Michael M. Frodyma

The application of spectral reflectance to thin-layer chromatography

Abstract The components of dye mixtures resolved on thin-layers plates were identified by direct examination of the plates by spectral reflectance The amounts of adsorbed dye were determined at the same time with a precision of approximatel ± 5%. Reflectance measurements carried out on spots removed from the plates and packed in an appropriate cell afforded a degree of precision identical to that attained with transmittance.

THE DETERMINATION BY REFLECTANCE SPECTROPHOTOMETRY OF AMINO ACIDS RESOLVED ON THIN-LAYER PLATES.

Abstract A procedure was devised whereby amino acids resolved on chromatoplates can be determined by spectral reflectance. Direct examination of plates yielded a degree of precision comparable to that afforded by direct transmission methods applied to paper chromatography. Precision approaching that afforded by transmittance is attained if the reflectance measurements are carried out on spots removed from the plates and specified precautions are observed in the generation of the ninhydrin color.

The application of ultraviolet reflectance spectroscopy to thin-layer chromatography.

Abstract A method which can be employed for both preparative and analytical purposes was devised for the resolution of salicylic acid-aspirin mixtures on chromatoplates. Ultraviolet reflectance spectroscopy was then used to determine the amounts of resolved material by carrying out measurements on spots removed from the dried plates and packed in a suitable cell.

An improved method for the determination of amino acids by spectral reflectance

Abstract A nonspray method is described whereby amino acids resolved on thin-layer plates can be estimated by spectral reflectance. In addition to facilitating the determination the elimination of the spraying operation with its attendant irregularities has resulted in a substantial increase in precision and accuracy. In this respect the method is competitive with paper chromatography, used in conjuction with such techniques as total scanning and the electronic integration of curves.

A simple semimicro cell for the measurement of spectral reflectance

Abstract The construction and method of employment of a simple cell suitable for the measurement of the spectral reflectance of semimicro samples, such as those removed from chromatoplates, are described. An attempt is also made to correlate the performance of the cell with current theories of reflectance spectroscopy using data obtained with a system consisting of Merck silica gel G and McCormick blue, a food dye.

Selection of the optimum concentration range for reflectance spectrophotometric analysis

Two graphical methods for selecting the optimum range and determining the maximum accuracy of reflectance spectrophotometric analysis are discussed. Results obtained with the use of two systems (Rhodamine B, which absorbs in the visible region of the spectrum, and aspirin, which absorbs in the ultraviolet region, both adsorbed on silica gel) are employed to illustrate how the methods might be employed in practice. Experimental results are contrasted with those expected by application of the Kubelka-Munk equation. The results indicate that the minimum relative error in concentration to be expected in reflectance spectrophotometric analysis is about 6% per 1 % reading error, and that the optimum range for analysis can be arrived at after plotting the reflectance data for either of the two systems discussed, whether the system conforms to the Kubelka-Munk equation or not.

Analysis by reflectance spectroscopy of nucleotides resolved on chromatoplates

Abstract A procedure has been devised whereby five nucleotides—adenosine-3′-(2′)-phosphoric acid, adenosine 5′-diphosphate, cytidine-2′(3′)-phosphate, disodium guanosine-3′(2′)-phosphoric acid—resolved on cellulose thin-layer plates can be analyzed by means of ultraviolet reflectance spectroscopy. The procedure makes it possible to determine the concentration of the adsorded nucleotides, which can also be identified by using reflectance spectra in conjunction with R f values, with a precision of 2–6%.

Cation analysis by thin-layer chromatography and reflectance spectroscopy : Part I. The rapid identificaiion of cations resolved on thin-layer plates

Abstract A rapid method has been devised whereby 14 cations — Al3+, Bi3+, Cd2+, Cr3+, Co2+, Cu2+, Fe3+, Pb2+, Mn2+, Hg2+, Ni2+, Ag+, Sn2+ and Zn2+ —. can be separated on one-dimensional, cellulose thin-layer plates and then identified by means of their reflectance spectra The procedure requires micro-amounts of sample and only one spray reagent.

Differential reflectance spectrophotometry—I: High-reflectance method for determination of micro amounts of substances resolved on thin plates

The basic principles of differential high-reflectance spectroscopy are discussed from the standpoint of the determination of substances resolved on chromatoplates. Results obtained with the use of two systems, nickel dimethylglyoximate or copper neocuproinate adsorbed on cellulose, are used as illustrations. A graphical method for selecting the optimum concentration range for analysis and for determining the maximum accuracy attainable is also outlined. When contrasted with the conventional method of measuring reflectance, the technique promises substantially increased accuracy over a wider concentration range and seems particularly suited to the analysis of trace amounts of material.

A rapid method for the determination of substances resolved on thin-layer plates

Abstract A method is described for the removal of spots from thin-layer plates, which, when used in conjunction with spectral reflectance, makes possible the rapid analysis of substances resolved on chromatoplates. Data are provided which indicate that the surfaces laid down by a commercial applicator are, with certain limitations, satisfactory for use with this technique.