Loss of surrogate (bromofluorobenzene) in Sequence- GCMS

Discussions about GC and other "gas phase" separation techniques.

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We have an ATOMX purge and trap connected to 6890 GC and 5973 MSD. We use the instrument to test VOC analysis on our effluent. Over time, we have seen our internal standard and surrogates drop off- mainly bromofluorobenzene. Now we are at a point where it will drop off within a sequence run. Bromofluorobenzene will starts with a response of 1946691 and by the 8th sample have a response of ~90,000. We have tried changing the analytical trap (vocarb 3000) and condenser trap. We have cleaned the mount and flushed the whole purge trap system with methanol as per Tekmar. We have changed the IS valve in the ATOMX.

We have spiked the IS right into water and bypassed the IS valves and still see the same drop. In soil mode, the IS's seem to be holding better. We have tried baking the MSD and direct injecting the IS into the GC and numbers still drop as you go.

The Atomx purge and trap is connected to the GC via transfer line.

Here is some of our instrument info:

5973 MSD Hewlett Packard
6890 Agilent GC
Column: 1st column was DB-624 Agilent 60m x 250um x 1.40um
Pressure: 16.1, Flow: 1, Carrier gas: Helium, Constant flow

Inlet: Split
Temperature: 250, Pressure: 16.1, Split ratio 40:1, Split flow: 39.7, Total flow: 43.2, Gas saver off

Oven:
Initial 35 for 5 mins
Ramp 1: 104
Ramp 2: 142
Ramp 3: 230
for total of 30 mins

Internal standards used in Atomx: d4-dichloroethane, tolene-d8, and bromoflurobenzene.

Any help is appreciated. I am going to start by replacing the drawout plate and filaments in the MSD.
I feel your issue is with water. this has been discussed here multiple times in the past so do a search and you should find lots of info.
Why do you need such a long column?
When I was using 0.25 columns I was using 60m also, just for added separation of some of the difficult pairs, and to keep the inlet pressure higher. I switched to an 0.18mm x 20m column and get much better results.

One trick you can try if it is moisture is after the desorb time, turn on the Gas Saver but set the split flow higher. You will use more helium but it can help dry out the transfer line between samples. Also if you can find one, put a trap just before the vacuum pump that contains molecular sieve to keep moisture out of the rough pump, change it every time you change the oil.

When you do the direct injection test, are you injecting into the GC port or a port on the purge and trap?

Have you taken the quads and source to max temperature overnight to bake out the analyzer? Sometimes that can remove any high boiling components that may have accumulated there and can cause similar problems. Also do a tune evaluation on the BFB in the first injection that is at full counts and on the last injection that is at lower counts and see if the mass ratio is changing during the run, that can be a sign of problems with the mass filter on the side board.
The past is there to guide us into the future, not to dwell in.
Like James, I'm using an 18um x 20m DB-VRX or DB-624. I have an Archon in soil mode, Tekmar 3000 with Vocarb 3000 trap with water management loop at 40C. I use a 1 minute dry purge (which should not affect water) and a 1 minute desorb at 250C. I run my 5973inert/6890 inlet cooler... 200C and start at 40C hold for 2 minutes before ramping T. Of course with that wider bore column you need to start out cooler.

I'm using Agilent CrossLab Ultra Inert Inlet Liners #8004-0157. These have a 1.2mm bore and give lower carryover and better sweep out. I'd try these liners. It might help with the water problem.

Also, have you considered the inlet split vent traps? If they are clogged, that might force more water onto your column. I'm using the Restek Optional Split Vent Trap Assembly Cat#23031. It has the larger diameter cartridges.
LALman wrote:
Like James, I'm using an 18um x 20m DB-VRX or DB-624. I have an Archon in soil mode, Tekmar 3000 with Vocarb 3000 trap with water management loop at 40C. I use a 1 minute dry purge (which should not affect water) and a 1 minute desorb at 250C. I run my 5973inert/6890 inlet cooler... 200C and start at 40C hold for 2 minutes before ramping T. Of course with that wider bore column you need to start out cooler.

I'm using Agilent CrossLab Ultra Inert Inlet Liners #8004-0157. These have a 1.2mm bore and give lower carryover and better sweep out. I'd try these liners. It might help with the water problem.

Also, have you considered the inlet split vent traps? If they are clogged, that might force more water onto your column. I'm using the Restek Optional Split Vent Trap Assembly Cat#23031. It has the larger diameter cartridges.


My overall setup is similar except Evolution P&T. I also use the narrow 0.75 inlet liners which are designed for SPME to reduce dead volume in the inlet and they work pretty well.
The past is there to guide us into the future, not to dwell in.
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