The construction and use of an improved thin-layer phosphorimeter is described. The device permits flexible chromatography media to be scanned at 77 K, and also allows a complete characterization of the luminescence properties of the chromatographically-separated solutes. It is shown that the phosphorescence intensities of a variety of adsorbed materials are greatly increased by spraying the chromatography medium with a suitable solvent immediately before examination. The magnitude of the effect depends on the stationary phase, the structure of the adsorbed material, and the solvent sprayed. With the aid of the enhancement effect, nanogram quantities of separated solutes can be analyzed. The instrument Is also suitable for examining the luminescence of adsorbed molecules at ambient temperatures.Combinations of chromatographic methods and fluorescence spectrometry a t room temperature have been repeatedly shown t o be powerful analytical techniques which combine the selectivity of chromatographic separations with the sensitivity of fluorimetry. T h e use of fluorimetry to locate and quantitate the components of complex mixtures separated by thin-layer chromatography (TLC) is a particularly convenient approach (e.g., Ref. 1) which permits the simultaneous study of several very small samples, and instruments designed for the quantitative fluorimetric scanning of TLC plates are commercially available. Although recent studies have amply demonstrated the analytical value of phosphorimetry ( 2 ) , a technique normally performed a t 77 K, combinations of TLC and phosphorimetry have so far been little used. Rinefordner and co-workers determined biphenyl in oranges ( 3 ) , 4-nitrophenol in urine ( 4 ) , and alkaloids in tobacco ( 5 ) by separating the samples on TLC plates, eluting the separated fractions with a suitable solvent, and determining them using conventional phosphorimetric sampling techniques. Studies have also been described in which the phosphorescence of samples separated by TLC have been detected visually by dipping the chromatography plates into liquid nitrogen and observing them under UV illumination. Sawicki et al. (6) investigated a series of aromatic atmospheric pollutants using this approach, and more recently de Silva and Strojny (7) have detected nanogram quantities of various drugs. In the authors' laboratory a thin layer phosphorimeter has been developed (8) as a n accessory suitable for commercially-available spectrofluorimeters. This device permits the in situ quantitative determination and spectroscopic characterization, a t 77 K, of solutes separated on flexible TLC media. The present paper describes the construction and evaluation of a n improved thin-layer phosphorimeter. In particular it is demonstrated that the phosphorescence of solutes adsorbed on TLC plates can sometimes be greatly enhanced by spraying the plates with organic solvents before scanning, a procedure which permits the determination of nanogram quantities of such solutes.'Present address,

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