Representative mass reduction in sampling—a critical survey of techniques and hardware

Abstract

We here present a comprehensive survey of current mass reduction principles and hardware available in the current market. We conduct a rigorous comparison study of the performance of 17 field and/or laboratory instruments or methods which are quantitatively characterized (and ranked) for accuracy (bias), reproducibility (precision), material loss (external as well as internal loss), user-dependency, operation time, and ease of cleaning. Graphical comparison of these quantitative results allow a complete overview of the relative strengths and weaknesses of riffle splitters, various rotational dividers, the Boerner Divider, the “spoon method”, alternate/fractional shoveling and grab sampling. Only devices based on riffle splitting principles (static or rotational) passes the ultimate representativity test (with minor, but significant relative differences). Grab sampling, the overwhelmingly most often used mass reduction method, performs appallingly—its use must be discontinued (with the singular exception for completely homogenized fine powders). Only proper mass reduction (i.e. carried out in complete compliance with all appropriate design principles, maintenance and cleaning rules) can always be representative in the full Theory of Sampling (TOS) sense. This survey also allows empirical verification of the merits of the famous “Gy's formula” for order-of-magnitude estimation of the Fundamental Sampling Error (FSE).