Rapid Commun. Mass Spectrom. 26, 37-42 (2012). Blotting method to transfer analytes separated on wettable HPTLC plates to a hydrophobic RP-8 HPTLC plate. The hydrophobic RP-8 HPTLC plate was wetted with 500 mL methanol then left to evaporate until solvent saturation on the surface was no longer visible. Then the wet plate was placed over the hydrophilic HPTLC plate and pressure was applied to the plates for 10 min. The two plates were separated, and the dried RP-8 plate was analyzed using a liquid microjunction surface sampling probe in combination with electrospray ionization mass spectrometry (LMJ-SSP/ESI-MS). This method provides different means of expanding the utility of the LMJ-SSP approach into the analysis of wettable-phase HPTLC surfaces.

J. AOAC Int. 93, 787-791 (2010). HPTLC of omeprazole on silica gel with chloroform - methanol 9:1 in a twin-trough chamber after saturation for 20 min. Quantitative determination by absorbance measurement at 302 nm. The hRf value of omeprazole was 39. Linearity was between 50 and 3000 ng/band. The intra-day and inter-day precision was 0.4-0.5 and 0.8-0.9 % (n = 2). The recovery was 98.4-99.1 %. LOD and LOQ were 8 and 24 ng/zone, respectively.

J. Planar Chromatogr. 24, 125-129 (2011). HPTLC of plant extracts and oxyresveratrol on silica gel, prewashed with methanol, with hexane - ethyl acetate - chloroform - methanol 15:10:17:8 in a twin-trough chamber lined with filter paper and saturated for 20 min. Quantitative determination by densitometry at 327 nm. LOD and LOQ were 50 and 200 ng/band, respectively. The hRf value of oxyresveratrol was 31. Intra-day and inter-day variation (%RSD) were consistently below 5.0 %. Within-day precisions for the replicate analysis (n = 3) were in the range of 1.1-4.1 %. Day-to-day replicates (n = 9) were between 2.1-2.8 %.

J. Trad. Chinese Veterinary Med. 5, 53-55 (2010). TLC of stachydrine on silica gel with acetone - ethanol - hydrochloric acid 10:6:1. Detection by spraying with bismuth potassium iodide - 1 % iron(III)chloride in ethanol 5:1 and heating at 100 ºC. Identification by comparison of the hRf value and zone color with the standard. Quantification of stachydrine by densitometry at 510 nm. Precision (%RSD within plate, n = 8) was 3.7 %. Stability of measurement (%RSD within 120 min, n = 5) was 4.5 %. Linearity was in the range of 3.2-38.3 µg/zone (r=0.997, n = 6). The recovery (by standard addition) was 96.6 % with a %RSD of 2.0 % (n = 6).

J. Planar Chromatogr. 24, 367-372 (2011). TLC of piroxicam, meloxicam, tenoxicam, and isoxicam on silica gel with ethyl acetate - ethanol - toluene 6:3:1 + 2 drops of 25 % ammonia. Quantitative determination by densitometry in absorbance mode at 360 nm. Linearity was between 50-500 ng/zone. The hRf value was 53 for piroxicam, 78 for meloxicam, 61 for tenoxicam, and 82 for isoxicam. LOD were 10, 30, 10, and 20 ng/zone and LOQ were 20, 80, 40, and 40 ng/zone for piroxicam, meloxicam, tenoxicam, and isoxicam, respectively. The recovery was in the range of 93.2-102.9 % with %RSD of less than 1 %. The inter- and intra-day precision (%RSD) was between 0.3-0.8 %.

Part II – is silica gel a reliable adsorbent for lipophilicity estimation? J. Planar Chromatogr. 25, 5-9 (2012). TLC of 35 simple compounds with known literature lipophilicity on silica gel with nine concentrations of six modifiers: acetone, dioxane, ethyl acetate, methylethylketone, propan-2-ol, and tetrahydrofuran as mobile phases. Different approaches for lipophilicity determination such as single TLC run, Soczewiñski-Wachtmeister equation coefficients, principal component analysis (PCA) of the retention matrix, and PARAFAC on a three-way array were applied.

J. Liq. Chromatogr. Relat. Technol. 35, 1686-1696 (2012). Reversed-phase TLC of azathioprine and nineteen of its derivatives on RP-18 with acetone-TRIS buffer pH 7.4 mixtures containing amounts of acetone in the range 40-80 % (v/v) in 5 % increments; detection at UV 254 nm. The lipophilicity parameters of these compounds were determined experimentally and compared with theoretical values.

J. of China Pharm. 20 (9), 19-20 (2011). Shujian capsules are a herbal TCM preparation prescribed clinically to treat shoulder arthritis. For quality control, TLC on silical gel for 1) for Cassia twig, with petroleum ether (60-90 ºC) – ethyl acetate 17:3, detection by spraying with 2 % 2,4-dinitrophenylhydrazine in ethanol and viewing in daylight; 2) for Radix sileris, with chloroform – methanol 4:1, detection at UV 254 nm; 3) for Angelica sinensis and Ligusticum wallichii, with toluene - ethyl acetate – formic acid 40:10:1, detection by spraying with 1 % ferric chloride – 1 % potassium ferricyanide 1:1 and viewing in daylight; 4) for the root of Kudzu vine, with chloroform – methanol – water 28:10:1, detection under UV 366 nm.