Upload
trankhue
View
224
Download
0
Embed Size (px)
Citation preview
1
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”
2
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
3
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
4
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
5
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
6
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”
7
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)
8
Chemical Equilibrium