If there is one, the whole gas industry would like to know about it. Other than separating the liquid from the gas first, there is no direct method. A GC tied to an equation of stae could get close, but predicting the properties of the heaviest componets in the back flush adds to uncertainty. I know PECO filters in Mineral Wells Texas has some equipment that can measure droplet size, they use to quantify them for their filters,
I'll watch for more responces too.