Frequency doubling scattering and second-order scattering spectra of phosphato-molybdate heteropoly acid-protein system and their analytical application.

In the sulfuric acid medium, the reaction of heteropoly compounds with proteins could result in the enhancement of frequency doubling scattering (FDS) and second-order scattering (SOS). Based on the characteristic, a novel method for the determination of trace amounts of protein by using the FDS and SOS method has been developed. Their maximum scattering wavelengths, lambda(ex)/lambda(em), appear at 940/470 nm for FDS and 350/700 nm for SOS, respectively. In a certain range, the concentration of proteins is directly proportional to the enhanced intensity of FDS and SOS. The suitable reaction conditions, affecting factors as well as the influence of some coexisiting substances were investigated. The methods exhibited high sensitivity, and the detection limits were in the range of 8.6-39.3 ng ml(-1) depending on different methods. The method had good selectivity, and was applied to the determination of protein in synthetic samples and practical samples with satisfactory results.