This document discusses key concepts in quality control and quality assurance for analytical chemistry methods and measurements. It defines accuracy, precision, calibration curves, blanks, spikes, limits of detection and quantification, and other method validation parameters. Accuracy measures how close a measurement is to the true value, while precision refers to the agreement between multiple measurements. Quality control measures like calibration, blanks, spikes and ongoing checks are used to validate methods and ensure quality data.

1. Quality is a Lousy Idea-
If it’s Only an Idea
the degree of excellence of
something.

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

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 (A)
• 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
Peak
area
x
10
6
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. METHOD
VALIDITY

27. Specificity
• It is the ability of instrument to assess the
analyte in the presence of different
components which may be expected to be
present in the form excipient, impurities,
and other degradative products.

28. Linearity

29. Range
• It is defined as the intervals between upper
and lower concentration of analyte present
in the sample.
• it is used to demonstrate that the result can
be obtained in specific limits.
• 10-50 mg/mL

30. Accuracy
• It is the nearness of the measured value to
the true value.
• It provides the indication of systematic error
if obtained in any method.
• Intrinsic accuracy (It shows error in the
sample preparation)
• Overall Accuracy ( it shows error in
calculation)

31. Accuracy
• Accuracy is generally expressed as
• C1/C2 X 100
• C1 Concentration of sample observed
• C2 Theoretical True concentration of
sample

32. Precision
• It consists of intermediate precision,
repeatability precision and reproducibility
precision
• It shows agreement between series of
measurements obtain from multiple
sampling of the same homogenous sample.

33. • Intermediate precision
• It is the results obtained which is in the lab
variation by different analysts/different
equipments/ different days.
• Repeatability precision is under same operating
conditions at short intervals of time.
• Reproducibility precision is between different labs
of different companies.
• It is given by relative standard deviation
• %RSD = standard deviation / mean x 100
• It should be less than 1%

34. LOD
• It is the lowest limit of the analyte that can
be detected but can not be quantified in the
sample.
• It is given as percentage or in ppm
• LOD = 3.3 x SD/Slop
• SD standard deviation
• Slop from calibration curve

35. LOQ
• It is the lowest limit of the analyte that can
be detected but can be quantified in the
sample.
• It is the ratio of 1:10
• LOQ = 10 x SD/Slop
• SD standard deviation
• Slop from calibration curve

36. Robustness
• It is the ability of analytical procedure to
remain unaffected by the small but delibrate
variations in the parameters like pH,
temperature, instrument and composition of
solution.