Ethylene glycol RT shift issue

Hi Wendy,

This is my first ever post here, but I have done a fair amount of work with loop & syringe injection of polar compounds by HS.

I am assuming that the vial is empty and your CTC heats the vial to ~50C and equilibrates for a few minutes?

If we assume that all of your Calibrators go into the vapour phase, the conditions in your column will vary depending on the amount of water you are adding. As you are starting at 35C water will tend to condense in the column with your ethylene glycol (EG).

Assuming that all of the Calibrators are in the vapour phase, then for: Calibrator1 your column will see (very roughly) 5ng of EG and 2000ng of water.

Calibrator4 would be 30ng EG and 12000ng of water, and Calibrator5 would be ~60ng EG and 25000ng of water.

As you say on a >0.25µ polar phase those amounts of EG should not overload the column, but I would expect that the extra amount of very polar water condensing in the (polar?) column would give the sort of increases in RT that you have seen. If you have a low polarity column it will overload, but I would expect the peak to "front" rather than the tailing you describe. Your water may also tend to act as a mobile phase while it evaporates. On a polar column it could take a while before it all goes into the gaseous phase, as it will tend to stay dissolved in the stationary phase.

The solution could be to inject the same amount of water for each level of Calibrator: Calibrator1 = 0.8 +9.2µLH20; Calibrator3 = 2.5 +7.5µLH20; etc.

Alternatively, you could try to avoid condensing the water in the column by having the initial oven hold at 110C, but you may need a pre-column/guard column; otherwise you could damage the analytical column. The Agilent Polyethylene Glycol Deactivated Polar type should be OK, but if you are going to do a lot of samples it might be worthwhile looking at a speciality pre-column (Look for hydroguard water resistant types).

Regards,

Tim

Hi Wendy,

This is my first ever post here, but I have done a fair amount of work with loop & syringe injection of polar compounds by HS.

I am assuming that the vial is empty and your CTC heats the vial to ~50C and equilibrates for a few minutes?

If we assume that all of your Calibrators go into the vapour phase, the conditions in your column will vary depending on the amount of water you are adding. As you are starting at 35C water will tend to condense in the column with your ethylene glycol (EG).

Assuming that all of the Calibrators are in the vapour phase, then for: Calibrator1 your column will see (very roughly) 5ng of EG and 2000ng of water.

Calibrator4 would be 30ng EG and 12000ng of water, and Calibrator5 would be ~60ng EG and 25000ng of water.

As you say on a >0.25µ polar phase those amounts of EG should not overload the column, but I would expect that the extra amount of very polar water condensing in the (polar?) column would give the sort of increases in RT that you have seen. If you have a low polarity column it will overload, but I would expect the peak to "front" rather than the tailing you describe. Your water may also tend to act as a mobile phase while it evaporates. On a polar column it could take a while before it all goes into the gaseous phase, as it will tend to stay dissolved in the stationary phase.

The solution could be to inject the same amount of water for each level of Calibrator: Calibrator1 = 0.8 +9.2µLH20; Calibrator3 = 2.5 +7.5µLH20; etc.

Alternatively, you could try to avoid condensing the water in the column by having the initial oven hold at 110C, but you may need a pre-column/guard column; otherwise you could damage the analytical column. The Agilent Polyethylene Glycol Deactivated Polar type should be OK, but if you are going to do a lot of samples it might be worthwhile looking at a speciality pre-column (Look for hydroguard water resistant types).

Regards,

Tim