Purpose of Sampling and the Chemometric Methods Applicable

A brief overview shall be given of the purpose of sampling on the one hand and the chemometric methods applicable on the other hand. In the field of environmental investigation, samples are taken mostly for purposes of  

To answer these questions, the following purposes of sampling have to be regarded [KATEMAN, 1987 1988]. 

The description of an object in the sense of environmental investigation may be the determination of the gross composition of an environmental compartment, for example the mean state of a polluted area or particular location. If this is the purpose, the number of individual samples required and the required mass or size of these increments have to be determined. The relationship between the variance of sampling and that of analysis must be known and both have to be optimized. The origin of the variance of the samples can be investigated by the study of variance contribution of the different steps of the analytical process by means of the law of error propagation (Eq. 4-21) according to Section 4.3.4. 

If the purpose of sampling is the detailed description of the composition of an object, the character of the internal correlation has to be investigated. The methods of autocorrelation and/or semivariogram analysis, as described in Sections 6.6 and 4.4.2, may be useful for clarification of the internal spatial and/or temporal relationships existing within the parent population to be sampled. Geostatistical methods, e.g. kriging, enable undistorted estimation of the composition of unsampled locations in the area of investigation. 

Principles of sampling for threshold control are described by KATEMAN and PIJPERS [1981]. The authors show that the sampling frequency depends on the distance between the last value measured and the threshold level. They explain both the adaptation of the sampling frequency to the existing state of the process or the environmental compartment under control, and the effect of the distance between samples on the cost of the project. 

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