ESIprot enables the charge state determination and molecular weight calculation for low resolution electrospray ionization (ESI) mass spectrometry (MS) data of proteins.

Electrospray ionization (ESI) mass spectrometry (MS) devices with relatively low resolution are widely used for proteomics and metabolomics. Ion trap devices like the Agilent MSD/XCT ultra or the Bruker HCT ultra are typical representatives. However, even if ESI-MS data of most of the naturally ocurring proteins can be measured, the availability of data evaluation software for such ESI protein spectra with low resolution is quite limited.

Main characteristics of ESIprot

  • Algorithm based on standard deviation optimization (scatter minimization).

  • Suitable for peak lists. No raw data and peak intensities required, therefore suitable to re-evaluate “historical” data.

  • Highly accurate calculation of molecular weights of proteins, even from low resolution data.

  • Only two peaks of one protein required, extremely robust.

  • Theoretically unlimited molecular weight range.

  • Designed for the analysis of pure proteins.

  • Open source license GPLv3: program and parts of it may be used for commercial and non-commerical purposes.

Screenshot of ESIprot


Winkler R, ESIprot: A universal tool for charge state determination and molecular weight calculation of proteins from electrospray ionization mass spectrometry data, Rapid Communications in Mass Spectrometry, 2010, 24 (3), 285-294,


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Windows Installer

Python Source Code (zip for Python 2 and 3) (GPLv3).

Git Repository:

You also can use ESIProt Online (without local installation!).