A novel fluorimetric method was developed for the rapid determination of DNA and RNA based on their quenching effect on the cationic red-region fluorescent dye Nile Blue (NB). In the investigation of the interaction of NB with DNA by steady-state polarization measurements, thermal denaturing study, determination of absorption and fluorescence characteristics, salt effect study and electrophoresis experiments, the results supported the suggestion that NB served as an intercalator to the stack base pairs of nucleic acids. Further evidence showed that the quenching could be ascribed to the static quenching mode. A binding constant of about 10(6) M-1 and a binding site size of about three base pairs were obtained by spectral methods. Under optimum conditions, the calibration curves for the determination of calf thymus DNA (CT DNA) and yeast RNA were linear over the ranges 3.0 ng mL-1-2.0 micrograms mL-1 and 27 ng mL-1-10 micrograms mL-1, respectively. The detection limits were 3.0 ng mL-1 for CT DNA and 27 ng mL-1 for RNA. The relative standard deviation (n = 6) was within 2.1% in the middle of the linear range. Interferences from some interesting co-existing substances in the determination of DNA were also examined.

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A sensitive, selective and rapid spectrofluorimetric method is proposed for the determination of thiamine by using mimetic enzyme iron(iii) tetrasulfonatophthalocynanine (FeTSPc) as a catalyst for the oxidation reaction between thiamine and hydrogen peroxide. It is based on the oxidation of thiamine in alkaline medium to give an intensively fluorescent compound, which has an excitation wavelength of 375 nm and an emission wavelength of 440 nm. The determination was found to be activated by fluorogenic substrates with a p-hydroxyphenyl structure such as L-tyrosine, tyramine and p-hydroxyphenylpropionic acid. Under optimum conditions, the responses for thiamine were linear from 1.0 x 10(-8) to 1.0 x 10(-4)mol L-1, with a detection limit of 4.3 x 10(-9) mol L-1. The relative standard deviation was 2.2% for 2.0 X 10(-7) mol L-1 thiamine (n = 6). The activation of the p-hydroxyphenyl substrates, the effects of some experimental conditions and the influence of foreign substances were investigated. The potential application of the method was tested by selectively determining thiamine in commercial vitamin B-1, vitamin B complex and rice

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