| 摘要 |
The invention relates to acquisition techniques for time-of-flight mass spectra with ionization of the analyte substances by matrix assisted laser desorption. Generally speaking, these acquisition techniques involve adding together a large number of individual time-of-flight spectra, each with restricted dynamic measuring range, to form a sum spectrum. The invention provides a method that improves, in particular, the reproducibility, the concentration accuracy and therefore the ability to quantify the mass spectra. Particular embodiments also increase the dynamic range of measurement. For this purpose, multiple series of mass spectra are acquired, whereby the energy density in the laser spot is increased in discrete steps. As a result, many ion signals saturate the detector and can therefore no longer be evaluated. However, it is possible to employ a technique in which the ion beam is increasingly defocused, or, secondly, to replace parts of the spectrum that are subject to saturation by intensity extrapolations from mass spectra acquired with lower energy density. In the first case, hundreds or thousands of individual mass spectra must be added together in order to increase the dynamic measuring range. In the second case, the finally acquired mass spectrum, with its replacements, forms a mass spectrum with a high dynamic measuring range, improved reproducibility and better concentration accuracy. The gradient of the increasing intensities of the ion signals, as a function of the energy density, supplies additional information about the proton affinity of the analyte ions. The concentration accuracy is enhanced because the increase in the number of proton donors in the ionization plasma leads to an increase in the ionization of those analyte substances that have a lower proton affinity. |
