A proposed sampling constant for use in geochemical analysis.

The error in a determination of an element in a rock or mineral sample depends on the analytical error, the weight of sample analysed, and the nature and history of the laboratory sample. The most probable result is not independent of the weight of sample analysed. This is due to the fact that trace constituents often reside in isolated mineral grains. The chance of such mineral grains appearing in any one analysed sample becomes more remote as the sample weight decreases, even when rock or mineral samples are reduced to fine powders. Such subsampling errors can be controlled through the use of sampling constants. These may be estimated by several procedures, including repetitive determination of a constituent and physical measurement of relevant sample characteristics. Sampling constants can be usefully employed during the establishment and certification of reference samples or standards. When subsampling is deficient, analytical results may yield erroneously low values, sometimes with high precision. High precision never implies high accuracy; it may be a symptom of gross error.