I am using a pharmaceutical drug substance, but
1) area is different same concentration same vial .
2) area is different same concentration different vial
Using Waters HPLC with UV detector.
Dear Suddhasatwa Banerjee ,
your observation: different area with repetitive injections of the same standard solution from the same vial, and different areas with repetitive injections from different vials could have two explanations:
- something is wrong with the injection device. Do you use an autosampler?
- the component could be decomposing or at very low concentrations be lost due to some "wall effects".
In the first case, I would perform a module qualification according to the instrument's vendor instructions. Usually, this is a test with a very stable component (e.g., caffeine) without a column (i.e., FIA), and then the reproducibility is checked against the vendor specifications. In most cases you find this information in the module manual. If the specification is met, continue with the next step, if not: Get the autosampler repaired.
In the latter case, things get complex. In most cases pharmaceuticals should survive the waiting period until injection. In some very (!) rare cases, however, we saw that depending on the glass quality used for the production of the autosampler vials decomposition was introduced. We solved that by either using a different supplier or swapped to polymer vials.
In case of a chemical instability (this should be known for the given component), you could try cooling of the sample, or chemically stabilizing, e.g. adjusting the sample pH.
If you use a known pharmaceutical, check the literature for articles and procedures describing the chromatographic analysis. Compare this information with the procedure used in your laboratory, and check for the possibility of chemical decomposition.
As a true believer in Okham's razor, I would put my money on the autosampler/injector being the culprit.
I hope this helps.
Good luck with your research
Detlef.
Dear Suddhasatwa Banerjee ,
your observation: different area with repetitive injections of the same standard solution from the same vial, and different areas with repetitive injections from different vials could have two explanations:
- something is wrong with the injection device. Do you use an autosampler?
- the component could be decomposing or at very low concentrations be lost due to some "wall effects".
In the first case, I would perform a module qualification according to the instrument's vendor instructions. Usually, this is a test with a very stable component (e.g., caffeine) without a column (i.e., FIA), and then the reproducibility is checked against the vendor specifications. In most cases you find this information in the module manual. If the specification is met, continue with the next step, if not: Get the autosampler repaired.
In the latter case, things get complex. In most cases pharmaceuticals should survive the waiting period until injection. In some very (!) rare cases, however, we saw that depending on the glass quality used for the production of the autosampler vials decomposition was introduced. We solved that by either using a different supplier or swapped to polymer vials.
In case of a chemical instability (this should be known for the given component), you could try cooling of the sample, or chemically stabilizing, e.g. adjusting the sample pH.
If you use a known pharmaceutical, check the literature for articles and procedures describing the chromatographic analysis. Compare this information with the procedure used in your laboratory, and check for the possibility of chemical decomposition.
As a true believer in Okham's razor, I would put my money on the autosampler/injector being the culprit.
I hope this helps.
Good luck with your research
Detlef.
Dear Suddhasatwa Banerjee,
Could you write accurately what the difference is in the area of case 1 and case 2 (and what was the concentration of your substance)?
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