Diquat in oil seeds

[Alita]

Hello, does anyone of you has experience analyzing diquat in chia grains? Currently, I'm trying with a method of Anastassiades, using a methanol with formic acid extraction and then filtration and injection.

We have an Agilent 6460 LC-MS-MS
The column is an Hilic from waters, and The mobile phase is a) 20 mM ammonium formiate pH 3 and b) Acetonitrile

I have tried too with 250 mM ammonium formiate pH 3,7

The problem is that making matrix extraction I only get to see 100 ppb, and I need to reach to 10 ppb. I also evaporate The methanol extract but without succes.

Could you give me some advice? How to make a better extraction
Any help Will be very useful

Thank you

[James_Ball]

Hello, does anyone of you has experience analyzing diquat in chia grains? Currently, I'm trying with a method of Anastassiades, using a methanol with formic acid extraction and then filtration and injection.

We have an Agilent 6460 LC-MS-MS
The column is an Hilic from waters, and The mobile phase is a) 20 mM ammonium formiate pH 3 and b) Acetonitrile

I have tried too with 250 mM ammonium formiate pH 3,7

The problem is that making matrix extraction I only get to see 100 ppb, and I need to reach to 10 ppb. I also evaporate The methanol extract but without succes.

Could you give me some advice? How to make a better extraction
Any help Will be very useful

Thank you

Are you using plastic extraction labware? Diquat has a problem with adhering to glass very well. Also it will adhere to nylon filters if not acidic. I have mostly worked with it in a drinking water matrix so it may not be as much of a problem in Methanol, but always good to take note of.

I do remember either Restek or ABSciex having applications for Diquat by LCMSMS, so maybe a good idea to look at their websites for some application notes.

[Alita]

Dear James, thank you for Your answer, yes, all my work materials are plastic, I believe that the oil is interfiring with my analysis, and that's why I don't have good recoveries, that's why I would like to try some clean up step, but I haven't found many references

[X]

Hello, does anyone of you has experience analyzing diquat in chia grains? Currently, I'm trying with a method of Anastassiades, using a methanol with formic acid extraction and then filtration and injection.

We have an Agilent 6460 LC-MS-MS
The column is an Hilic from waters, and The mobile phase is a) 20 mM ammonium formiate pH 3 and b) Acetonitrile

I have tried too with 250 mM ammonium formiate pH 3,7

The problem is that making matrix extraction I only get to see 100 ppb, and I need to reach to 10 ppb. I also evaporate The methanol extract but without succes.

Could you give me some advice? How to make a better extraction
Any help Will be very useful

Thank you

Hi Alita,

The extraction method you used also extracted lots of matrix components from the oil seed sample, such as fatty acids, which may affect your sensitivity, I would suggest an ion exchange solid phase extraction method to get cleaner extracts.

1. Dissolve a small amount of oil seed sample in 20 mL 1:1 methanol: pH 7 phosphate buffer.
2. Condition a SPE cartridge (UCT part#: EUCCX11Z) with 3 mL methanol, and 3 mL pH 7 phosphate buffer.
3. Load sample at about 2 mL/min.
4. Wash the SPE cartridge with 3 mL pH 7 phosphate buffer, 3 mL methanol and 3 mL n-hexane.
5. Dry the SPE cartridge under full vacuum for 5 min.
6. Elute the retained diquat to polypropylene test tubes using 3 x 1 mL of 10 % formic acid in acetonitrile.
7. Evaporate the eluate to dryness, reconstitute in 100 to 200 uL of the initial mobile phase (use plastic insert) and analyze by LC/MS/MS.

Please contact me at xwang@unitedchem.com if you have any questions.

Xiaoyan Wang

[richiekichi]

Hello Alita,

You could also try introducing a freezing step. After extraction with water:methanol, centrifuge and decant the solvent to another plastic tube and freeze for a few hours or overnight. Centrifuge again and filter into your plastic instrument vials.

I never had much luck with ion exchange cartridges myself.

You can always reduce the amount of sample too.

[Alita]

Thank you very much to all for your answers!
We made the analysis just as Xiaoyan Wang mentioned with excellent results.
The line base stabilized and I could reach to the limit of 10 ppb. I bought a commercial brand of chia in the supermarket to use it as a negative sample and make the calibration curve in matrix, and my blank wasn´t blank! it had diquat and even paraquat! Even though, my calibration curve had a good linearity and the recovery at 10 ppb was 98%.

Thank you very much and specially to Xiaoyan!
Best regards.
Alicia

[X]

Thank you very much to all for your answers!
We made the analysis just as Xiaoyan Wang mentioned with excellent results.
The line base stabilized and I could reach to the limit of 10 ppb. I bought a commercial brand of chia in the supermarket to use it as a negative sample and make the calibration curve in matrix, and my blank wasn´t blank! it had diquat and even paraquat! Even though, my calibration curve had a good linearity and the recovery at 10 ppb was 98%.

Thank you very much and specially to Xiaoyan!
Best regards.
Alicia

Alicia,

I'm glad you got good results, please contact me if you need any help in your future research.

Xiaoyan

[Alita]

Dear friends:

Unfortunately I´m still having some doubts about my paraquat and diquat analysis in chia (Salvia hispanica). Do you remember that in the previos post I told you that I bougth a chia to use it as a blank matrix from the supermarket and found peaks in the retention time of PQ and DQ. Even though, I could perform the analysis substracting the signal of my blank, and the recovery was of my quality control in matrix were good.

I wanted to prepare a poster for a congress analyzing all the brands of chia that are sell in the supermarket, because only the ones that are exported are analyzed in my country, so, using the extraction technique that Xiaoyan recommend me, I found was that everyone gave my signals in the retention time of PQ and DQ, so now I have the doubt if is really PQ and DQ what I´m seeing. Some of them were organic, so shouldn´t be contaminated. My reagent blank don´t give any signal.

As my calibration curve is in matrix, substracting the signal of the matrix blank I have good linearity and recovery, but what about the samples? According to your knowledge, what other kind of compounds could be that are giving me the same response of PQ and DQ? I thought maybe Tryptophan (MW 186 and has an amino group for the PQ)

My final mobile phase was a) 250 mM ammonium formiate pH 3,7 with formic acid and b) Acetonitrile (65-35) - Hilic column from Agilent.
The ions that I´m using are:
PQ: 186 - 171; 186 - 144; 186 - 77
DQ: 183 - 130; 183 - 157; 183 - 168

I would appreciate any comment.

Best regards