spectrum, fragment 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 parameter named spectrum, fragment monoisotopic mass error. The interpretation of the two values are described below.

1. Daltons: If this value is set, then the value of spectrum, fragment monoisotopic mass error (T_f) is simply interpreted as a mass and the condition for a fragment ion to be considered found is given by:
   | m - p | < T_f
   where m is a mass in a spectrum and p is the calculated mass of a peptide fragment.
2. ppm: If this value is set, then the value of T_f 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:
   | m - p | < m(T_f x 10^-6)