I am trying to develop a pre-column dervitization reaction for a sample that does not absorb light very well using FMOC.

I had an original procedure for an impurity determination, but it also seemed feasible for the main component as well. We wanted to modify the procedure slightly by combining solution A and Solution B into a common diluent. The problem with this originally was that we had precipitation occur after a while, and it appears that FMOC is not soluble in water, and Boric Acid is not soluble in Acetone. I tried to fix the problem by reducing the concentration so as to not cause precipitation. I also tried adding methanol as a co-solvent, however, I believe that methanol reacts with FMOC and will cause it to be in competition with my main analyte.
does anyone have any suggestions on this procedure? The problem is that when we've tried the method, we will get the derivative peak one day then mysteriously, the peak will not form another day. Here is our experimental conditions.

Original Method
Solution A:
0.4gram FMOC in 500mL Acetone
Solution B:
15grams Boric Acid in water adjust to pH 7.7 with 50% Sodium Hydroxide

Standard:
10mg of standard -> into 50mL of Water
1.0mL standard + 4.0mL of Solution B + 5.0mL of Solution A. Allow to stand 5 minutes. Add 3.0mL Ethyl Acetate, mix, use lower layer for analysis.

Modified Method
Solution A:
0.1gram FMOC in 500mL of Acetone
Solution B:
1.5 grams Boric Acid in water, adjust pH to 7.7 with 50% Sodium Hydroxide

Diluent:
50:50 Solution A + Solution B

Standard
10mg standard -> into 50mL Dissolve in Water
5.0mL -> into 100 Dissolve in diluent. Allow to stand for 5 minutes. (10ug/mL)