Chromatography Forum

Using Archon autosampler, p&t OI 4560,GC 5980 series II and MSD 5972 having issues with erratic BFB recoveries. Clean matrix recovery ok , however introduce high concentration sample or 200 ppb level cal std and BFB recovers high . MSD source was clean recently.

Larger amounts of Methanol from standards can cause sensitivity changes such as this though I have normally saw it happen with lighter early eluting analytes more. I used to have the same problem with 1,2-Dichloroethane-d4 surrogate.

Are you using a dry purge in the cycle?

What is desorb time and flow rate?

Are you using the regular K&M electron multiplier?

When was the last time you changed the fluid in the diffusion pump?

Do you have a molecular sieve moisture trap at the rough pump?

A few things I am thinking of that all have an effect on volatiles as I have seen in the past.

no dry purge (using #10 trap)

desorb time 1.0 min @10 mL/minute

yes K&M electron multiper

pump fluid replace when the source was clean

yes to moisture trap

The Tenax, Silica Gel, Charcoal #10 trap tends to hold a lot of water which gets desorbed onto the MS, the water loading of the source on the 5972 can cause some problems like this.

We moved away from this trap many years ago and went to the VoCarb3000 which can use the dry purge to remove some of the water, it does help some.

Is this going through a split injection port? If so you may want to increase the desorb flow/split ratio to also introduce less water and methanol into the system. The higher flow rate will also help pull things off the trap better.

The one thing we did to improve stability for instruments like this was switch to the ETP ribbon style Electron Multiplier, they seem to be less prone to having sensitivity changes as you load the instrument up with organics. One thing that I used to notice the the K&M was when you get hit with something such as gasoline at high levels in a sample was that the sensitivity would increase for several injections afterwards before returning to normal, similar problems with high level standards.

thanks for assistance, the problem was a bad lot of refurbished filaments. Replace with agilent filaments and problem corrected.