Zoltán Végh

The frustrated reviewer — Recurrent failures in manuscripts describing validation of quantitative TLC/HPTLC procedures for analysis of pharmaceuticals

Analytical procedures to be used in pharmaceutical quality control have to be validated strictly in accordance with highly formalized standards and guidance. Manuscripts submitted for publication presenting new procedures must therefore describe the corresponding validation characteristics and the validation approach and procedure accordingly. Interestingly, many of these manuscripts and — what is worse — already published (and therefore accepted) articles in various periodicals are characterized by several typical methodological failures and misconceptions — even though authors have regularly been informed of such mistakes in the hope they can be avoided. The corresponding ICH guideline seems to be well-known, and is frequently cited in these manuscripts, but to some extent is not fully understood and is even partially neglected. In this paper the authors present a collection of typical failures, misconceptions, and misleading data captured as reviewers and readers of published articles over the last two years, thus giving a survey of the most frequent problems of TLC/HPTLC validation. Moreover, the authors provide a list of references describing optimum approaches to validation of specific TLC/HPTLC procedures. We suggest these are followed in addition to the general concepts of the ICH guideline.

OPLC, a Method between TLC and HPLC, for Purity Testing of Norethisterone Bulk Drug Substance and Tablet

An OPLC purity test suitable for routine analysis of norethisterone bulk drug substance and in tablets has been developed. Separation was performed on a fine-particle silica gel adsorbent layer by continuous development with n-hexane and butyl acetate—chloroform, 85 + 15 (v/v), as mobile phases. Visualization of the chromatogram by use of sulfuric acid enables detection of less than 0.05% of possible impurities by use of long-wave UV illumination. The selectivity and efficiency of this OPLC method were compared with those of the pharmacopeial TLC methods and those of HPLC method.

Comparison of OPLC and other Chromatographic Methods (TLC, HPLC, and GC) for In-Process Purity Testing of Nandrolone

A semiquantitative OPLC purity test has been developed for in-process control of nandrolone and compared with other chromato-graphic methods. TLC was not sufficiently selective, a key impurity with low UV absorption could not be detected by HPLC, and nan-drolone was slightly degraded during gas chromatography. OPLC proved to be a suitable means of testing for all potential impurities in nandrolone. The separation was performed by multiple development on fine-particle silica gel with cyclohexane—ethyl acetate—chloroform, 50 + 25 + 25 (v/v), as mobile phase. After spraying the chro-matograms with sulfuric acid, then heating, the impurities could be sensitively detected by visual inspection in long-wave UV light. Detection limits were ≤0.01 μg.

Optimization of the Visualization of Steroids Separated by OPLC

The acidic visualization methods most often used for steroids have been optimized and compared. Sulfuric acid at three different concentrations, phosphomolybdic acid, and phosphoric acid, with different heating temperatures for different times, have been examined as reagents for visualization of seven steroids separated by OPLC on HPTLC silica gel as adsorbent. For sulfuric and phosphoric acids the chromatograms were evaluated by inspection under long-wavelength UV light (366 nm). For phosphomolybdic acid the chromatograms were evaluated in daylight. It was found that visualization at higher temperatures for shorter periods usually results in greater sensitivity, although heating for longer periods at lower temperatures results in a more stable, robust visualization.

OPLC Analysis of Polyamines in Wheat Seedlings under Cadmium Stress

Two wheat cultivars (Triticum aestivum L. cv. Chinese Spring and Cappelle Desprez) differing in drought stress tolerance were treated with two concentrations of cadmium (10-7 and 10-3 M) to investigate whether there is also any difference in their heavy-metal tolerance. Overpressured layer chromatography (OPLC) with off-line fluorescence detection was used to monitor cadmium stress-induced changes in the polyamine content of wheat seedlings. Significant differences were found between the spermidine (Spd) and putrescine (Put) content of the two wheat cultivars. The Spd content of the moderately drought-tolerant Chinese Spring increased both in shoots and roots at the higher Cd concentration compared with the control whereas in the drought-sensitive Cappelle Desprez the Spd level was reduced by both Cd treatments. Put content increased with the amount of Cd to which the roots of Chinese Spring wheat were exposed. In the Cappelle Desprez cultivar the Put content of both organs was higher at both Cd concentrations compared with the control.

2.5. Planar chromatography

Publisher Summary Planar chromatography is an essential tool for testing the impurity profile of pharmaceutical drug substances and products . When synthesising a new molecule or establishing a new technology this simple method is the first tester in the synthetic chemical research laboratory. For testing the impurity profile of a new entity, the use of different independent chromatographic techniques is advisable to explore all of the potential known and unknown related substances contained in it as impurities. These methods are usually thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC). As HPLC usually works in the reversed phase and TLC in normal phase mode, these methods complement each other and they are suitable for testing all types of impurities, both highly polar and non- polar, of the new entity and an old drug prepared by a new or modified technology.