Practical Considerations

12.3.1 Preparation of the ceramic dosimeter for field application

In order to prevent background contamination, the sorbent materials have to be cleaned with acetone prior to use. The acetone is decanted and the washing step repeated until the solvent stays clear with no

Fig. 12.4. Illustration of a stainless steel cage used in application of the ceramic tube in the field.

discoloration. The sorbents are then stored dry or under water until application. Prior to use, the sorbents are wetted with distilled water. About 1.5 g is placed into each ceramic tube, e.g., with the aid of a glass pipette. The tube is closed with the caps and mounted into a stainless steel holder put together by screws. An additional option is to place the ceramic tube into a stainless steel cage for protection from physical damage, impurities (dirt etc.) and easy access of water (Fig. 12.4).

The device is then placed into a bottle filled with distilled water and evacuated in an exsiccator to remove any air within the tube and to ensure a complete water saturation of the ceramic membrane. The prepared ceramic dosimeters can be stored in amber glass bottles filled with distilled water in the dark at 4°C for at least 4 weeks until deployment.

For deployment in the field, the ceramic dosimeter is tied by means of a polyethylene or nylon string to the stainless steel holder. The length of the string is chosen such that the samplers can be placed in the middle of the screened portion of a groundwater well or at the depth of interest in rivers and lakes. After the termination of sampling, the ceramic dosimeters are removed and placed in bottles with distilled water, or wrapped in tissue soaked in distilled water, and packed in zip plastic bags for transportation back to the laboratory.

12.3.2 Sampling rates

Sampling rate is a frequently used parameter for passive sampling devices. It describes the volume of water that is extracted with regard to the chemical of concern within a certain time. In the case of the ceramic membrane, sampling rates (R in mL day-1) are defined by Fick's first law according to the following equation [12]:

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