low response for VOC - MIBK and MBK by P&T

[milenuj]

Hi all,
I need help to fix this issue. i have problem with MIBK and MBK, the peaks for these ketones just disappeared and response was very low. any idea what may indicate this problem? Could it be the trap or just the transfer line?

thanks

[rb6banjo]

Do you see anything else that is similar in molecular weight? Can you also tell us something about the nature of your sample and how your P&T conditions/sequence of events?

[James_Ball]

Check your purge flow first. If the purge flow is lower you can lose ketones and acetone. Also I have seen loss of these compounds as the column ages while other functional groups remain at the same responses.

[Steve Reimer]

Also ketones will hang out wherever water collects. Cold spots, water management heater not working, tranfser lines, trap not heating completely.

[milenuj]

Thanks for the replies.
I was just running a fresh voc calibration standards and found loss of MIBK and MBK but all other voc Analytes were good with perfect linearity. Purge flow is not low and It has remain like this since I started. So I started to suspect it may associated with the column, will trim it and see how it goes.

I sometimes have problem with only acetone. Just could not achieve linearity curve and responses were consistently high in the full calibration run. Any idea about this?

[James_Ball]

Thanks for the replies.
I was just running a fresh voc calibration standards and found loss of MIBK and MBK but all other voc Analytes were good with perfect linearity. Purge flow is not low and It has remain like this since I started. So I started to suspect it may associated with the column, will trim it and see how it goes.

I sometimes have problem with only acetone. Just could not achieve linearity curve and responses were consistently high in the full calibration run. Any idea about this?

What trap are you using? Flow and purge times?

Sometimes increasing purge flow a few ml/min will increase responses for Acetone. Our worse problem for Acetone is that we get small amounts into the water from lab air, this causes the low standards to be higher than they should and makes the calibrations quadratic. If not the low standards or blanks can have a negative concentration when using linear calibration fits.

What column do you use and how old is it?

[Bigbear]

What temp. is the sparge vessel? For water soluble cpd's you may need to up the temp. This can be cause problems with more water going to the trap.

[milenuj]

Hi

We are using vocarb3000 for stratum PTC (purge time: 6 min, flow: 80ml/min, purge temp: 20C)
and J&W DB-VRX 30mx0.25mm column.

Column was 1 month old. Now MIBK and MBK are better after i trimmed the column except i can only see it on higher conc.

Acetone has always been one of the biggest problem in our lab, either losing it completely or higher than they should as coming from lab air.

[James_Ball]

Hi

We are using vocarb3000 for stratum PTC (purge time: 6 min, flow: 80ml/min, purge temp: 20C)
and J&W DB-VRX 30mx0.25mm column.

Column was 1 month old. Now MIBK and MBK are better after i trimmed the column except i can only see it on higher conc.

Acetone has always been one of the biggest problem in our lab, either losing it completely or higher than they should as coming from lab air.

Does that column have a 1.4um film thickness?

For volatiles I normally use the Restek Rtx-502.2 or Rtx-VMS in the 40m X 0.18mm with 1.0um film. If using the 0.25mm ID they are at 1.4um film.

With volatiles it is normally the entire column that becomes the problem not just the first few centimeters since you are injecting a gas into it and not loading up the inlet and head of the column with injected junk like when doing solvent injections.

[milenuj]

Yes it is 1.4um film thickness. May I know what if we run high surfactants sample and it went all the way to the transfer line? Thanks

[James_Ball]

Yes it is 1.4um film thickness. May I know what if we run high surfactants sample and it went all the way to the transfer line? Thanks

If you have a foaming sample and it pushes over to the trap and desorbs to the column then that will definitely cause problems with the ketones. You will probably want to change the transfer line too.