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Quality is a Lousy IdeaQuality is a Lousy Idea--

If its Only an IdeaIf its Only an Idea

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Quality Assurance vs.Quality Assurance vs.

Quality ControlQuality Control

Quality AssuranceQuality AssuranceAn overall

management plan to

guarantee the

integrity of data

(The system)

Quality ControlQuality ControlA series of

analytical

measurements used

to assess thequality of the

analytical data

(The tools)

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True Value vs. MeasuredTrue Value vs. Measured

ValueValue

True ValueTrue Value

The known,accepted value of

a quantifiable

property

Measured ValueMeasured Value

The result of anindividuals

measurement of a

quantifiableproperty

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Accuracy vs. PrecisionAccuracy vs. PrecisionAccuracyAccuracy

How well ameasurement

agrees with an

accepted value

PrecisionPrecision

How well a seriesof measurements

agree with each

other

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Accuracy vs. PrecisionAccuracy vs. Precision

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Systematic vs.Systematic vs.

Random ErrorsRandom ErrorsSystematic ErrorSystematic Error

Avoidable errordue to controllable

variables in a

measurement.

Random ErrorsRandom Errors

Unavoidable errorsthat are always

present in any

measurement.

Impossible toeliminate

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Quality Control MeasuresQuality Control Measures Standards and Calibration

Blanks

Recovery Studies

Precision andAccuracy StudiesMethod Detection Limits

NJQLs

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Standards and CalibrationStandards and Calibration

Prepared vs. PurchasedStandard

Signals: PeakArea, Beers Law

Calibration Curves

Continuing Calibration Checks

InternalStandards

Performance Testing.

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Calibration CurvesCalibration CurvesGraphical representation of theGraphical representation of the

relationship between:relationship between:

The analytical signal

The concentration of the analyte

and

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Calibration Curve for DDT

y = 9.3005x + 4.3313

0

100

200

300

400

500

0 10 20 30 40 50 60

Parts per trillion DDT

P

eak

area

x

106

R2

= 0.9989

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Continuing CalibrationContinuing Calibration

VerificationVerification

Many methods dont require that

daily calibration curves areprepared

A

calibration verification isanalyzed with each batch of samples

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Sample BatchSample Batch

10 - 20 samples (method defined)

or less

Same matrix

Same sample prep and analysis

Contains a full set ofQC samples

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Internal StandardsInternal Standards

A compound chemically similar to

the analyte

Not expected to be present in thesample

Cannot interfere in the analysis

Added to the calibration standards

and to the samples in identical

amounts.

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Performance TestingPerformance Testing

Blind samples submitted to

laboratories

?

?

?Labs must periodically

analyze with acceptableresults in order to maintain

accreditation

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Blanks, Blanks, BlanksBlanks, Blanks, BlanksLaboratory Reagent Blanks

Instrument Blanks

Field Reagent Blanks

Trip Blanks

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Instrument BlankInstrument Blank A clean sample (e.g., distilled water)

processed through the instrumentalsteps of the measurement process;

used to determine instrument

contamination.

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Field Reagent BlanksField Reagent Blanks

Prepared 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 BlanksTrip Blanks

Prepared in the lab, taken to the

field

Not opened

Returned to the lab

Not always required in EPA methods

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RecoveryS

tudiesRecoveryS

tudiesMatrix Spikes

Laboratory ControlSamples

Surrogates .

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Matrix SpikesMatrix Spikes

Sample spiked with a known

amount of analyte

Subjected to all sample prep and

analytical procedures

Determines the effect of the matrixon analyte recovery

Normally one per batch

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Laboratory ControlS

ampleLaboratory ControlS

ample

Subjected to all sample prep andanalytical procedures

Analyte spiked into reagent water

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Laboratory ControlS

ampleLaboratory ControlS

ampleAlso known as:Also known as:

Laboratory Fortified Blank (LFB)

Quality ControlSample (QCS)

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SurrogatesSurrogates

Similar to an internal standard

Added to all analytical samples,

and to all QC samples to monitormethod performance, usually

during sample prep

Methods often have specific

surrogate recovery criteria

Most common in Organic methods

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Quality Control MeasuresQuality Control Measures Standards and Calibration

BlanksRecovery Studies

Precision andAccuracy Studies

Method Detection Limits

NJQLs

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Precision and AccuracyPrecision and Accuracy

Required for initial certification

and annually thereafter

A series of four laboratory control

samples

Must meet accuracy (recovery) andprecision (standard deviation)

requirements, often in method

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Precision and AccuracyPrecision and AccuracyRequired with a change in

instrumentation or personnel Specific to the analyst

Other names include:

P&A, DOC, IDOC

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Method Detection LimMethod Detection LimititThe minimum concentration of a

substance that can be measured andreported with 99% confidence that the

analyte concentration is greater than

zero

N.J.A.C 7:18N.J.A.C 7:18 -- 1.71.7

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Method Detection LimitMethod Detection Limit MDLs are determined according to

40

CFR, part136

,Appendix B

Seven replicate laboratory control

samples, analyzed for precision

Multiply standard deviation by

3.14 (Students t- value)

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Method Detection LimitMethod Detection LimitMust be performed initially for

certification

Must meet criteria specified inmethod

Must be performed with change in

instrumentation or test method

Annually with ELCP

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