Elsevier

Journal of Chromatography B

Volume 767, Issue 2, 15 February 2002, Pages 363-368
Journal of Chromatography B

Short communication
Ion chromatographic separation and determination of phosphate and arsenate in water and hair

https://doi.org/10.1016/S0378-4347(01)00424-8Get rights and content

Abstract

A simple and sensitive method for the sequential determination of phosphate and arsenate was developed based on initial ion chromatographic separation followed by detection as the ion-association complex formed by heteropolymolybdophosphate and arsenate with bismuth. With 200 μl sample injection and separation on a AS4A-SC column using an eluent of 3.5 mM sodium hydrogen carbonate–10.0 mM sodium hydroxide, the detection limits which are calculated as the concentration equivalent to twice the baseline noise, were found to be 0.8 μg/l and 4.2 μg/l for P and As, respectively. Spiked samples were analyzed and recoveries were found to be satisfactory in the range of 95–105% for phosphate and 90–105% for arsenate. Samples of water and hair were analyzed by the proposed method.

Introduction

Arsenic is toxic to living systems. If ingested, it tends to accumulate in certain parts of the body. Biological samples of blood, tissues, urine, nail, hair are considered as indicators of arsenic poisoning [1]. The LAFA in a study conducted in seven countries has brought out the significance of hair mineral analysis (in which As is included), as a means for assessing internal body burdens of environmental pollutants [2]. Based on a study of 2059 hair samples, Bozsai has reported that a good correlation exists between As in hair and that in water supply [3]. Because of its toxic nature, WHO has put a limit of 0.05 pg/l arsenic in drinking water. On the other hand, phosphate is an important nutrient for biological growth and is present in all natural waters. Many of the chemical reactions of phosphorous and arsenic, when present as phosphate and arsenate, are common. For example, phosphate and arsenate react with molybdate to yield heteropolymolybdate, which on reduction can form ion association complexes with bismuth or antimony. Thus, the separation of phosphate and arsenate is very often required. It is in this context that ion chromatographic separation in combination with suitable detection methods appears attractive. Not only that, ion chromatography is suitable for speciation studies, which are relevant from the point of view of bioavailability and toxicity.

Scanning the literature, ion chromatographic separation for arsenic followed by its determination in natural water and biological samples by AAS, ICP-AES, ICP-MS etc. has been reported [4], [5], [6], [7], [8], [9], [10].The methods, though attractive, require high cost instrumentation. In a few cases, ion chromatographic separation followed by conductivity detection has been used [11], [12]. Li et al., while reviewing the methods on speciation of arsenic, proposed an ion chromatographic separation followed by sequential determination of As(III) electrochemically and As(V) based on ion association complex formed by heteropolymolybdoarsenic acid with bismuth [13]. Regarding phosphate, there are a few papers related to ion chromatographic separation with conductivity detection [14], [15], [16]. However, no attempt has been reported for the sequential determination of As and P when present together. Therefore in the present work, an ion chromatographic separation of phosphate and arsenate followed by a simple spectrophotometric determination of the reduced species of the ion-association complex formed with ammonium molybdate and bismuth is presented. During this, the method of Li et al. is also improved. The present method has been applied for the determination of phosphate and arsenate in natural water and human hair samples.

Section snippets

Instrumentation

The layout of the ion chromatograph Dionex model DX-30, coupled to a post column reactor and UV–VIS detector is shown Fig. 1. The separating column was AS4A-SC in combination with a SC guard column. The reagent flow through the post column reactor is kept constant by maintaining 60 p.s.i. of nitrogen gas.

The experiments are run at an eluent flow-rate of 1.65 ml/min using a degassed solution of 3.5 mM sodium hydrogen carbonate and 10.0 mM sodium hydroxide. The wavelength used for the

Effect of eluent concentration and flow-rate

Preliminary studies with various concentration ratios of NaHCO3 and Na2CO3 indicated that the resolution between P and As(V) is optimum at a concentration of 3.5 mM NaHCO3 and 10.0 mM NaOH.

The effect of flow-rate on the peak heights of P and As in the chromatogram is investigated by varying the flow-rate from 1.3 to 1.8 ml/min. The peak height is optimum at 1.65 ml/min and all further experiments were carried out using this flow-rate.

Post column reagent

A suitable colour developing system for the

Conclusion

A simple IC procedure has been developed for the determination of phosphate and arsenate. This is the first time that an online sequential ion chromatographic separation with spectrophotometric determination of phosphate and arsenate is reported. The procedure is based on the ion chromatographic separation of phosphate and arsenate on an anionic column AS4A using 3.5 mM NaHCO3–10.0 mM NaOH as the eluant and spectrophotometric determination of the reduced species of the ion association complex

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