TOS forum, Issue 2, p. 22 (2014)

Visualisation of sampling error effects in near infrared analysis—comparison between Petri dish, roll bottle and spiral sampler

Marie Sørensen,a Anders Larsena and Kim H. Esbensenb,c,d
aQ-Interline A/S, Tølløse, Denmark
bGeological Survey of Denmark and Greenland (GEUS), Copenhagen, Denmark
cACABS Research Group, Aalborg University (AAUE), Denmark
dTelemark University College (HIT), Porsgrunn, Norway

With spectroscopic methods, e.g. near infrared (NIR) analysis, using a constant beam aperture, the effective scanning footprint will be different for a spinning Petri dish, a rolling bottle and a new spiral sampler configuration. This will significantly influence the analytical accuracy and precision of a NIR analytical determination of heterogeneous materials, for example barley with differing protein contents. Here we present the results from a bench-top experiment that evaluates the total analytical bias and precision characteristics for three alternative sample presentation approaches using a mixture of two plastic polymer pellets as a test material with significant heterogeneity. After removal of all incorrect sampling errors (ICS), there are still significantly varying correct sampling error [Fundamental Sampling Error (FSE) and Grouping and Segregation Error (GSE)] uncertainties associated with these standard analytical approaches—but there is a clear winner.

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