Water suction samplers

Porous cups can be used as probes in the monolith and suction can be applied to them to move water out of the soil and into a sample container under unsaturated conditions. Passive samplers that do not involve pressure or vacuum are also available [11]. 

For the soil pore water sampling, the procedure described by Knight et al. (1998) and Tye et al., (2003) can be normally followed. Samplers are inserted into soil containers and soil pore water extracted by connecting a syringe to each sampler and applying a suction. 

When suction is generated within the sampling system, water is sucked inwards through the pores of the sampler until a corresponding capillary pressure occurs in the pores. If the capillary pressure in the sampler is lower than that in the soil, water flows from the soil into the sampler until the capillary pressure in the sampler and in the soil are equal. The maximum capillary pressure in a pore can be calculated by the following equation (Schubert, 1982) ... 

The Metrohm 676 COD sample changer Is based on the standard procedure for measurement of the amount of K2Cr2C>7 required to oxidize the oxidlzable matter present in 1 L of water, so that the water sample is treated with excess Cr(VI) in a concentrated sulphuric acid medium containing Ag2SO as catalyst and heated at 175 C. The excess of Cr(VI) is determined by back-titration with Fe(II). The end-point is detected potentiometricaily by means of a metal —ideally gold— electrode. The titrated solution Is removed by suction and the titration vessel is washed with distilled water to make It ready for a new sample from the sampler, capable of holding up to sixteen pretreated samples. 

Non-flushing samplers employ a suction effect for sampling. This is caused by a pressure difference between the device chamber and water... 

Automated samplers function without the need for an operator, giving the possibility of selection of a sampling regime arranged in dependence on time or flow-through quantity. One of these is the sampler shown in Fig. 3.66 [7]. The system has a simple battery-driven peristaltic pump, which can take samples heavily polluted with suspensions of solid material using a suction basket immersed in water. The pump feeds the sample into a 5 1 bottle at the required times determined by the timing unit. 

Sternberg et ai, 1991). For different vertical resolutions, the water is collected in multi-chamber samplers. The transport is performed across filter and dialysis membranes, either actively by suction via pumps and vacuums or passively driven by concentration gradients and diffusion. 

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