Environmental Engineering Reference
In-Depth Information
3.3 Influence of different steps in the analysis of a feedstock sample on
the total error (source: Schwedt G (2007) Taschenatlas der Analytik.
Wiley-VCH, Weinheim, Germany; Figure A on p. 19; copyright Wiley-
VCH Verlag GmbH & Co. KGaA; reproduced with permission).
VDI 4630, in order to obtain the best results, the rationale for and the
methodology of sampling needs to be clarified in advance, to include
.
the aim of investigation
.
origin of material
.
expected sample characteristics
.
variation of sample characteristics with time and location of sample
taking
.
parameters to be analysed
.
need for security and protection measures for sample taker.
Sampling procedure
A representative sampling procedure is essential for obtaining accurate data
because many substrates are of inhomogeneous consistency. Therefore, to
receive accurate data, a representative sampling procedure is a prerequisite.
Details on sampling of biogas feedstocks in general can be found in
VDI 4630 and details for sampling of sludges and wastewater are described
in ISO 5667-13. Petersen (2005) gives a practical guide on sampling.
Figure 3.3 shows the influence of the different steps of an analysis on the
accuracy of a result. It can be seen that the biggest error occurs during
sample taking. The second biggest influence on error is sample treatment
and preparation. The analysis itself normally causes the smallest error.
For homogeneous material, one sample is generally sufficient for a
representative analysis. If the material shows very inhomogeneous phases, at
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