ABSTRACT
When a food scientist needs to measure a quantity, such as sample mass or volume, he or she performs a direct measurement, having a good idea of the accuracy and precision involved. But when the concentration of a substance in a sample matrix must be found, the analyst has to make an indirect measurement by calculating the quantity from the measurement of other quantities [1]. Indirect measurements are obtained by correlating a result with sample concentration, which introduces the possibility of decreased accuracy and precision. An equation relating analyte concentration and the instrumental response is formed by using standards and calibrations, and then applied to predict the concentration of the unknown [2]. The procedure must demonstrate traceability, defined as an unbroken chain of comparisons from the measurement to the appropriate national or international standards [3]. This chapter outlines the various techniques available for relating the output of an instrument with the quantity being sought and the necessary criteria involved.
