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31 concepts related to method validation: Method Validation – The laboratory uses experiments to provide objective and valid evidence that a specific testing method meets the intended purposes. Note: Method validation should establish the performance characteristics and limitations of the method, identify the factors affecting method performance and their degree of influence, determine the matrices for which the method is suitable, as well as the accuracy and precision of the method. (ISO/IEC Guide 99:2007, 2.45) 2 Method Verification: The laboratory provides objective and valid evidence through verification to demonstrate that the requirements specified for the method are met. (ISO/IEC Guide 99:2007, 2.44)3 In-house Method Validation: Analytical experiments conducted within a laboratory, at reasonable intervals of time, using a particular method under specified conditions on the same or different test samples, in order to demonstrate that a specific testing method meets the intended purpose. 4 Interlaboratory Method Validation: Method validation carried out among two or more laboratories. The laboratory conducts measurements on the same samples using the same method under predetermined conditions, in order to demonstrate that a specific testing method meets its intended purpose. 5 Qualitative Methods: Analytical methods that identify substances based on their chemical, biological, or physical properties. 6 Quantitative Method: An analytical method for determining the mass or mass fraction of the analyte, which can be expressed as a numerical value in appropriate units. A confirmatory method is a technique that can provide all or some of the information and clarify the identity, and can be used for quantification at the concentration levels of interest when necessary. 8 Screening Method: A method with the capability to process large numbers of samples, used to determine whether a substance or a group of substances is present at the concentration levels of interest. These methods are used to screen a large number of samples for possible positive results and to avoid false negative results. The test results obtained using such methods are usually qualitative or semi-quantitative. 9 Permitted Limit, PL: The maximum value established and specified for a certain quantitative property, such as the maximum residue limit, the highest allowable concentration, or other maximum permissible amounts. 10 Level of Interest: The concentration level that is decisive for determining whether a substance or analyte in a sample meets regulatory provisions and requirements (such as allowable limit concentrations). 11 Selectivity: The property of a measurement system, when used according to the specified procedures, whereby the value measured for each quantity being assessed is independent of other quantities being measured or of other phenomena, objects, or substances under study. (ISO/IEC Guide 99:2007, 4.13)12 Matrix Effect: In chemical analysis, the matrix refers to the components in a sample other than the analyte. The matrix often causes significant interference in the analysis of analytes and affects the accuracy of the analytical results. For example, the ionic strength of a solution can affect the activity coefficient of analytes, and these effects and interferences are known as matrix effects. 13 Linearity of Calibration: For analytical methods, it refers to the range within which a linear mathematical model is used to define the relationship between instrument response and concentration. 14 Limit of Detection, LOD: It is the value obtained through a given measurement procedure, such that the probability of misjudging the absence of a certain component in the substance is b, and the probability of misjudging the presence of such a component is a. Note 1: The International Union of Pure and Applied Chemistry (IUPAC) recommends default values of 0.05 for a and b. Note 2: The detection limits are often divided into two types: the method detection limit and the instrument detection limit (ISO/IEC Guide 99:2007, 4.18). The method detection limit (MDL) is the lowest concentration or amount of an analyte at which it can be reliably identified or distinguished from the background of a specific matrix using a particular method. 16 Instrumental Detection Limit (IDL): The lowest concentration or amount of an analyte at which the instrument can reliably identify or distinguish the analyte signal from the instrumental background (noise). 17 Limit of Quantification, LOQ: The lowest concentration or amount of the component of interest in a sample that can be quantitatively determined; at this level, the analytical results should still maintain a certain degree of accuracy and precision. 18 Precision: Under specified conditions, it refers to the degree of consistency among the values obtained from repeated measurements of the same or similar objects being measured. (ISO/IEC Guide 99:2007, 2.15) 19 Sensitivity: The quotient obtained by dividing the change in the indication value of a measuring system by the corresponding change in the value of the quantity being measured. Note 1: The sensitivity of the measurement system may depend on the value being measured. Note 2: The variation in the measured quantity under consideration should be greater than the resolution of the measurement system. (ISO/IEC Guide 99:2007, 4.12). 20 Measuring interval: Under specified conditions, it refers to a set of values of the same type that can be measured by a measuring instrument or system equipped with certain instruments, taking into account the measurement uncertainties associated with those instruments. Note 1: In some fields, this term is also referred to as “measurement range”. Note 2: The lower limit of the measurement range should not be confused with the “detection limit”. (ISO/IEC Guide 99:2007, 4.7) 21 Repeatability Condition of Measurement: A set of measurement conditions under which repeated measurements are taken on the same or similar test objects within a short period of time, using the same measurement procedure, the same operator, the same measurement system, the same operating conditions, and at the same location. (ISO/IEC Guide 99:2007, 2.20) 22 Repeatability: The precision of measurements under a set of repeated measurement conditions. (ISO/IEC Guide 99:2007, 2.21) 23 Reproducibility Condition of Measurement: A set of measurement conditions under which repeated measurements are taken on the same or similar test objects at different locations, by different operators, and using different measurement systems. (ISO/IEC Guide 99:2007, 2.24) 24 Reproducibility: The precision of measurements under reproducible measurement conditions. (ISO/IEC Guide 99:2007, 2.25) The number of degrees of freedom for 25 degrees of freedom is equal to the number of terms in the sum minus the number of constraints among those terms. (GB/T 3358.1-2009, IDT ISO 3534-1:2006, 2.54) 26 Accuracy/Trueness: The degree of agreement between the average of the measured values obtained from an infinite number of repeated measurements and a reference value. (ISO/IEC Guide 99:2007, 2.14) 27 Bias is an estimate of the systematic measurement error. (ISO/IEC Guide 99:2007, 2.18) Standard Addition in the 28 standard involves dividing the test sample into two or more portions when conducting the test using the same method. Some are subjected to routine analysis, while known amounts of standard analytes are added to the others before analysis. The amount of the standard analyte added should be 2 to 5 times the estimated content of the analyte in the sample; it can also be an amount of the standard analyte determined based on the method’s quantitative limit, tolerance limit, etc. Standard addition can be used to determine how the recovery rate of a method may be affected by factors such as the concentration of the analyte in the sample and the matrix, and it can also be used to assess the accuracy at levels such as the limit of quantitation and the tolerance limit. 29 Recovery: The analyte with a known concentration is added to the sample, and testing is carried out using the predetermined analytical method. The actual concentration measured is subtracted from the concentration of the sample before the analyte was added, and then divided by the percentage of the concentration that was added. Note 1: In the absence of certified reference materials, the recovery rate can be used in the method validation process. Note 2: The addition concentration in the definition is the calculated concentration of the additive in the sample. 30 Accuracy: The degree of consistency between the measured value of a quantity and its true value. Note 1: The concept of “measurement accuracy” is not a quantity, nor does it provide a numerical value for a quantity. When the measurement yields a smaller error, it is more accurate. Note 2: The term “measurement accuracy” should not be used to denote “measurement correctness,” and “measurement precision” should not be used to denote “measurement accuracy,” although measurement accuracy is related to these two concepts. Note 3: Measurement accuracy is sometimes understood as the degree of consistency among the measured values assigned to the quantity being measured. (ISO/IEC Guide 99:2007, 2.13) 31 Robustness: The degree to which changes in experimental conditions affect the analytical method. These conditions are specified in the method or slightly modified according to the specifications, including the type of sample, matrix, storage conditions, environment, or sample preparation conditions. Any changes in the experimental conditions that could affect the analysis results in practice (such as reagent stability, sample composition, pH, temperature, etc.) should be indicated