DETERMINATION OF TOTAL PROTEIN ADSORBED ON SOLID (MEMBRANE) SURFACE BY A HYDROLYSIS TECHNIQUE - SINGLE PROTEIN ADSORPTION

We developed a new analytical technique for single protein adsorption in the context of basic studies on membrane fouling. This method simply combines two well-established techniques, HCl hydrolysis and reaction of the resultant amino acids with ninhydrin (10(-6) M sensitivity). The HCl hydrolysis step, using 6 N HCl solution, breaks up the adsorbed protein into its constituent amino acids by hydrolyzing the peptide bonds, resulting in complete removal of the adsorbed protein from the surface. After the HCl hydrolysis, the condition of the hydrolysate is adjusted for ninhydrin derivatization by mixing with 6 N NaOH and 6 m sodium acetate. The optimal pH for the ninhydrin derivatization reaction of the hydrolysate is approximately 6. This technique uses an unmodified protein and determines protein loading on the membrane's surface (external and/or pore wall), under static or filtration environments, in a consistent manner. This method provides an absolute measurement of the total protein adsorbed and holds good promise for high sensitivity, accuracy, and reproducibility at a relatively low cost. Other amino acid analytical techniques (such as fluorescence and HPLC) may be used to eliminate artifacts, improve sensitivity, and extend the approach to multi-protein adsorption.