Continuous flow method for the simultaneous determination of phosphate/arsenate based on their different kinetic characteristics

Abstract

This paper proposes a new automated spectrophotometric method for the simultaneous determination of phosphate and arsenate without pre-treatment, which is faster, simpler, less expensive and hazardous than other well-known methods used with water samples. Such method is based on the different kinetic characteristics of complex formation of phosphate and arsenate with ammonium molybdate. A flow system was used in order to achieve good mixing and to provide precise time control. All the measurements were performed at the isosbestic point wavelength (885nm). Chemical variables were optimized by factorial design (ammonium molybdate 0.015molL−1, potassium antimony tartrate 1×10−4molL−1, and sulphuric acid 0.7molL−1). An appropriate linear range for both analytes (0.50–8.00μmolL−1), good inter-day reproducibility (4.9% [P] and 3.3% [P+As]) and a sample throughput of 6h−1 were obtained. The detection limits are 0.4μmolL−1 P and 0.19μmolL−1 [P+As] (3.3Sy/x). The method was validated.