VOC 524.2: My calibration curves fail too soon...

[Chroman]

I dont have that option.

Latest news:

Replaced transfer line, increased injection port temperature to 180 oC, reduced desorb time from 1.2 to 0.8 minutes, split ratio 40 and... no tailing anymore!!! But obviously my responses are kind of low now...

[Bigbear]

Great. Don't obsess about responses. When I solved this problem my fluorobenzene response was about 300000. It had been closer to a million!
What we care about is consistency.

[Omaejel]

So are you still running with the 6min dry purge?

We have decreasing IS over time and are cleaning the sources more often than I feel we should be. I have had suspicions that it is the water causing the problems with the dropping IS's but I have been dense and haven't thought about raising the dry purge (duh!) . Any more information you could provide would be helpful. We are using an Agilent 6890/5975 setup with an Encon as our concentrator.

We are already running 50:1 split.

[Bigbear]

Yes. My P&t conditions are:
Vocarb 3000 trap
11 min purge of 25 mls @ 40 cc/min , ambient temp (~ 20C)
6 min DP @ 40 cc/min
pre heat @ 245C
desorb for 3 min @ 250C
Bake for 6 min @ 260 C and 250 cc/min ( Supelco claims this is the maximum flow for these traps)
transfer line and valve temp 150C

I use a 6890/5973 as well
inlet @ 150C
I use the single gooseneck liner and the gold seal with an X ( for high split applications). I split 75:1.
I use an 20M X 0.18 column (inserted 5mm above the ferrule). Column flow is 0.6 cc/min.
A trick to rid water from the transfer line and inlet ( from an Agilent rep) Set the inlet gas saver option to come on half way through the desorb step ( in my case 1.5 min). Set the flow rate to 100-150 cc/min ( I use 150). This will crank the flow thru the transfer line and out the split vent to help with the water buildup. The inlet flows will go back to the set parameters @ GC ready. I added more time by holding my oven at max T for about 10 min. I set this by seeing how long my purge cycle takes when running a sequence. I got it so my GC is ready when the P&T is about half done it's dry purge.

Another trick from Agilent is to use the 6mm draw out plate in your source.

My MS does not like the BFB "canned" Agilent tune. I use a ramped emission manual tune that works well. If you want to try it it would be best to call the 800 number for help. In my case the Agilent rep set up a webx session and walked me through the process.

Good luck.

[Omaejel]

Thank-you.

I will try that as soon as we get a low sample volume for our drinking water samples. I appreciate the help.

[coombs_ryan]

Switching from 25mL to 5mL sparger will also help with your water management. I also agree with Big Bear that holding at the high temperature at the end of the run for at least 5 minutes too.

[Chroman]

Update:

I replaced Vocarb 3000 with trap #9 and results are spectacular: no tailing at all, better resolution, long lasting calibration curves.

Bottomline: wrong trap

[Bigbear]

Congratulations. I wish you the best of luck with that trap. I tried it but found it wasn't up to the task. We went back to the Vocarb 3000 .