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Pharmaceutical Technology REGULATORY SOURCEBOOK SEPTEMBER 2021 27 ASTM's nomenclature for sampling and testing Unlike the IUPAC 1990 guidelines, the ASTM Standard Guide for Defining the Test Result of a Test Method (6) is fo- cused on the testing part of the process, and while some pro- cess elements are common, the nomenclature is not. Sadly, it would appear that the originators of this American standard were either unaware of it or chose to ignore it. The resultant mismatch of most terms for Stage 2 and 3 is regrettable. For example, in the IUPAC 1990 guide, Stage 5 is called a Laboratory Sample while in ASTM it is simply called Sample. Similarly, in IUPAC, Stage 6 is called Test Sample, whereas in ASTM the same stage is called Test Unit. Stage 13, which was called Determination in IUPAC 1990, is called Test Method in the ASTM standard and is defined as a definitive procedure that produces a test result. The overall flow is shown as the central column of Figure 2. Furthermore, the ASTM test method is defined as having three distinct parts within Phases 2 and 3: 1. the direct measurement or observation of properties, or the occurrence of an event (the observed value) 2. the arithmetical combination of observed values to obtain a single determination 3. the arithmetical combination of a number of deter- minations to obtain the test result of a test method. Table I. Definitions for process flow shown in Figure 2, Phase 0 Statistical Sampling Plan. Adapted from International Union of Pure and Applied Chemistry's Nomenclature for Sampling in Analytical Chemistry (4). Term Definition 0_Statistical sampling plan A predetermined procedure for the selection, withdrawal, preservation, and preparation of the portions to be removed from a population as samples. It is intended to minimize the difference between the properties as estimated from a sample and the actual properties of the lot, and to limit or control the uncertainty generated by the sampling operation, all within practical constraints. 0-1_Characteristic A property or attribute of a material that is to be measured, compared, or noted. 0-2_Sample A portion of material selected from a larger quantity of material 0-3_Static sampling condition The composition of the parent material can be considered as permanent with respect to position in space and stable in time such that the only variable is the sampling position within the space occupied by the lot or batch. 0-4_Dynamic sampling condition If the parent material is almost always changing with respect to time (dynamic) and the removal of a portion of the parent material at any instant reflects only a state at that time and at a particular site 0-5_Specimen A specifically selected portion of a material taken from a dynamic system and assumed to be representative of the parent material at the time it is taken 0-6_Sampling error That part of the total error (the estimate from a sample minus the population value) associated with using only a fraction of the population and extrapolating to the whole, as distinct from analytical or test error. It arises from a lack of homogeneity in the parent population. Sampling error is determined by replication of the laboratory samples and their multiple determinations. Since sampling error is always associated with analytical error, it must be isolated by the statistical procedure of analysis of variance. 0-7_Homogeneity (Heterogeneity) The degree to which a property or a constituent is uniformly distributed throughout a quantity of material. The degree of heterogeneity (the opposite of homogeneity) is the determining factor of sampling error. 0-8_Sampling Uncertainty If replicate test portions have been prepared from the laboratory sample, the sampling uncertainty at this stage can be estimated although method performance variability will always be a confounding factor 0-9_Unit/item/portion/ individual Each of the discrete, identifiable portions of material suitable for removal from a population as a sample or as a portion of a sample, and which can be individually considered, examined, or tested, or combined 0-10_Random sample The sample so selected that any portion of the population has an equal (or known) chance of being chosen 0-11_Representative sample A sample resulting from a sampling plan that can be expected to adequately reflect the properties of interest of the parent population 0-12_Selective sample A sample that is deliberately chosen by using a sampling plan that screens out materials with certain characteristics and/or selects only material with other relevant characteristics 0-13_Stratified sample A sample consisting of portions obtained from identified subparts (strata) of the parent population. Within each stratum, the samples are taken randomly. 0-14_Subsample A portion of the sample obtained from the aggregated sample or an individual unit (increment) of the batch or lot taken as part of the gross sample 0-15_Umpire sample/Referee sample/Reserve sample A sample taken, prepared, and stored in an agreed upon manner for the purpose of settling a dispute 0-16_Replicate sample Two or more samples taken under comparable conditions accomplished by taking units adjacent in time or space