spectrum, parent monoisotopic mass error units

Syntax

The value for this parameter is an ASCII string, with two possible values: Daltons or ppm

Notes

1. If this parameter is not present or set to a unexpected value, a default value is substituted.
2. No error message is generated when a bad value is used for this parameter.

Description

The value for this parameter alters the interpretation of the value for the parameters named spectrum, parent monoisotopic mass error plus and spectrum, parent monoisotopic mass error minus. The interpretation of the two values are described below.

1. Da: If this value is set, then the value of spectrum, parent monoisotopic mass error plus (T_+p) is simply interpreted as a mass and the condition for a parent ion to be considered found is given by:
   0 < m - p < T_+p
   where m is a parent ion in a spectrum and p is the calculated mass of a peptide. The interpretation for spectrum, parent monoisotopic mass error minus (T_-p) is given by: 0 > m - p > T_-p
   
2. ppm: If this value is set, then the value of T_+p is interpreted as representing parts-per-million (commonly used in mass spectrometry to express precision), altering the condition for a fragment ion to be as follows:
   0 < m - p < m(T_+p x 10^-6)
   The interpretation for spectrum, parent monoisotopic mass error minus (T_-p) is given by: 0 > m - p > m(T_-p x 10^-6)