A label-free strategy for both qualification and quantitation of protein based on tandem mass spectrometry

Protein quantitation has become one of the hottest research points in proteomics. Previous research has shown that a novel label-free technique based on liquid chromatography and mass spectrometry is proposed for quantification of glycoprotein and phosphoprotein. Herein, we present a label-free mass spectrometry-based approach to qualify and quantify bovine serum albumin (BSA). First, the conditions of high-performance liquid chromatography (HPLC) were optimized, such as program of gradient elution and flow rate. Then, BSA was determined in optimal conditions with HPLC-quadrupole time-of-flight tandem mass spectrometry (Q-TOF) after digesting with trypsin in-solution, and the data were processed with MassHunter Qualitative Analysis software. The results indicated that the concentration of protein is associated with the sequence coverage of peptides in a logarithmic manner. Furthermore, among the eight peptides of BSA that have strong responses, two were found to measure the BSA qualitatively and quantitatively, respectively. The recoveries of the two quantitative peptides were 105.88% and 111.50%. This method can be employed for screening characteristic peptides with qualitative and quantitative assay on specific proteins.