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. Chapter 5 Quality Assurance and Calibration Methods

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 use objectives for data and results is a critical step in quality assurance and helps prevent misuse of data and results.

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 capability of responding reliably and measurably A detection limit(discussed in Section 5-2)

Method blank is sample containing all components except analyte through all steps. Reagent blank has not 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.

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.

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

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, and robustness. Specificity The ability of an analytical method to distinguish the analyte.

Linearity Linearity measures how well a calibration curve follows a straight line. LINEST function in Excel A value of R 2 above or, perhaps, 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

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.

[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

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, y blank. 5. Signal detection limit : y dl = y blank + 3s 6. Calibration line : y sample – y blank = m ⅹ sample concentration

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.

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)