Distributed Pharmaceutical Analysis Laboratory
Draft of procedures for method validation
16 April 2015
M. Lieberman
1. Version: Updated 16 April, 2015 ................................................................................ 2
2. Caveats.................................................................................................................................. 2
3. Limitations of the analytical methodology .............................................................. 3
4. Sample preparation ......................................................................................................... 4
Sample storage and tracking: ......................................................................................................... 4
External standards:............................................................................................................................ 4
Pharmaceutical dosage forms:....................................................................................................... 5
5. Method Validation ............................................................................................................ 7
6. Suggested instrument parameters, solvents, and gradients ............................. 8
a)
b)
c)
d)
e)
Amoxicillin ...................................................................................................................................... 8
Ampicillin--use amoxicillin HPLC conditions. ................................................................. 10
Amoxicillin-clavulanate (or amoxicillin-clavulanic acid) ........................................... 10
Ciprofloxacin ............................................................................................................................... 12
Oxytetracycline (this procedure is under development/testing)............................ 13
7. Analytical metrics (how to tell if your HPLC is behaving properly): ........... 14
8. Assay and Quality Control........................................................................................... 15
1. Version: Updated 16 April, 2015
This manual was drafted 11/4/2014
Updated 28 Jan 2015 to fix errors in amoxicillin/amoxy-clav gradients
Updated 16 April 2015 to fix more gradient errors.
2. Caveats
Participants in the DPAL must be aware of some legal issues related to
pharmaceutical analysis. We report poor quality drugs to the medical regulatory
authority (MRA) in the country where the drugs originated, and also to the WHO
Rapid Alert system. Since we are doing single tablet analysis, analytical results must
be replicated on several samples before triggering a report to the MRA or WHO. If
your laboratory turns up a poor quality product that meets these criteria, Prof.
Lieberman will work with you to report to the appropriate authorities. Please
preserve such samples carefully; in some cases, we may want to subject the sample
to LC-MS, or the country MRAs may want to analyze the samples themselves (eg to
support legal action).
Second, due to the prevalence of counterfeit and improperly labeled products in
developing world markets, it is possible that information such as manufacturer name,
lot numbers, or expiration dates on the packaging materials are falsified or missing.
Legal counsel at UND recommends that we all use the term "stated to be
manufactured by thus and such company" in communications about specific
pharmaceutical products. This information must be conveyed to students who work
on the analyses.
Third, students must obtain written permission from their instructor before posting
pictures of products, analytical data, or other product-specific information in a public
forum such as a poster session, news article, web site, or social media posting. Please
check that the students adhere to the necessary wording describing the origin of the
drugs and that their comments about the products are factual and non-inflammatory.
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3. Limitations of the analytical methodology
Our procedures for quantifying the active ingredients in pharmaceutical dosage forms
are based on monographs published in the United States Pharmacopeia (USP) or
British Pharmacopeia (BP), but they are not pharmacopeia methods. Modifications
must be made to the assay methodology to accommodate the circumstances of sample
collection. For example, we analyze single drug tablets, rather than pooled samples of
20-50 tablets, simply because the samples available are single packs that do not
include large numbers of tablets. Because the analysis is carried out in academic
facilities or teaching laboratories, we may not have the level of quality assurance,
maintenance, and record keeping in our HPLC facilities that a commercial lab must
maintain.
In order to ensure that the strengths and limitations of the analytical methods are well
understood by each user, we require that DPAL participants jump through a few
hoops. First, before any pharmaceutical products can be assayed, the user must
demonstrate the accuracy, precision, and linearity of their method and instrumentation
according to standards laid out in USP <1226> and detailed below. We call this step
method verification. Second, specific quality control samples must be run during the
assay of pharmaceutical products. If these control samples do not assay correctly, as
described in the directions for each analyte, the results from the pharmaceutical
products must be thrown out and the samples re-run. We call this step quality
control. Data from method verification must be satisfactory before pharmaceutical
products are sent to participant laboratories for analysis, and quality control data must
be submitted to the DPAL database along with the product results.
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4. Sample preparation
Sample storage and tracking:
The pharmaceuticals sent for analysis are forensic samples. They must be stored in
a way that does not promote degradation or contamination, and you must keep
good records of each sample so you can track who performed what tests on it and
what the results were.
Samples must be stored in a cool, dark environment. We recommend a plastic bin
with a snug lid in a refrigerator. Allow the sample to come to room temperature
before you work with it, so water does not condense on the cold surfaces.
Each product sample in the batch you will receive consists of at least 3 tablets or
capsules which will be shipped in a plastic bag labeled with a UND tracking number.
The tracking number will be of the form "14-xxxx" for a sample collected in 2014.
When you run tests on individual tablets or capsules, label them as "14-xxxxa, b, c,
etc" Have the students sign out samples for analysis and make sure they use the
proper sample tracking number in their records and chromatogram labels.
External standards:
External calibration standards are created from analytical grade reagents that are
traceable to USP or BP standards. The standard should include a certificate of
analysis, and you must take the reagent purity into account when calculating final
concentrations (the Excel template will guide you through this process). Store dry
standards as directed on the bottle. Most must be kept cold.
amoxicillin: Sigma-Aldrich PHR1127-1g is traceable to USP and costs $51 per gram.
ampicillin
clavulanate
clavulanic acid
ciprofloxacin
azithromycin
The "known" API standard should contain about 0.5 mg/ml of ampicillin,
amoxicillin, or ciprofloxacin, and 0.5 mg/ml of amoxycillin plus 0.2 mg/ml of
clavulanate if you're analyzing amoxi-clav. You will use this standard to determine
all the other concentrations.
For method verification, you will need calibration standards; a set of normal,
overdosed, and deficient samples; and a dosage form of the product for a spikerecovery experiment.
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Calibration standards should span the range from 5% to 200% of the expected API
concentration in the experimental samples and at least 5 standards should be used
to construct the calibration curve. You will use these standards to establish
linearity over the range of interest. It is OK to use the calibration curve if the
samples are run at the same time as the unknown. A calibration curve generated on
one day cannot be used to assay concentrations of samples run on another day.
Since it takes 5 runs to do the calibration curve we prefer to establish linearity and
then use a single-point external standard to assay concentrations of unknown.
Prepare a "normal" unknown sample in the 95-105% range, an "overdosed" sample
in the 140-160% range, and a "deficient" sample in the 20-50% range. Also prepare
a method blank which is nominally 0%. For the spike recovery experiment, we can
send you a dosage form, or you may be able to obtain a sample of the right drug and
dosage form from a physician or extra tablets from a personal prescription.
Pharmaceutical dosage forms:
Samples for analysis should contain about 0.5 mg/ml of ampicillin, amoxicillin, or
ciprofloxacin, and 0.5 mg/ml of amoxycillin plus 0.2 mg/ml of clavulanate if you're
analyzing amoxi-clav.
Accurately weigh a tablet or the contents of a gel capsule and take a portion of the
powder that will give a 0.5 mg/ml solution of the API when diluted to volume.
Tablets should be crushed to fine powder in a mortar and pestle and well mixed, and
contents of capsules should be well mixed. For preparation of the analytical
sample, weigh out at least 25 mg (preferably 50 mg) of powder on an analytical
balance; remaining powder should be labeled and frozen for storage.
For example, the total contents of an amoxicillin capsule with a nominal dose of 500
mg amoxicillin might weigh 627 mg due to excipients. To prepare a 0.5 mg/ml
solution, a portion of roughly 63 mg would be accurately weighed and dissolved in
100 ml of solvent. Samples should be thoroughly mixed (eg by stirring on a
magnetic stirrer for 5 min, or 5 min sonication) plus 2 min of hand shaking and
inversion of the volumetric flask. All samples must be filtered through a fresh 0.45
micron syringe filter to remove particulates that might clog the HPLC column.
Typically we will filter about 1 ml of the sample into an autosampler vial, discarding
the first drops of filtrate.
Amoxicillin: Use 20 mM monobasic sodium phosphate at pH of 4.4 to make
the samples. The pH is important, as amoxicillin hydrolyzes rapidly at basic
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pH. Keep standards and standard solutions refrigerated. Use standard
solutions within 3 weeks. Alternatively, freeze for storage up to 2 months.
Ampicillin: Use 20 mM monobasic sodium phosphate at pH of 6.7 to make
the samples. Keep standards and standard solutions refrigerated. Use
standard solutions within 3 weeks. Alternatively, freeze for storage up to 2
months.
Amoxi-clav: Use DI water to make the samples. Clavulanate is thermally
unstable and these samples should be used within 6 hours of preparation.
Ciprofloxacin: Use 25 mM phosphoric acid, adjusted to a pH value of 3, to
make the samples. Keep standards and standard solutions refrigerated. Use
standard solutions within 3 weeks. Alternatively, freeze for storage up to 2
months.
It would be a good mini-experiment to run periodic chromatograms for a
standard sample that is left out at room temperature for several days.
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5. Method Validation
The goal is to establish that a standard USP or BP method, when run on your
instrument and with your reagents, satisfies a set of analytical metrics. These
directions are specific for HPLC methods using an external standard with a fixedwavelength UV-Vis or diode-array detector.
 Establish control chart: Set up a record keeping mechanism so you can track metrics such as
the integrated intensity of the known standard for different analysts and days of operation. A
page in the instrument log book can be used, or a paper chart, or a computer spreadsheet.
 Precision: The relative standard deviation (RSD) for the integrated intensities of 6 consecutive
injections of the known standard should be below 2%.
 Linearity: Prepare and run at least five calibration standards over the concentration range of
5% to 200%. Calculate a regression line for the calibration data, including correlation
coefficient, y-intercept, slope, and residual sum of squares. The correlation coefficient should
be 0.98 or better and the y intercept should be zero within error of measurement.
 Accuracy and range: Perform three replicate assays each of the overdosed sample, the normal
sample, the deficient sample, and a solvent blank (total of 12 determinations). Run the
external standard after every 5 runs and check that the values of the integrated intensity for the
external standard fall within 2% RSD. Use the average external standard signal to determine
the concentrations of the overdosed, normal, deficient, and blank samples. The measured
concentration of each sample should be within 2 standard deviations of its true concentration.
 Accuracy via spike recovery: If available, a sample of a pharmaceutical dosage form (tablet or
capsule) of the target drug should be prepared for analysis and a portion spiked with an extra
30% of the API. Calculate the % recovery of the spike; it should be within 90-110%.
 Specificity: This can be demonstrated by showing that a spike can accurately be recovered
from a dosage form matrix (the test in the "accuracy via spike recovery" section). A more
robust demonstration which provides a higher level of impurities and degradation products is
to stress the dosage form (eg by baking the tablet or powder for an hour at 60C), then use that
as the matrix for a spike recovery experiment.
 Optional: LOD and LLOQ: LOD or LLOQ determination is carried out using the slope of the
calibration curve and the SD of low concentration samples. Best practice is to prepare a
sample at about 2-3 times the expected LOD; you could also use the SD for the blank runs.
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However you measure the LOD and LLOQ, samples near the LOD or LLOQ limit should be
run and their chromatograms shown in the report.
6. Suggested instrument parameters, solvents, and gradients
a) Amoxicillin
Instrument: Waters e2695 High Performance Liquid Chromatograph
Column: Kinetex 250 x 4.6 mm C18 column, 5 μm particle size and 100 Å
Temperature: 30°C
Detector: Waters 2998 Photodiode Array Detector
Analytical Wavelength: 220 nm
Amoxicillin and Amoxicillin/clavulanate Method I:
high flow rate, fast runs
Mobile Phase
Buffer
Monosodium
Phosphate
Time (min)
0.0
7.0
7.1
8.5
10.0
Concentration of
Buffer (mM)
20
Methanol (%)
pH of Buffer
4.4
Sample Injection
Volume (μL)
20
Buffer (%)
Flow
Ramp
(mL/min)
5
95
1.5
None
90
10
1.5
None
90
10
1.5
Linear
5
95
1.5
Linear
5
95
1.5
None
Table 1. Amoxicillin and Amoxicillin/Clavulanate Method I
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13-0131 6-5-14 Sm (SG, 10x10)
Diode Array
220
Range: 4.883e-1
Area
3.45
38724
4.0e-1
3.5e-1
AU
3.0e-1
2.5e-1
2.0e-1
2.46
12102
1.5e-1
1.0e-1
5.0e-2
0.0
0.00
Time
2.00
4.00
6.00
8.00
10.00
12.00
14.00
Method 1 chromatogram (clavulanate at 2.46 min, amoxi at 3.45 min)
Amoxicillin and Amoxicillin-clavulanate Method II:
lower flow rate, better if your column pressure is too high.
Mobile Phase
Buffer
Monosodium
Phosphate
Concentration of
Buffer (mM)
20
Time (min)
Methanol (%)
Buffer (%)
0.0
5
10.0
pH of Buffer
4.4
Sample Injection
Volume (μL)
10
Ramp
95
Flow
(mL/min)
0.5
80
20
0.5
Linear
13.0
5
95
0.5
Linear
18.0
5
95
0.5
None
None
Table 2. Amoxicillin or Amoxicillin/Clavulanate Method II
Analytical metrics for amoxicillin:
Column capacity factor 1.1-2.8 (if isocratic program is used),
column efficiency >1700 theoretical plates,
tailing factor <2.5 ,
RSD for replicate injections <2.0%.
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b) Ampicillin--use amoxicillin HPLC conditions.
c) Amoxicillin-clavulanate (or amoxicillin-clavulanic acid)
Instrument: Waters e2695 High Performance Liquid Chromatograph
Column: Kinetex 250 x 4.6 mm C18 column, 5 μm particle size and 100 Å
Temperature: 30°C
Detector: Waters 2998 Photodiode Array Detector
Analytical Wavelength: 220 nm
Amoxicillin and Amoxicillin/clavulanate Method I:
high flow rate, fast runs
Mobile Phase
Buffer
Monosodium
Phosphate
Concentration of
Buffer (mM)
20
Time (min)
Methanol (%)
Buffer (%)
0.0
5
7.0
pH of Buffer
4.4
Sample Injection
Volume (μL)
20
Ramp
95
Flow
(mL/min)
1.5
90
10
1.5
None
7.1
90
10
1.5
Linear
8.5
5
95
1.5
Linear
10.0
5
95
1.5
None
None
Table 1. Amoxicillin and Amoxicillin/Clavulanate Method I
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13-0131 6-5-14 Sm (SG, 10x10)
Diode Array
220
Range: 4.883e-1
Area
3.45
38724
4.0e-1
3.5e-1
AU
3.0e-1
2.5e-1
2.0e-1
2.46
12102
1.5e-1
1.0e-1
5.0e-2
0.0
0.00
Time
2.00
4.00
6.00
8.00
10.00
12.00
14.00
Method 1 chromatogram (clavulanate at 2.46 min, amoxi at 3.45 min)
Amoxicillin and Amoxicillin-clavulanate Method II:
lower flow rate, better if your column pressure is too high.
Mobile Phase
Buffer
Monosodium
Phosphate
Concentration of
Buffer (mM)
20
Time (min)
Methanol (%)
Buffer (%)
0.0
5
10.0
pH of Buffer
4.4
Sample Injection
Volume (μL)
10
Ramp
95
Flow
(mL/min)
0.5
80
20
0.5
Linear
13.0
5
95
0.5
Linear
18.0
5
95
0.5
None
None
Table 2. Amoxicillin or Amoxicillin/Clavulanate Method II
Analytical metrics:
resolution between the amoxicillin and clavulanate peaks must be at least 3.5,
column efficiency for each peak at least 550 theoretical plates,
tailing factor below 1.5,
RSD for replicate injections less than 2.0%.
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d) Ciprofloxacin
Instrument: Waters e2695 High Performance Liquid Chromatograph
Column: Kinetex 250 x 4.6 mm C18 column, 5 μm particle size and 100 Å
Temperature: 30°C
Detector: Waters 2998 Photodiode Array Detector
Analytical Wavelength: 220 nm
Mobile Phase
Buffer
Phosphoric acid
Time (min)
0
3
5
7
10
Concentration of
Buffer (mM)
25
Buffer %
95
70
70
95
95
pH of Buffer
3
Acetonitrile %
5
30
30
5
5
Sample Injection
Volume (μL)
???
Flow Rate (mL/min)
1
1
1
1
1
retention times?
Analytical metrics:
column efficiency >2500 theoretical plates,
tailing factor <4.0,
RSD for replicate injections <1.5%
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e) Oxytetracycline (this procedure is under development/testing)
(usually this will be a veterinary product)
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7. Analytical metrics (how to tell if your HPLC is behaving
properly):
Measuring theoretical plates: We recommend the British Pharmacopia method
due to the simplicity of measuring peak width at 1/2 max height. tr is the
retention time of the peak. This method will slightly underestimate column
efficiency.
Measuring resolution of two peaks: Again, for peaks with tailing, it's easier to
use a formula with peak widths measured at 1/2 max height:
Measuring tailing factor (USP method)
Measuring column capacity factor (for isocratic methods only): k'=(tr - t0)/t0,
where tr is the peak retention time and t0 the dead volume of the column
(measured by the elution time for the solvent front).
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8. Assay and Quality Control
External calibration standards are created from analytical grade reagents as directed
in section 4. Five injections of the external standard must show a peak area within 2%
relative standard deviation (RSD), and the range of retention times must be within 0.3
minutes. After every five unknown sample runs, the standard is injected as a quality
check and it must assay within 2% RSD of the 5 initial injections and be within the 0.3
minute time range. If a quality check fails, data after the last passed quality check is not
used.
Typically we analyze one pill from each package. If a sample fails analysis (assay
value <90% or >120% of stated API content) then a new sample is prepared from the
remaining powdered pill material and re-assayed (it would be good practice to perform
this duplicate assay routinely). If this also fails, two more tablets are assayed. The
spreadsheet posted at the DPAL web site has macros set up to do the analytical
calculations--but make sure you understand how those macros work!
A copy of this Excel spreadsheet is posted on the DPAL site.
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