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Dear Group,
I have a question regarding internal standard variation in the batch
run. I have not seen any concrete guideline as to what is the allowed
variation in IS response throughout the batch run. Going by the
acceptance criteria for standards, I guess a 20% variation is
expected. How do reguators look at the variation of, say, 50? Will it
warrant a 483?
Regards,
Vinayak
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Dear Vinayak,
There is no guidance for IS variation. One of the way to select
samples for repeat analysis based on IS area variation is to compare
the IS area of study samples with average IS area of standards and
QCs. If it deviates more than 50%, repeat to confirm the initial
concentration.
regards,
Jignesh
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First, did the instrument/system pass system suitability?
Are all the peak shapes and peak responses within tolerance?
What can lead to a high variability in IS? Poor precision in adding
the IS
to the samples, poor injector performance, poor responsiveness of
detector,
poor stability of the IS, poor reproducibility of peak area or peak ht,
differential absorbance to the well material or absorbance or release
from
the pelletized material if in the same well.
What have you eliminated/ or identified as the source of variability?
What does your SOP/ protocol direct you to do?
Since most IS are added to the organic ppt solution you want to make
sure
you are using the best pipette for low viscosity solutions.
You may want to add the IS in an aqueous solution.
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Dear Vinayak
Its true there is no guidance for IS variation. Its acceptance
criteria very from lab to lab.
As jignesh wrote it is the way to select the sample for IS variation
for repeat analysis that's absolutely true.
For this we follow -- Samples are to be repeated, if the response of
internal standard is not within +- 30% of the mean response of the
internal standard in accepted calibration curve standards.
Previously we also kept 50% deviation, but after some audits we
decrease it to 30% deviation as per their suggestions. This repeat
analysis is required to confirm the initial concentration.
Hope this will help you.
Regards
laxman kaswan
LifeSan Clinical Resaerch (Unit of Centaur pharma)
Mumbai
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Dear Ed thanks for response.
1) I am yet to look at stability issue of IS
2) Peak shapes are good. What you mean by peak response within
tolerance?
3) Before beginning batch there will be system suitability followed by
calibration curve
4) There will be a calibration curve at the end of batch run
5) Calibration curve at the beginning and at the end of batch are
passing
within 20% accuracy
6) System suitability passes before start of analysis
Precision in adding the IS seems to be OK- RSD of IS area counts varies
from 0.4 to 23.8(Is it precise enough, considering this is final area
count after LLE?) I have tabulated IS data for your comments.
IS response data for PO samples
Time Subject1 Subject2 Subject3 Average SD RSD
0.25 95470.2 96000.2 95218.6 95563.0 399.0 0.4
0.5 100938.2 83730.8 103552.7 96073.9 10769.1 11.2
1 92645.5 113445.8 129720.4 111937.2 18583.4 16.6
2 128520.1 143625.0 126067.0 132737.4 9508.4 7.2
4 155329.4 160287.7 168529.8 161382.3 6668.0 4.1
8 175346.8 177808.9 196663.3 183273.0 11661.5 6.4
24 196879.4 190171.3 200080.9 195710.5 5057.1 2.6
IS response data for IV samples
Time Subject1 Subject2 Subject3 Average SD RSD
0.083 198417.1 204006.3 192483.5 198302.3 5762.3 2.9
0.25 191315.8 185968.8 177882.1 185055.5 6763.3 3.7
0.5 205175.7 187785.6 198111.3 197024.2 8745.9 4.4
1 220196.9 202744.2 206653.1 209864.8 9158.9 4.4
4 210315.6 244701.9 182937.4 212651.6 30948.4 14.6
8 215025.4 223934.5 232391.8 223783.9 8684.2 3.9
24 180259.9 186346.3 117066.6 161224.3 38362.5 23.8
Regards,
Vinayak
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IS minimum/maximum area or ht counts if you have one. What is the IS CV
response for the QCs and your system suitability? It does seem like a
pipetting issue. If your SOP allows, reprocess the samples. If it
does
not, issue a deviation and re-write the SOP to allow re-analysis when
the IS
variability exceeds your set point.
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Dear Ed O'Connor ,
Now I have a question, If IS variation is calculated based on the
average IS area of the acceptated CC and QCs and acceptable variation
is +-40%. What if the IS area of any of the QC or Std. is outside
acceptable variation?Should we reject those std or QCs and again
calculate the average and check for variation?
Jayanta
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Dear Vinayak Nadiger
* In calculation of the RSD for the IS area one should not consider
w.r.t the sampling time points. One has to consider all the batch
standards, QCs, unkown samples etc irrespective of IV and PO.
* It seems that you reported IV in place of PO, if that is the case
your vehicle in IV was major concern.
* let us know vehcle for PO, IV and IS area in standards and QCs
also.
* One least possibility is ionisation competetion if the analyte
and IS RT were matching.
Dev
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