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

•A flow analysis system determines trace dissolved reactive phosphate (DRP).•It is based on UV photoreduction of phosphomolybdate in the presence of ethanol.•The use of unstable reducing agents (e.g. SnCl2 or ascorbic acid) is not required.•The system can measure DRP in the concentration range 5–5000 μg L−1 P.•The flow system was successfully applied to a number of natural water samples.

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 1.3 μg L−1 P, linear range of 5–1000 μg L−1 P, dynamic range of 5–5000 μg L−1 P, repeatability of 0.8% (1000 μg L−1 P, n=10) and 5.6% (10 μg L−1 P, n=10), and sample throughput of 57 h−1. It is expected that this method will improve the feasibility of autonomous long-term environmental monitoring of dissolved reactive phosphate using inexpensive apparatus.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slide