The analytical challenges associated with quality assurance range from establishing the identity of the botanical source from which an extract was derived to measuring the amount of one or more constituents. While numerous publications describe procedures for determining constituents of interest, few methods have been evaluated for accuracy, precision or reliability, and often the analysis of finished products is not within the scope of the published method. The bottom line is that within the context of the cGMP the quality of products is frequently reliant on test methods and the way you ensure a method is working (i.e., fit for purpose) is to engage in a series of experiments called a validation.
The International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) defines fitness for purpose as the "degree to which data produced by a measurement process enables a user to make technically and administratively correct decisions for a stated purpose." This relates to scope and applicability; in order for a method to be of use, it needs to be tailored to specific analytes, matrices and expected concentration ranges. How often the method will be used and the intended application must also be determined (i.e., qualitative, quantitative or both); is it for stability testing, research and development, process uniformity determination, or detection of adulterants and pesticides? There are two different types of methods-specification based and performance based. Specification based methods are prescriptive, (e.g., defining column size, column packing particle size, porosity, flow rate, etc.), while performance based methods describe the minimum acceptable performance that must be achieved for the data to be deemed acceptable.
Method development and validation can be challenging when dealing with poorly defined analytes, such as antioxidants, flavonoids and phenolics, as well as the complex matrices of raw materials, extracts, tablets, capsules, soft gels and drink mixes. Defining analytes and matrices in the fitness for purpose statement is important for developing a successful method. Analytical methods are not universal; characteristics, techniques, scope and applicability can differ substantially. Thus, it is impossible to have a single set of instructions that can be used to validate all methods. However, analytical methods do share some basic commonalities.
Analytical Method Validation
What? Method validation is the process used to confirm that the analytical procedure employed for a specific use is suitable for that intended use. This includes the initial assessment of performance characteristics, several types of inter-laboratory testing and quality control.
Why? Validation is concerned with assuring that a measurement process produces valid measurements; results from method validation can be used to judge the quality, reliability and consistency of analytical results. It is an integral part of any good analytical practice. A measurement process producing valid measurements for an intended application is fit for purpose.
When? Analytical methods need to be validated or revalidated before their introduction into routine use; when conditions (such as matrix) change from those under which the method was validated; and when the method is changed and that change is outside the original scope of the method.
How? Certain performance characteristics must be specified and met in order for a method's results to have meaning. FDA provides a table-"Text on Validation of Analytical Procedures"-which is meant to assist in determining what has to be done to prove a method is suitable for its intended purpose.
There are generally accepted methodologies to evaluate and establish these performance characteristics (refer to guidance documents discussed later in this column for details). Only through systematic method validation can a scientist confidently show their analytical method is fit for purpose and thereby present the resultant data as meaningful.
Different levels of method validation include single laboratory validation (SLV), peer verification and full collaborative study. The SLV applies to a specific laboratory, technician and equipment. Peer verified validation applies to several labs (2 to 7) and is intended to provide information on how a method is interpreted outside of the original lab. Full collaborative study applies when eight or more labs provide acceptable data using the method. The different levels of validation range in their degree of ruggedness; the most rigorous form of method validation is achieved through a full collaborative study.
Collaborative studies are not always practical or possible for laboratories to manage as they require specific time commitments from personnel and equipment in multiple laboratories. It is important that laboratories employ a level of validation that is suitable for the method's intended use; it should ensure that the methodology is accurate, precise and rugged for the specified analyte and concentration range.
Method Validation Resources
There are different organizations involved with method validation; their purpose and contributions are all slightly different. The following descriptions are intended to introduce a few of these organizations involved and identify their main objectives.
International Union of Pure and Applied Chemistry (IUPAC), representing organizations of chemists from different countries, publishes chemical data and establishes standard methods for analytical, clinical, quality control and research laboratories.
United States Pharmacopeia/National Formulary (USP/NF) sets the official standards for all prescription and over-the-counter medicines manufactured and sold in the U.S. (http://www.usp.org/USPNF/).
ICH is a joint initiative between regulators and industry representatives of the European Union, Japan and the U.S., which resulted in a collaboration of validation procedures required to assess the safety, quality and efficacy of pharmaceuticals. ICH developed the guidelines: "Validation of Analytical Methods: Definitions and Terminology" (http://www.ich.org/cache/ compo/276-254-1.html).
Eurachem is a network of European organizations that aims to promote good quality practices and develop an international system for traceability of chemical measurements (http://www.eurachem.org/). The Eurachem Guide presents method validation by discussing what it entails, why it is necessary, and how it can be achieved.
FDA's "Guidance for Industry: Analytical Procedures and Methods Validation" provides recommendations on submitting analytical procedures, validation data and samples to support the documentation of the identity, strength, quality, purity and potency of drug substances and drug products (http://www. fda.gov/downloads/Drugs/GuidanceComplianceRegulatoryInformation/Guidances/ucm122858.pdf). A more specific guidance document that focuses on not just the "what" but also the "how" for conducting method validation on chromatographic methods can be found at: http://www.fda.gov/downloads/ Drugs/GuidanceComplianceRegulatoryInformation/Guidances/UCM134409.pdf.
AOAC is a non-profit organization that aims to provide analytical methods and quality measuring systems for government, industry and academic laboratories. AOAC's validation guidelines are well recognized and the most rigorous. While the website is difficult to navigate, there is valuable information to be found. For more information, visit: http://www.aoac.org/dietsupp6/Dietary-Supplement-web-site/DSHomePage2.html and then select the side menu item "Training Materials"; there you can find the SLV guidelines (http://www.aoac.org/dietsupp6/Dietary-Supplement-web-site/slv_guidelines.pdf) and accompanying acceptance criteria (http://www.aoac.org/dietsupp6/Dietary-Supplement-web-site/SLV_criteria.pdf.), as well as an example validation protocol and study report.
The Office of Dietary Supplements (ODS) at the National Institutes of Health (NIH) also offers support in the area of method validation. Information on its Dietary Supplements Analytical Methods/Reference Materials (AMRM) Program can be accessed at http://dietary-supplements.info.nih.gov/factsheets/AMRMProgramWebsite.asp.
Validation is an ongoing process for regulatory agencies and commercial laboratories presented with new products. The validation of analytical methods is a worthwhile investment that will yield positive outcomes, including compliance with the GMPs, credibility from industry, academia and government, and ultimately increased consumer confidence in dietary supplement quality.