The use of internal standards is the accepted strategy to facilitate quantitation via MS. The closer the chemical properties of the internal standard to its analyte, the better it compensates for the various sources of error, and thus the most desirable internal standard is typically an isotopically labeled version of the analyte itself. Consequently, the optimal internal standard for a glycoprotein is a labeled glycoprotein.  This led GlycoScientific to develop monoclonal antibodies with a range of labeled moieties, which can be added directly to the sample prior to processing and thus overcoming systematic errors associated with parallel sample handling. 

 Background information on isotopically labeled quantitation standards. 

IgG1 Standards

IgG4 Standards

IgG2 Standards

Epo