5. Quality Assurance and Calibration

1. Chapter 5 Quality Assurance and Calibration Methods 5. Quality Assurance and Calibration • Quality assurance is • We do to get the right answer for our purpose. • Have Sufficient accuracy and precision to support decisions • Standard addition and internal standards.

2. 5-1 Basics of Quality Assurance Use Objectives • ex)Therapeutic dose is just a little less than the lethal dose, you should be more careful than if you make spaghetti sauce. • Quality assurance is making sure that results meet the customer’s needs. • Writing clear, concise useobjectives for data and results is a critical step in quality assurance and helps prevent misuse of data and results.

3. Specifications: • What level of accuracy and precision will satisfy the use objectives? • Quality assurance begins with sampling. • A false positive • A false negative • Selectivity and sensitivity • Selectivity(also called specificity) means being able to distinguish analyte from other species in the sample(avoiding interference). • Sensitivity is the capabilityof responding reliably and measurably • A detection limit(discussed in Section 5-2)

4. Method blank is sample containing all components except analyte through all steps. • Reagent blank hasnot been subjected to all sample preparation procedures. • Field blank exposed to the site of sampling. • Matrix; everything else except analyte in an sample. • Spike also called a fortification, is a known quantity of analyte added to a sample to test whether the response to a sample is the same as that expected from a calibration curve.

6. Performance test samples (quality control samples or blind samples) : to help eliminate bias. Unknown sample in known composition. • Standard operation procedures what steps will be taken and how they will be carried out for quality assurance. • - Meaningful analysis requires a meaningful sample that represents what is to be analyzed.

8. Assessment • Collecting data to show that analytical procedures are operating within specified limits • Verifying that final results meet use objectives. • Control carts can be used to monitor performance on blanks, calibration checks, and spiked samples

9. 5-2 Method Validation • Method Validation • Process of proving that an analytical method is acceptable for its intended purpose. • Method specificity, linearity, accuracy, precision, range, limit of detection, limit of quantitation, androbustness. Specificity • The ability of an analytical method to distinguish the analyte.

10. Linearity • Linearity measures how well a calibration curve follows a straight line. • LINEST function in Excel • A value of R2 above 0.995 or, perhaps, 0.999 Accuracy Nearness to the truth. 1. Standard Reference Material 2. Different analytical methods. 3. Analyze a blank sample spiked with a known addition of analyte. 4. Make standard additions(Section 5-3) of analyte to the unknown

11. Precision • Instrument precision • Intra-assay precision is evaluated by analyzing aliquots of a homogeneous material several times by one person on one day with the same equipment. • Ruggedness, intermediate precision • Interlaboratory precision Range • Range is the concentration interval over which linearity, accuracy, and precision are all acceptable.

12. [Box 5-2] The Horwitz Trumpet: Variation in Interlaboratory Precision The coefficient of variation (CV) is the standard deviation divided by the mean : CV = s/ x Usually the coefficient of variation is expressed as a percentage of the mean : CV(%) = 100 ⅹ s/ x

13. Limits of Detection and Quantitation • Detection limit, the smallest quantity of analyte that is “significantly different” from the blank. • The signal from samples near the detection limit is similar to the standard deviation from blanks. 1. sample whose concentration is ~1 to 5 times the detection limit. 2. signal from n replicate samples(n ≥ 7) 3. deviation (s) of the n measurements. 4. measure the signal from n blanks (containing no analyte) and find the mean value, yblank. 5. Signal detection limit : ydl = yblank + 3s 6. Calibration line : ysample – yblank = m ⅹ sample concentration

15. Detecton limit • Minimum detectable concentration = 3s/ m • Lower limit of quantitation ≡ 10s/m • Robustness is the ability of an analytical method to be unaffected by small , deliberate changes in operating parameters.

16. 5-3 Standard Addition • Standard addition • A matrix effect is a change in the analytical signal caused by anything. • 5-4 Internal Standards • Internal standard is a known amount of a compound , different from analyte, that is added to the unknown. • Response factor, F ( eq. 5-11)