Chromatography Forum

Hi, collegues,
I would be grateful to you for the advice in paraquat and dfiquat analysis:
-Sample preparation
-ion-pair building reagent, buffer
-column
-Vcap and Fragm V

In my conditions I have no problem for chlormequat and mepiquat but almost no responce for named PQ and DQ + very unstable base line. I use Agilent, MonoChrom (Varian) column, A: H2O / NH4OAc 5 mMol / AcOH 1% vv ; B: CH3CN. Grad A 5% to A 95%. Vcap 1000, Frag 150.

Thank you very much.

The instrument you are using is Agilent 1100 MSD?

If so, VCap seems low, unless you found experimentally that the lower voltage gives you better signal to noise. Normal for this parameter is 3500 to 4000 V. Fragmentor you should optimize yourself for each compound. Then if you are running a SIM experiment, you should be able to enter a different fragmentor voltage for each compound. But, let me know if this is not possible. It's been a few years since I've used the 1100 MSD.

Paraquat has two quaternary amine groups, so it should be doubly charged (I can't find the structure for diquat, so don't know if it's similar). Do you see any signal at m/z 93 when you analyze a paraquat standard?

Here is method for analysis of paraquat and diquat without ion-pairing reagent. One method is with ACN-water-TFA and another one is ACN-water-ammonium acetate pH=4. Both methods are UV, ELSD, LC/MS friendly, although some people do not like TFA in LC/MS application:

http://hplcmethods.com/compound_160.php

Is this an MS problem or a problem with chromatography? Are you seeing diquat and paraquat with direct injection, no column? I ask this because I know that they are "sticky" and like to hang up on unsilanized glass surfaces.
Diquat is similar to Paraquat in structure except that the nitrogens are ortho in the rings and there is a bridging ethyl group.

Here is a new method that uses HILIC instead of RP with ion-pairing.
You can get the details from the Waters website.

A Novel SPE Sorbent and a Novel LC-MS Method for Determination of Paraquat and Diquat In Environmental Samples
Document Type: Lecture
Author: Michael S. Young, Kevin M. Jenkins and Claude Mallet [Waters]
Source: Pittcon 2005; Orlando Florida; February 27th-March 4th / Year: 2005 / Volume: / Page: 18 pp / File Size: 1.25MB
Library No.: WA41855

Many thanks to everybody who has answered.

To MG: Yes, I use Agilent 1100 MSD. Optimal Vcap and Frag were determined in FIA. But I've tried others as well. Frag I can change, no problem. At V cap 3500 or 4000 response much worse, but base line is smooth (for 4-5 runs). I don’t see peak m/z 93, but I see in baseline 173, 475 and much of them.

To SIELC_Tech: I’ve seen this advertising. Seems too much NH4OAc (75 mM). TFA I’ve tried instead AcOH. No signal at all, including while direct injection in chamber.

To Steve Reimer: I really do know. I think the both ones. I‘ve made injection without column and mass response was several times lower then for the same concentration of two other compounds of similar (?) structure: mepiquat (N,N-dimethyl piperidin) and chlormequat (2-Cl-Ethyl-trimethyl-ammonium). The samples were dissolved in H2O or in H2O/ AcOH/ NH4OAc.
Concerning the chromatography. The quter. amines chlomequat and mepiquat in the same conditions have passed the column (perfluoroPh) without problems. In the case of PQ and DQ I see either nothing or in the best case unclear signal with tailing 1km. I’ve read about the sorption in glass, so I used different concentrations - no visible improvement. May be the problem in structure: bipyridilium salts and aliphatic and their interaction with column?
Thank you

Without question, they are sticky. This is why people use the ion-pair reagent with UV detection. If you do not want to use the ion-pair reagent, a column other than C18 is probably needed. This is why Young used the HILIC approach.

Thank you Uwe Neue. According to Waters recomendation to HILIC Silica for PQ and DQ , 250 mM NH4OAc should be taken. Isn't it too much for instrument?

Dear Osten,

An alternative to the Waters silica HILIC column, and other silica HILIC columns for that matter, is the ZIC®-HILIC column from SeQuant (which I represent). I totally agree with Uwe in that HILIC is a suitable alternative for your compounds. However, the PQ and DQ will have very strong interactions on a silica phase. With our zwitterionc phases, you will experience a much weaker interaction, and thus lower salt concentrations are needed. I have been hesitating in answering your query as we do not have an application for exactly your compounds, but analogues ( Chlormequat and Mepiquat) have been separated successfully using only 25 mM ammonium acetate.

http://www.sequant.com/products/zichili ... 00-14A.pdf

/Patrik

Patrik, thank you for your advice. The matter is that I have analysed MQ and CQ and met no problem. But I failed while tried to apply the same conditions for PQ and DQ. My column is Monochrom, pentaFluoroPhenyl (Varian). I.e. the last ones require smth special.

Osten,
If you contact me, I could arrange a column for you. If you are interested, that is. As these compounds are banned in Sweden, I have not possibilities in testing them myself.
/Patrik

Hi, Patrik,
I have visited your site and will keep it in mind. For the time being I managed to get these compounds from column by applying pH 2.0 The lowest limit for column is 1.5. I hope it will work for some period.