Interference of some aqueous two-phase system phase-forming components in protein determination by the Bradford method

摘要

The interference of some specific aqueous two-phase system (ATPS) phase-forming components in bovine serum albumin (BSA) determination by the Bradford method was investigated. For this purpose, calibration curves were obtained for BSA in the presence of different concentrations of salts and polymers. A total of 19 salts [Na _2SO _4, (NH _4) _2SO _4, MgSO _4, LiSO _4, Na _2HPO _4, sodium phosphate buffer (pH 7.0), NaH _2PO _4, K _2HPO _4, potassium phosphate buffer (pH 7.0), KH _2PO _4, C _6H _8O _7, Na _3C _6H _5O _7, KCHO _2, NaCHO _2, NaCO _3, NaHCO _3, C _2H _4O _2, sodium acetate buffer (pH 4.5), and NaC _2H _3O _2] and 7 polymers [PEG 4000, PEG 8000, PEG 20000, UCON 3900, Ficoll 70000, PES 100000, and PVP 40000] were tested, and each calibration curve was compared with the one obtained for BSA in water. Some concentrations of salts and polymers had considerable effect in the BSA calibration curve. Carbonate salts were responsible for the highest salt interference, whereas citric and acetic acids did not produce interference even in the maximum concentration level tested (5 wt%). Among the polymers, UCON gave the highest interference, whereas Ficoll did not produce interference when used in concentrations up to 10 wt%. It was concluded that a convenient dilution of the samples prior to the protein quantification is needed to ensure no significant interference from ATPS phase-forming constituents.