Could organic phosphorus compounds contaminate the analysis of phosphate oxygen isotopes in freshwater matrices?

Davies, Ceri and Surridge, Ben and Gooddy, Daren C. (2014) Could organic phosphorus compounds contaminate the analysis of phosphate oxygen isotopes in freshwater matrices? In: EGU General Assembly 2014, 2014-04-26 - 2014-05-02.

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Variation in the stable isotope composition of oxygen within dissolved phosphate (δ18Op) represents a novel and potentially powerful environmental tracer, providing insights into the sources of phosphorus and the extent to which phosphorus from different sources is metabolised. The analysis of δ18Op within freshwater matrices requires isolation of the phosphate ion from possible sources of contaminant oxygen within the bulk matrix, prior to pyrolysis (usually of a silver phosphate precipitate) and analysis of the oxygen isotope composition. The majority of published research uses co-precipitation of phosphate with brucite (Mg(OH)2) as an initial step in the isolation of the phosphate ion. However, freshwater matrices also contain a wide range of organic phosphorus compounds, including adenosine 5’-triphosphate (ATP) and phosphonates such as 2-aminoethylphosphonic acid. In this paper, we initially examine the potential for co-precipitation of organic phosphorus compounds with brucite. Our data indicate that ATP, sodium pyrophosphate and inositol hexakisphosphate are almost entirely removed from solution through co-precipitation with brucite, whilst glucose-6-phosphate and 2-aminoethylphosphonic acid are less readily co-precipitated. Subsequently, we assessed the potential for acid-hydrolysis of organic phosphorus compounds during re-dissolution of the brucite precipitate, using a range of acid systems. Our data indicate that up to 17% of ATP and up to 5% of sodium pyrophosphate can be hydrolysed by concentrated acetic acid, yielding fresh phosphate ions in solution. Our findings have potentially significant implications for analysis of δ18Op because the fresh phosphate ions produced following acid hydrolysis will be subjected to inheritance and kinetic isotope fractionations, likely altering the bulk δ18Op within a freshwater sample.

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Contribution to Conference (Other)
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EGU General Assembly 2014
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© Author(s) 2014. CC Attribution 3.0 License.
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14 Aug 2014 10:34
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17 Feb 2024 01:29