Measurement Of Phosphorus In Situ By DGT Devices With New Binding Phases

The technique of diffusive gradients in thin films?DGT?has been developed for the in situ measurement of reactive phosphorus species in natural waters,sediments and potentially soils.In this study,polyacrylamide/basic magnesium carbonate,magnesium hydroxide,and the phosphate-selective molecularly imprinted polymer were first used as the novel binding phase of DGT.Various factors,such as initial concentration,deployment time,temperature,pH and ionic strength,which may affect the adsorption of phosphate to the DGT were investigated.Field performance of DGT in nature water and sediments were explored.The main conclusions were summarized as follows:?1?Polyacrylamide/Basic magnesium carbonate was used as the novel binding phase of DGT.H₂SO₄?0.25 mol/L,10mL?was used for elution of phosphate from the binding gel,and an elution efficiency of 85%±5% was obtained.The DGT measurement was independent of ionic strength?0.001-0.05 mol/L?and pH?4.10-9.15?.The results indicated that the maximum adsorption capacities of DGT were limited to 20.4?g per disc?T=25°C,pH=7.00,[P] = 2mg/L?.For each sample,the concentration was obtained using DGT and additionally by direct measurement using the molybdenum blue method.Good agreement was obtained between the two measurements in the P concentration from0.001 to 20mg/L.The method detection limit?MDL?was 102.4 ng/L.Field performance of DGT in synthetic seawater,the coastal seawater of Xiamen,Lake Yihai,Lake Chaohu and Nanfei River indicated that the basic magnesium carbonate-DGT method was more reliable than the commonly used Ferrihydrite-DGT method in this study.?2?Polyacrylamide/magnesium hydroxide was used as the novel binding phase of DGT.The magnesium hydroxide was obtained in situ by hydration of calcined magnesium oxide.Mg?OH?₂-DGT also exhibited fine particle size??5.0 ?m?which was observed by the scanning electron microscopy?SEM?.With 10 mL 2.0 mol/L NaOH as the eluting agent,efficiency of elution of phosphorus on Mg?OH?₂gel was 72%±5%.The measured mass of PO4 increased rapidly with increasing temperature from 22 to 38 °C.Accumulation of PO4 by the Mg?OH?₂-DGT were independent of pH?3.02-7.98?or ionic strength?1 ?mol/L-0.3 mol/L NaNO3?.The method detection limit?MDL?was 90.7ng/L.When stored for up to 12 months,the Mg?OH?₂-DGT still had binding efficiency which was superior to that of the Ferrihydrite-DGT.In situ evaluations in synthetic seawater and fresh water confirmed that Mg?OH?₂-DGT was more accurate than Ferrihydrite-DGT for measurement of phosphorus over a long time period.?3?Polyacrylamide/phosphate-selective molecularly imprinted polymer was used as the novel binding phase of DGT.KOH?1.0 mol/L,5mL?was used for elution of phosphate from the binding gel,and an elution efficiency of 70.4%±5% was obtained.The measured mass of PO4 increased rapidly withincreasing temperature from 22 to 52°C.The DGT measurement was independent of ionic strength?0.0001-0.1 mol/L?and pH?2.83-9.13?.Good agreement was obtained between the DGT and the molybdenum blue method in the PO4 concentration from 0.1 to 6.0mg/L.In situ evaluations in Lake Chaohu confirmed that MIPs-DGT was more accurate than NIPs-DGT for measurement of phosphorus.MIPs-DGT showed high binding ability to and selectivity for phosphate than NIPs-DGT.