ISO 19036:2019 pdf – Microbiology of the food chain — Estimation of measurement uncertainty for quantitative determinations

ISO 19036:2019 pdf – Microbiology of the food chain — Estimation of measurement uncertainty for quantitative determinations.
1 Scope This document specifies requirements and gives guidance for the estimation and expression of measurement uncertainty (MU) associated with quantitative results in microbiology of the food chain. It is applicable to the quantitative analysis of: — products intended for human consumption or the feeding of animals; — environmental samples in the area of food production and food handling; — samples at the stage of primary production. The quantitative analysis is typically carried out by enumeration of microorganisms using a colony- count technique. This document is also generally applicable to other quantitative analyses, including: — most probable number (MPN) techniques; — instrumental methods, such as impediometry, adenosine triphosphate (ATP) and flow cytometry; — molecular methods, such as methods based on quantitative polymerase chain reaction (qPCR). The uncertainty estimated by this document does not include systematic effects (bias). 2 Normative references There are no normative references in this document. 3? Terms,? definitions? and? symbols 3.1? Terms? and? definitions? For the purposes of this document, the following terms and definitions apply. ISO and IEC maintain terminological databases for use in standardization at the following addresses: — ISO Online browsing platform: available at https:// www .iso .org/ obp — IEC Electropedia: available at http:// www .electropedia .org/ 3.1.1 sample <general> one or more items (or a proportion of material) selected in some manner from a population (or from a large quantity of material) intended to provide information representative of the population, and, possibly, to serve as a basis for a decision on the population or on the process which had produced it [SOURCE: ISO/TS 17728:2015, 3.2.2, modified — Note 1 to entry has been deleted.] 3.1.2 laboratory sample sample (3.1.1) prepared for sending to the laboratory and intended for inspection or testing [SOURCE: ISO 6887-1:2017, 3.1]
3.1.3 test sample sample (3.1.1) prepared from the laboratory sample (3.1.2) according to the procedure specified in the method of test and from which test portions (3.1.4) are taken Note 1 to entry: Preparation of the laboratory sample before the test portion is taken is infrequently used in microbiological examinations. [SOURCE: ISO 6887-1:2017, 3.4] 3.1.4 test portion measured (volume or mass) representative sample (3.1.1) taken from the laboratory sample (3.1.2) for use in the preparation of the initial suspension Note 1 to entry: Sometimes preparation of the laboratory sample is required before the test portion is taken, but this is infrequently the case for microbiological examinations. [SOURCE: ISO 6887-1:2017, 3.5] 3.1.5 measurand particular quantity subject to measurement [SOURCE: ISO/IEC Guide 98-3:2008, B.2.9 modified — The example and the Note 1 to entry have been deleted.] 3.1.6 trueness measurement trueness closeness of agreement between the average of an infinite number of replicate measured quantity values and a reference quantity value Note 1 to entry: Trueness is not a quantity and thus cannot be expressed numerically, but measures for closeness of agreement are given in ISO 5725 (all parts). Note 2 to entry: Trueness is inversely related to systematic measurement error, but is not related to random measurement error. Note 3 to entry: “Measurement accuracy” should not be used for “trueness” and vice versa. [SOURCE: ISO/IEC Guide 99:2007, 2.14, modified — The preferred term has been changed from “measurement trueness” to “trueness”.] 3.1.7 bias measurement bias estimate of a systematic measurement error [SOURCE: ISO/IEC Guide 99:2007, 2.18, modified — The preferred term has been changed from “measurement bias” to “bias”.]
3.1.10 standard uncertainty u uncertainty of the result of a measurement expressed as a standard deviation [SOURCE: ISO/IEC Guide 98-3:2008, 2.3.1, modified — The symbol has been added.] 3.1.11 combined standard uncertainty u c (y) standard uncertainty (3.1.10) of the result of a measurement when that result is obtained from the values of a number of other quantities, equal to the positive square root of a sum of terms, the terms being the variances or covariances of these other quantities weighted according to how the measurement result varies with changes in these quantities [SOURCE: ISO/IEC Guide 98-3:2008, 2.3.4, modified — The symbol has been added.] 3.1.12 expanded uncertainty U quantity defining an interval about the result of a measurement that may be expected to encompass a large fraction of the distribution of values that could reasonably be attributed to the measurand (3.1.5) Note 1 to entry: The fraction may be regarded as the coverage probability or level of confidence of the interval. Note 2 to entry: To associate a specific level of confidence with the interval defined by the expanded uncertainty requires explicit or implicit assumptions regarding the probability distribution characterized by the measurement result and its combined standard uncertainty (3.1.11). The level of confidence that may be attributed to this interval can be known only to the extent to which such assumptions may be justified. Note 3 to entry: An expanded uncertainty U is calculated from a combined standard uncertainty u c (y) and a coverage factor k (3.1.13) using: U = k × u c (y) [SOURCE: ISO/IEC Guide 98-3:2008, 2.3.5, modified— The symbol has been added and Note 3 to entry has been replaced.]