Electrospray ionization mass spectrometry: Deconvolution by an entropy-based algorithm

Abstract

Summary The more demanding complication of the entropy processing of ES1 spectra is the presence of large, unresolved backgrounds on which many individual peaks are superimposed. In working with these spec- tra, we generally employ a combination of Fourier deconvolution and baseline subtraction. Such steps can be managed as a preftlter to the entropy deconvo- lution since the optimization (Fourier cutoff, exponen- tial factor) does not require knowledge of the entropy fit parameters. Figure 4 illustrates the application of these strategies to an ES1 mass spectrum of a gly- copeptide with two glycosolation sites. ties of the data. rates which are modeled as multiply charged Gauss- ian ion profiles. The other noise is shot noise corre- The computer spectra were generated by a numeri- cal simulation of a Poisson process in which a param- sponding to the finite ion counts. Of course, back- eter representing the expected number of counts for each mass value mi is defined. Independent scans are ground peaks or chemical “noise” are, from the obtained by sampling the Poisson distribution corre- sponding to this parameter [7]. In these simulations standpoint of the simulation, just additional real noise can arise in two ways. The ftrst is the relative fraction of counts that are real ions to counts that are peaks. representing background. From the standpoint of the simulation program they are distinguished only be- cause the background has a mass-independent arrival rate while the signal corresponds to mass-dependent This report has discussed a novel algorithm for ex- tracting parent masses from spectra containing multi- ply charged ions, a common feature of ESI. The algo- rithm works with raw data and does not require the