title: The development of iodide-based methods for batch and on-line determinations of phosphite in aqueous samples.
abstract: Recent developments in the field of microbiology and research on the origin of life have suggested a possible significant role for reduced, inorganic forms of phosphorus (P) such as phosphite [HPO(3)(2-), P(+III)] and hypophosphite [H(2)PO(2)(-), P(+I)] in the biogeochemical cycling of P. New, robust methods are required for the detection of reduced P compounds in order to confirm the importance of these species in the overall cycling of P in the environment. To this end, we have developed new batch and flow injection (FI) methods for the determination of P(+III) in aqueous solutions. The batch method is based on the reaction of P(+III) with a mixed-iodide solution containing tri-iodide (I(3)(-)) and penta-iodide (I(5)(-)). The oxidation of P(+III) consumes free I(3)(-) and I(5)(-) in solution. The remaining I(3)(-) and I(5)(-) subunits are then allowed to react with the amylose content in starch to form a blue complex, which has a lambda(max) of 580 nm. The measurement of this blue complex is directly correlated with the concentration of P(+III). The on-line FI method employs the same reaction between P(+III) and mixed-iodide producing phosphate [P(+V)] that is determined spectrophotometrically by the molybdenum blue method employing ascorbic acid at a lambda(max) of 710 nm. The linear range for both the batch and FI determination of P(+III) was 1.0-50 microM with detection limits of 0.70 and 0.36 microM, respectively. Interference studies for the batch method show that arsenite [As(+III)] and sulfite [S(+IV)] can also be determined by this technique; however, these interferences can be circumvented by oxidizing As(+III) and S(+IV) using KMnO(4) which is an ineffective oxidant for P(+III). Both methods were applied to P(+III) determinations in ultra-pure water and simulated creek water. Results and analytical figures of merit are reported and future work is considered.
authors.affiliation: Department of Biological Sciences, California State University, Los Angeles, CA, USA.
authors.forename: Roman A
authors.initials: RA
authors.lastname: Barco
authors.forename: Deepa G
authors.initials: DG
authors.lastname: Patil
authors.forename: Weihong
authors.initials: W
authors.lastname: Xu
authors.forename: Lin
authors.initials: L
authors.lastname: Ke
authors.forename: Crist S
authors.initials: CS
authors.lastname: Khachikian
authors.forename: Grady
authors.initials: G
authors.lastname: Hanrahan
authors.forename: Tina M
authors.initials: TM
authors.lastname: Salmassi