ASTM D 6512 : 2007 : R2014

1.1This practice establishes a uniform standard for computing the interlaboratory quantitation estimate associated with Z % relative standard deviation (referred to herein as IQE_Z %), and provides guidance concerning the appropriate use and application. The calculations involved in this practice can be performed with DQCALC, Microsoft Excel-based software available from ASTM.²

1.2IQE_Z % is computed to be the lowest concentration for which a single measurement from a laboratory selected from the population of qualified laboratories represented in an interlaboratory study will have an estimated Z % relative standard deviation (Z % RSD, based on interlaboratory standard deviation), where Z is typically an integer multiple of 10, such as 10, 20, or 30, but Z can be less than 10. The IQE_10 % is consistent with the quantitation approaches of Currie (1)³ and Oppenheimer, et al. (2).

1.3The fundamental assumption of the collaborative study is that the media tested, the concentrations tested, and the protocol followed in the study provide a representative and fair evaluation of the scope and applicability of the test method as written. Properly applied, the IQE procedure ensures that the IQE has the following properties:

1.4The IQE applies to measurement methods for which calibration error is minor relative to other sources, such as when the dominant source of variation is one of the following:

1.5Data Quality Objectives—Typically, one would compute the lowest % RSD possible for any given dataset for a particular method. Thus, if possible, IQE_10 % would be computed. If the data indicated that the method was too noisy, one might have to compute instead IQE_20 %, or possibly IQE_30 %. In any case, an IQE with a higher % RSD level (such as IQE_50 %) would not be considered, though an IQE with RSD <10 % (such as IQE_1 % ) would be acceptable. The appropriate level of % RSD may depend on the intended use of the IQE.