Method validation materials

CRMs to finalise the method development, to validate analytical procedures and finally control in time the accuracy of procedures, are rare and valuable materials, in particular matrix CRMs. They should tell the analyst how his entire measurement procedure is performing. He will receive information on precision as well as on trueness. CRMs are primarily developed to check for trueness, which is the most difficult property to verify. Precision can be tested on RMs or can be estimated from published data e.g. the performance required by a standard method, whereas the evaluation of trueness is possible only with external help a CRM or a properly organised interlaboratory study. Having a CRM allows one to perform the verification of trueness whenever the operator wants it. The analyst should never forget that only when accurate results (precise and true) are achieved, comparability in space and over time is guaranteed. But to exploit to a maximum the information on trueness delivered by the CRM, the precision must also be sufficient and verified. 

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Control All control points starting with the basic raw materials right through to the finished product must be identified. Descriptions of the specifications, test methods, reference standards, and methods validation data should be included. 

Chandra, A., Rana, J., and Li, Y., Separation, identification, quantification, and method validation of anthocyanins in botanical supplement raw materials by HPLC and HPLC-MS, J. Agric. Food Chem., 49, 3515, 2001. 

As laboratory accreditation becomes more established, the requirements to demonstrate traceability and to determine uncertainty will inevitably feature as part of method validation (Christensen 1996). The fundamental role which reference materials play in these steps has already been alluded to in the Introduction. 

Christensen JM (1996) Correcting measurement errors using reference materials in method validation. Mikrochim Acta 123 231-240. 

Identification of sources of analytical bias in method development and method validation is another very important application of reference materials in geochemical laboratories. USGS applied simplex optimization in establishing the best measurement conditions when the ICP-AES method was introduced as a substitute for AAS in the rapid rock procedure for major oxide determinations (Leary et al. 1982). The optimized measurement parameters were then validated by analyzing a number of USGS rock reference samples for which reference values had been established first by classical analyses. Similar optimization of an ICP-AES procedure for a number of trace elements was validated by the analysis of U S G S manganese nodule P-i (Montaser et al. 1984). 

Established in 1894, AOAC International is an independent association of scientists and organizations in the public and private sectors devoted to promoting methods validation and quality measurements in the analytical sciences. AOAC has a mission to ensure the development, testing, validation, and publication of reliable chemical and biological methods of analysis for foods, drugs, feed-stuffs, fertilizers, pesticides, water, forensic materials and other substances affecting public health and safety and the environment. 

Interest in promoting the use of reference materials in method validation studies led in March 1993 to the formation of a Technical Division on Reference Materials, TDRM (Heavner 1995). The stated purpose of the TDRM is to improve the quality of... 

Different sample materials often need some adjustment of pesticide residue methods. The insufficient consideration of matrices in thcNKML method validation protocol may be a tribute to the wide scope of this standard. 

You may have noticed that sampling does not appear in Table 4.6. Although sampling is an important issue in chemical analysis, it is not part of method validation. It is assumed that there is sufficient sample available and that the method is validated using materials that have the same or very similar physical and chemical form. Sampling is discussed in detail in Chapter 3. 

Associated with method validation, but not part of it, are two properties of results that have been previously mentioned. These parameters are measurement uncertainty and metrological traceability. Measurement uncertainty is covered in Chapter 6 and metrological traceability in Chapter 5. If considered at the planning stage of method validation, the information obtained during validation is a valuable input into measurement uncertainty evaluation. Traceability depends on the method s operating procedures and the materials being used. 

Note (4) is very important as it highlights the fact that the reference material used for the method validation cannot be used again when the method is in routine use for calibration purposes. The same type of material can be used, but it needs to come from a different supplier. The same material cannot be used for calibration purposes and then as a quality control material. 

The guidelines stress, however, that internal quality control is not foolproof even when properly executed. Obviously it is subject to errors of both kinds , i.e. runs that are in control will occasionally be rejected and runs that are out of control occasionally accepted. Of more importance, IQC cannot usually identify sporadic gross errors or short-term disturbances in the analytical system that affect the results for individual test materials. Moreover, inferences based on IQC results are applicable only to test materials that fall within the scope of the analytical method validation. Despite these limitations, which professional experience and diligence can alleviate to a degree, internal quality control is the principal recourse available for ensuring that only data of appropriate quality are released from a laboratory. When properly executed it is very successful. 

Equipment Maintenance/Calibration/Monitoring Method Validation Standard/Reference Material Storage of Labile Components Laboratory SOPs Testing Quality Identity... 

There are different reasons for interlaboratory tests. One is method validation, e.g. prior to the standardization of characterization of reference materials, which have to be certified. The third and most important for quahty assurance is proficiency testing of laboratories. There are different requirements for each type of interlaboratory test. 

Sampling is just the beginning of the analytical process. On the way from sampling to the test report a lot of different requirements for high quality measurements have to be considered. There are external quality assurance requirements on the quality management system (e.g. accreditation, certification, GLP), internal quality assurance tools (e.g. method validation, the use of certified reference material, control charts) and external quality assurance measures (e.g. interlaboratoiy tests). 

The roles of method validation in the achievement of reliable results are (1) to include all possible effects or factors of influence on the final result, (2) to make them traceable to stated references [reference methods, reference materials, or International System of Units (SI)], and (3) to know the uncertainties associated with each of these effects and with the references. Validation is thus a tool to establish traceability to these references [2,4]. In this context, it is important to see the difference between traceability and accuracy. A method which is accurate, in terms of true (i.e., approximating the true value), is always traceable to what is considered to be the true value. The opposite however is not correct. A method that is traceable to a stated reference is not necessarely true (accurate). Errors can still occur in this method, depending on the reference [12]. 

Analytical method validation forms the first level of QA in the laboratory. Analytical quality assurance (AQA) is the complete set of measures a laboratory must undertake to ensure that it is able to achieve high-quality data continuously. Besides the use of validation and/or standardized methods, these measures are effective IQC procedures (use of reference materials, control charts, etc.), with participation in proficiency testing schemes and accreditation to an international standard, normally ISO/IEC 17025 [4]. Method validation and the different aspects of QA form the subject of Section 8.2.3. 

The ISO definition of validation is confirmation by examination and provision of objective evidence that the particular requirements of a specified intended use are fulfilled [15]. Method validation is needed to confirm the fitness for purpose of a particular analytical method, that is, to demonstrate that a defined method protocol, applicable to a specified type of test material and to a defined concentration rate of the analyte —the whole is called the analytical system — is fit for a particular analytical purpose [4]. This analytical purpose reflects the achievement of analytical results with an acceptable standard of accuracy. An analytical result must always be accompanied by an uncertainty statement, which determines the interpretation of the result (Figure 6). In other words, the interpretation and use of any measurement fully depend on the uncertainty (at a stated level of confidence) associated with it [8]. Validation is thus the tool used to demonstrate that a specific analytical method actually measures what it is intended to measure and thus is suitable for its intended purpose [11,55,56]. 

Before any method validation is started, the scope of validation must be fixed, comprising both the analytical system and the analytical requirement. A description of the analytical system includes the purpose and type of method, the type and concentration range of analyte(s) being measured, the types of material or matrices for which the method is applied, and a method protocol. On the basis of a good analysis lies a clear specification of the analytical requirement. The latter reflects the minimum fitness-for-purpose criteria or the different performance criteria the method must meet in order to solve the particular problem. For example, a minimum precision (RSD, see below) of 5% may be required or a limit of detection (LOD) of 0.1% (w/w) [2,4,15,58]. The established criteria for performance characteristics form the basis of the final acceptability of analytical data and of the validated method [58]. 

Lauwaars, M., and Anklam, E. (2004), Method validation and reference materials, Accred. Qual. Assur., 9, 253-258. 

Analytical methods validation is one of the most regulated validation processes in the pharmaceutical industry. Analytical validations are required to demonstrate that the methods employed are the most indicated for each product and that the results obtained are reliably correct. All methods employed in raw and finished product materials analysis are required to be validated. 

The test material is chosen to fulfill the aims of the study. In a proficiency testing scheme or a method validation study, the test material is usually as near as possible to typical field samples. There is no advantage in competently analyzing an artificial sample if the same laboratory has difficulty with real samples. The organizing laboratory must know the composition of the test material, and must be sure that the analyte for which a quantity is to be measured is present in about the desired amount. For pure materials this is not a problem, but for natural test materials or complex matrix materials, the organizing laboratory may have to do some analyses before the samples can be sent out to the participants. If the value of the measurand is to be established by an independent laboratory before the study, then the identity requirement is also fulfilled when the measurand is stated. 

This chapter has two aims to demonstrate the necessity of using properly validated and verified methods and to explain what constitutes a validated method, and to provide an introduction to method validation for in-house methods. There is an abundance of published material that defines, describes, and generally assists with method validation, some of which is... 

Interlaboratory Quality Control. In addition to the mandatory quality control practices just outlined, the laboratory is encouraged to participate in interlaboratory programs such as relevant performance evaluation (PE) studies, analysis of standard reference materials, and split sample analyses. Participation in interlaboratory analytical method validation studies is also encouraged. 

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