Oxygen isotope studies of phosphite oxidation: Purification and analysis of reactants and products by high‐temperature conversion elemental analyzer/isotope ratio mass spectrometry. (27th September 2015)

• Record Type: Journal Article
• Authors: Chang, Sae Jung; Blake, Ruth E.
• Is Part Of: Rapid communications in mass spectrometry. Volume 29:Number 21(2015)
• Page Start: 2039
• Page End: 2044
• Publication Date: 2015-09-27
• Subjects: Mass spectrometry -- Periodicals; 543.65
• DOI: 10.1002/rcm.7293
• Languages: English
• ISSNs: 0951-4198

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <sec id="rcm7293-sec-0001" sec-type="section"> <title>Rationale</title> <p>Increased attention has been recently focused on the origin and reactions of reduced‐P oxyanions such as phosphite [PO<sub>3</sub>(III)] in terrestrial and biological systems. We present new methods for studying O‐isotopic reactions between PO<sub>3</sub>(III) and other oxygen sources during oxidation of PO<sub>3</sub>(III) to PO<sub>4</sub>(V).</p> </sec> <sec id="rcm7293-sec-0002" sec-type="section"> <title>Methods</title> <p>Na<sub>2</sub>(HPO<sub>3</sub>)·5H<sub>2</sub>O, used as a PO<sub>3</sub>(III) source, contains structural water due to its hygroscopic nature; thus, we developed a method for determining the δ<sup>18</sup>O value of PO<sub>3</sub>(III) after the removal of structural water. Next, we tested two techniques for purifying PO<sub>4</sub>(V) from aqueous PO<sub>3</sub>(III)/PO<sub>4</sub>(V) mixtures: (1) precipitation of PO<sub>4</sub>(V) as ammonium phosphomolybdate (APM); and (2) precipitation of PO<sub>4</sub>(V) as magnesium ammonium phosphate (MAP). The O‐isotope compositions, <sup>18</sup>O:<sup>16</sup>O (δ<sup>18</sup>O values), of Na<sub>2</sub>(HPO<sub>3</sub>) and Ag<sub>3</sub>PO<sub>4</sub> were analyzed by TC/EA/IRMS.</p> </sec> <sec id="rcm7293-sec-0003" sec-type="section"> <title>Results</title> <p>Structural water was removed from Na<sub>2</sub>(HPO<sub>3</sub>)·5H<sub>2</sub>O after drying at 100 °C under vacuum and the δ<sup>18</sup>O value of PO<sub>3</sub>(III) was obtained. The δ<sup>18</sup>O values of PO<sub>4</sub>(V), which was extracted from <sup>18</sup>O‐labeled PO<sub>3</sub>(III)/PO<sub>4</sub>(V) mixtures by APM and MAP precipitations, were not altered by the precipitation process. This result confirms that PO<sub>3</sub>(III) is not converted into PO<sub>4</sub>(V) by oxidation or hydrolysis under either strong acidic/oxidizing (APM) or alkaline (MAP) conditions for up to a 24‐h period.</p> </sec> <sec id="rcm7293-sec-0004" sec-type="section"> <title>Conclusions</title> <p>We conclude that both APM and MAP precipitation are reliable and effective methods for the separation and purification of PO<sub>4</sub>(V) from aqueous PO<sub>3</sub>(III)/PO<sub>4</sub>(V) mixtures. The methods described here will permit the study of the isotopic evolution of various pathways of geochemical as well as biological PO<sub>3</sub>(III) oxidation. Copyright © 2015 John Wiley & Sons, Ltd.</p> </sec> </abstract>