Glycerol-3-Phosphate detection

[CHRIS SMALL]

Hello,
I am trying to quantitate low levels (nM-uM) of G-3-P.  One strategy is
to enzymatically attach a non-radioactively labelled CTP (biotin/etc) to
get CDP-glycerol and then detect the label.  I'm trying to figure out
the best way to remove the free CTP-biotin.  I cannot use
sephadex/columns etc.  Ideally, I would like to do the assay in a
microtiter plate with few manipulations.  Does anyone know of an
efficient way to remove the free CTP or know of a label that will behave
differently if coupled than it does if it is free in solution (diff
absorbance, etc) ? 
Or, of course, does anyone know of another strategy to quantitate 
G-3-P?
Thanks!