Study on sensitized photochemical fluorescence of menadione sodium bisulfite and its application in pharmaceutics analysis

Menadione sodium bisulfite (MSB), vitamin K3, a non-fluorescent compound, was converted into an intensive fluorescent compound (λexλem = 340 nm465 nm) on irradiation with ultraviolet radiation in an anaerobic alkaline medium, and acetone showed a strong sensitizing effect on this photochemical reaction when the radiation used was absorbed by acetone. The reaction rate increased as the concentration of acetone increased, the maxima of the fluorescence spectra, however, remained unchanged. The sensitized photochemical reaction was assumed to begin with the absorption of photons by acetone and a triplet-triplet energy transfer process was proposed for the sensitizing mechanism, in which acetone acted as an energy donor, and MSB as an energy acceptor. A new in situ photochemical fluorimetric method was consequently proposed for the determination of MSB. The solutions were pumped through a PTFE mixing-tube and then stopped and kept in an 18 μl flow cell where the photochemical reaction took place in situ on irradiation for 120 s (with an excitation wavelength, λex, 280 nm, excitation slit, EX, 7 nm), and then λex was changed from 280 to 340 nm promptly to measure the fluorescence intensity of the photochemical product at 465 nm. Na2SO3 was used as the deoxygenation reagent. The calibration graph was linear up to 1.1 μg ml−1 MSB (r = 0.999), and the limit of detection (LOD) was 0.76 ng ml−1. The coefficients of variation were 1.0% (n = 6) and 0.99% (n = 6) for 0.44 and 1.1 μg ml−1 MSB, respectively. Its application to the analyses of vitamin injections and urine samples was satisfactory, and the recovery of vitamin K3 in urine was 92–94%. The kinetic behavior of this reaction and the effects of some experimental conditions as well as the mechanism for the sensitization by acetone were investigated and discussed in detail.