoisotopic molecular ion and a low-resolution moment analysis of its isotope pattern is described. The combined method is more selective than a precise mass analysis alone. Factors affecting the enhancement in selectivity and some instrumental factors are discussed. [ABSTRACT FROM AUTHOR]

The basic principles of an approach to mass spectral elemental analysis based on the moments of the low-resolution isotopic pattern are presented. The moment analyses are faster and more general than conventional methods of isotopic pattern analysis. The procedure is applied to the analysis of compounds which exhibit 'pure' molecular ions and the analysis of compounds which produce significant fragment ions at masses overlapping the molecular ion. It appears as though reasonable selectivity can be achieved for low relative molecular mass compounds (relative molecular mass < 400 a) using standard instrumentation and data acquisition softy are. Preliminary studies of instrumental factors affecting the measurement of moments are discussed. [ABSTRACT FROM AUTHOR]

The application of the fundamental equation for isotopic dilution mass spectrometry to real samples often requires using approximations which can lead to significant errors. A new approach relating the composition of isotopic mixtures to the average mass of the mass spectral pattern is presented. The fundamental equations are completely general; they should be applicable to a wide range of problems and may provide improved accuracy and precision in some cases. [ABSTRACT FROM AUTHOR]