| Popis: |
The occurrence of ions that differ by one or more hydrogen atoms (M-nH) is very common in mass spectrometry. In this article, we introduce a chemometric method (M-nH method) that allows one to eliminate this interference over the isotope pattern of the M ion. A reasonably simple mathematical formulation is achieved by disregarding the deuterium abundance for the hydrogen atoms involved in the fragmentation process. The resulting nonlinear system of equations is solved by the Newton-Raphson method with comprehensive initial guesses. The method was applied to a simulated spectrum of CH 2 Cl 2 showing good agreement with the data used to simulate the spectrum, which indicates that the approximations used in the method are reasonable. Good results were obtained for the experimental cluster at the molecular ion region of CH 2 Cl 2 where the ions M + , M-H + , and M-2H + were found to be in the approximate ratios of 140:8:1. For the cluster at the region of the C 7 H 12 ·+ ion from decahydronaphthalene, 6 different formula ions were found (C 7 H 7 + to C 7 H 12 + ) with the approximate ratios of 1:0:27:10:393:517. The M-nH method was also applied to the elimination of interference from metal hydrides at the mercury cluster of the dimethylmercury electron impact spectrum from the NIST/EPA/NIH database and electrospray mass spectrum of a lead solution from the literature. In this last case, the hydride had a significant amount of deuterium due to the deuterated methanol used as solvent, but, since there were no M + 2H + and over, a similar mathematical formulation could be used, and the M-nH method was successfully applied. The approximate ratios of Pb + , Pb 1 H + , and Pb 2 H + were found to be 60:3:2. |
