Composite proportional sampling device

A consumer-operated device, attached to the tap, collects the composite proportional sample. The composite proportional sampling device is connected to the kitchen tap through a coupling nut or a hose clip. In practice, this might cause problems, as some taps are shaped in a w that makes it very difficult to attach the sampling device (e.g. mixer and spr -type taps). The gap between device and tap should be as short as possible. The device should be coimected horizontally. 

The composite proportional sample is taken with a consumer operated device fitted to the drinking water tap, which splits off a small constant proportion ( 5 %) of every volume of water drawn for dietetic purposes during one week. Figure 3.5 gives a schematic view of a proportional sampling device. 

By definition, the proportional sampling procedure scores 100 % for the criteria of representativeness and reproducibility. However, this applies only when consumers operate the proportional device correctly. To test whether the consiuner has used the device correctly, the volume of the composite proportional sample can be checked. In some test areas the volmne of the composite proportional sample was noted and used to calculate the average daily water consumption per person. Figure 3.7 shows the water consumption distribution for these test areas, and Figure 3.8 shows the... 

As a basic rule, flow-proportional sampling is recommended flow-proportional composite samples can be produced from the individual samples taken, where necessary, with automatic sampling devices. In the case of time-proportional sampling, no account is taken of the quantity of water. 

Nevertheless, this must be regarded as a better solution than a single or multiple random sample. Production of time-proportional composite samples is also possible, using automatic sampling devices where applicable. The composite samples can be taken with or without settleable substances. If the water contains many settleable substances, it is more favourable to remove these substances before producing the composite samples and to investigate them separately in the laboratory. After removing the settleable substances, the water from the composite samples should be used for laboratory tests. If secondary turbid substances have formed in the water, these should be included in analyses. 

Nersesyants et al. [91] were successful in using this method for the separate determination of aluminium and aluminium carbide. A solid sample was treated with an acid, and the gas evolved was collected in a gas volume-measuring device. The gas composition was determined on a column containing molecular sieves by conventional gas chromatography. The hydrogen content is proportional to that of the metal in the sample, and the content of the organic gaseous component corresponds to that of the carbide [91]. 

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