524.2 P&T parameters for EST Evolution

Discussions about GC-MS, LC-MS, LC-FTIR, and other "coupled" analytical techniques.

6 posts Page 1 of 1
Hi,

Can anyone who runs 524.2 on an EST Evolution share your settings for the P&T? I currently run this method on a Tekmar 3000 with a Varian GCMS but am looking to get it going on our EST Evolution with Agilent 7890/5977B. I am having trouble with both surrogates dropping by half in clean samples and blanks but recovering fine in standards and fortified blanks.

I have tried desorb flow control to decrease the moisture getting to the detector and also methanol matching but nothing seems to be helping me.

Thanks in advance!
I just dealt with that issue using a Stratum. Cleaned or replaced the complete flow path in the Stratum to no avail. Also rinsed the transfer line and injection port.
What corrected the problem was a source cleaning!
We use the Evolution for 524 and have dealt with similar problems in the past, even with the first gen Encon and Tekmar 2000.

The cause is related to the total analyte concentration. The higher the total concentration the better the recovery especially with the later eluting compunds. I had a three or four page thread going on that here in the past. I did a study where I calculated the total mass of analytes and compared that to recoveries of the 1,4-Dichlorobenzene. As the total concentration increases the area of the internal standard also increases. One solution was to increase the concentration of the internal/surrogate spike. I currently use 25ppb in the sample for all the internal/surrogate compounds and it works well, if you increase to 50ppb or 75ppb it works even better.

With a calibration from 0.5ppb to 200ppb the 25ppb internal works well. I discovered the relationship when I was trying to do calibrations from 0.05ppb to 40ppb using 1ppb or 5ppb internal standard/surrogate concentrations, the effect was greatly exaggerated. I then tried the same calibration range but had the internal/surrogates at 50ppb and the areas over the curve had very low %Diff sometimes as low as 5% or less. If you add up the total analyte concentration plus internal standard/surrogate in each standard you get much less change in total concentration with the higher internal/surrogate and therefore have better results on the calibration and less change between a blank or clean sample and spiked calibration checks.

There was much speculation in that old thread about the possible causes for the effect. I did find I have better results if I only bake the MORT at 180C though. I wonder if possibly a higher bake temperature causes char formation, just a very thin film, on the MORT that adsorbs small amounts of analytes but becomes saturated with large amounts which allows more analyte to make it through to the trap in the more concentrated standards. MORT bake temperature and turning off the gas saver and allowing the full split flow during analysis are the only changes I have really made to the system, the latter to help flush out any moisture in the system between samples. So far I can go much longer before I see any problems with high %rec of the internal/surrogates and increasing area counts over the calibration range for both my 524 and 8260 setups.
The past is there to guide us into the future, not to dwell in.
Thanks everyone for your input!

Big bear, I have been having this issue since the instrument was brand new and I have not cleaned the source yet. Any chance it was dirty or contaminated when installed? Surely the installation check run would have shown that...

James Ball, do you utilize the desorb pressure control or the desorb flow control? I think that in theory it helps and have seen EST's paper regarding desorb flow control and reduction of moisture but I am curious to hear from another person in the field how it really works.

Do you use different IS/SS solutions for 8260 than for 524? We are currently using fluorobenzene as the IS for 524 with BFB and 1,2-dichlorobenzene-d4 being the surrogates. Our 8260 analysis uses 3 internal standards and additional surrogates.
For 524 I am using the 524 internal standard surrogate mix plus the internal standard mix for 8260 which has Pentafluorobenzene, Chlorobenzene-d5 and 1,4-Dichlorobenzene-d4. That last one really helps with stability of the later eluting compounds since it behaves more like those compounds than the early eluting single internal listed in 524. In the method it allows for extra internal standards to be used so I have never had problems with audits. If you go to 524.3 it already has the last two extras there added in to that mix for internal standards, and you can alter the desorb down to 1 minute instead of the 4 minutes required by 524.2. With modern trap packing materials 4 minutes is far too long to desorb, everything is off the trap by 0.5 to 1.5 minutes so the extra time is just loading up water on the column. I haven't tried desorb flow control yet, but it just diverts the extra desorb time to vent instead of to column, so you are actually desorbing for 4 minutes even though only the shorter amount of time is actually going to the inlet.
The past is there to guide us into the future, not to dwell in.
To get around the water issue with 524.2, I desorb for 3 min ( method says "about" 4 min, auditor freaked to find I was using 2, we agreed on 3). At 1.5 min of desorb I set the gas saver to 200 cc/min which diverts most of the remaining water to the split vent.
I use a 20Mx0.18 column @ ~0.6 cc/min, splitting 150:1.
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