" However, during sample analysis, the current decreases rapidly, although the current is still stable and there are no present of spikes " Please edit because the statement is self-contradictory. It would also be nice to see a real electropherogram showing this effect.

Good day Mr. Wahab, I meant that the current is clean of spikes but rapidly decreases and is almost zero throughout the analysis. Here is an image of the current signal.

Hope you resolved the issue, but if otherwise, I would suggest running several blanks and monitoring current. If current drops with blank injection (carrier liquid for your sample), it is the equipment issue. If no current drop, your sample contains interference compounds or have ionic strength greater than your buffer. Depending on the sample nature, solutions may include sample clean-up, capillary coating, or buffer modification.

Vanessa Ancla Alag , I think your capillary is being clogged or your sample is contaminating the electrodes. You got a very good suggestion above. Check the blank and see what happens with respect to time.

Thank you so much for the suggestion and help Ms. Elena V Romanova and Mr. M. Farooq Wahab . Will do so, thank you again!

Hello Vanessa, if your problems still persist, I would focus on the compatibility of the sample with BGE as Dr. Romancova suggested. In such case, what are your BGE and sample composed of?

Hello Mr. Jan Schejbal , my sample consists of benzophenone-3 whereas my BGE consists of sodium tetraborate-sodium hydroxide buffer and SDS surfactant.

Hi Vanessa Ancla Alag , I understand that you are still facing the problem, correct? The important part of your sample would be the solvent you use to dissolve your analyte, what is it? Also what are the concentrations of Borax and SDS in your BGE?

Yes Mr. Jan Schejbal , even in the analysis of the standard. I used a little amount of filtered HPLC grade methanol to dissolve the standard and filtered 50%(w/w) methanol to dilute. As for the BGE, I prepared 200mM SDS and 200 mM Borax to produce 150mM SDS and 50mM Borax as final concnetrations in a 1.5 mL amber vial

Hi Vanessa Ancla Alag, all the parameters seems reasonable. The last point that may cause problems is sample injection (sample overloading). What are your capillary (id, lengths) and injection parameters (pressure, time)?

Hello Mr. Jan Schejbal, my capillary is 50 micrometer id, 75 cm length and the injection time is 15s for 50 mbar.

Hi Vanessa Ancla Alag , everything seems within normal, so I have no clear answer yet. My best bet would be still the sample plug. I would try to decrease the sample volume (inject 10s at 50mbar and then further decrease to 10s at 25 mbar) and search for any changes in electric current behavior. Also for such simple sample (1 analyte in 50% MeOH - if I understand correctly) this is quite high performance capillary. I would try shorter capillary with larger id, e.g. 75 micrometer i.d. at 40 cm effective length (if I remember coreclty that's 48.5 cm total length for Agilent system). Long capillaries with small i.d. may be more prone to cause issues. If you choose to try the more open and shorter capillary remember to adjust your sample injection (there will be lower backpressure, thus overloading may occur). You can use this site to estimate sample volume: https://sciex.com/ce-features-and-benefits/ce-expert-lite

Good luck

Hello Mr. Jan Schejbal , thank you for the recommendations. I sincerely appreciate your guidance and effort to help. Thank you so much!

Best regards,

VAA