This publication uses a column 150 x 4.6 mm, the void volume of this column is 1.75 mL. At the flow rate of 1.2 mL/min, the non-retain peak should be out at 1.75/1.2 = 1.45 min. However, the glyphosate is eluted at 0.86 min. Something is missing here.
Chapter Residue Analysis of Glyphosate and Aminomethylphosphonic Aci...
Dear Narong
The void volume that one determines on an HPLC systems is not only dependent on the column but also the dead volume of the system. Your system most probably have a much smaller dead volume than the one used for the publication. You can check the true void volume of you column + system by injecting 10 uL of a 1% or 0.1% acetone (depending on the sensitivity of your detector. You can also run the system in your organic phase en inject pure water and this will give you and injection peak/trough that you can use to determined the void volume.
I would also like to suggest that you try to get better retention of you glyphosate on the column. You can consider using ion pairing agents in you solvent system that will help to retain the very polar glyphosate. Alternatively I would move to a more polar silica based solid phase.to retain the glyphosate.
Hope it helps.
Regards
Marina
Dear Narong,
we analyse glyphosate (ionic compound) after derivatisation with 9-methylfluorenylchloroformiate chloride (FMOCCl), which improves retention on RP-sorbent and improves selectivity and sensitivity on LC/MS/MS. If you want to analyse glyphosate without derivatisation try Hypercarb. Alternatives are ion chromatography or capillary electroforesis.
Regards
Martin
Martin is right. Glyphosate is difficult to analyse by RP-LC. FMOC is a common way to derivatize difficult compounds (quaternary ammonium herbicides for instance). I know some people use capillary electrophoresis, but if you want to stick with LC without derivatizing you need other mecanisms for retention. Some columns you could try are Diamond Hydride from Cogent or Obelisc R from SiELC. Or look for polymeric based column brands as Shodex.
This is MS/MS method, so cannot detect acetone like in the UV detector. HPLC system volume will add more to the column volume so the non-retained peak will be eluted much longer. The publication has RT of glyphosate of 0.8 min, the rt to move 1.75 mL (column void volume of 150 x 4.6) at 1.2 mL/min is 1.45 min. With the HPLC system volume add to it, it will be more. I e-mailed the author my questions and hopefully I got it later.
To Martin, FMOC is too complicated and will do only glyphosate. Here's what I have so far, injecting two group of the polar analytes uisng one column in pos and neg run isocratically. I plan to do shake, dilute, and shoot.
@victor thank for comment. I tried Obelisc R, Imtakt, and Thermo because I want to do more analytes using the same column e.g., Quats (paraquat, diquat, mepiquat, chlormequat), glyphosate, glufosinate, AMPA, ethyphon, forsetyl alumina, diaminozide, and maleic hydrazide. These are polar pesticide cannot be run by RP-HPLC and would need total extraction, (they would stay in water phase after QuEChERS extraction). see my chromatogram in the previous post.
We analyse quats by HILIC (Waters, Atlantis HILIC) with methanol/water(am. formate) LC/MS/MS. I have not tried glyphosate and AMPA by this method, because we need higher sensitivity for water and sediment analyses, that is why we derivatize with FMOCCl for glyphosate and AMPA analysis.
I have seen a nice presentation for your application by IC-MS/MS, but it was in Czech.
Please send it to me. Microsoft word can translate to Czeck, Thanks,
Dear Narong,
Could you get the explanation of this situation? Did you get a response from the author or any other source?
Best regards,
Gizem
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