SPECTROPHOTOMETRIC DETERMINATION OF FLAVONOIDS BY THE REACTION WITH (4-NITROPHENIL)DIAZONIUM TETRAFLUOROBORATE
(4-Nitrophenil)diazonium tetrafluoroborate (4-NPD) has been suggested as a reagent for the spectrophotometric determination of flavonoids. It has been shown that in alkaline medium 4-NPD enters into the diazotization reaction with quercetin, naringenin, chrysin, morin, rutin and naringin to form peach-coloured products. The conditions for the spectrophotometric reaction have been optimized. Spectrophotometric method for the determination of flavonoids with detection limits (1.5 -3.9)·10<sup>-7</sup> М (0.05 - 0.16 μg/mL) has been developed. Quercetin has been determined in some pharmaceutical compositions.