Solvent enhancement effects in thin-layer phosphorimetry

Abstract

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,

Enhancement of Fluorescence in Thin-Layer Chromatography Induced by the Interaction between n-Alkanes and an Organic Cation

“…It has been long reported that the luminiscence of a broad variety of solutes adsorbed on TLC plates can sometimes be greatly enhanced by spraying or dipping the plates with a variety of organic solvents. − From this, phosphorescence and fluorescence enhancements caused by paraffins have merited considerable interest. , As an example, n -hexane increases TLC phosphorescence in the detection of certain drugs. ,, In some cases, higher enhancements have been obtained using other solvents such as alcohols. , With respect to fluorescence in TLC, enhancements with alkanes of the respective fluorescence responses of some alkaloids, polycyclic aromatic hydrocarbons (PAHs), and dansyl derivatives are reported to have been carried out on silica gel, alumina, and charge-transfer plates. − In general, they involve dipping the dry, developed plate into a solution of dodecane in hexane, liquid paraffin in hexane, or liquid paraffin in ether. Likewise, it has been reported that the fluorescence response in TLC for identical amounts of a PAH is significantly greater on a octadecyl-bonded plate than for a silica gel plate…”

“…[1][2][3] From this, phosphorescence and fluores-cence enhancements caused by paraffins have merited considerable interest. 4,5 As an example, n-hexane increases TLC phosphorescence in the detection of certain drugs. 4,6,7 In some cases, higher enhancements have been obtained using other solvents such as alcohols.…”

“…4,5 As an example, n-hexane increases TLC phosphorescence in the detection of certain drugs. 4,6,7 In some cases, higher enhancements have been obtained using other solvents such as alcohols. 4,5 With respect to fluorescence in TLC, enhancements with alkanes of the respective fluorescence responses of some alkaloids, polycyclic aromatic hydrocarbons (PAHs), and dansyl derivatives are reported to have been carried out on silica gel, alumina, and charge-transfer plates.…”

Low-temperature filter paper phosphorescence

“…Beside this potential source of errors, deviations may result from the very rapid decrease of the sensitivity of the formaldehyde determination which occurs when the S solution is used for a longer period: after 4 days the absorbance does not increase any more upon addition to a formaldehyde solution together with a P reagent. This is due to the decrease of the sulfite concentration owing to oxidation to sulfate in the weakly basic S solution (8).…”

“…It should be noted that Miller et al (7,8) have described a thin-layer phosphorimeter for scanning thin-layer chromatographic plates at 77 K. However, in their work (8), the sample (5 pL) was separated by TLC, the TLC plate was dried The luminescence intensity was measured at the emission maxima for each compound. Signals given in this table have been corrected for background emission.…”