lecture # 6 (january 24, 2008)

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Lecture #6 - OverviewQuality Assurance and Quality Control

Tools to Ensure Quality for your Clients• Quality Assurance and Quality Control• Calibration Methods• Validation of Methods of Analysis

Good Laboratory Practice (GLP)“embodies a set of principles that provides aframework within which laboratory studies areplanned, performed, monitored, recorded, reportedand archived…GLP helps assure regulatoryauthorities that the data submitted are true reflectionof the results obtained during the study and cantherefore by relied upon whenmaking…assessments.”

Regulatory Agencies

EPA - Environmental Protection Agency

FDA - Food and Drug Administration

DEA - Drug Enforcement Agency

Rules of Experimental Design

Control - e.g. blanksRandomize - e.g. “double-blind”Replicate

Quality Control: “a system of routine technicalactivities, to measure and control the quality ofthe inventory as it is being developed”

Quality Assurance: “a planned system of reviewprocedures conducted by personnel not directlyinvolved in the inventory compilation/developmentprocess”

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Time

μ

μ + 2σ/√nμ + 3σ/√n

μ - 2σ/√nμ - 3σ/√n

Upper action line

Upper warning line

Lower action line

Lower warning line

Quality Control Charts

Quality Control

Standard Operating Procedure (SOP) = “what stepswill be taken and how they will be carried out”

False Positives: “says concentration exceeds limitwhen it is below”

False Negatives: “says concentration below limitwhen it exceeds”

Quality Assurance

1. Use Objectives2. Specifications3. Assessment

Method Validation“the process of proving that an analytical methodis acceptable for its intended purpose”

1. Specificity2. Linearity3. Accuracy4. Precision5. Range6. Limit of Detection7. Limit of Quantitation8. Robustness

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Specificity(= Selectivity)

Extent to which a method can measure theanalyte concentration without interferencefrom matrix* or other sample analytes.

* Matrix = “everything else in the sample other than the analyte”

BlanksReagent Blank = a sample containing all componentsexcept the analyte

Method Blank = “a sample containing all componentsexcept the analyte, and is taken through all steps of theanalytical procedure”

Field Blank = a sample containing all componentsexcept the analyte, and is taken through all steps of theanalytical procedure, and “has been exposed to the siteof sampling”

LinearitySquare of Correlation: [Σ(xi-x)(yi-y)]2Coefficient R2 =

Σ(xi-x)2 Σ(yi-y)2

Accuracy

1. Analyze a Standard Reference Material2. Compare Results from Two (or More) Different

Analytical Methods3. Recovery Studies

a. Analyze a Blank Sample “Spiked”b. Standard Addition

Precision

1. Instrument Precision2. Intra-Assay Precision3. Ruggedness4. Interlaboratory PrecisionP

reci

sion

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Method Validation“the process of proving that an analytical methodis acceptable for its intended purpose”

1. Specificity2. Linearity3. Accuracy4. Precision5. Range6. Limit of Detection (LOD)7. Limit of Quantitation (LOQ)8. Robustness

Sensitivity

LOQLOD

Limit ofLinearity

Dynamic Range

Concentration

Res

pons

e

Limit of DetectionConcentration of the average of theblank samples + 3 standard deviations

Limit of QuantitationConcentration of the average of theblank samples + 10 standard deviations

yblank ysample

Detection Limit

3s

ss50%

1%

1. Measure n (≥ 7) samples, and calculate standarddeviation (s)

2. Measure n (≥ 7) blanks, and calculate the meanvalue (yblank).

3. Minimal detectable limit (ydl) : (ydl) = yblank + 3s4. The corrected measure (ysample - yblank) is proportional

to sample concentration:

ysample - yblank = m x sample concentration

5. Substitute ydl for ysample:

(yblank + 3s) - yblank = m x sample concentration 3s = m x sample concentration

Minimum Detectable Concentration = 3s/m

Calculating Minimum Detectable Concentration

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Limit of DetectionConcentration of the average of theblank samples + 3 standard deviations

Limit of QuantitationConcentration of the average of theblank samples + 10 standard deviations

= 3s/m

= 10s/m

“Signal-to-Noise” (S/N) Ratio

Noise = 1

Signal = 10

Noise = 1Signal = 3

S/N = 10 S/N = 3

“Signal-to-Noise” (S/N) Ratio

Limit of Quantitation Limit of Detection

Robustness

“the ability of an analytical method to be unaffectedby small, deliberate changes in the operatingparameters”

Standard Recovery

1. “Spike” Recovery2. Standard Addition3. Internal Standards

Matrix Effects

Standard Addition

Unknown

Solvent

Standard

Measure

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Standard Addition

MeasureMeasureMeasureMeasureMeasure

Successive Standard Addition

Standard Addition

Signal ∝ Analyte Concentration

[X]i = Ix[S]f + [X]f Is+x

[X]fVf = [X]0V0 [S]fVf = [S]0Vs

[X]f = [X]0 V0

V[S]f = [S]0 Vs

V

Standard Addition

Is+x V = Ix + Ix [S]i VsV0 [X]i V0

[S]i Vs V0

Unknownwithoutstandard

-[X]i

1 2 3 4 5-1-2-3 0

Is+x V V0

Successive Standard Addition

Standard Addition

Is+x V = Ix + Ix [S]i VsV0 [X]i V0

[S]f

-[X]f

1 2 3 4 5-1-2-3 0

Is+x

Standard AdditionInternal Standard“a known amount of a compound different from theanalyte, that is added to the unknown”

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Standard Addition

Response Ax = F As

[X] [S]

Internal Standard“a known amount of a compound different from theanalyte, that is added to the unknown”

Where Ax is response of analyte (X), andAs is response of internal standard (S)

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Chemical Equilibrium