Method validation terms quality control and assurance
- 1. Quality is a Lousy Idea- If it’s Only an Idea the degree of excellence of something.
- 2. Quality Assurance vs. Quality Control Quality Assurance An overall management plan to guarantee the integrity of data (The “system”) Quality Control A series of analytical measurements used to assess the quality of the analytical data (The “tools”)
- 3. True Value vs. Measured Value True Value The known, accepted value of a quantifiable property Measured Value The result of an individual’s measurement of a quantifiable property
- 4. Accuracy vs. Precision Accuracy How well a measurement agrees with an accepted value Precision How well a series of measurements agree with each other
- 6. Systematic vs. Random Errors Systematic Error Avoidable error due to controllable variables in a measurement. Random Errors Unavoidable errors that are always present in any measurement. Impossible to eliminate
- 7. Quality Control Measures • Standards and Calibration • Blanks • Recovery Studies • Precision and Accuracy Studies • Method Detection Limits
- 8. Standards and Calibration • Prepared vs. Purchased Standard • Signals: Peak Area, Beer’s Law • Calibration Curves • Continuing Calibration Checks • Internal Standards • Performance Testing.
- 9. Calibration Curves Graphical representation of the relationship between: • The analytical signal (A) • The concentration of the analyte and
- 10. Calibration Curve for DDT y = 9.3005x + 4.3313 0 100 200 300 400 500 0 10 20 30 40 50 60 Parts per trillion DDT Peak area x 10 6 R2 = 0.9989
- 11. Continuing Calibration Verification • Many methods don’t require that daily calibration curves are prepared • A “calibration verification” is analyzed with each batch of samples
- 12. Sample Batch • 10 - 20 samples (method defined) or less • Same matrix • Same sample prep and analysis • Contains a full set of QC samples
- 13. Internal Standards • A compound chemically similar to the analyte • Not expected to be present in the sample • Cannot interfere in the analysis • Added to the calibration standards and to the samples in identical amounts.
- 14. Internal Standards • Refines the calibration process • Analytical signals for calibration standards are compared to those for internal standards • Eliminates differences in random and systematic errors between samples and standards
- 15. Performance Testing Blind samples submitted to laboratories ? ? ? Labs must periodically analyze with acceptable results in order to maintain accreditation
- 16. Blanks, Blanks, Blanks • Laboratory Reagent Blanks • Instrument Blanks • Field Reagent Blanks • Trip Blanks
- 17. Laboratory Reagent Blanks • Contains every reagent used in the analysis • Is subjected to all analytical procedures • Must give signal below detection limit • Most methods require one with every batch
- 18. Instrument Blank • A clean sample (e.g., distilled water) processed through the instrumental steps of the measurement process; used to determine instrument contamination.
- 19. Field Reagent Blanks • Prepared in the lab, taken to the field • Opened at the sampling site, exposed to sampling equipment, returned to the lab.
- 20. Trip Blanks • Prepared in the lab, taken to the field • Not opened • Returned to the lab • Not always required in EPA methods
- 21. Recovery Studies • Matrix Spikes • Laboratory Control Samples • Surrogates .
- 22. Matrix Spikes • Sample spiked with a known amount of analyte • Subjected to all sample prep and analytical procedures • Determines the effect of the matrix on analyte recovery • Normally one per batch
- 23. Laboratory Control Sample • Subjected to all sample prep and analytical procedures • Analyte spiked into reagent water
- 24. Laboratory Control Sample Also known as: • Laboratory Fortified Blank (LFB) • Quality Control Sample (QCS)
- 25. Surrogates • Similar to an internal standard • Added to all analytical samples, and to all QC samples to monitor method performance, usually during sample prep • Methods often have specific surrogate recovery criteria • Most common in Organic methods
- 26. METHOD VALIDITY
- 27. Specificity • It is the ability of instrument to assess the analyte in the presence of different components which may be expected to be present in the form excipient, impurities, and other degradative products.
- 28. Linearity
- 29. Range • It is defined as the intervals between upper and lower concentration of analyte present in the sample. • it is used to demonstrate that the result can be obtained in specific limits. • 10-50 mg/mL
- 30. Accuracy • It is the nearness of the measured value to the true value. • It provides the indication of systematic error if obtained in any method. • Intrinsic accuracy (It shows error in the sample preparation) • Overall Accuracy ( it shows error in calculation)
- 31. Accuracy • Accuracy is generally expressed as • C1/C2 X 100 • C1 Concentration of sample observed • C2 Theoretical True concentration of sample
- 32. Precision • It consists of intermediate precision, repeatability precision and reproducibility precision • It shows agreement between series of measurements obtain from multiple sampling of the same homogenous sample.
- 33. • Intermediate precision • It is the results obtained which is in the lab variation by different analysts/different equipments/ different days. • Repeatability precision is under same operating conditions at short intervals of time. • Reproducibility precision is between different labs of different companies. • It is given by relative standard deviation • %RSD = standard deviation / mean x 100 • It should be less than 1%
- 34. LOD • It is the lowest limit of the analyte that can be detected but can not be quantified in the sample. • It is given as percentage or in ppm • LOD = 3.3 x SD/Slop • SD standard deviation • Slop from calibration curve
- 35. LOQ • It is the lowest limit of the analyte that can be detected but can be quantified in the sample. • It is the ratio of 1:10 • LOQ = 10 x SD/Slop • SD standard deviation • Slop from calibration curve
- 36. Robustness • It is the ability of analytical procedure to remain unaffected by the small but delibrate variations in the parameters like pH, temperature, instrument and composition of solution.