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4475296 
Journal Article 
In situ measurement of dissolved phosphorus in natural waters using DGT 
Zhang, H; Davison, W; Gadi, R; Kobayashi, T 
1998 
Yes 
Analytica Chimica Acta
ISSN: 0003-2670
EISSN: 1873-4324 
370 
1 (1998) 
29-38 
WOS:000074830700004 
The technique of diffusive gradients in thin films (DGT) is described for the in-situ measurement of reactive phosphorus species in natural waters, sediments and soil. Phosphorus species diffuse through a layer of polyacrylamide gel and then bind to ferrihydrite embedded in a further layer of gel. Colorimetric measurements are performed after acid elution. The effects of various solution conditions were investigated and the first field application is reported. The diffusion coefficient for orthophosphate in the gel was 0.00000605 cm2 per second at 25C. From this DGT could be used to measure phosphate in solutions without the need for calibration. DGT units of 0.8 mm thick diffusive gel, stirred in 200 ug per litre phosphorus solutions for different times, showed a measured mass increase linearly with time. Solutions of different gel layer thicknesses showed the measured mass was proportional to the reciprocal of the gel layer thickness. The capacity of the DGT choice was linear and theoretically predictable to a concentration of up to 0.6 mg phosphorus per litre. Linear regression analysis of in-situ samples in a eutrophic pond gave 95 per cent confidence for a phosphorus concentration of 100.8 ug per litre. DGT measurements of sediment increased from below detection limits in the over-lying water to almost 300 ug per litre at a depth of 50-60 mm. This preliminary work required further investigation into the relationship between the DGT response and plant uptake but measurements in soil and sediment are feasible. There are 30 references.