The use of on-line UV photoreduction in the flow analysis determination of dissolved reactive phosphate in natural waters

Abstract

A highly sensitive flow analysis manifold for rapid determination of dissolved reactive phosphate was developed which uses ethanol and UV light to reduce phosphomolybdic acid, instead of the reactive and short-lived chemical reductants typically employed in molybdenum blue chemistry. This reaction is impractical to perform reproducibly in batch mode, yet is very simple to handle in a flow analysis system and uses a single, very long-lived reagent solution. Interference from common inorganic anions and organic phosphorus species was minimal, and good spike recoveries for a range of sample matrices were obtained. The proposed flow analysis system is characterised by a limit of detection of 1.3μgL−1 P, linear range of 5–1000μgL−1 P, dynamic range of 5–5000μgL−1 P, repeatability of 0.8% (1000μgL−1 P, n=10) and 5.6% (10μgL−1 P, n=10), and sample throughput of 57h−1. It is expected that this method will improve the feasibility of autonomous long-term environmental monitoring of dissolved reactive phosphate using inexpensive apparatus.