Determination of phosphite (HPO3-2) by a new IC/MS/MS method using an 18O-labeled HPO3-2 internal standard

Sepideh Sadeghi; Todd A Anderson; W Andrew Jackson

doi:10.1016/j.talanta.2021.122198

Determination of phosphite (HPO₃^-2) by a new IC/MS/MS method using an ¹⁸O-labeled HPO₃^-2 internal standard

Talanta. 2021 Aug 1:230:122198. doi: 10.1016/j.talanta.2021.122198. Epub 2021 Feb 13.

Authors

Sepideh Sadeghi¹, Todd A Anderson², W Andrew Jackson³

Affiliations

¹ Department of Civil, Environmental, and Construction Engineering, Texas Tech University, Box 41023, Lubbock, TX, 79409-1023, USA. Electronic address: Sepideh.Sadeghi@ttu.edu.
² Department of Environmental Toxicology, Texas Tech University, Box 41163, Lubbock, TX, 79409-1163, USA. Electronic address: todd.anderson@ttu.edu.
³ Department of Civil, Environmental, and Construction Engineering, Texas Tech University, Box 41023, Lubbock, TX, 79409-1023, USA. Electronic address: andrew.jackson@ttu.edu.

PMID: 33934758
DOI: 10.1016/j.talanta.2021.122198

Abstract

A new method has been developed to determine trace amounts of phosphite (HPO₃^-2) in environmental samples using ion chromatography with electrospray tandem mass spectrometry (IC-ESI/MS/MS). The method includes the production and use of an ¹⁸O-labeled HPO₃^-2 internal standard (IS). This isotopically labeled IS significantly improved sensitivity and could account for matrix suppression. The method detection limit (MDL) was determined as 0.017 and 0.034 μg L^-1 of HPO₃^-2 (6.5 and 13 ng P L^-1) using a 500 and 25 μL injection loop, respectively. Precision (1-10%) and accuracy (recoveries = 96-106%) were established for a range of environmental samples using known (spiked) addition. The impact of ionic interferences was investigated by evaluating the response of the internal standard in the presence of common anions with respect to distilled deionized water. The most significant interference was due to nitrate (100 mg-NO₃^- L^-1) with a 99.99% reduction in IS intensity. The method was successfully applied to wastewater effluent, surface water, tap water, and soil samples. Relatively low concentrations <0.25 μg HPO₃^-2 L^-1 were measured in tap water, surface water and wastewater effluent, and ~1.6 μg kg^-1 HPO₃^-2 in soil samples, using both injection loops. Limited suppression was observed for all matrices. The largest IS peak area suppression (~98%) was observed in WW effluent with 500 μL injection loop; however, this method was able to quantify HPO₃^-2 with good recoveries and precision despite the mentioned suppression, supporting the ability of the proposed method to quantify HPO₃^-2 in different environmental matrices.

Keywords: IC/MS/MS.; Internal standard; Phosphite..