Contamination-free sampling device

Sampling Devices—Sampling devices are described in detail under each of the specific sampling procedures. Sampling devices shall be clean, dry, and free of all substances that might contaminate the material being sampled. 

Approaches to minimising sampling errors (Guder and Wahlefeld, 1983) and preventing the introduction of chemical contamination (Versieck et al., 1982 Heydorn, 1984 Aitio and Jarvisalo, 1994) have been published. To reduce the risks of introducing errors during sampling, metal-free and sterile devices, and standardised procedures should be used. 

As pointed out by Yeoman (1983), the simplest yet one of the most important sources of random error is in the volumetric handling of liquid samples or standards. Differences in the surface tension and viscosity of specimens, calibration solutions or controls may cause major problems in analytical performance. The usefulness of lyophilised control material can often be abrogated by inaccurate reconstitution or unforeseen contamination. Any pipettes (manual or automatic devices) used in volumetric measurements should be of grade A quality and regularly checked for bias they must be carefully washed and kept clean, free of contamination. 

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