A simple and cost-effective manual solid phase extraction method for the determination of nanomolar dissolved reactive phosphorus in aqueous samples.

Phosphate is a typical limiting nutrient in oligotrophic oceans and its concentration can be as low as the nanomolar level, especially in surface seawater. Different techniques for nanomolar level phosphate determination have been studied, most of which are automatic and high throughput methods based on flow analysis. However, these techniques need expensive commercial or laboratory-made instruments, and experienced operators. This study reports an operationally convenient, sensitive and practical method for the determination of nanomolar dissolved reactive phosphorus in aqueous samples, based on classic phosphomolybdenum blue chemistry and solid phase extraction methodology. Under acidic conditions, the formed phosphomolybdenum blue can be preconcentrated on a hydrophilic-lipophilic balance solid phase cartridge, eluted with 0.2 M NaOH, and detected at 700 nm after color recovery with the addition of more reagents. After optimization of the recovery reagents volumes, the effectiveness of the method was evaluated. This simple manual method is sensitive (detection limit of 3.0 nM using 50 mL sample, which can be lowered to ∼ 1 nM by preconcentrating more sample), reproducible (relative standard deviation of 2.6%, n = 81, with different operators), free of interferences from salinity (0-35), silicate (up to 200 μM) and arsenate (up to 100 nM) and suitable for different aqueous matrixes. The effects of a series of phosphorus-containing compounds ( n = 13) were evaluated, with more than half showing hydrolysis during the experiment. This method was applied to determine the phosphate concentration in samples collected from the Western Pacific. [ABSTRACT FROM AUTHOR]