Nuclear Magnetic Resonance Methods
Nuclear magnetic resonance is one of the most powerful noninvasive experimental techniques available for providing atomic and molecular structure information based on changes in resonance frequency of the intramolecular magnetic field around an atom in a molecule. Dissolved phosphorus species such as orthophosphate, phosphonates, orthophosphate monoesters, and diesters were detected by 31P-NMR spectroscopy in lake and river waters after ultrafiltration and reverse osmosis of 250-500 mL samples.
Soluble unreactive phosphorus was also analyzed with the use of praseodymium ethylenediamine tetraacetate, alkaline bromination degradation procedures, and adjustment of sample pH. Cade-Menun et al. developed a procedure for characterization of dissolved and particulate phosphorus species from river waters. Detected phosphorus species included orthophosphate, phosphonates, myo-inositol hexakisphosphate, and orthophosphate diesters. Further investigation is required due to possible alteration of the phosphorus forms when using lyophilization of the samples in NaOH-EDTA solutions. A thorough spe- ciation of dissolved and particulate phosphorus forms in the eutrophic Lake Mendota (Wisconsin, USA) by 31P-NMR spectroscopy was performed by Read et al.
The results showed that particulate phosphorus species contained phosphonate, orthophosphate mono- and diesters, orthophosphate, pyrophosphate, and polyphosphate. Dissolved phosphorus contained all particulate phosphorus forms, with orthophosphate being the dominant species. Biochemical regression analysis of the results provided insights into mechanisms of phosphorus dynamics. Similar 31P-NMR study of the dissolved and particulate phosphorus species in an eutrophic lake was done in the shallow Lake Taihu, China. D2O was added into the supernatant to reach 10% proportion required for signal lock prior to the analysis.
The 31P-NMR spectra were measured at 161.84 MHz on an Agilent AV400 spectrometer, with orthophosphate and phosphate monoesters as the dominant phosphorus species in both fractions. While phosphonate was detected in dissolved fraction, pyrophosphate was mainly found in the particulate phosphorus fraction. At this time, there was no NMR standard method for phosphorus species analysis. Chemical shifts of phosphorus species are affected by pH and salt concentrations, a challenge for data reproducibility.
More than 50 phosphorus compounds were analyzed under standardized conditions in order to establish a P-compounds library for easier repeatability of the experiments and 31P-NMR identification of the compounds. Forms and lability of phosphorus species in algae and aquatic macrophytes were investigated by 31P-NMR coupled with enzymatic hydrolysis using alkaline phosphatase. Eleven phosphorus species were identified in the mono- and diester region as well as orthophosphates, pyrophosphates, and phosphonates.
Conclusions. As a direct result of nutrient control policies introduced by many countries, there is a decline in total phosphorus loadings in natural waters, with more than 50% reduction of TP observed in Lake Erie since 1967. Similar decreases in TP were reported in a long-term study of Boreal lakes in Sweden. However, algal blooms are still occurring and the climate changes may influence the frequency of these events. As the composition of the nutrient pool impacts the harmful algal blooms, phosphorus speciation methods with trace- and ultra-trace-level detection limits will be required. Currently, FIA spectrophotometric methods are the major analytical technique of choice in the environmental analysis of orthophosphate and total phosphorus. The and a possibility to analyze simultaneously a large number of phosphorus species. Increasing availability and decreasing cost of instrumentation will support development of highly selective and sensitive analytical methodologies for phosphorus speciation.
References:
1. O'Neil, M.J., Heckelman, P.E., Koch, C.B., and Roman, K.J. (ed.) (2006). The Merck Index, 14e. Whitehouse Station, NJ, USA: Merck and Co., Inc.
2. Mellor, J.W. (1962). A Comprehensive Treatise on Inorganic and Theoretical Chemistry. Wiley.
3. Toy, A.D.F. (1973). Chem. Phosphorus 3: 389-406. doi: 10.1016/B978-0-08-018780-8.50005-1.
4. Stwertka, A. (2012). A Guide to the Elements, 3e. New York, NY, USA: Oxford University Press, Inc.
5. Bingham, E., Cohrssen, B., and Powell, C.H. (2001). Patty’s Toxicology, 5e, vol. 9. Wiley.
6. Jacobs, M.B. (1967). The Analytical Toxicology of Industrial Inorganic Poisons. Interscience Publishers.
7. Siekierski, S. and Burgess, J. (2002). Concise Chemistry of the Elements, 107-114. Woodhead Publishing.
8. Greenwood, N.N. and Earnshaw, A. (1997). Chemistry of the Elements, 2e, 473-546. Butterworth-Heinemann.
9. Theocharis, C.R. (1990). J. Chem. Technol. Biotech- nol. 47: 182-182. doi: 10.1002/jctb.280470215.
10. Waggaman, W.H. (1952). Phosphoric Acid, Phosphates, and Phosphatic Fertilizers. LWW.
Date added: 2025-01-04; views: 29;