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A SIMPLE FLUOROMETER CHARLES E. WHEELOCK Ilion, New York
A
SIMPLE fluorometer, easy to construct and use and reliable in operation, is described here. An external view of the instrument and the arrangement of integral parts is shown in Figure 1. Inside a black, wooden box fitted with a flanged lighttight cover is a rectangular cell to hold solutions of fluorescent materials, an annular filter cell assembly containing a pbototube, and a metal coolmg jacket surrounding a B-H-4 lamp with a Corex envelope. See Figure 2 for latter two assemblies in greater detail. By placing the ultraviolet light source inside a coolmg jacket, a closer arrangement of B-H-4 lamp and rectangular cell and consequently, a stronger excitation of the fluorescent solution is achieved without incurring solvent loss or troublesome temperature fluctuations. -4NNULA/T F I L T F e CELL
-COOLING JACUt7-
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Fi(luin 2
Fluorescent light produced by excitation of the solution reaches the phototube through the annular filter, constructed of two pyrex tubes sealed one inside the other as indicated in Figure 2. The filter cell contains 2 per cent sodium nitrite solution, which absorbs ultraviolet frequencies. An aluminum foil covering much of the outer surface of the filter cell together with the absorbing interior surfaces of the box minimizes the effectof scattered light. In conventional instruments, the intensity of fluorescent light from some interior point of the solution is measured. Consequently, in the case of a solution which absorbs ultraviolet light strongly, in which the fluorescence appears only along the cell-solution interface nearest the ultraviolet source, a misleading observation is likely. As shown in Figure 1, fluorescent light reaches the phototube from every point of the solution in the rectangular cell, which is supported by a spacer block and grooves in the anti-reflection vanes. In the photoelectric circuit are used a vacuum tube amplifier and a balanced resistance method of detection containing no novel feature. In operation, a fluorescent solution is compared to a standard; both cells being alternated several times in the instrument to minimize variations in line voltage. A fresh solution in ethanol of 4-methyl-7-hydroxyconmarin (3 g./l.) sealed under nitrogen in a cell is a suitable standard.
