Gerstel Twister - Strange response of certain pesticides

Discussions about sample preparation: extraction, cleanup, derivatization, etc.

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Hello all

This is my first post, just as a quick presentation of myself I want to say that I have been working with Gerstel SBSE Twisters during the last ten years (and I still do) focused on water analysis of pollutants.
Despite this experience I have a problem that I can´t resolve, I don´t find any clue searching in internet and I can´t find help from the few colleagues that work with this technique in my area.
So I would like to ask yo looking for any idea to solve the problem.

It´s about reproducibility of the signals of:


Those compounds are included in a mix with more pesticides.
For calibration pourposes I allways use comercial JTBaker LCMS Water and the same Twisters are allways used for the same purpose, I mean, Twister for calibration level one is allways used to prepare calibration level one, etc.
We use erlenmeyer flasks of 100 ml for the extraction, washed with water and solvents and remains overnight at 300ºC.
We use internal estandards and surrogates.
All the Twisters are cleaned after use with a TC-2 Gerstel tube conditioner and eventually we clean them with organic solvent.
As I say, we care so much about the materials and conditions for sample preparation.
Finally we use a Gerstel TDU for thermal desorption of the Twisters.

Despite all of this we eventually found that the signals for those 4 compounds falls. Sometimes is half of expected (while the many others compounds of the mix are working fine), sometimes near to 0, sometimes 75% of expected...
And it sometimes happens in calibration level 1, another day on point 4 and 6... aleatory. And the rest of the calibration points for those problematic compounds are fine.

When this happens we isolate the Twister and test it, and the response is good.

The Twisters are fine, always exposed to very clean LCMS quality water.

Endosulfans are isomers but very different of the other two, but the problem affect to all four. Different structures, ions, retention times... I don´t understand the cause that affects those four compounds simultaneously.
Yes, they have Cl but our mix has many other chlorinated compounds with no problem.

I thought about glassware but, as far as I know, this are not the kind of compounds that are affected by active points in the glassware. nevertheless I´m going to renovate glassware and see.

Sorry for the extension, I just wanted to explain it properly, I´m open to receive any idea or suggestion.

Many thanks in advance.
Do you add NaCl or Methanol to the water in the extraction? We add Methanol (5ml/100ml H2O) for the analisys of cipermetrines and Nacl (20g/100ml H2O) for the endosulphanes

Sorry for my english
2 posts Page 1 of 1

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