62nd Indian Pharmaceutical Congress Abstract No. F-235 (2010). TLC of metformin and glimepiride on silica gel with 0.5 % ammonium sulfate – water – methanol – ethyl acetate 2:2:1:1. Quantitative determination by absorbance measurement at 254 nm. The method was found to be linear in the range of 300-500 ng/band for glimepiride and 150-250 µg/band for metformin.

62nd Indian Pharmaceutical Congress Abstract No. F-266 (2010). TLC of metformin and pioglitazone, extracted with methanol from bulk and pharmaceutical formulation, on prewashed silica gel with toluene – methanol – triethylamine 40:10:1. The hRf values of metformin and pioglitazone were 25 and 50, respectively. Quantitative determination by absorbance measurement at 230 nm. The linearity was in the range of 100-1000 ng/band for metformin and 200-1200 ng/band for pioglitazone: the correlation coefficients (r) were 0.9958 and 0.9992, respectively.

Brazilian Journal of Microbiology 42, 172-180 (2011). TLC of patulin on silica gel with toluene – ethyl acetate – formic acid 5:4:1. Detection by spraying with 0.5 % aqueous methyl-benzothiazolinone hydrazone hydrochloride monohydrate, followed by heating at 130 °C for 15 min. Quantitative determination by absorbance measurement at 366 nm. Linearity was between 45 and 2100 µg/kg. The limits of detection and quantification were 0.005 µg/kg and 14 µg/kg. The relative standard deviation for repatibility was 6.2 %. Recovery (by standard addition) was 88 % for patulin.

Acta Chromatographica 22 (2), 297-305 (2010). Description of a simple, precise, and accurate method for simultaneous quantification of aspirin, atorvastatin calcium and clopidogrel bisulphate by HPTLC on silica gel with toluene – methanol - formic acid 65:35:1. The hRf values were 26, 47, and 78 for aspirin, atorvastatin calcium, and clopidogrel bisulphate, respectively. Quantification by densitometry at 254 nm. The precision intra-day and inter-day was in the ranges of 0.2–0.7 %RSD and 0.5–1.0 %RSD for aspirin, 0.4–0.9 %RSD and 0.4–0.6 %RSD for atorvastatin calcium, and 0.3–0.7 %RSD and 0.4–0.9 %RSD for clopidogrel bisulphate.

Acta Chromatographica 21(1), (2009) . This study focused on the attempt to suppress the spontaneous oscillatory in-vitro chiral conversion of a-substituted propionic acids using, as example, L-lactic acid dissolved in water in the presence of copper(II) cations to check whether the coordinate covalent bonds between copper(II) and L-lactic acid ligands prevented the latter species from oscillatory chiral conversion. Aqueous solutions of copper(II) acetate and lactic acid in the molar ratios 1:1, 1:2, and 1:3 were stored and the possible chiral conversion of L-lactic acid was monitored by TLC, polarimetry, and circular dichroism spectroscopy. It was found that chelating of copper(II)cations with L-lactic acid did not result in suppression of the spontaneous oscillatory in-vitro chiral conversion of the acid from the TLC data. Different molar proportions of copper(II) cation and L-lactic acid had somewhat different effects on the dynamics of conversion, in contrast, when L-lactic acid is dissolved in water in the presence of copper(II)cations almost no chiral conversion is observed from polarimetric and circular dichroism studies. It was therefore concluded that chelating of copper(II) cations with L-lactic acid stabilizes the chiral structure of the acid in solution. The structure-stabilizing effect of copper(II) cations is weakened by the TLC system due to the interaction of the copper(II)-L-lactic acid complex with the silica gel.

J. Planar Chromatogr. 24, 206-210 (2011). HPTLC of free sterols, free fatty acids, triacylglycerols, methyl esters, and steryl esters in larvae samples on silica gel with concentration zone, with petroleum ether - diethyl ether - glacial acetic acid 80:20:1 in a twin-trough chamber saturated for 20 min at 21 +/- 1 °C and a relative humidity of 25 %. Detection by spraying with 5 % ethanolic phosphomolybdic acid solution. Quantitative determination by densitometry at 610 nm.

J. Liq. Chromatogr. Relat. Technol. 32, 1273-1288 (2009). HPTLC of Sudan I (1), II (2), III (3), IV (4), Sudan Red B (5), Sudan Red 7B (6), Sudan Red G (7), Para Red (8), FD&C Orange 2 (9), Butter Yellow (10), Citrus Red 2 (11), Toluidine Red (12), and Disperse Orange 11 (13) in paprika, chili, and curry on RP-18 with acetonitrile - ammonia 25 % 19:1. Quantitative determination by absorbance measurement at absorption maxima of each dye. The hRf values of compounds (1) - (13) were 61, 54, 48, 29, 18, 11, 69, 63, 56, 48, 39, 18 and 11, respectively. Visual detection limits were 3 ppm for most dyes in either matrix, 5 ppm for Sudan I, 13 ppm for Disperse Orange, and 7 ppm for Butter Yellow. The limits of detection by densitometry were lower by a factor of 2 for all dyes and values of 1-3 ppm were reached except for Disperse Orange with a limit of detction of 7 ppm. Average recoveries ranged from 95.0-110.8 %. The HPTLC method is successfully applied in the routine control of illegal dyes in food by surveillance authorities.

J. AOAC Int. 93, 765-770 (2010). HPTLC of paracetamol (PAR), diclofenac potassium (DCL), and famotidine (FAM) on silica gel (prewashed with methanol) with toluene - acetone - methanol - formic acid 500:200:200:1 in a twin-trough chamber after preconditioning for 30 min at room temperature (25 +/- 2°C ) at a relative humidity of 60 +/- 5 %. Quantitative determination by absorbance measurement at 274 nm. The hRf value of paracetamol was 62, of diclofenac potassium 75, and of famotidine 17. Linearity was between 1625-9750 ng/zone for PAR, 250-1500 ng/zone for DCL, and 100-600 ng/zone for FAM. The %RSD values for repeatability and intermediate precision were below 2 %. The LOD and LOQ were 50 and 100 ng/zone for PAR and DCL, and 10 and 50 ng/zone for FAM. The %RSD of peak areas was calculated for each parameter and was found to be less than 2 %. Recoveries (by standard addition) were in the range of 95-98 % at various added concentrations.