Sampling

Sampling is a simple, but important procedure in numerous industries. Particularly in the food industry, it is an integral and indispensable part of quality assurance. Incorrect sampling can have devastating effects on test results and thus on the quality and safety of the products.

If errors occur at the start of the sampling procedure, it continues through all further analysis steps leading to inaccurate results. Here are a few of the most common sampling errors:

1. Contamination

Inaccurate test results are often caused by impurities found in the sample taken. Keeping to a single standard sampling protocol in every laboratory ensures specific DIN standards are obeserved and quality standards are complied with. The risk of contamination can be reduced by a fixed sequence of all recorded important work steps.

In addition, it is very important to only work with clean analysis devices. Sampling equipment used for example for soil sampling, must be clean and free of impurites to guarantee accurate test results. Only special agents may be used to clean the equipment as inappropriate cleaning substances may lead to incorrect analysis results. Accurate and representative results may be obtained only when these aspects have been observed.

2. Inappropriate equipment

The use of an inappropriate tool may also negatively affect test results. This does not only refer to an unsuitable equipment for sample taking, but also the quality/condition of the equipment.

If a low quality instrument is used, the material of the instrument may not be sufficiently robust and inert to take representative samples. Apart from high quality stainless steel, equipment made of the material PTFE is very suitable for taking samples.

Poorly processed samplers pose additional problems. Besides being made of an unsuitable material, some equipment may sometimes have indentations or fine cracks in which residues of the sample may settle in and cannot be removed. As a result, all future samples will be contaminated by this residue and will therefore not be representative.

3. Untrained / Inexperienced personnel

Sampling must be performed by an experienced trained personnel. There is an increased risk of error if done by an untrained employee. Even if equipment has been properly cleaned and quality standards carefully observed, an inexperienced employee will not be able to respond to errors or problems during the sampling procedure as well as an experienced employee. Therefore, samples should only be taken by trained specialists with the necessary expertise and familiarity with the procedure in order to rule out any potential errors.

Sampling techniques

In general, there are two ways to take samples - all-layer sampling or targeted sampling. Soil sampling can also be performed.

All-layer sampling:

In this method, a sample that includes all layers of the material is taken to obtain a representative cross-section of the whole. For example, all-layer samples are taken from grain silos. However, if the sample is a heterogeneous material, samples should be taken across the entire depth or width at several points. This is particularly common when taking samples of bulk material as small, dust-like particles may collect on the floor due to transport and a single sample from the top of the sample would give an incorrect result.

Targeted sampling:

This method is used when there is suspected spot contamination of the sample. Sampling at a targeted area can indicate the condition of the material at the specific point, or a representative cross-sectional result can be achieved by taking it at several target points.

Soil sampling:

Soil sampling is carried out particularly when there are indications of pollution in bodies of water and ground water. Through soil sampling, deposits or harmful residues in the soil are extracted, detected and analysed.