Chromatography Forum

Hello,

I'm having some issues with recovery of some analysts for my 515.4 analysis. Picloram and Aciflourofen namely. I'm following the method as written except for the addition of the copper sulfate. It seems that when I re-inject a standard as a control check (CCC) the concentrations of these two analyst are failing low. I could see this happening if the run was long (50+ samples) but it is happening within 10 injections of the first. Each injection is about an hour long.

Any insights would be helpful. If you would like to chat more directly my email is mdewald@nd.gov

Do you know the role of Copper Sulfate (was it to enhance the recoveries)? Did you do a literature search? If not, why did you eliminate it?

Sounds like you're in 'deep trouble'!

Copper sulfate is there to help differentiate between the water and solvent layers.

Correct, copper sulfate is only there as a colorant to see the boundary layer.

I am not that familiar with 515.4 but if there is a neutralization step and it doesn't completely neutralize the samples before injection, you could be losing the compounds because of active sites forming in the liner or column.

Correct James, CuSO4 is a colorant that does help only to make the solution "pretty", we have eliminated it years ago with good results.
Of your 2 problem children, we do only picloram and have issues with it when the peak shape goes bad. Liner change and column clip puts things right.

How long do you allow the silica gel to neutralize the diazo methane?

We let the gel work for 30 minutes. How long do you let yours go?