| Heavy metals exist as variety of chemical species in seawater. Nowadays scientists are increasingly recognizing that it is the bioavailability of heavy metals that controls the potential of adverse effects rather than the total or filterable concentrations. Knowledge of the concentrations and chemical speciation of trace metals is essential to understand influence of those metals on marine organism.To do the speciation analysis of heavy metals in sweater, the collected samples are ordinarily shipped back to laboratory for determination. The heavy metal species could be changed during transportation, pretreatment and preservation. The chemical reagents added might also change the distribution of chemical species. Therefore, it is necessary to develop in situ collection methods of heavy metal species in natural waters.Diffusive gradients in thin films (DGT) is a recently developed technique, which is capable of in situ enrichment of labile metal species in aqueous systems for quantitative measurement. The key components of DGT device are ion-exchange resin and diffusive gel. Metals transport through the diffusion gel in a controlled way, which makes it possible to explore the concentration of labile species over the deploying time.In this study classical polyacrylamide hydrogel was used as the diffusion gel, and three ion-exchange sorbents were chosen to develop the DGT devices. Those were Chelex-100resin impregnated with polyacrylamide, glutaraldehyde-crosslinked chitosan membrane and glutaraldehyde-crosslinked L-cysteine modified chitosan membrane. The DGT devices had been characterized and deployed for enrichment of heavy metals in seawater. The main contents and results of the study are as follows:(1) The DGT device consisted of a polyacrylamide diffusive gel and a Chelex-100resin impregnated with polyacrylamide was built for the measurement of Mn, Co, Ni, Cu, Zn, Cd and Pb in seawaters. The molecular diffusion coefficient D of various metals through the polyacrylamide gel had been determined. With Chelex-100resin as the ion-exchange resin, pH in the range of5.6-8.6would not influence the enrichment. It was found that the results were independent of ionic strength between10mmol·L-1and700mmol·L-1. The DGT device had been applied for the preconcentration of heavy metals in coastal seawater of Xiamen for seven days. The result showed that the DGT-labile part in the fraction of0.45μm filterable portion varied from6.67%～45.33%for those metals. The relative standard deviations of the preconcentration and analysis were all below10%(n=3). The DGT had a number of advantages, such as being simple, easy for in situ use, independent of pH, ionic strength and matrix. The DGT had been confirmed to be a very promising tool for preconcentration trace metals in seawaters.(2) Base on the above work, glutaraldehyde-crosslinked chitosan membrane was developed and used as the ion-exchange sorbent. The DGT device was applied to enrich the labile Co, Ni, Cu, Zn and Cd in seawater. With the same metal concentration, glutaraldehyde-crosslinked chitosan membrane showed greater absorption ability than Chelex-100resin. The use of glutaraldehyde-crosslinked chitosan membrane was independent of pH between5～8and ionic strength at10mmol·L-1and700mmol·L-1. The DGT device had been deployed in spiked seawater for three days. The result showed that the DGT-labile concentration as a proportion of the0.45μm filterable concentration varied from12.57%to64.68%for target metals. The relative standard deviations of the preconcentration and analysis were all below10%(n=3).The new type of DGT device was a suitable preconcentration tool for the trace metals in seawater. To hand the glutaraldehyde-crosslinked chitosan membrane was easier than Chelex-100resin.(3) A glutaraldehyde-crosslinked L-cysteine modified chitosan membrane was developed as the ion-exchange sorbent. This new type of resin was also independent of pH between5and8and ionic strength at10mmol·L-1and700mmol·L-1. The new type of DGT device was reliable for in situ specie collection of trace metals in seawater. The DGT device had been used in the enrichment of labile Co, Ni, Cu, Zn and Cd in spiked seawater samples. The DGT-labile fraction as a percentage of the0.45μm filterable portion ranged between26.06%～87.25%for those metals. The relative standard deviations of the preconcentration and analysis were all below10% (n=3). In the same seawater, the DGT device with glutaraldehyde-crosslinked L-cysteine modified chitosan membrane showed higher adsorption ability towards metals than the other two types of DGTs mentioned above. |
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