My current separations are being done on 5 um, 1x5 (or 1x10) mm columns at a flow rate of 1 mL/min. Elution is done under "ballistic" gradient conditions (95% water to 95% acetonitrile) over 0.7 minutes. I am also using an initial 0.3 minute hold at 95% A. Peak width at base is approximately 3 seconds and would be narrower if I didn't have so much tubing post column (divert valve and the mass spectrometer source are the largest contributors). My peaks are retained (k* of 20, RT of 0.6 - 0.9 min) and symmetrical (no shouldering, fronting, or splitting).

I've looked up the calculations for Reynolds, but am uncertain as to how to handle the changes in viscosity and pressure over the gradient. Is there a way to determine if my flow is turbulent?

Thanks!

It is guaranteed not turbulent, but you can use an upper and a lower estimate for the Reynolds number using the conditions at the beginning and the end of the gradient. This will bracket the true Reynolds number. If you want to go beyond this, you can calculate the composition around the point of elution.