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Questions and Answers
What is the primary purpose of method evaluation?
What is the primary purpose of method evaluation?
Which performance characteristic refers to the consistency of results under the same conditions?
Which performance characteristic refers to the consistency of results under the same conditions?
When is it recommended to validate or verify an analytical method?
When is it recommended to validate or verify an analytical method?
What does the concept of accuracy in an analytical procedure primarily relate to?
What does the concept of accuracy in an analytical procedure primarily relate to?
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Which of the following factors is NOT typically considered when selecting an analytical method?
Which of the following factors is NOT typically considered when selecting an analytical method?
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What aspect of precision refers to the agreement of results from different analysts using various instruments?
What aspect of precision refers to the agreement of results from different analysts using various instruments?
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How does repeatability differ from reproducibility in analytical procedures?
How does repeatability differ from reproducibility in analytical procedures?
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Which of the following would NOT typically trigger a method validation process?
Which of the following would NOT typically trigger a method validation process?
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Study Notes
Analytical Techniques and Instrumentation - Lecture 2
- Learning Goals: Students should be able to list, define, and distinguish among performance standards; explain the importance of method evaluation; make inferences about method acceptability based on evaluation; and formulate or judge the soundness of a method evaluation plan.
What is Method Evaluation?
- Method evaluation (or method validation) is a procedure for conducting assessments to ensure an analytical test system is suitable for its intended use and produces reliable analytical data.
Why Evaluate Methods?
- Ethical Considerations: Good science/good medicine, illness or health/life or death, establish fitness-for-purpose.
- Commercial Considerations: Product liability, laboratory reputation.
- Regulatory/QA Requirements: Legal requirements, consistent application of method, comparability between analysts/labs.
When to Validate/Verify?
- After periods of non-use.
- Periodically as per Quality Management System.
- New methods.
- Methods developed in-house.
- Amended standard/commercial methods.
- If there are changes to: application (use), working environment, or analyst.
Selecting an Analytical Method
- Considerations: Sample matrix, analyte concentration, accuracy needed, number of samples to be analyzed (turnaround time), cost, time and available equipment/expertise.
Evaluation of Methods: How to Evaluate?
- Define the analytical requirement.
- Develop/Identify a candidate method.
- If the analytical requirement isn't met go to the next step.
- If the analytical requirement is met, determine acceptability.
- Plan evaluation experiments.
- Carry out experiments.
- Use data to assess acceptability.
- Statement of acceptability.
Performance Standards/Characteristics
- Method evaluation (or method validation) is a process involving numerous assessments.
- Performance standards/characteristics involve tests or assessments used to evaluate an analytical method.
A Validation Puzzle
- Limit of detection
- Precision
- Working range
- Selectivity
- Uncertainty
- Linearity
- Limit of quantitation
- Bias/Trueness
- Ruggedness
Precision
- Precision expresses the closeness of agreement (degree of scatter) among measurements obtained from multiple samplings of the same homogeneous sample under specified conditions.
- Precision can be considered at two levels: repeatability and reproducibility.
Repeatability
- Expresses precision under the same operating conditions over a short time interval (e.g., same analyst, same instrument, same day).
Reproducibility
- Refers to the degree of agreement between results from experiments conducted by different individuals, at different locations, with different instruments.
Accuracy
- Accuracy expresses the closeness of agreement between a measured value and a known or accepted reference value (often referred to as trueness).
Precision vs. Accuracy
- High accuracy/high precision
- Low accuracy/high precision
- High accuracy/low precision
- Low accuracy/low precision
Specificity
- Specificity refers to the ability to unequivocally assess the analyte of interest in the presence of other components like impurities, degradation products, and matrix components.
- Concerns the extent to which other substances interfere with the analyte's identification.
Limit of Detection (LOD) and Limit of Quantitation (LOQ)
- LOD: The lowest analyte amount detectable in a sample, but not necessarily quantifiable under specified conditions.
- LOQ: The lowest analyte amount quantifiable in a sample with acceptable precision and accuracy under specified conditions.
Linearity and Range
- Linearity: Ability of test results to be directly proportional (or have a defined mathematical transformation) to analyte concentration over a given range.
- Range: The interval between the upper and lower levels demonstrated to have suitable precision, accuracy and linearity with the method.
Ruggedness
- Ruggedness measures reproducibility of test results under various conditions (different labs, analysts, instruments, reagents, temperatures, time intervals)
- Normally expressed by the lack of influence of inherent variables on test results.
Robustness
- Method robustness describes the method's ability to remain unaffected by small deliberate changes in method parameters (e.g., pH, temperature, reagents, brands).
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Description
Explore key concepts in analytical method evaluation in this lecture. Understand performance standards, the importance of method validation, and how to assess method acceptability. This quiz will help solidify your knowledge of ethical, commercial, and regulatory factors in method evaluation.
