Indirect determination of protein content by inductively coupled plasma-mass spectrometry

Three standard proteins including bovine serum albumin (BSA), superoxide dismutase (SOD) and metallothionein (MT) were separated by size exclusion chromatography and on-line determined via sulfur by inductively coupled plasma-mass spectrometry. Molar ratios of the proteins were calculated by the analytical results and the known sulfur content in proteins. The mobile phase was 0.1 mol/L Tris-HAc. In order to avoid the polyatomic interferences on the sulfur determination, oxygen was added into the collision cell and reacted with sulfur to form sulfur-oxide ion. Therefore, the intensity of (SO+)-S-32-O-16 represented sulfur content during the measurement. These results were in good agreement with the gravimetric results. The RSDs for the proteins are less than 3% and the detection limits for BSA, SOD and MT-II are 14, 52 and 27 pmol, respectively.