HR: 0800h
AN: B21C-0903    [Abstracts]
TI: Development of a Starch Iodide Method for the Determination of Phosphite in Natural Waters.
AU: * Barco, R A
EM: romanb7@sbcglobal.net
AF: California State University, Los Angeles, Biological Sciences Dept., 5151 State University Drive, Los Angeles, CA 90041 United States
AU: Patil, D
EM: deepa052@yahoo.com
AF: California State University, Los Angeles, Biological Sciences Dept., 5151 State University Drive, Los Angeles, CA 90041 United States
AU: Salmassi, T M
EM: tsalmas@exchange.calstatela.edu
AF: California State University, Los Angeles, Biological Sciences Dept., 5151 State University Drive, Los Angeles, CA 90041 United States
AU: Hanrahan, G
EM: ghanrah@exchange.calstatela.edu
AF: California State University, Los Angeles, Biological Sciences Dept., 5151 State University Drive, Los Angeles, CA 90041 United States
AB: Phosphorus (P) is believed to occur almost exclusively in the environment as fully oxidized phosphate (H$_{3}$PO$_{4}$, oxidation state +V). Recent developments in the field of microbiology and research on the origin of life have suggested a possibly significant role for reduced, inorganic forms of P such as phosphorus acid [H$_{3}$PO$_{3}$, P(+III)], hypophosphorus acid [H$_{3}$PO$_{2}$, P(+I)] and various forms of phosphides [P(-III)] in the biogeochemical cycling of P. In order to confirm the importance of reduced forms of P, we need to develop new and better methods for the detection of these compounds in the environment, often at levels below 1 mM. Traditional methods of P determination are based on the reaction of P with acidified molybdate in aqueous solution to yield phosphomolybdate heteropolyacid, which is then reduced and analyzed spectrophotometrically to quantify the total amount of P in the sample. Limitations in this technique have resulted in our development of a new method using a starch iodide complex for the detection of phosphorus acid or phosphite. Under laboratory conditions, phosphite [P (+III)] is oxidized to phosphate [P (+V)] by tri-iodide (I$_{3}$). Starch reacts with excess tri-iodide present in solution to form a blue colored complex having a $\lambda$max of 580 nm. The I$_{3}$, as well as other species such as I$_{5}$, are responsible for the formation of the complex when they fit inside the coiled amylose structure of starch. Linear determination is possible in water samples containing 1 - 80 mM of P (+III). Measurement of the loss of blue color complex can then be correlated with phosphite concentration in the starting sample. Current efforts to optimize this method in order to reach limits of detection below 1 mM are underway. We believe that with better detection methods, the evidence for reduced P in the environment will increase. Due to chemical kinetics, microbial activity, surface catalyzed reactions and possible storage effects, it is difficult to effectively measure the low concentrations present after removing the samples from their natural environments for laboratory analysis. Therefore, to fully understand the importance of reduced P, ultimately, we hope to develop the starch iodide method into an in situ detection technique for measuring phosphite directly in natural waters where sensitive and reliable field-based methods of analysis are needed.
DE: 1899 General or miscellaneous
DE: 1806 Chemistry of fresh water
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting