This method is used routinely in our lab to measure total phenol. The procedure is also used for analysis of total phenol in tea. It uses the minimum volume of reagents and almost eliminates wasted reagent. Good micro pipets must be used for reproducibility. Plastic or glass cuvettes can be used. It is based on the method reported in Slinkard, K.; Singleton, V. L. Total Phenol Analysis: Automation and Comparison with Manual Methods. American Journal of Enology and Viticulture 1977, 28: 49-55; only the volumes have been reduced. If you cannot reproducibly measure such small volumes, try to reduce the volumes to the smallest you can. This reduces waste and disposal volume.
Folin Ciocalteu Reagent. This is usually purchased as the 2N reagent available from Sigma (F9252) or from Fisher Scientific (ICN19518690), and presumably others. Singleton and Rossi AJEV 1965, 16: 144-158, describe the preparation of the reagent from sodium tungstate, sodium molybdate, lithium sulfate, bromine, and some acids. Solutions containing the FC reagent must be disposed of as hazardous waste.