G. C. Lolor University oi the West lndies Kingston 7, Jamaica
Apparatus for Measuring Spectra of Oxygen-Sensiti~eReactions
The method is particularly suited for quantitative measurement of the absorption spectrum of a product which can be formed by mixing two rcactant solutions. The apparatus is shown below. A hypodermic syringe needle is used as an adaptor between the pressure tubing of a gas mashing train and fine bore (ca. 1 mm) polythene tubing. The flushing gas is "pure" nitrogen which is passed t,hrough a scrubber containing vanadium (11) in sulfuric acid over zinc amalgam to remove traces of oxygen and then through water. The zinc amalgam is replaccd whenever the color of the vanadium solution changes from lilac to blue. A is a Pyrex test tube which is stoppered with a selfsealing rubber cap of the type used on vaccine bottles. Two small holes are drilled in the rubber, and the polythene tubing is led through by inserting a hypodermic syringe needle up through the hole in the stopper, fit-
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Apporatur for rpectrophotometericmearurementr in the absence of oxygen.
90
/
Journal of Chemical Education
ting the tubing over the needle and slowly feeding tubing and needle through the tightly fitting hole. The tubing connected to the nitrogen supply is pushed almost to the bottom of the tube; the outlet tube fits flush with the bottom of the cap and is fed in the same way through another cap, which fits tightly over the rim of a stoppered spectrophotometer ccll and extends nearly to the bottom of the cell. The final gas exit is, conveniently, a syringe needle. The spectrophotometer cells being used are the type supplied by Unicam Instruments, Cambridge, England. Measured volumes of each reactant solution are placed in the test tube and spectrophotometer cell, respectively, the caps are tightly fitted, and the solutions are thoroughly flushed with nitrogen. The test tube is then inverted and nitrogen forces the liquid into the spectrophotometer cell. When the transfer is complete, the tubing inside the cell is carefully withdrawn to just above the surface of the solution to avoid bubbling in the light path. The gas stream is continued during measurements. The method is obviously also applicable to thc preparation of a solution from a solid. However, accuracy would be low unless the extinction coefficientsof the substance are high enough to allow the weighing into the spectrophotometer cell of at least a few hundred micrograms of sample. Acknowledgment is made to Petroleum Research Fund for the support of this work.
