This document discusses key concepts in quality control and quality assurance for analytical chemistry measurements. It defines terms like quality assurance, quality control, accuracy, precision, calibration curves, blanks, recovery studies, method detection limits, and quantitation limits. Accuracy refers to how close a measurement is to the true value, while precision refers to the agreement between multiple measurements. Systematic errors can be controlled, while random errors are unavoidable. Quality control measures like calibration, blanks, spikes, and duplicate samples ensure accuracy and precision.

1. Quality is a Lousy Idea-
If it’s Only an Idea

2. Quality Assurance vs.
Quality Control
Quality Assurance
An overall
management plan to
guarantee the
integrity of data
(The “system”)
Quality Control
A series of
analytical
measurements used
to assess the
quality of the
analytical data
(The “tools”)

3. True Value vs. Measured
Value
True Value
The known,
accepted value of
a quantifiable
property
Measured Value
The result of an
individual’s
measurement of a
quantifiable
property

4. Accuracy vs. Precision
Accuracy
How well a
measurement
agrees with an
accepted value
Precision
How well a series
of measurements
agree with each
other

5. Accuracy vs. Precision

6. Systematic vs.
Random Errors
Systematic Error
Avoidable error
due to controllable
variables in a
measurement.
Random Errors
Unavoidable errors
that are always
present in any
measurement.
Impossible to
eliminate

7. Quality Control Measures
• Standards and Calibration
• Blanks
• Recovery Studies
• Precision and Accuracy Studies
• Method Detection Limits
• NJQLs

8. Standards and Calibration
• Prepared vs. Purchased Standard
• Signals: Peak Area, Beer’s Law
• Calibration Curves
• Continuing Calibration Checks
• Internal Standards
• Performance Testing.

9. Calibration Curves
Graphical representation of the
relationship between:
• The analytical signal
• The concentration of the analyte
and

10. 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
Peakareax106
R2
= 0.9989

11. Continuing Calibration
Verification
• Many methods don’t require that
daily calibration curves are
prepared
• A “calibration verification” is
analyzed with each batch of samples

12. Sample Batch
• 10 - 20 samples (method defined)
or less
• Same matrix
• Same sample prep and analysis
• Contains a full set of
QC samples

13. Internal 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.

14. Internal 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

15. Performance Testing
Blind samples submitted to
laboratories
?
?
?Labs must periodically
analyze with acceptable
results in order to maintain
accreditation

16. Blanks, Blanks, Blanks
• Laboratory Reagent Blanks
• Instrument Blanks
• Field Reagent Blanks
• Trip Blanks

17. Laboratory 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

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

19. Field Reagent Blanks
• Prepared in the lab, taken to the
field
• Opened at the sampling site,
exposed to sampling equipment,
returned to the lab.

20. Trip Blanks
• Prepared in the lab, taken to the
field
• Not opened
• Returned to the lab
• Not always required in EPA methods

21. Recovery Studies
• Matrix Spikes
• Laboratory Control Samples
• Surrogates .

22. Matrix 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

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

24. Laboratory Control Sample
Also known as:
• Laboratory Fortified Blank (LFB)
• Quality Control Sample (QCS)

25. Surrogates
• 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

26. Quality Control Measures
• Standards and Calibration
• Blanks
• Recovery Studies
• Precision and Accuracy Studies
• Method Detection Limits
• NJQLs

27. Precision 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

28. Precision and Accuracy
• Required with a change in
instrumentation or personnel
• Specific to the analyst
• Other names include:
P&A, DOC, IDOC

29. 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

30. Method 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)

31. Method 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

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