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The development of iodide-based methods for batch and on-line determinations of phosphite in aqueous samples |
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| Authors: | Barco Roman A Patil Deepa G Xu Weihong Ke Lin Khachikian Crist S Hanrahan Grady Salmassi Tina M |
| Institution: | aDepartment of Biological Sciences, California State University, Los Angeles, CA, USA bDepartment of Chemistry & Biochemistry, California State University, Los Angeles, CA, USA cDepartment of Civil Engineering, California State University, Los Angeles, CA, USA dCenter for Environmental Analysis, California State University, Los Angeles, CA, USA eChemical Engineering Department, Ningbo University of Technology, Ningbo, China |
| 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 HPO32−, P(+III)] and hypophosphite H2PO2−, 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 (I3−) and penta-iodide (I5−). The oxidation of P(+III) consumes free I3− and I5− in solution. The remaining I3− and I5− subunits are then allowed to react with the amylose content in starch to form a blue complex, which has a λmax 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 λmax of 710 nm. The linear range for both the batch and FI determination of P(+III) was 1.0–50 μM with detection limits of 0.70 and 0.36 μM, 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 KMnO4 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. |
| Keywords: | Phosphite Reduced phosphorus Spectrophotometric detection Batch method Flow injection (FI) |
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