ELSD saturates and monoaromatic compounds

Dear all.

I hope this reach you well. Actually I’m developing a oil and as method in ELSD and DAD.

Is a normal phase method, DNAP column and heptane mobile phase, in order to separate mono, di, tri, tetra and penta ring of aromatics; and saturates.

Di, tri, tetra and penta aromatics look very good in DAD; but I couldn’t see saturates and mono aromatics in ELSD.

I’ve used different parameters:

1. Temperatures: 30, 35, 40, 50 °C.
2. Gain: 1, 3, 5, 7, 10, 12.
3. Noise filter: 0.5, 5, 10 s.
4. Injected a 100% gasoline and toluene and just see a little peak 100 mV.

I tried this:

1. Background Noise (Stray Light) Test. Get a mv signal of 250 mV for heptane, looks line good according the service manual. For gain 12, 150 mV for water and 200mv for normal phase.
2. We cleaned the nebulizer as manual said.

What do you recommend to do in order to increase the sensitivity? Or test what’s going on…

Thanks in advanced.

Best regards