The photolysis of a flowing stream to produce a reactive titrant has been reported (7). It was found that a solution could be completely or partially photolyzed with precision of 1 % or better (See Table II, Reference 7). However it was then necessary to add the photolyzed solution to a batch sample; this is cumbersome and time consuming for routine

Important operating conditions for a new analytical technique, based on dye-sensitized reactions carried out in flowing streams, are evaluated. The photoredox reaction used is a form of triplet energy transfer wherein a colored organic dye absorbs light to generate the excited state triplet, which then abstracts electrons from a suitable substrate. The products of the reaction are colorless reduced dye and substrate oxidation products; spectrophotometric measurement of dye photobleaching is employed. The rate and stoichiometry of photoredox reactions are dramatically affected by the structures of dye and substrate used, dissolved oxygen, and reaction pH. Other important parameters, largely associated with the apparatus used, are dyecarrier flow rate, photolysis source power, and reaction temperature. Data for DCPA measurements, using Methylene Blue and Rose Bengal, are reported for the model substrates ascorbic acid, epinephrine, nicotine, and caffeine. Appropriate operating conditions yield low micromolar limits-of-detection and 1 YO precision.

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Vitamin K1 (2-methyl-3-phytyl-1,4-naphthoquinone) is not naturally fluorescent, but yields a fluorescent photochemical product upon ultraviolet irradiation. Among several solvents, dioxane was found to be the most suitable for the determination of vitamin K1. A photochemical-fluorimetric method is proposed for measurement of original vitamin K1 concentration using two different readout methods: (1) digital integration of the fluorescence increase due to the photoproduct at 431 nm; and (2) analog recording of photoproduct fluorescence as a function of irradiation time. The two methods gave limits of detection of 5 ppb, with a better precision for the digital procedure. Limits of detection and speed of analysis are shown to be more satisfactory for the determination of vitamin K1 than in previously reported analytical methods. The specific data obtained depends greatly on the quality of the solvent and excitation-photolysis source used.

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