Analytical Techniques And Instrumentation Lecture 2 PDF

ANALYTICAL TECHNIQUES AND INSTRUMENTATION MLS 2100 LECTURE 2 LEARNING GOALS: ◼ On completing this topic, the student should be able to: ◼ List, define and distinguish among performance standards ◼ Explain the importance of method evaluation ◼ Make inferences about method acceptability based...

ANALYTICAL TECHNIQUES AND INSTRUMENTATION MLS 2100 LECTURE 2 LEARNING GOALS: ◼ On completing this topic, the student 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 ◼ Formulate or judge the soundness of a plan for method evaluation What is Method Evaluation? ◼ “Method evaluation [or method validation] is a procedure of performing assessments designed to verify that an analytical test system is suitable for its intended [use] and is capable of providing [reliable] analytical data.” Why do we evaluate methods? WHEN TO VALIDATE / VERIFY? ◼ After a period of non‐use ◼ Periodically as required by Quality Management System ◼ New methods. ◼ Methods developed in house. ◼ Amended standard/commercial methods. ◼ If there are Changes: ◼ Application (use) ◼ Working environment ◼ Analyst Selecting an analytical method ◼ Consideration: ◼ Sample Matrix ◼ Expected concentration of the analyte ◼ Accuracy needed ◼ Number of samples to be analysed (Turnaround time) ◼ Cost ◼ Time ◼ Available equipment and ◼ Expertise Evaluation of Methods: How do you evaluate? Performance standards/characteristics Performance standards/characteristics Precision ◼ The precision of an analytical procedure expresses the closeness of agreement (degree of scatter) between a series of measurements obtained from multiple sampling of the same homogenous sample under the prescribed conditions. ◼ Precision may be considered at two levels: repeatability and reproducibility. Precision Precision ◼ Repeatability: expresses the precision under the same operating conditions over a short interval of time. For example: the same analyst analyses samples on the same day with the same instrument. ◼ Reproducibility: refers to the degree of agreement between the results of experiments conducted by different individuals, at different locations, with different instruments. Accuracy ◼ The accuracy of an analytical procedure expresses the closeness of agreement between the value that is accepted either as a conventional true value or an accepted reference value and the value found. This is sometimes termed trueness. Precision Vs Accuracy Specificity ◼ Specificity refers to the ability to assess unequivocally the analyte in the presence of components that may be expected to be present eg impurities, degradation products, matrix components ◼ This parameter is concerned with the extent to which other substances interfere with the identification. Ruggedness Robustness ◼ Robustness is the method’s capability to remain unaffected by small, but deliberate changes in method parameters, eg. pH, temperature, reagents, brands,