Problems with different brands of Acetonitrile

[chemist91]

Hi all,

Since this acetonitrile shortage we are running our samples (API and Impurities) with different brands of Acetonitrile. However, we cannot get good results when we use another brands other than JT.

We are reading at 217 and we are using gradient.

I will like to know if someone else is having the same problem or any idea why? We had been trying, Acros, Fluka, B&R...etc....all of them had so many bumps on the MP B (78%acn) that we cannot integrate the impurities.

Any ideas? suggestions?

Thanks so much!

[TimB]

I know it seems stupid, but make sure the ACN is HPLC grade. If it's not then I could see that having an effect on your mobile phase and separations.

[chemist91]

no...it is not an stupid question....but unfortunately they are HPLC grade so that shouldn't be the problem.

We run a UV/Vis we all have different absorvances at 217...Any other ideas../

Thanks

[sball]

Chemist91,

We use the Far UV grade of Acetonitrile from Fisher Scientific (p/n A/0627/17), which works really well for the work I do. It is a HPLC gradient grade solvent, so seems to work better than their standard HPLC grade. I quite often run my UV detectors at 210-220nm, and get very little baseline drift/noise even during gradient elution.

Unfortunaly, due to current global shortage, you might struggle to get hold of any as I think this might be one of Fisher's rarest grades of acetonitrile. Might be worth asking though....

[Assembler]

We are using EMD Chemical's HPLC grade ACN from VWR with no problems. We do use it in almost all our mobile phases we detect from 210nm-280nm.

[chemist91]

I guess my question is if someone else is having trouble when using a different brand of ACN.

For example with the original brand (JT Baker) we have a smooth gradient; with the other brands is so bumpy that we cannot even integrate the impurities.

Any ideas.

Thanks

[Bruce Hamilton]

Within each brand there are often several different grades. I would start with the Low UV Gradient HPLC grades and/or the LC_MS grades.
Yes they can be a little more expensive than normal Low UV grades - but sometimes are cheaper - depending on bulk-purchasing by the local retailer.

It's possible that some cheaper middle-of-the-road grades don't come with "no extra charge" peaks when you test them, but can you be sure they won't in the next batch, that's why product specification is important.

Given the recent issues with availability, I suspect almost every supplier is clearing their warehouses of any historical stock, and also perhaps some brands are purchasing from new suppliers. The gradient gradient grades should be tested by the manufacturer for unwanted peaks during gradients.

My personal stance on HPLC solvent suppliers is to find one or two whose products cost-effectively meet my needs ( usually gradient grade, where available ) and develop a good purchasing relationship with them. You many pay a little more initially, but discounts often accrue with time, greatly reducing the margin.

Also, alway remember that the water quality is critical for aqueous gradients, and ensure the unwanted peaks do originate from the solvent.

Please keep having fun,

Bruce Hamilton

[DR]

If you're certain that the issue is the ACN, use a UV to cherry pick your bottles for low wavelength methods. Scan a sample from ea. incoming lot (or bottle) from ~250nm down to 190nm. The ones w/ the lowest cutoffs get reserved for low wavelength methods. Leave the higher cutoff ones for the people running at >280nm (and/or isocratically).

[tmatthew01]

Are you also using Tetrahydrofuran in your mobile phase? What else are you adding to the mobile phase, besides ACN and water? I have seen emulsions develop between the THF and mobile phases containing higher (>50%) aqueous concentrations. The solutions appear cloudy when all ingredients are mixed, and the emulsion adversely affects the baseline.

[chemist91]

Sorry took me so long to get back

We check the ACN with the UV and the ACROS is the only one that has a positive absorsion at 217nm. Unfortunatelly this is the only one that we were able to find.

We do use TFA but we never had problems with that and it is not affecting the other brands of ACN...we can run the same mobile phase (that has TFA) with another brand with no problems.

[HW Mueller]

tmatthew01, you used a "cloudy" mobile phase and only got some adverse effects of the baseline?

[justo]

tmatthew01 I strongly recomend you not to use cludy mobile phase you may have bigger problems than a baseline problem

[DR]

Sorry took me so long to get back

We check the ACN with the UV and the ACROS is the only one that has a positive absorsion at 217nm. Unfortunatelly this is the only one that we were able to find.

We do use TFA but we never had problems with that and it is not affecting the other brands of ACN...we can run the same mobile phase (that has TFA) with another brand with no problems.

If there's a UV cutoff listed on the bottle (and it's <220nm), you're probably entitled to replacement given your UV result. I'd pursue it as ACROS is seldom the least expensive option for many chemicals...

[chemist91]

We run a sample on the UV and we got at 217nm = +0.0076, however it differ from other brands in the fact that all other brands read a negative number at 217 nm (-0.017,-0.016, -0.0096). That is the only difference so far.

So we cannot really ask for replacement since the COA said that at 220 is <=0.02 and it was 0.02

This is as expensive as the others, however at taht time the others were sold out.

Thanks,

Maria

[HW Mueller]

If you got negative absorbances for some samples you must have used the wrong reference. Maybe if you do it right your absorbance will be above the specification? Anyway, in my experience the manufacturers have been very reluctant to exchange their bad stuff, one just became completely silent when I proved that 3 out of 4 bottles were strongly fluorescing.