Improving selectivity and sensitivity of protein quantitation by LC-HR-MS/MS:Determination of somatropin in rat plasma

AIM: Protein quantitation by digestion of a biological sample followed by LC-MS analysis of a signature peptide can be a challenge because of the high complexity of the digested matrix. Results/methodology: The use of LC with high-resolution (quadrupole-TOF) MS detection allowed quantitation of the 22-kDa biopharmaceutical somatropin in 60 μl of rat plasma down to 25 ng/ml with minimal further sample treatment. Reducing the mass extraction window to 0.01 Da considerably decreased the interference of tryptic peptides, enhanced sensitivity and improved accuracy and precision. Analysis with LC-MS/MS resulted in a less favorable limit of quantitation of 100 ng/ml.CONCLUSION: HRMS is an interesting option for the quantitation of proteins after digestion and has the potential to improve sensitivity with minimal method development.