Chromatography Forum

I am a new bird for the analysis of pesticide resiude in fruit and vegetable.
I have a problem on anlaysis of organochlorine pesticide (OC) in some kind of fruit and vegetable.
We use the AOAC 2007.01 method for extraction and dispersive SPE for clean up.
The ACN clean-up extract is solvent-excanged to toluene and anlaysis by GC-ECD.
And, it is unfortunately we can only use dual column ECD for analysis on these sample;

For most common fruit and vegetable, it seems okay.
However, this method is not okay for Garlic, Onion and Leek sample.
The chormatogarm is messy by the matrix peak. All anlaytes of interest is masked by the matrix peak.
Is the dispersive SPE clean-up not sufficient?

Are there any suggestion for further clean-up or alternative for the analysis of these type of sample.
Is it better to be using SPE cartridege? Any suggestion for the type of cartridge? Florisil, Supelco CARB/LC-NH2 SPE or others

I am thankful for any replies.

It sounds like you are seeing sulfur compounds. They are not as big of a problem with triple quads or MS/SIM. QuEChERS wasn't really designed for ECD.

Here is something to try. Add 4g of activated copper granules to your extract and vortex for 10 minutes. After 10 minutes, immediately separate the copper from the extract as it will start damaging your analytes.

If that doesn't work, you might try adding Florisil or alumina to your dSPE.

Let us know if you need more ideas to try. I am very curious to find out what will work for you.

Don

Hi Don. Thanks for suggestion.
I have try to clean up the touluen extract (solvent exchanged from 4mL ACN clean-up extract(AOAC method) with 4g activated copper granules by vortex for 10 minutes. But, it doesn't work. The messy sulphur interference peak still hear.
Please kindly give further suggestion.

Also, I have tried to solvent exchange the QuECHERS clean-up ACN extract to n-hexane.
Then, I have conduct sulphuric acid treatment.
The matrix has been removed most and the chormotagram become much more clear.
However, some of anlaytes are also removed.
Please kindly give advice(s) for clean up method with final determinative method using ECD.

Is it okay to remove the sulphur interference using florisil column clean up?

You can certainly use Florisil, but I'm not sure if it will remove your sulphur issues.

Use a 1 gram Florisil column.
1. Rinse column with 10 mL hexane and discard
2. Add 2 mL extract in hexane to column and allow to drip by gravity
3. Collect everything
4. Add 10 mL 90:10 hexane/acetone and continue to collect by gravity
5. Evaporate to 2 mL final volume for analysis

The other option might be GPC.

Don

Florisil doesn't remove sulfur. A slightly dated description of copper cleanup and my old favorite TBA sulfite are at http://www.epa.gov/epawaste/hazard/test ... /3660b.pdf.
I have used a smaller scale version of the TBA sulfite procedure for nasty marine sediment samples. The copper is the easiest to do and as effective. It does eat a couple of the organochlorine pesticides though.

Thanks agian for everybody.
Your replies are valuable for me to conduct further experiment.

Don, I have previously used the W company EnviroGel GPC column (DCM as mobile phase) for clean up.
Perform QuECHERs extract as AOAC 2007.01, Solvent ex-change the ACN extract to DCM, then GPC clean up
Collect the DCM eluate at the time window for the analyte of interests (35 OC pesticides).
Solvent exchange the DCM to ACN, and perform dSPE (PSA, PSA+C18 both tried) clean up.
The messary sulfur peak still retained in the final solution.
It seems my GPC method seems not work for GPC clean-up.
Is it the size of the sulfur compound garlic are similiar to OC pesticides.
I don't know if I can use the Biobead SX-3 GPC as USEPA 3640A mentioned as the column will work better or not.

Steven, Thanks for your information.
But, I may just try to use the florisil column as I don't have any ideas and other materials at this moment.
For the Florisl clean up, I have searched a powerpoint using 500mg florisil column for clean up as page 19 in the following link
http://www.govtlab.gov.hk/g/texchange/pesticide.pdf
It use petroleum ether as elution solvent. I thinks it sould be much easier to evaporate and may save more time for concentration.
I may try this later but with final solvent of toluene.

By the ways, Steven, I have tried the copper method as Don Mentioned Earlier.
But, its seems doesn't work. I don't konw whether I have any important steps missing in the sulphur clean up.
Is the time and/or size of copper power/granule issue.
I have only used the copper wire to chop down to about 1mm x 1mm for Cu graunle, then activaite with HCl, rinse with water,MeOH and final with DCM.
The 1mL Garlic extract(in toluene) in mixed the 4g Cu granule in a 10mL clear glass culture tube for 10min Vortex.
Centrifuge the mixute and analyze the upper toluene extract.
Please give advice(s).

Also, I have just check the 3660B method.
TBA sulfite is used in it. But, what is TBA sulfite? Is it Tetrabutylammonium hydrogensulfate (CAS no.: 32503-27-8 )

And, I have one small questions on the 3660B.
The sulfur clean up on 3660B is target on elemental sulphur, inorganic sulphur (sulfide, ...) and/or organic sulphur?
The sulphur compund in the Garlic, onion and leek sample seems to be organic type.
Is the 3660B method will work on it?

Thanks for everyone comment.

I have found that I have problem in prepare a solution.
How can I prepare a 15% EtOH in petroleum ether.

I have a bottle of absolute ehtanol and a bottle of petroleum ether(35-60'C).
But, I have found they are not miscible to each together.

Any ideas?

Your problem may be the wire.The critical point with copper clean up is lots of clean surface area. I used a fine copper powder that was acid cleaned.
It works well on inorganic sulfur. I don't know how well it will work on the diallyl sulfides.

How to make the TBA sulfite solution is in the 3660 method.

Why are you making ethanol in petroleum ether? If you are looking for a polar elution solvent for the Florisil use acetone with your petroleum ether. Many years ago we used diethyl ether with some ethanol preservative mixed with hexane or pet ether for the solvent but it wasn't worth keeping small amounts of diethyl ether around.

Please keep in mind that copper, TBA and GPC are primarily used for elemental sulphur. You are dealing with thiols.

Thank you Don and Steve.

Apart from the Florisil, are there any suggestions or ideas for the clean up method of this type of matrix(leek, onion, garlic)?

Many labs use HPLC, but I am not sure which phase or conditions they use.

Yes...
We also use the LC tandem MS for anlaysis for pesticide.
However, Organochlorine pesticide seems not LC amenble(ESI shold be not work, some of them may work for APCI).

I am still trying the clean-up methods in the holiday...
And, looking for any advices.

Thank you very much for any replies.