A paper-based device for measurement of reactive phosphate in water

The preparation and evaluation of a simple paper-based device for the determination of reactive phosphate in natural and soil waters based on the formation of phosphomolybdenum blue is reported. Hydrophilic reagent zones were defined by printing filter paper with a hydrophobic paper-sizing agent using an inkjet printer. The molybdate/potassium antimony(III)-tartrate reagent and ascorbic acid reductant merged together from adjacent hydrophilic zones after spotting the liquid sample onto the paper. The colour intensity of the phosphoantimonylmolybdenum blue complex produced was measured using a flat bed scanner. Under optimal conditions, the paper-based device is characterised by a working range of 0.2–10 mg L−1 P, limits of detection and quantitation of 0.05 and 0.16 mg L−1 P, respectively, and repeatability of less than 2% RSD at 1 and 5 mg L−1 P (n=10 and 8). There was no significant difference between the results obtained using the paper-based device and reference methods (t=0.0135, P (T≤t) two-tail=0.9892, df=38). In its optimum form, the paper-based device was stable for up to 15 day under ambient conditions, and up to 122 day when stored at ≤−20 °C. The small dimensions, minimal reagent consumption, low cost (a few cents), ease of operation and favourable analytical performance make the proposed paper-based device attractive for on-site environmental monitoring and analysis.