Chromatography Forum

I recently started using a Tekmar Atomx for my VOC analysis. Initial tests showed a clean baseline; however, after doing a test calibration, there appears to be substantial carryover and dirty baseline that is continuing to appear after several blank samples have been run. I have tried altering some of the Purge and Trap parameters beyond the recommended settings, but high point tests with subsequent blanks appear to have no change. I am currently using a 25mL fritted sparger with a 10mL sample volume. The High point being used is 80ug/L for most of the EPA 8260 analytes and 2000 ug/L for Ketones. The analytes with the most substantial carryover are the last few including Naphthalene. Any help would be appreciated. Thank you!

We have been running method 8260 with the Atomx, and have had very few carry over issues.
We use the 5ml sparger, and calibrate to 200 ug/L.

Could you provide more info as to your acquisition parameters, trap, etc..

It would also help if you could describe your GC/MS configuration.

I'm running an Agilent 5977 MS with a 7890B GC. The Trap is a Tekmar Vocarb 3000. Here are the purge and trap parameters:

Purge:
Valve Oven Temp: 160 C
Transfer Line Temp: 160 C
Sample Mount Temp: 90 C
Water Heater Temp: 90 C
Sample Vial Temp:20 C
Sample Equilibrate Time: 0.00min
Soil Valve Temp: 110 C
Standby Flow: 10mL/min
Purge Ready Temp: 40 C
Condensate Ready Temp: 45 C
Presweep Time: 0.25min
Prime Sample Fill Volume: 3mL
Sample Volume: 10 mL
Sweep Sample Time: 0.25min
Sweep Sample Flow: 100mL/min
Sparge Vessel Heater: On
Sparge Vessel Temp: 50C
Prepurge Time: 0.00 min
Prepurge Flow: 0mL/min
Purge Time: 11 min
Purge Flow: 40mL/min
Purge Temp: 20 C
Condensate Purge Temp: 20 C
Dry Purge Time: 1 min
Dry Purge Flow: 100 mL/min
Dry Purge Temp: 20C

Desorb:
Methanol Needle Rinse:Off
Methanol Needle Rinse Volume: 3mL
Water Needle Rinse Volume: 12mL
Sweep Needle Time: 0.50 min
Desorb Preheat Temp: 245 C
GC Start Signal: Start of Desorb
Desorb Time: 0.50 min
Drain Flow: 100mL/min
Desorb Temp: 250 C

Bake:
Methanol Glass Rinse: Off
Number of Methanol Glass Rinses: 1
Methanol Glass Rinse Volume: 3mL
Number of Water Bake Rinses: 3
Water Bake Rinse Volume: 12 mL
Bake Rinse Sweep Time: 0.25 min
Bake Rinse Sweep Flow: 100mL/min
Bake Rinse Drain Time: 0.4 min
Bake Time: 8 min
Bake Flow: 200mL/min
Bake Temp: 260 C
Condensate Bake Temp: 200 C

Cryo is not used.
Thank you for taking the time to look at these settings:

Here are the parameters that we use on our Atomx

Purge:
Valve Oven Temp: 125 C
Transfer Line Temp: 125 C
Sample Mount Temp: 40 C
Water Heater Temp: 80 C
Sample Vial Temp:20 C
Sample Equilibrate Time: 0.00min
Soil Valve Temp: 110 C
Standby Flow: 10mL/min
Purge Ready Temp: 45 C
Condensate Ready Temp: 40 C
Presweep Time: 0.25min
Prime Sample Fill Volume: 3mL
Sample Volume: 5 mL
Sweep Sample Time: 0.25min
Sweep Sample Flow: 100mL/min
Sparge Vessel Heater: Off
Sparge Vessel Temp: 20 C
Prepurge Time: 0.00 min
Prepurge Flow: 0mL/min
Purge Time: 11 min
Purge Flow: 40mL/min
Purge Temp: 20 C
Condensate Purge Temp: 20 C
Dry Purge Time: 2 min
Dry Purge Flow: 100 mL/min
Dry Purge Temp: 20C

Desorb:
Methanol Needle Rinse:Off
Methanol Needle Rinse Volume: 3mL
Water Needle Rinse Volume: 7 mL
Sweep Needle Time: 0.25 min
Desorb Preheat Temp: 245 C
GC Start Signal: Start of Desorb
Desorb Time: 0.50 min
Drain Flow: 100mL/min
Desorb Temp: 250 C

Bake:
Methanol Glass Rinse: Off
Number of Methanol Glass Rinses: 1
Methanol Glass Rinse Volume: 3mL
Number of Water Bake Rinses: 3
Water Bake Rinse Volume: 7 mL
Bake Rinse Sweep Time: .40 min
Bake Rinse Sweep Flow: 100mL/min
Bake Rinse Drain Time: 0.60 min
Bake Time: 6 min
Bake Flow: 250 mL/min
Bake Temp: 280 C
Condensate Bake Temp: 200 C

These are parameters that we implemented with Agilent's VOC kit.
Water management issues prior to the changes were a real headache.
The Atomx is coupled to a 5975C with a 7890A oven with a DB624 UI column, and ultra inert 1 mm liner.
We also had to make changes to our MS acquisition parameters.

Give it a try and let me know how it works out.

Forgot to mention that we use a 5 ml sparger.

So the sample volumes and rinse rinse volumes will be slightly different.

Looking through those settings I don't see any setting for sparge tube temperature during bake. It looks like you were using 50C during purge but nothing at bake.

On my Centurion/Encon Evolution setup have my sparge tube at 40C during purge and 80C during bake, which seems to help carryover. Also we use 5ml purge volume and the 5ml sparge tubes which you can rinse at about 8-9ml volume to help get the spatter off the sides.

Doubling the volume purged does not double the sensitivity of the analysis because as you increase purge volume the purge efficiency drops. The larger the volume of the sparger the larger the surface area for analytes to adhere to, which also causes problems. Larger tubes are better if you have samples that foam, but it is a balancing act between protecting from foaming and purge efficiency/carryover problems.

Oh, forgot to mention, the carryover of those last few compounds in the run: Naphthalene, Trichlorobenzenes and such, has always been a problem in purge and trap analysis. If you get it below 1% you are doing good, less than that you are doing great.

Check the transfer line from the purge and trap. Often the fittings from the transfer line to the inlet are exposed and can trap or condense some of the higher boiling analytes. If you have an unused sparger heating jacket you can wrap it around the the exposed nut and line. If not, glass wool and foil will help insulate the exposed bits. Without insulating the exposed section of transfer line, we tend to see 1-2% carryover, with it, it drops to negligible.

If you still see carryover after trying that, then try heating your sparger.