Determination of dissolved inorganic phosphorus in natural waters at nanomolar concentrations using a long capillary cell detector

Abstract

A high sensitivity spectrophotometric system using a long capillary cell (LCC) detector was developed to determine dissolved inorganic phosphorus (DIP) at nanomolar concentrations in natural waters. The colorimetric chemistry used is based on the classical molybdophosphate blue technique. The radiation source is a near-infrared light-emitting diode and a silicon phototransistor is used as a detector. Method parameters were optimized for the final LCC design. With a 600-mm LCC, a detection limit (twice the standard deviation of the blank) of 1 nmol l −1 was obtained with a relative standard deviation of 6%. The working range of the instrument is 1–500 nmol l −1 DIP, and a sample volume of 10 ml is required for each analysis. The technique was applied to both fresh and marine water. The instrument is compact, relatively simple and easy to use in the laboratory and the field.