Good Laboratory Practice: Quality Assurance of Analytical Measurements Section Four Good Laboratory Practice: Quality Assurance of Analytical Measurements

What is Good Laboratory Practice (GLP)? The goal of GLP is to certify that every step of the analysis is valid. Standard Operating Procedures (SOP) Quality Assurance Unit (QAU)

Validation of Analytical Methods Defintion Example Technique Scientific principle gives compositional information Spectrophotometry Method Distinct adaptation of technique selected measurement purpose Pararosaniline method to determine SO2 Procedure Written directions to use a method ASTM D2914 Sulfur Dioxide Protocol Set of definitive directions that must be followed, without exception EPA Reference Method Determine SO2 Atmosphere

Fig. 4.1. General process for evaluation/validation of methodology. Validation involves determining: selectivity linearity accuracy precision sensitivity range limit of detection limit of quantitation ruggedness/robustness Standard reference materials (SRMs) best for determining accuracy. Fig. 4.1. General process for evaluation/validation of methodology. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)

Fig. 4.2. Response factor plot for Figure 3.8. (p. 104) RF = (signal – y intercept)/(concentration). A zero slope indicates linear response over the concentration range selected. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley) Fig. 4.2. Response factor plot for Figure 3.8. (p. 104)

Fig. 4.3. Dependence of relative standard deviation on concentration. The precision becomes poorer at low concentrations. (Also sometimes at high concentrations, as in spectrophotometric measurements –see spectrometric error, Fig. 16.27.) Fig. 4.3. Dependence of relative standard deviation on concentration. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)

Fig. 4.4. Representative z-value distributions for Z = (Xi-X)/s = (mean conc. of lab – accepted conc.)/(S.D. accepted conc.) A z-value of 2 means a lab is two S.D. away from the accepted value (95% chance of systematic error). Fig. 4.4. Representative z-value distributions for proficiency tests with a series of laboratories. ©Gary Christian, Analytical Chemistry, 6th Ed. (Wiley)