title: A kinetic method for determination of free vanadium(IV) and (V) at trace level concentrations.
abstract: A kinetic method based on alkaline phosphatase has been developed to measure free trace levels of vanadium(IV) and (V). The method involves measuring the rate of the alkaline phosphatase-catalyzed hydrolysis of p-nitrophenyl phosphate with (Vi) and without (Vo) a competitive inhibitor in the assay. Michaelis-Menten kinetics for a competitive inhibitor was used to express the relationship between Vo/Vi and the inhibitor concentration. Measuring both Vo and Vi thus yields a Vo/Vi ratio that allows calculation of the competitive inhibitor concentration. Determination of free vanadium in complex fluids can be accomplished by comparing the ratio of rates of p-nitrophenyl phosphate hydrolysis with and without a sequestering agent to the ratios of rates measured on addition of a known vanadium concentration. Free vanadium(V) can conveniently be measured from 10(-7) to 10(-5) M and free vanadium(IV) can be measured at 10(-8) M and above. The error limits on the vanadium determinations range from +/- 3 to +/- 12% of the concentration under investigation depending on the conditions under which the assay was conducted.
authors.affiliation: Department of Chemistry, Colorado State University, Fort Collins 80523.
authors.forename: D C
authors.initials: DC
authors.lastname: Crans
authors.forename: M S
authors.initials: MS
authors.lastname: Gottlieb
authors.forename: J
authors.initials: J
authors.lastname: Tawara
authors.forename: R L
authors.initials: RL
authors.lastname: Bunch
authors.forename: L A
authors.initials: LA
authors.lastname: Theisen
mesh_terms: D000469:Alkaline Phosphatase / Q000037:antagonists & inhibitors; D002021:Buffers; D006863:Hydrogen-Ion Concentration; D007202:Indicators and Reagents; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D011868:Radioisotopes; D012015:Reference Standards; D013056:Spectrophotometry, Ultraviolet; D013696:Temperature; D014639:Vanadium / Q000032:analysis* / Q000494:pharmacology
chemical_list: D002021:Buffers; D007202:Indicators and Reagents; D011868:Radioisotopes; D014639:Vanadium; D000469:Alkaline Phosphatase