Shoulder/ broad peak shape after subsequent runs

Shoulder or broad peaks can come from a variety of issues.

• Check the split flow, it should not be zero.
• Have you checked for leaks?
• Is the goldseal ok and undamaged?
• Is the liner's O-ring ok and not squeezed
• Did you also change the septum? Is it too tight?
• Is the height of the column in the liner/injector ok? Maybe it moved. If it's too high, you will get broad tailing peaks
• Does the liner volume fit the injection volume?
• How does a methane injection look like?

Those are the starting points. 

Regards,

Norbert

Split flow is fine. No leaks. O ring not squeezed in and septum is just finger-tightened. Gold seal not checked as it is not part of our routine maintenance. But whenever a new liner is replaced, there will be no problem on the first few runs until it becomes broad again.

That would point to active parts in the flow path. Which liner do you use?

Are you able to post the temp program/method and the sample components?

Liner used is 23305 - Split Precision Liner w/Wool from restek.

Temp program as follows:

40degC for 6mins,

260degC for 0.5mins (50degC/min)

Sample component is just water.

Below is the example of the peak broadening after subsequent runs, the blue peak represent peak right after liner replacement and and the green peak is after subsequent run.

The injection temp, injection volume, head pressure and split ratio would be interesting as water injections are tricky, esp. with glass wool (and also the ID of the liner). Water can activate glass wool and then subsequently hold analytes (ACN in this case) and maybe release it slowly.

Injection temp: 220, Injection Vol: 0.5uL, Pressure:20psi, Split Ratio: 10:1, Liner ID: 23305 (Restek), AG2-0A03-25 (Phenomenex).

As per image, 1st picture is after subsequent runs, while the bottom photo is run right after liner change.

First of all, the injection temp for an aqueous injection is far too low. The evaporation water will coll down the liner severely and then maybe you'll get some water condensation in the liner. This condensation would activate the liner and could lead to tailing peaks. It could also activate the start of the column more by additional phase degradation by the more water condensate than necessary. Increase T_inj to 270-300 °C.

Use an extra deactivated liner like our UltraInert liners for better performance.

Thank you for the suggestion but with our injection volume of 0.5uL, will increasing the injection temperature affect the vapor volume of the liner which might then affect repeatability of the injection? As previously we had problems with repeatability and the engineer pointed out that our vapor volume exceeds the liner capacity.

Hi,

Based on the inlet parameters you listed, our Vapor Volume calculator shows that you are at roughly half of the liner volume.

Increasing the temperature up to 300C would still keep the vapor volume below 600 uL, which is well below what Restek states for that particular liner

(Please ignore the liner that I selected in this tool. It is the closest we have to the volume and dimensions of the Restek liner that you're using.)

Thanks.

Hi,

Based on the inlet parameters you listed, our Vapor Volume calculator shows that you are at roughly half of the liner volume.

Increasing the temperature up to 300C would still keep the vapor volume below 600 uL, which is well below what Restek states for that particular liner

(Please ignore the liner that I selected in this tool. It is the closest we have to the volume and dimensions of the Restek liner that you're using.)

Thanks.