Determination of traces of phosphate in sea water automated by programmable flow injection: Surfactant enhancement of the phosphomolybdenum blue response

An assay protocol, based on programmable Flow Injection (pFI), is optimized by tailoring flowrates appropriately to the individual steps of an assay, thus allowing sample and reagent metering, mixing, incubation, monitoring and washout to be carried out more efficiently and in different time frames. This novel approach to flow based methods is applied here to optimize the determination of orthophosphate at nanomolar levels. Programmable Flow Injection was also used to facilitate an investigation of the properties of the phosphomolybdenum blue (PMoB) formed during this assay, by using the stop flow technique an approach that revealed for the first time the influence of surfactants on the kinetics of formation of PMoB and its spectral characteristics. It was discovered that the two most frequently used surfactants (SOS and Brij) have profound and different influences on the spectra and formation of PMoB and this finding was used to enhance the sensitivity of the phosphate assay at nanomolar levels. The method was applied to the assay of trace levels of phosphate in sea water.