Chromatography Forum

I am trying to set up herb methods 8151a.

First thing just want to see how efficient of diazomethane methylation.

I diluted matrix spike solution (from Accustandard) with ether, and using diazomethane bubble method to bubble the Matrix spike solution. The recoveries were terrible. Anybody know why? Thanks.

Sea,

A couple of questions; is the spike miscible with ether? Did the solution turn yellow and stay yellow? Are you using black stoppers in your apparatus?

Don

Hi Don, Thank you for your reply.

The MS is in methanol. it should be miscible with ether, right? The solution did turn yellow, and stay yellow for at least 1hr, then turned to no color. I didn't use black stopper. I was only using a 40ml vial with PTFE cap to try it.

Sea,

We have ruled out the usual suspects. It will be hard to figure this out without reviewing your procedure and analysis step by step.

Is the standard very old? I am cautious about using acidic standards stored in methanol. They will methylate over time. It's possible that they are not acids any more. See if you can find a matrix spike made in a different polar solvent.

Don

Thank you, Don.
I just order the standard last month.

we began making up our working standards in ACN...it helped recoveries improve. we've always had horrible herbicide recoveries and really, if you look at 8151a closely you'll see that the epa got horrible recoveries as well. Even our PT samples would have acceptable ranges of 0-30% on some of the analytes (ie..dinoseb). is this a new issue or have you always had low recoveries? (low herbicide recoveries are quite common, our lcs lower limits were generally 10% and soils had a tendency to be worse than waters). what kind of recoveries are you seeing?

I do herbicides via 515.4. I find it works better than alll the ones I tried before, starting with a SM method that was l/l with ether and BF3 derivitization. (yes I've been around a while!).
515.4 uses MTBE as the extraction solvent. My standards are also in MeOH and I don't see problems as there is a basic hydrolysis as the first step.
Derivitization is with diazomethane/MTBE solution that I prepare. Its sort of like what you use but all the diazomethane is collected in 10 ml. MTBE ( works best if the MTBE is in an ice bath). I then add 300 ul of the diazomethane solution into 3-4 ml of dry sample extract. Sit for at least 30 min. then quench with silica gel.

Read 515.4 as you may pick up some ideas.

Hi My name is Sharlene from the GEL Group of Charleston SC. I have done the preparation on soil and water matrix for herbicides and have been successful with very good recoveries even for dinoseb. We are using Diazomethane but not the bubbling technique. The sigma aldrich diazomethane kit is what is used. The method that we are certified for is 8151A for target analytes Dalapon, Dicamba, MCPP, MCPA, Dichloroprop, 2,4-D, Pentachlorophenol, 2,4,5-TP,
2,4,5-T, 2,4-DB and Dinoseb. The standard is made up in Methanol.