Amruta S. Tambe

Crown ethers as stationary phases in gas chromatography : comparison between dibenzo-18-crown-6, dibenzo-24-crown-8 and dicyclohexano-24-crown-8- with respect to polarity, selectivity and stability

Abstract Chromatogrpahic characteristics, including thermal stability, polarity and selectivity, of dibenzo-18-crown-6 (DB18C6), dibenzo-24-crown-8 (DB2C8) and dicyclohexano-24-crown-8 (DCH24C8) were compared. Phase transition studies were carried out by plotting graphs of log(specific retention volume) against the inverse of absolute temperature. Nitrochlorobenzene, nitrophenol, nitroaniline, chloroaniline, cresol, chlorophenol and dimethylphenol isomers were injected onto these crown ether stationary phases at 3%, 10% and 20% loadings. Dimethylphenol and nitrochlorobenzene isomers were separated well on 10% DB24CB and 10% DCH24C8 columns. DB18C6 is useful for the direct analysis of nitrophenol and nitroaniline isomers without any derivatization.

Separation of opium alkaloids by thin-layer chromatography combined with flame ionization detection using the peak pyrolysis method☆

Abstract A fast, efficient and reproducible method for the separation of the five major opium alkaloids by thin-layer chromatography coupled to flame ionization detection is reported. The alkaloids were separated without derivatization on silica rods of type SII using the partial scanning or peak pyrolysis method —where organic matter separated on the rods are burnt when they pass through the hydrogen flame— between the stages of a two-step development system. The first development, in benzene-acetonitrile-ethyl acetate (60:20:20, v/v) separated narcotine and papaverine. Morphine, codeine and thebaine were separated during the second development in ethyl acetate-benzene-acetonitrile-ammonium hydroxide (25:30:40:5, v/v). The best binary solvent system was benzene-ethanol (9.5:0.5, v/v) and (9:1, v/v) which separated all the five alkaloids simultaneously.

Genetic programming based quantitative structure–retention relationships for the prediction of Kovats retention indices

The development of quantitative structure-retention relationships (QSRR) aims at constructing an appropriate linear/nonlinear model for the prediction of the retention behavior (such as Kovats retention index) of a solute on a chromatographic column. Commonly, multi-linear regression and artificial neural networks are used in the QSRR development in the gas chromatography (GC). In this study, an artificial intelligence based data-driven modeling formalism, namely genetic programming (GP), has been introduced for the development of quantitative structure based models predicting Kovats retention indices (KRI). The novelty of the GP formalism is that given an example dataset, it searches and optimizes both the form (structure) and the parameters of an appropriate linear/nonlinear data-fitting model. Thus, it is not necessary to pre-specify the form of the data-fitting model in the GP-based modeling. These models are also less complex, simple to understand, and easy to deploy. The effectiveness of GP in constructing QSRRs has been demonstrated by developing models predicting KRIs of light hydrocarbons (case study-I) and adamantane derivatives (case study-II). In each case study, two-, three- and four-descriptor models have been developed using the KRI data available in the literature. The results of these studies clearly indicate that the GP-based models possess an excellent KRI prediction accuracy and generalization capability. Specifically, the best performing four-descriptor models in both the case studies have yielded high (>0.9) values of the coefficient of determination (R(2)) and low values of root mean squared error (RMSE) and mean absolute percent error (MAPE) for training, test and validation set data. The characteristic feature of this study is that it introduces a practical and an effective GP-based method for developing QSRRs in gas chromatography that can be gainfully utilized for developing other types of data-driven models in chromatography science.

High-performance liquid chromatographic determination of cyclohexylhydantoin and cyclohexylidenehydantoin formed during the synthesis of phenylhydantoin from hydantoin and cyclohexanone

Abstract dl -Phenylhydantoin can be converted into d -phenylglycine by an enzymatic process. d -phenylglycine is an important starting material in the production of β-lactams such as semisynthetic penicillins and cephalosporins. In our laboratory, the synthesis of phenylhydantoin was achieved from hydantoin and cyclohexanone in the presence of a base. An efficient and fast isocratic reversed-phase high-performance liquid chromatography method was developed for the determination of phenylhydantoin, cyclohexylhydantoin and cyclohexylidenehydantoin. Quantitative analysis was carried out by an external standard method.

Gas chromatographic analysis of diastereomers and enantiomers of β,γ-unsaturated esters and various analogues of butenolides including mint and isomint lactone and comparison with the high-performance liquid chromatographic analysis of their diastereomers☆

Abstract Butenolide is an α,β-unsaturated lactone. The butenolide moiety is present in numerous biologically active natural products, especially insect sex hormones. A method was developed for the synthesis of butenolides from β,γ-unsaturated esters. Separation of diastereomers and enantiomers of these esters and butenolides including mint and isomint lactone and heritionin by GC is reported. The order of elution of isomers of mint and isomint lactone was identified as RR, SS, SR and RS on a Chirasil-Val-D column. This was also confirmed by injecting these samples on to a column with an l -configuration. The separation of diastereomers by HPLC was also tried and the results were compared with those obtained by GC.

Gas chromatographic method for the determination of chlorobenzophenone isomers

Abstract A simple, rapid and an efficient gas chromatographic method for the determination of chlorobenzophenone isomers is described. This was necessary in order to determine the amounts of o- and m-chlorobenzophenone isomers in p-chlorobenzophenone, which is a starting material in the manufacture of Systral, an anti-Parkinsonism agent. Complete separation of chlorobenzophenone isomers was achieved using Apiezon L as stationary phase. The determination of o-chlorobenzophenone in p-chlorobenzophenone was carried out by using benzophenone as an internal standard. The minimum detectable amount of m-chlorobenzophenone in p-chlorobenzophenone was established.