dmso intefering with active peak

[sluggo]

Hello,

I have a drug formulation that includes our active along with dmso and some other ingredients. I am having problems with a large dmso peak at the same retention time as the active. The mobile phase is acn:water, and I've tried various ratios for isocratic and gradient runs. As well, I've tried using a C18 column along with a PFP column (the PFP column being suitable for the active). I'm using methanol as a dilutant for our sample.

Are there any techniques that will help minimize the effect of dmso on chromatograms? The only suggestion I've gotten so far is to try and use SPE to remove the dmso prior to running my method.

Any thoughts or suggestions would be appreciated

thanks

[MG]

My only experience with DMSO was running a long slow gradient on a C18, and a sample contained 10% DMSO (v/v). My detector was APCI+ MS, and the DMSO actually ionized so I could see it quite well. My gradient started at 5% methanol, and the DMSO eluted near the void volume. So to me it sounds like you need more retention for your compound, and my suggestion would be to reduce the organic component in your mobile phase, at least until the DMSO elutes, or maybe switch to a column that provides retention in highly aqueous mobile phases. For example, start with an isocratic hold at 5% organic until the DMSO is completely off the column, then run a gradient to elute your compound.

If the DMSO or methanol in your sample is causing the poor retention for your analyte (injection solvent mismatch), you could try instead using water as your sample diluent.

[sluggo]

Thanks for your reply.

I'm confused at what is going on with my experiments. I ran a 10% dmso solution in my c18 column. I used 20% acn for the mobile phase, and the dmso had a broad peak that starts around 12min and ends at 15min. The tech support from the column manufacturer thought the dmso should elute quickly on the c18 (although she didn't have any applications or experience with using dmso on a c18 column). I'm just not getting that. I'm using methanol as the dilutant.

regards

[Uwe Neue]

Please explain your results a bit better! If I understand you correctly, you get a broad peak eluting in the time frame of your analyte when you inject the analyte dissolved in DMSO. If this is correct, then the DMSO is causing band broadening, because it is a strong solvent for your mobile phase. Dilute the sample with water, and the problem should go away. If I did not guess your problem correctly, please correct me by giving more information.

[sluggo]

Yes, that is close.
I have drug dissolved in a solution that is about 10% dmso. The sample is further diluted with methanol for analysis. When injected into the hplc I get a peak from my analyte at around 6min. At about 7min there is a much larger, broader peak from the dmso. This peak interferes with the analyte. The part that confuses me is that a few people I've talked to say that when they run a simliar test with dmso, that the dmso elutes in under 2 min.

As a subsequent test, I ran dmso only, diluted in methanol. Using a c18 I had the same 7min retention time as above. This was also the case with a pfp column. I know that others are seeing dmso elute closer to 2min.

I've tried various isocratic and gradient runs, including your suggestion. Basically the dmso seems to have similar retention properties as my analyte. This is strange given that others can get the dmso to elute in 2min. 6 minutes is about the fastest I can get the dmso to elute on either column.

[Uwe Neue]

How about diluting the sample with water instead of with methanol?

[HW Mueller]

Could it be that your DMSO peak is dirt in your DMSO, or dirt dissolved by DMSO (in your syringe, pipet, injection mechanism....)?

[Supercritical]

Try substituting Methanol for the Acetonitrile in your mobile phase. You may observe a change in selectivity.

[sluggo]

Could it be that your DMSO peak is dirt in your DMSO, or dirt dissolved by DMSO (in your syringe, pipet, injection mechanism....)?

I used a plastic pipette for the dmso. I know that plastic shouldn't be used for dmso, but I didn't think much would happen in transfering a few drops. Perhaps the dmso is reacting with the plastic.

How about diluting the sample with water instead of with methanol?

I pretty sure that won't work for us because of our analyte.

Try substituting Methanol for the Acetonitrile in your mobile phase. You may observe a change in selectivity.

That may work.

thanks

[Uwe Neue]

It could be that the DMSO is dirty. It could also be that a slug of DMSO dissolves some residual or precipitated analyte (the active) from your instrument (especially injector). I bet that the "DMSO peak" is a peak distortion by DMSO of your active.

Add at least some water to your sample, and the problem will improve. I know that sometimes one thinks that sample solubility prevents one from using water, but in most cases, some addition of water creates few problems, and in situations like yours, might improve the situation.