Sampling by pressure filtration

Preferably, the filtration unit should provide a volume for 1L of sample water. This will not only speed up the procedure, but also minimize contamination risks due to repeated opening and refilling. Inert gases (Ar, N2) are preferred for pressure filtration of samples which are under-saturated with regard to ot gen. Otherwise, the use of pressurized air is possible. The pressure should be adjusted to allow a filtration rate of 100mL/min but should not exceed 80 kPa (0.8 bar). An air-filter and a gas-washing bottle filled with acidified 

For waters with much less than 0.5 mg/L SPM, the amount of material obtainable from the typical 0.5-2 L sample volume is insufficient for subsequent precise and accurate TE analyses. Off-line processing of the much larger volumes of water then necessary becomes very laborious and should be replaced by on-line filtration from appropriate samplers (Fig. 12-30). To this end, the filter holder is attached to the drain spigot, and the necessary additional pressure is applied via the sampler s air-vent. The suspended particulate matter is collected by filtering all the water held by the sampler. To remove the seasalt from the loaded filters, the on-line filter holder is disconnected from the sampler and attached to a plastic syringe. Manually, two 20 mL portions of high-purity distilled water are drained through the filters. The further treatment of the loaded, salt-free filters is identical to the procedure applied to filters obtained by off-line filtration. 

---