Laboratory Control of Analytical Method Inaccuracy with Respect to a Given Inaccuracy Standard

Abstract

A typical laboratory control chart provides a means for detecting any intolerable change in the precision or bias of an analytical method away from its historical performance level. But in many laboratories, it would be more desirable to control accuracy, rather than either precision or bias. Thus, a procedure is given here for preparing an accuracy (or more correctly, inaccuracy) control chart for an analytical method. The procedure assumes that the user knows the minimum accuracy that the method is required to exhibit. In this case, knowledge of the prior performance characteristics of the analytical method is not required for establishing the control Limits, as is commonly true for other control-charting schemes. This control-charting procedure involves the daily analysis of spiked control samples. The estimation of total method inaccuracy from the control sample data, the computation of control limits, and the plotting of the control parameter (i.e., inaccuracy) on the control chart. Although the cont...