Although drug products issued from biotechnology have now been on the market for many years, accurate protein quantification remains a challenge. There are many colorimetric methods for protein quantification (Lowry, Bradford, BCA) but they all lack precision, and suffer from interferences and matrix effects. Moreover, the accuracy is highly dependent on the protein used for calibration. On the other hand, the LC-MS/MS determination of specific tryptic peptides lacks reproducibility due to the variability of the digestion process.

In order to address the need for a fast analytical method capable of accurately quantifying a protein (or peptide) without any specific reference substance, Quality Assistance has developed and validated an isotope dilution ICP-MS method based on sulfur determination.