Quality Assurance
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Chapter 29. Quantitative Chemical
Analysis, Daniel C. Harris, 6th Edition,
2003.
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New to this edition and a very important topic
in industry today.
GLP/GMP in the pharmaceutical industry. Other
quality standards ISO, CE and other quality
systems.
Data Quality
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How do we know that we have done a good
job in lab? We are well trained scientists so
we should be doing good work.
Are We????
This is where Quality Assurance comes in.
It will vary from lab to lab but it should be
something that is taken very seriously.
Why has this become so important?
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Let us look at the next three examples
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There are many testing labs that one can
have analyses done at. Let’s see how they
do.
Pb in polyethylene film (lab self
designation)
Pb in River Water (all having a quality
management system)
Pb in River Water (National
Measurement Institutes)
QC / QA
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Quality Control – measures taken ensure that
there is accuracy and precision in an
analytical result
Quality Assurance – Assessment that the
quality standards have been met.
Quality Control
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In Pharmaceuticals this is usually the process
of verifying the product quality. That the
products meets specification.
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That
That
That
That
the label claim is correct. ( 1 mg table)
impurities are below certain limits
raw materials are in manufacturer specs
returned materials are within specs
Quality Control
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Governed by detailed procedures.
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Called SOPs – Standard Operating Procedures
There will be SOPs for 1) Equipment maintenance
and repair, 2) Method Development and Validation,
3) Data tracking and record keeping, 4) Computer
validation and data issues, 5) Setting of shelf life
and other lab management issues, 6) Staff
training requirements, 7) chain of custody of
samples etc. etc. etc.
The real issue is record keeping and adherence to
the procedures of the lab.
Quality Assurance
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An independent function within the company
to assure that the QC functions are working
properly.
They hold routine audits and internal
inspections.
They will be the staff that host visits from the
FDA and coordinate the FDA site visit (every
two years)
They are inspected first
GLP / GMP
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Good Laboratory and Good
Manufacturing Practices.
Other agencies have different rules.
EPA will certify labs doing
environmental tests. Many of these
tests are specified and must be followed
exactly
Quality Objectives
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When rules are changed this might
require that better methods be
developed.
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Perhaps with better detection limits or
improved precision.
One must work to get the best
information from the resources at hand.
Quality Objectives
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It is not required that the best possible
analysis be carried out. Only that it provide
the data required, meet the data quality
objective.
Cost considerations of course are important
here. This must be considered when
developing new methods such as new HPLC
methods.
Method Validation
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The process of proving that the analytical method is
acceptable for the intended purpose. (Issues to
addressed)
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Specificity
Linearity
Accuracy
Precision
Range
Limit of detection
Limit of quantization
Robustness
Specificity
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The ability to distinguish the analyte from
everything else that might be in the sample.
Lets look at a separation for the drug
Cefotaxime by MEKC.
O
S
NH
H2N
N
N
O
S
O
N
CH3
O
O
OH
CH3
O
Specificity
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The drug is seen with the impurities that
might show up in an assay.
 Ideally you should get baseline resolution.
This is when R > 1.5.
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Failing this you might state that the unresolved
impurities at their maximum level not effect the
assay of the drug by more than 0.50%
A impurity assay might be specified with all
expected impurities > 0.1% be resolved
from the major component.
Specificity
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Just were do you get the impurities to test?
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What is likely to be present in a drug formulation of bulk
substance sample?
For a compound like aspirin this is fairly simple. We know what
things to expect since it has been around for a long time.
What about an NCE?
This is not a trivial challenge.
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Make impurities.
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Subject the compound to heat (solid phase), heat (in solution),
light, humidity, acidic media, basic media and oxidants to the point
of consuming about 20% of the parent.
Add Synthetic starting materials, by-products, synthesis
intermediates and known synthesis degradation products.
Add all expected excipients.
Linearity
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For bulk component you will want you standard curve
to have five standards spanning 0.5 to 1.5 expected
range. Include a blank
For impurity assay you will wish you standards to
span 0.05% to 2% (wt/wt). Given that impurities
might fall in the 0.5% to 1% range.
These ranges would be fixed in the SOP for the
developed analysis and based on the product
specification.
Linearity Testing
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We have discussed this.
R2 is a poor measure as we have stated
before.
Look at residuals
For zero intercept
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Bulk assay - 2% from the target value of the
analyte
Impurity assay – 10% of the target value of the
impurity.
Accuracy
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Analyze – Standard Reference Materials (if available)
Results of two or more different analytical methods.
Blank sample spiked with analyte. Ranges as in
linearity.
Standard additions.
Spikes should be recovered at (100 + 2)% for major
components and 0.1% absolute or + 10% relative for
minor components
Precision
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Expressed as relative standard deviations for
at least 10 experiments.
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Instrument precision (< 1%)
Intra-assay precision – prep each sample from
start, same person, same day. (< 2%)
Intermediate precision (Ruggedness) – Different
people, different days and different instruments.
Interlaboratory precision is also called just
reproducibility (3% to perhaps 40% or more)
Horwitz Trumpet
Horwitz Trumpet
CV (%)  2
(10.5 logC )
Where C is the weight fraction
Range
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The range is the concentration interval where
linearity, accuracy and precision are all
acceptable.
Limits of Detection and Quantitation
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Also called the lower limit of detection.
Smallest quantity that gives a signal
significantly different from the blank.
This term had lead to much disagreement
and controversy.
Finding the detection limit.
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Prepare a sample that is 1 to 5 larger than
the estimated detection limit.
Measure the signal for n replicate analyses (n
> 7.
Calculate s for this data set.
Measure the signal from n replicate analyses
of the blank. (n > 7) Calculate the mean
value. (yblank)
Finding the detection limit.
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ydl = yblank + ts
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Where t is the Student’s t value for degrees of
freedom at 98% confidence.
This gives you the signal detection limit.
Concentration Detection Limit.
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Minimum detectable concentration = (ts)/slopecalib
Limit of Quantitation
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We can find the analyte at this low end but it
would be difficult to quantify it accurately so
we have another term
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Limit of Quantitation.
yloq = yblank + 10s
Limit of Detection (Alternate way)
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Common shortcut
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ydl = yblank + 3s
From Least Squares Line.
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Signal detection limit
ydl = b + 3sy
Other consideration
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Instrument detection limit
Method detection limit
Reporting Limit
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A level below which you may report not
detected. Regulatory specified.
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This level might be different in different matrix
systems.
Robustness
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The ability for a method to be unaffected by
small changes.
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Solvent composition
pH
Buffer concentration
Temperature
Injection volume
Detector wavelength
Shelf life of solutions used
Quality Tracking
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SOP directs how you keep an assay under
control.
Directs how samples are handled and stored.
Will dictate how and when the method should
be checked.
Analytical Standards
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Can be purchased from NIST.
Must be handled with care.
Care should be taken with matrix effects.
Compound used to make up solutions should
have no analyte.
Elemental purity measured on nines scale.
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Four nines is 0.9999 pure. Only in terms of other
metal and not other contaminants.
Standards
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You may elect to purchase NIST traced
certified solutions.
There are many pitfalls to avoid and many
are discussed on page 732.
Blanks
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Analysis of blanks can be very informative.
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Will detect carry over.
Method Blank – all steps except addition of
analyte.
Field Blank – all steps including being taken
to the field.
Quality Control Samples
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A sample that is known and analyzed along
with the rest of the samples and standards.
Blind samples are best.
Collaborative and round robin testing will help
assess analysis proficiency.
Control Charts.
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Plot the results for a process or an analytical
procedure. (with your quality control
samples).
When do you shut down.
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Single observation outside action lines
2 out of 3 consecutive measurements between the
warning and action lines
7 consecutive measurement all or above the center
line
6 consecutive measurements all increasing or
decreasing
14 consecutive measurements alternating up and
down
An obvious nonrandom pattern.