## 3 Results and Discussion
### Comparisons of DI-, HS- and HS-TWA SPME Methods toward Water Analysis  
Water sampling was carried out at the two municipal surface drinking water ponds near Corner Brook, NL, Canada: Trout Pond and 3 Mile Pond. Triplicate water samples were analyzed on-site for: conductivity, dissolved solids, pH and temperature (results are presented Table 1) and 1 L samples were collected for analysis for THMs. All methods used SPME fibers with 65 \(\upmu\)m PDMS/DVB film. This fiber gave the best component extraction for all target THMs, based upon their GC peak areas under optimized conditions. Further, a zero sink test was performed to assess fiber compatibility for analysis of THMs. The results found that no analyte loss (<2%) from the fiber was seen during transfer periods from extraction to analysis. Such results suggest that the fiber is suitable for use in TWA studies for THM analysis. Samples were studied for THMs in two scenarios. A portion of the collected water was sealed in vials with septum sealed tops. SPME sampling and extraction were achieved within 12 h from collection for DI- and HS-SPME methods. HS-TWA SPME method extracted analytes over a two days period with the SPME fiber retracted by 20 mm into the needle casing (optimized conditions). Otherwise similar optimized conditions were used in the HS-TWA method as for DI- and HS- sampling. The second scenario was by on-site sampling, whereby the TWA-SPME fiber was left to sample for two days in the pond and then retrieved and analyzed. When on-site TWA water analysis data was compared to TWA-SPME vial sampling, results from on-site sampling showed consistently lower but reproducible results. Such differences were attributed to the change in solution conductivity, where salt had been added to the sampling vial method. Under natural on-site sampling conditions, the water conductivity was low (60 \(\upmu\)S). With the addition of high salt (10% wt./vol. added) content, the relative volatility in the headspace is increased, because the increased salt concentration causes an increase in the gas/liquid equilibrium toward the fiber. Hence larger GC peaks areas would be obtained for smaller amounts of a THM component under salt enriched conditions. It has been reported that sodium sulfate provides a maximum extraction efficiency around 2.5 g of salt per 10 mL water for lower molecular weight THMs like (CHCl\({}_{3}\) and CHCl\({}_{2}\)Br) [16; 27]. The effect of adding salt to the sampling vial produced a \(\sim\)10% signal enhancement in THM GC peak areas, found for all DI-, HS- and TWA- SPME analysis methods. Calibration curves constructed from this data also gave lower LODs for individual THM components (see Table 2). Hence a further calibration curve was necessary for TWA sampling from a vial where no salt was added. After comparing TWA vial sampling data, obtained under non-salted conditions, to on-site TWA sampling, the corrected results obtained were comparable to those obtained by HS- and DI- methods. The calibration curve produced under non-salt added conditions was used for quantification of TWA sampling of pond water by both on-site and by sampling vial methods, Data is given in Table 1. Under non-salt conditions, the method detection limits were usually higher for the individual THMs and generally smaller extracted peak areas were obtained for individual THM components for similar concentrations (see Table 2). This is perhaps a limitation to on-site sampling method development as careful attention has to be made to ensure the matching of ionic strength conditions for calibration samples to water samples analyzed. However, it may be the case, where the natural waters being sampled are bring or saline. Here the natural conductivity might closer mimic the artificial conditions to the \"salt added\" sample vial conditions and hence show minimal deviations. All SPME methods were able to achieve low ppb detection limits and hence these methods were amenable to quantification of THMs in the analyzed waters.