engleski

Optimization of mobile phases for the TLC separation of benzodiazpins

One of the major problems in chromatographic analysis is separation and identification of structurally similar substances, as well as evaluation of chromatographic systems and choice of optimal combination of mobile phase for identification of certain group of substances. On a set of twelve benzodiazepines (alprazolam, diazepam, medazepam, oxazepam, triazolam, prazepam, lorazepam, chlordiazepoxide, clonazepam, acetoxylorazepam, bromazepam and carbamazepine) optimal mobile phase was selected using numerical taxonomy methods. Plates coated with silica gel 60 RP 18F254s were used as stationary phase and detection was performed using CAMAG TLC Scanner 3 and Reprostar 3 system under UV light λ = 254 nm. From the pool of forty mobile phases described in literature the most suitable mobile phase was selected based on three numerical methods were used: calculation of information content (I), determination of discriminating power (DP) and the methods of numerical taxonomy. Comparison of the efficacy of chromatographic separation of examined substances regarding development time was also evaluated. Presuming the error range of 2% (E = 0.02) optimal mobile phase is n-hexane + chloroform + 99.5% acetic acid = 3 : 1 : 0.3 (v/v/v) having the highest DP = 0.9697 and midrange I = 3.585, development time being 27 minutes. This mobile phase was also optimal for the separation of benzodiazepines presuming the error range E = 0.03 (DP = 0.9697, I = 3.585) and E = 0.05 (DP = 0.9091, I = 3.252). For the combination of mobile phases all 10 combinations tested in error range 2 and 3% had DP and T values of 1.000 which means that all analyzed substances can be unambiguously distinguished. Results obtained in this work show that numerical approach for qualitative identification of structurally similar compounds present good mathematical basis for precise identification of the mentioned compounds.

TLC; optimization; benzodiazepins

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