Quality is a Lousy Idea-Quality is a Lousy Idea-

If it’s Only an IdeaIf it’s Only an Idea

Quality Assurance vs. Quality Assurance vs. Quality ControlQuality Control

Quality AssuranceQuality AssuranceAn overallmanagement plan to guarantee theintegrity of data(The “system”)

Quality ControlQuality ControlA series of analytical measurements usedto assess thequality of the analytical data(The “tools”)

True Value vs. Measured True Value vs. Measured ValueValue

True ValueTrue Value

The known, accepted value of a quantifiable property

Measured ValueMeasured Value

The result of an individual’s measurement of a quantifiable property

Accuracy vs. PrecisionAccuracy vs. Precision

AccuracyAccuracyHow well a measurement agrees with an accepted value

PrecisionPrecisionHow well a series of measurements agree with each other

Accuracy vs. PrecisionAccuracy vs. Precision

Systematic vs. Systematic vs. Random ErrorsRandom Errors

Systematic ErrorSystematic ErrorAvoidable error due to controllable variables in a measurement.

Random ErrorsRandom ErrorsUnavoidable errors that are always present in any measurement. Impossible to eliminate

Quality Control MeasuresQuality Control Measures

• Standards and Calibration

• Blanks

• Recovery Studies

• Precision and Accuracy Studies

• Method Detection Limits

• NJQLs

Standards and CalibrationStandards and Calibration

• Prepared vs. Purchased Standard

• Signals: Peak Area, Beer’s Law

• Calibration Curves

• Continuing Calibration Checks

• Internal Standards• Performance Testing.

Calibration CurvesCalibration Curves

Graphical representation of the Graphical representation of the relationship between:relationship between:

• The analytical signal

• The concentration of the analyteand

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

Pea

k ar

ea x

10

6

R2 = 0.9989

Continuing Calibration Continuing Calibration VerificationVerification

• Many methods don’t require that daily calibration curves are prepared

• A “calibration verification” is analyzed with each batch of samples

Sample BatchSample Batch• 10 - 20 samples (method defined)

or less

• Same matrix

• Same sample prep and analysis

• Contains a full set of QC samples

Internal StandardsInternal Standards• A compound chemically similar to the

analyte

• Not expected to be present in the sample

• Cannot interfere in the analysis• Added to the calibration standards and

to the samples in identical amounts.

Internal StandardsInternal Standards• Refines the calibration process• Analytical signals for calibration

standards are compared to those for internal standards

• Eliminates differences in random and systematic errors between samples and standards

Performance TestingPerformance TestingBlind samples submitted to laboratories

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

Blanks, Blanks, BlanksBlanks, Blanks, Blanks• Laboratory Reagent Blanks

• Instrument Blanks

• Field Reagent Blanks

• Trip Blanks

Laboratory Reagent BlanksLaboratory Reagent Blanks• Contains every reagent used in the

analysis• Is subjected to all analytical

procedures• Must give signal below detection limit• Most methods require one with every

batch

Instrument BlankInstrument Blank

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

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.

Trip BlanksTrip Blanks• Prepared in the lab, taken to the

field

• Not opened

• Returned to the lab

• Not always required in EPA methods

Recovery StudiesRecovery Studies

• Matrix Spikes

• Laboratory Control Samples

• Surrogates .

Matrix SpikesMatrix Spikes

• Sample spiked with a known amount of analyte

• Subjected to all sample prep and analytical procedures

• Determines the effect of the matrix on analyte recovery

• Normally one per batch

Laboratory Control SampleLaboratory Control Sample

• Subjected to all sample prep and analytical procedures

• Analyte spiked into reagent water

Laboratory Control SampleLaboratory Control Sample

Also known as:Also known as:

• Laboratory Fortified Blank (LFB)

• Quality Control Sample (QCS)

SurrogatesSurrogates

• Similar to an internal standard

• Added to all analytical samples, and to all QC samples to monitor method performance, usually during sample prep

• Methods often have specific surrogate recovery criteria

• Most common in Organic methods

Quality Control MeasuresQuality Control Measures

• Standards and Calibration

• Blanks

• Recovery Studies

• Precision and Accuracy Studies

• Method Detection Limits

• NJQLs

Precision and AccuracyPrecision and Accuracy

• Required for initial certification and annually thereafter

• A series of four laboratory control samples

• Must meet accuracy (recovery) and precision (standard deviation) requirements, often in method

Precision and AccuracyPrecision and Accuracy

• Required with a change in instrumentation or personnel

• Specific to the analyst

• Other names include:

P&A, DOC, IDOC

Method Detection LimMethod Detection Limitit “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 - 1.7N.J.A.C 7:18 - 1.7

Method Detection LimitMethod Detection Limit

• MDLs are determined according to 40 CFR, part 136, Appendix B

• Seven replicate laboratory control samples, analyzed for precision

• Multiply standard deviation by 3.14 (Student’s t- value)

Method Detection LimitMethod Detection Limit• Must be performed initially for

certification• Must meet criteria specified in method• Must be performed with change in

instrumentation or test method• Annually with ELCP

New Jersey New Jersey Quantitation LimitsQuantitation Limits

(NJQLs)(NJQLs)• The minimum concentration of an

analyte that can be quantified with statistical confidence

• 5 x MDL, for the NJ Lab Certification Program