styrene double peaks

[amy-e]

Styrene keeps giving me two peaks. I am running a 1/20 styrene dilution in acetonitrile on a stabilwax-DA column. At first, I thought that my styrene bottle was old, so I opened a new bottle of greater than 99% pure styrene, limiting my air exposure and reblanketing it with nitrogen. I received the same results. The first peak is always 3-fold smaller than the second. I am running a single temp., splitless program. I have set my injector to either 70 or 175 C. My column is running at 40 C with a 200 C detector. Any ideas on why I am getting these two peaks, and what I could do to fix the problem?

Thanks,

Amy

[AICMM]

amy-e,

Try running split at 20:1 or so. You should have plenty of material on column and you won't be overloading the column.

Best regards.

[Peter Apps]

Hi Amy

It is just possible that the other peak is an impurity in the acetonitrile - but it would have to be at unexpectedly high levels - about 8% (1/3 of 20%). Can you try another batch of acetonitrile ?.

What is the aim of the analysis - what information do you need to get out of it ? That has to influence how you fix the problem.

Peter

[chromatographer1]

Are you running hydrogen carrier?

As Peter began, if you are injecting too high an amount in your syringe you may be flashing the plug into two parts and thus getting two peaks of styrene. This appears to be your problem.

Catalytic conversion of the stryrene is much less likely and should be somewhat variable and usually only happens in trace amounts, not the 25% level you see.

best wishes,

Rod

[chromatographer1]

Sorry, that was Michael that suggested the sample size was the issue. Sorry AICMM. I should have my coffee before I post in the morning.

If you inject using direct injection and not splitless your split peak will become a single peak, but that will require a different injection port configuration.

So split your sample at a reasonable ratio and all should be fine.

best wishes,

Rod

[amy-e]

This is what I have ruled out, thus far. It's not a contaminant in the acetonitrile. Smaller, injected amounts of styrene/acetonitrile does not change the fact that two peaks are still present. Even at 0.1uL, I can still see two peaks (however, the peaks are very small). I talked to Restek, and they have had problems, in the past, with acetonitrile causing strange peak distortion. I am going to try a different solvent with and without the split today.

Thanks for your suggestions thus far,

Amy

[AICMM]

Amy,

What column are you using? At 1:20 and 0.1 uL you are still putting about 4 ug of styrene on column which is a lot.

Also, what is the separation between acetonitrile and stryene?

Best regards.

[chromatographer1]

What detector are you using, Amy?

Are you using a split/splitless injector?

Others have mentioned splitting but you have not stated that you ARE splitting the injection or the ratio you have chosen.

Do not try to do direct injections with a split/splitless injector.

best wishes,

Rod

[Peter Apps]

Hi Amy

If you inject 0.1 ul splitless you should still have enough (20 ug) styrene to give you a HUGE peak. That the peaks are very small suggests a problem with the set up, most likely a very large leak somewhere, or the column end way out of position in either inlet or detector.

Peter