Determination of molecular formulae from low-resolution mass spectral data by matching experimental and calculated isotope patterns of logical sets of daughter ion candidates

Abstract

The determination of molecular formulae from low-resolution mass spectral data is described. The data are handled by a microcomputer program which generates not only candidate molecular formulae but also logical sets of candidate formulae of fragments corresponding to several detected ions in the same mass spectrum, and tests how well the calculated isotope patterns of these sets match the corresponding experimental isotope patterns. The sets of fragment candidates are formed so that the sum of the elemental compositions in the sets is logical and either equal or close to the elemental composition of the current candidate for the molecular formula. The generated molecular candidate which gives the best matching fragment set and the best total match represents the most probable elemental composition of the unknown compound. Some structural information is obtained simultaneously. Comparison of the results obtained with the new algorithm with those obtained with previous microcomputer programs shows that both performance and reliability are improved considerably.