Basic Principles of Quality Assurance and Quality Control

Quality is a Lousy Idea-

If its Only an Idea

Quality Assurance vs. Quality ControlQuality AssuranceAn overallmanagement plan to guarantee theintegrity of data(The system)Quality ControlA series of analytical measurements usedto assess thequality of the analytical data(The tools)

True Value vs. Measured ValueTrue ValueThe known, accepted value of a quantifiable property Measured ValueThe result of an individuals measurement of a quantifiable property

Accuracy vs. PrecisionAccuracyHow well a measurement agrees with an accepted value

PrecisionHow well a series of measurements agree with each other

Accuracy vs. Precision

Systematic vs. Random ErrorsSystematic ErrorAvoidable error due to controllable variables in a measurement. Random ErrorsUnavoidable errors that are always present in any measurement. Impossible to eliminate

Quality Control MeasuresStandards and CalibrationBlanksRecovery StudiesPrecision and Accuracy StudiesMethod Detection LimitsNJQLs

Standards and CalibrationPrepared vs. Purchased StandardSignals: Peak Area, Beers LawCalibration CurvesContinuing Calibration ChecksInternal StandardsPerformance Testing.

Calibration CurvesGraphical representation of the relationship between: The analytical signal The concentration of the analyteand

Continuing Calibration VerificationMany methods dont require that daily calibration curves are prepared A calibration verification is analyzed with each batch of samples

Sample Batch10 - 20 samples (method defined) or lessSame matrixSame sample prep and analysis

Contains a full set of QC samples

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Internal StandardsA compound chemically similar to the analyteNot expected to be present in the sampleCannot interfere in the analysisAdded to the calibration standards and to the samples in identical amounts.

Internal StandardsRefines the calibration processAnalytical signals for calibration standards are compared to those for internal standardsEliminates differences in random and systematic errors between samples and standards

Performance TestingBlind samples submitted to laboratories

???Labs must periodically analyze with acceptable results in order to maintain accreditation

Blanks, Blanks, BlanksLaboratory Reagent BlanksInstrument BlanksField Reagent BlanksTrip Blanks

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Laboratory Reagent BlanksContains every reagent used in the analysisIs subjected to all analytical proceduresMust give signal below detection limitMost methods require one with every batch

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Instrument BlankA clean sample (e.g., distilled water) processed through the instrumental steps of the measurement process; used to determine instrument contamination.

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Field Reagent BlanksPrepared in the lab, taken to the field

Opened at the sampling site, exposed to sampling equipment, returned to the lab.

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Trip BlanksPrepared in the lab, taken to the field

Not opened Returned to the lab Not always required in EPA methods

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Recovery StudiesMatrix SpikesLaboratory Control SamplesSurrogates .

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Matrix SpikesSample spiked with a known amount of analyteSubjected to all sample prep and analytical proceduresDetermines the effect of the matrix on analyte recovery Normally one per batch

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Laboratory Control Sample Subjected to all sample prep and analytical procedures Analyte spiked into reagent water

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Laboratory Control SampleAlso known as: Laboratory Fortified Blank (LFB) Quality Control Sample (QCS)

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SurrogatesSimilar to an internal standardAdded to all analytical samples, and to all QC samples to monitor method performance, usually during sample prepMethods often have specific surrogate recovery criteriaMost common in Organic methods

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Quality Control MeasuresStandards and CalibrationBlanksRecovery StudiesPrecision and Accuracy StudiesMethod Detection LimitsNJQLs

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Precision and AccuracyRequired for initial certification and annually thereafterA series of four laboratory control samplesMust meet accuracy (recovery) and precision (standard deviation) requirements, often in method

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Precision and AccuracyRequired with a change in instrumentation or personnelSpecific to the analystOther names include: P&A, DOC, IDOC

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Method Detection Limit The minimum concentration of a substance that can be measured and reported with 99% confidence that the analyte concentration is greater than zero N.J.A.C 7:18 - 1.7

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Method Detection LimitMDLs are determined according to 40 CFR, part 136, Appendix BSeven replicate laboratory control samples, analyzed for precisionMultiply standard deviation by 3.14 (Students t- value)

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Method Detection LimitMust be performed initially for certificationMust meet criteria specified in methodMust be performed with change in instrumentation or test methodAnnually with ELCP

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New Jersey Quantitation Limits(NJQLs)The minimum concentration of an analyte that can be quantified with statistical confidence5 x MDL, for the NJ Lab Certification Program

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Sheet4

Chart11045107225467

y = 0.0177x + 0.0214ppb ArsenicAbsorbenceCalibration Curve for ArsenicR2 = 0.9961

Chart21045107225467

R2 = 0.9989Parts per trillion DDTPeak area x 106Calibration Curve for DDTy = 9.3005x + 4.3313

Sheet1110545101072522550467

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