What are the sampling methods

Kessler ProData

The basis for any modeling is to obtain reliable and, above all, representative samples, which can then be characterized with different measuring systems. With homogeneous substrates this is relatively easy, with heterogeneous systems it is the decisive factor for a reliable method development. Because the individual sample must agree with the total property. In chemical analysis, sampling encompasses the entire process from taking the sample to analysis with any conditioning and sample preparation carried out, such as crushing, mixing and dividing.

As many studies show, the total variance of the error of an analysis (sampling + sample preparation + analysis) depends to over 80% on the sampling. It is therefore nonsensical to develop the analytical procedure to the highest accuracy in the case of high sampling errors. Material flows of solids always show spatial and temporal inhomogeneities. Therefore, the number and mass of the individual samples are decisive in determining how representative the sample is.

Since optical spectroscopy is non-invasive, fast and extremely reproducible, it can also characterize very inhomogeneous substrates quickly and representatively and even with spatially resolved measurements (spectral imaging) quantify and, if necessary, sort the inhomogeneity.

The "golden rules" of sampling turn out to be:

  • Sampling whenever the sample is moving. This minimizes aggregation or sedimentation.
  • It is better to examine the entire sample stream in a short period of time than just a partial stream over a longer period of time. This avoids systematic errors

In recent years, modern spectroscopic online and inline analysis techniques are increasingly replacing traditional offline methods. As a rule, the offline analysis technique is referred to as the primary method and considered “true” and the spectroscopic technique is referred to as the secondary method. As a result, as a first approximation, spectroscopy cannot provide more precise results than the primary method. With the development of new analytical methods based on the spectroscopic information, however, because of the better reproducibility, significantly more precise and reproducible values ​​can be achieved than with the wet chemical methods.