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.