Chromatography Forum

I wonder if anyone is using an alternate surrogate for EPA 515.4. I do not like using 2,4-dichlorophenylacetic acid as it is not a useful marker for the other herbicides in my mix.
As an example of what I see, I ran one sample this week in duplicate and spiked it as well. The surrogate recoveries for the sample and dupe were both out ( 60% recovery) while the surrogate in the spike was 84%. The herbicide recoveries in the spike ranged from 95-105%.
Having a hard time understanding what is going on in the extracts. I have tried increasing the amount of diazomethane solution added with little or no effect.
I think the next thing I'll try is using an IPA/dry ice bath while collecting my diazomethane.

Follow up question. Anyone know what surrogate is used in ASTM D 5317.

We had similar problem about six month ago and found out it was the amount of Add sodium sulfite crystals added to eliminates residual chlorine in the sample. I can't say for sure whether it would be the same for your lab nor explain why but I think it's worthwhile to try.

Thanks, worth a shot. We use 6 mg/ 60 ml now which is 2X what the method requires.

Does anybody have a suggestion for an alternate surrogate as originally asked? My chemist is having the same issues with 2,4-DCAA as the surrogate also, erratic responses. I know of a lab that switched to 2,4,5-T, but that is a method analyte for us. Any other suggestions would be appreciated. Thanks.

Have your chemist try adding sodium sulfite to the blank water used to prepare calibration standards. This cured my problem. Still using 2,4-DCAA.

I have tried aciflurfen (late elution) and 2,4,6-trichlorophenol- they mimicked the DCAA recovery, so wasn't much help.
ASTM uses DCAA as well.