problem with glyphosate analysis

[leon]

Hi

I am trying to set up the method of analysis for glyphosate. But so far there is no peak(for both glyphosate and AMPA). I am using the pickering post column derivatiser. Column used is the pickering potassium cation exchange column. Detector is Fluorescence Detector (Ex=340, Em=445). Mobile phase is water+methanol PH=1.9.(Isocratic). Flow rate = 0.4 ml/min.
Anyone has any experience with glyphosate analysis or used of cation ion exchange column?

[Mark Tracy]

I used to do this assay on Pickering equipment. Your symptom could be caused by two things: your OPA reagent is bad or you have iron contamination on the column. Usually it is iron; sometimes the columns come that way from the factory. Buy a bottle of Glyphosate Restore from Pickering and give it a try.

(Disclosure: I used to work for them, and supported this application. We developed Restore especially for this complaint.)

[leon]

Thanks Mark. We actually followed EPA method 547 in using LC grade water for restoration. But seems that it doesn't work. What's the Content of Pickering Restore ? Is it 0.005M KOH? If it is, can we prepare that solution ourselves?

[Mark Tracy]

Leon,

Since I have not worked there for a few years, I have forgotten the exact formula. It is a mixture of phosphoric acid and potassium phosphate, similar to the eluent, but about 5x stronger, and balanced so that you can rapidly re-equilibrate the column after cleaning. It is designed to go with the Pickering column and eluent, but works OK with BioRad too.

The EPA Method 547 is full of bugs, and you have just found one. Neither D.I. water nor KOH will remove iron contamination. 0.005 M KOH would take all day just to neutralize the acid in the column, and then it would take another whole day for you to re-equilibrate the column with eluent.

If you don't have it, get the glyphosate application manual from www.pickeringlabs.com It's a free download, and explains everything I would otherwise have to write here.

[SIELC_Tech]

Here is the method we developed for the production of glyphosate. You can use low UV (with sulfuric acid at 205 nm) or ELSD (with TFA)-assuming that this is okay with your LOD.

http://allsep.com/makeCmp.php?cmp=Cmp_048

[Mark Tracy]

SIELC_tech,
Can your method equal the performance requirements of EPA 547? If so, perhaps you should be pitching to the EPA, not the folks who are required to use EPA methods.

[leon]

Thanks Mark. Seems that we need to get those pickering chemicals (Restore, K200) to make it work. I was hoping we could avoid that to cut cost. Thanks for your advice.

[Steve Reimer]

Leon,
I have done this analysis periodically for a dozen years. One thing I found out quickly was that trying to save a few dollars on supplies and a few minutes on maitenance was false economy. Extra time cleaning and flushing the system at the end of your run will pay back in much lower maintenance. If the system is used for other analyses, extensively clean it before you hook up those expensive columns.
I found Restore works to fix guard columns that aren't in too bad of shape, but if the contamination had made it through to the main column, both were history. The only time I had that happen was on converting the system to run glyphosate after running some nasty carbamates, thus the suggestion to preclean the system.

[leon]

Thanks for your advice, Steve.
Do you have to add NAOH to the OPA solution to get a PH of 9.5 for the reaction?

[sjmarin]

I haven't done glyphosate for a long time, but I recall having to make the sodium hypochlorite solution up fresh daily or at least every other day because it loses strength quickly.

I also thought that the pH of the OPA was critical to good sensivitity. Make sure it is above 9.5 and add NaOH if you have to in order to get a pH above 9.5

[Mark Tracy]

Leon,
If you are making up your own OPA buffer, don't start with sodium tetraborate. You will get excess noise and particulate matter. Start with boric acid, titrate with sodium hydroxide, then filter it. Once you know what amount of each you need, you don't need to use a pH meter, just weigh it.

The advise about NaOCl is good. I found unscented Clorox bleach works as well as what you buy from the chemical supply companies. Calcium hypochlorite (as EPA calls for) will cause all kinds of trouble with precipitation.

[sjmarin]

Hey, I should have mentioned it, but we used regular old Clorox too. Worked well. Didn't know the trick about the borate, but it makes sense. We used to have to heat the borate to get it to dissolve, the prep was a pain.

[Steve Reimer]

I'll agree on the borate. Boric acid makes an easier prep. Of course the easiest is buy it premade. I found that I needed to check the Clorox for age before use. Our consumption is low and a poorly closed bottle will loose its hypochlorite with time. So I check for yellow color before use.

[leon]

Thanks guys for all your advice. About the Regenerant and Eluent K200, do you all buy from pickering or prepare your own?