Chromatography Forum

Hi people!

I analize pesticides in fruits, vegetables, water and soil with an Agilent GC6890/MSD5973.
I used a column DB-1701 and the Multi-Pesticide Residue Analysis method of Fillion-Thorp, but I changed the column by a HP5ms. After that, I noticed coelution of two pesticides. I tried to change some ions, but without success.

Can anybody recommend me other method?

Thanks

What you have seen is the reason for so many stationary phases available. If the retention indicies of two compounds are close on a particular stationary phase, you will have a hard time separating them. So, Is there a partular reason for changinf from a DB-1701 to a DB-5? If not, I would reccomend reinstalling a 1705. If you were attempting to resolve a different coeltuion, then you may have to try again. And, there are some phases designed for specific applications - like pesticides. Check the vendor web sites and see if they have a column that separates all the compunds of interest to you.

If the peaks are almost resolved, sometimes changing to a column that is longer, narrower, or has a thinner film can do the trick. Longer increases the time that the compounds are on the column - and the peaks become broader, adversely affecting LOD's. Narrower columns and thinner films can give a lower height equivalent theoretical plate - but, you can not put as much material on the column.