Absolute Quantification of Transferrin and Albumin in Human Serum by Species-unspecific Isotope Dilution-Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry
A method based on species-unspecific isotope dilution-high performance liquid chromatography coupled with inductively coupled plasma mass spectrometry( HPLC-ID-ICP-MS) was established for the absolute quantification of proteins by measuring sulfur and iron. Four standard proteins including transferrin, lactoglobulin,myoglobin and lysozyme were separated and on-line determined via sulfur or iron by enriched34S or54Fe isotopic solutions continuously mixing with the eluate from liquid chromatography. Absolute quantification of proteins was calculated by the isotope dilution equation and sulfur or iron content in proteins. The methodology was validated by comparing with gravimetric analysis results. Furthermore,this method was successfully applied to the quantification of transferrin and albumin in human serum by means of changing the flow rate of isotopic solution. The measured results of transferrin via sulfur and iron were( 2. 35 ± 0. 01) g / L,( 2. 22 ±0. 13) g/L,respectively,which was in good agreement and the RSDs were all within 10%. The method can be used to quantify sulfur containing proteins and metalloproteins in biological samples.