This is a Windows console application for calculating isotope distributions for molecules. It is suitable for automation using a script as all parameters are specified on the command line and there is no subsequent user interaction. It is designed to work with both small molecules, proteins and other macromolecules, and can cope with most elements and isotopes. The element definitions are provided in a separate text file, which can easily be edited to allow for isotopically labelled compounds. The output is to the console by default, but can be redirected to a file, and consists of pairs of mass and abundance values.
To use the software, just download the zip archive, and extract the files. Start up the windows command prompt (under accessories on the Start Menu on XP, or type cmd in the search box under later Windows versions) then cd to the directory where you unpacked the files. Then run by typing:
where formula is the molecular formula of interest. It currently understands "standard" elements, but not any other chemical abbreviations. Valid formulae could include C254H377N65O75S6 for insulin and C2H6O for ethanol. CH3CH2OH will work too. Parentheses are not yet supported.
There are various other options:
isotopes formula filename.txt
The optional filename specifies that the program should use a different atom definition file. The file format is straightforward, and contains the element symbol, followed by atomic number and then pairs of mass and abundance values for each isotope.
-n Normalizes the most intense peak to 100%, as is conventional for mass spectra
-f filt Normalize and only output peaks of intensity >= filt
-mtz charge Outputs m/z for charge state charge
-z charge Sets charge state to charge
-r res Merges peaks separated by <res, defaults to 0.1
-t thr Specifies a probability threshold thr, defaults to 0.001. Lower thresholds will find more peaks (and take longer).
-p prec Specifies the output precision prec, default is 8.
-c Outputs a comma separated table. The default is tab.
isotopes C254H377N65O75S6 Calculates isotope distribution for insulin using default settings.
isotopes C254H377N65O75S6 -n -p 5 -c > insulin.csv This calculates the insulin isotope distribution, outputting 5 figures of precision, normalizing the most intense peak to 100%, and sends the results to a comma separated file called insulin.csv (which will open in MS Excel if this is installed).
isotopes C254H377N65O75S6 -t 0.00001 Calculates the distribution, but will consider less likely isotopomers than with the default thr setting of 0.001
The algorithm used is based on a published procedure (J. A. Yergey, Int. J. Mass Spectrom. Ion Phys. 1983, 52, 337) but is implemented rather differently from the way described in the paper, and will not give numerically identical results.
The values for masses and abundances in the supplied file are those given by NIST.
Windows 64 bit Download (isotopes_win64.zip 510kb)
Windows 32 bit Download (isotopes_win32.zip 518kb)
Pdf documentation, also included in the zip files.