spectrum, fragment mass error units

# spectrum, fragment mass error units ## Syntax The value for this parameter is an ASCII string, with two possible values: Daltons or ppm ## Notes If this parameter is not present or set to a unexpected value, a default value is substituted. No error message is generated when a bad value is used for this parameter. Interpretation of this value depends on the value set for spectrum, fragment mass type. ## Description The value for this parameter alters the interpretation of the value for the parameter named spectrum, fragment mass error. The interpretation of the two values are described below. Daltons: If this value is set, then the value of spectrum, fragment mass error (Tf) is simply interpreted as a mass and the condition for a fragment ion to be considered found is given by: | m - p | < Tf where m is a mass in a spectrum and p is the calculated mass of a peptide fragment. ppm: If this value is set, then the value of Tf 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(Tf x 10-6) see also: spectrum, fragment mass error | spectrum, fragment mass type | X! TANDEM API description project