Rapid and Portable Electrochemical Quantification of Phosphorus

Abstract

Phosphorus is one of the key indicators of eutrophication levels in natural waters where it exists mainly as dissolved phosphorus. Various analytical protocols exist to provide an offsite analysis, and a point of site analysis is required. The current standard method recommended by the Environmental Protection Agency (EPA) for the detection of total phosphorus is colorimetric and based upon the color of a phosphomolybdate complex formed as a result of the reaction between orthophosphates and molybdates ions where ascorbic acid and antimony potassium tartrate are added and serve as reducing agents. Prior to the measurements, all forms of phosphorus are converted into orthophosphates via sample digestion (heating and acidifying). The work presented here details an electrochemical adaptation of this EPA recommended colorimetric approach for the measurement of dissolved phosphorus in water samples using screen-printed graphite macroelectrodes for the first time. This novel indirect electrochemical sensing protocol allows the determination of orthophosphates over the range from 0.5 to 20 μg L(-1) in ideal pH 1 solutions utilizing cyclic voltammetry with a limit of detection (3σ) found to correspond to 0.3 μg L(-1) of phosphorus. The reaction time and influence of foreign ions (potential interferents) upon this electroanalytical protocol was also investigated, where it was found that a reaction time of 5 min, which is essential in the standard colorimetric approach, is not required in the new proposed electrochemically adapted protocol. The proposed electrochemical method was independently validated through the quantification of orthophosphates and total dissolved phosphorus in polluted water samples (canal water samples) with ion chromatography and ICP-OES, respectively. This novel electrochemical protocol exhibits advantages over the established EPA recommended colorimetric determination for total phosphorus with lower detection limits and shorter experimental times. Additionally this electrochemical adaptation allows the determination of dissolved phosphorus without the use of ascorbic acid and antimony potassium tartrate as reducing agents (as used in the colorimetric method). The potential portability of this protocol is demonstrated in the development of the PhosQuant electrochemical device and provides a portable device for the rapid electrochemical detection of dissolved phosphorus using screen-printed electrodes.

The molybdenum blue reaction for the determination of orthophosphate revisited: Opening the black box

“…In fact, the correlation between the anionic charge of 12-MPA and its first reduction potential is linear [38,43]. Voltammetric analysis of 12-MPA in aqueous 0.2 mol L À1 H 2 SO 4 solutions (pH z 0.78) has shown that 12-MPA may undergo two successive and reversible two-electron reductions at þ0.31 V and þ0.17 V [42], which decrease to þ0.27 V and þ0.13 V at pH 1 [44]. A third two-electron reduction at about À0.08 V is possible but this renders the product highly unstable, resulting in immediate decomposition [42] (Fig.…”

Metal–Organic Framework-Based Sensors for Environmental Contaminant Sensing

“…Nutrients such as phosphate ions (PO 4 3− ) in water lead to eutrophication and result in the reduction or elimination of dissolved oxygen, resulting in a negative effect on the water ecosystem [ 53 ]. Various luminescent MOF sensors have been employed for the selective detection of nutrient ions.…”

Sensing Technology for Rapid Detection of Phosphorus in Water: A Review

“…A variety of electrodes and electrochemical methods has been used to detect phosphorus in water. Kolliopoulos et al (2015) proposed a fast and portable electrochemical device to detect dissolved phosphorus by using screen-printed graphite electrodes. This work focused on the alteration of a colorimetric method to an electrochemical one in order to increase the measurement range.…”