I performed a batch test to evaluate the removal of a drug using a locally produced adsorbent
at pH 3, pH4 , pH5 and pH6. I noticed a reduction in peak areas for pH 3 and 4
But at pH 5 and 6, the peak area was rather increasing. How do i explain this?
Peaks area for pH 5 and 6 with adsorbent had higher values than the control set up(without adsorbent)
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Hi, Amen Ekhosuehi,
I am not sure I can explain your results without the details (i.e., the detection method, the type of an adsorbent and the possibility for release of soluble material from the adsorbent phase) but I would check several points (assuming your analysis is based on HPLC?):
(1) was the shape of the peak changed? Wasn't there any tail or a shoulder?
(2) Was pH the same in your test solutions and in the controls, and, if not, could it have effects on analytics?
My (general) suspicion is related to changes in speciation of your drugs which are often ionizabe organic acids. At pH 3-4, you might have non-ionized forms whereas at pH 5-6, there is an ionization. Different species behave differently during detection, having different spectral properties et cetera. So, perhaps, the effects you have observed are related to differences between the samples due to the differences in drug speciation not accounted properly in the controls?
Thank you Mikhail your answer was helpful. I am using HPLC and the conditions in the controls and treatment were the same
Amen,
Adding to the comment of M. Borisover:
- it's a good idea to have a control samples with the adorbent but without the drug, because the adsorbent can release substances that can have similar retention time as the drug you want to measure, thereby increasing the apparent signal of the drug,
- if your HPLC allows it, you can also check spectrum for the peak in question and compare it with a standard; try analysing your samples at various wavelengths, the background effects should differ at various WL;
- finally, it's good to use a buffer mobile phase, so that the speciation of the substance isn't changed for various samples.
Thank you Adam for your answer. I would try control with adsorbent. My current mobile phase is 0.1%(v/v) formic acid(30%) and Acetronitrile (70%).
Thank you Adam for your answer. I would try control with adsorbent. My current mobile phase is 0.1%(v/v) formic acid(30%) and Acetronitrile (70%).
You're welcome, Amen. Please note that formic acid is not a buffer. You can use this acid together with ammonium formate to obtain a buffer with acidic range:
Practical HPLC method development screening (crawfordscientific.com)
However, I'd start with checking the background with adsorbent only.
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