J Chromatogr A 1638, 461895 (2021). Samples were sphingolipid-rich fractions of unproteinated blood plasma from healthy humans or from Fabry’s disease patients, as well as standards of sphingomyelin (SM) and of globotriaosylceramides (Gb3 = ceramide trihexosides), and related compounds (lyso-ceramide trihexosides, lactosyl ceramide, glucosyl ceramide). HPTLC on silica gel (Lichrosphere with spherical particles) by automated multiple development with a 9-step gradient, starting with pure methanol and ending with dichloromethane – methanol 9:1. Visualization and densitometry under UV 190 nm. Derivatization for Gb3 and derivatives (but not for SM) by immersion into orcinol solution (0.2 %, with sulfuric acid 10 %), followed by 15 min heating at 100 °C and by densitometry under visible light 550 nm. Bands of interest were directly eluted with methanol from underivatized plates into an ion-trap MS, through the oval head of a TLC-MS interface (with stainless steel frit to remove silica gel particles). Two different ionization processes were used: (A) electrospray ionization (ESI, capillary voltage 4 kV, endplate offset voltage -0.5 kV, nebulizer pressure 40 psi, drying gas 9 mL/min at 350 °C); (B) atmospheric pressure chemical ionization (APCI, capillary voltage 2–3 kV, current intensity 4.5 µA, nebulizer pressure 45 psi, drying gas 5 mL/min at 350 °C; vaporization at 450 °C). Full MS spectra were recorded up to m/z 1500 in positive ion mode. The relative ion intensities were used to quantify the detected species. Previous to this study, the precision of the elution head positioning was tested on Gb3 standard zones, comparing 3 positions for analyte elution: from the centre and from each higher or lower side of the band. The same main m/z peaks were observed in the 3 positions, but in different proportions. This was explained by the presence of coeluting Gb3 subclasses (the ceramide moiety CM being either saturated, mono-unsaturated fatty acyl with a slightly higher migration distance, or polar hydroxyl fatty acyl with the opposite effect on migration) and of coeluting Gb3 isoforms (the hexoside moiety consisting of glucose and/or galactose units). This resulted in the broadening and partial splitting of the standard band. In the plasma samples, 19 molecular species of Gb3 were identified (depending on the CM, the sugar isoforms being undistinguishable by MS): 5 with a saturated CM, 7 with two additional double bonds on the CM, 7 with a methylated CM. In case of Fabry’s disease, most Gb3 species with saturated CM were highly increased, whereas other species were decreased.

J. Sep. Sci. 45, 3800-3810 (2022). HPTLC of favipiravir (1) and meropenem (2) in human plasma on silica gel with ethyl acetate - methanol - water - formic acid 50:40:15:3. Quantitative determination by absorbance measurement at 300 nm for (1) and (2). The hRF values for (1) and (2) were 34 and 10, respectively. Linearity was between 0.1 and 20 µg/mL for (1) and 10 and 60 µg/mL for (2). Inter-day and intra-day precisions were below 5 % (n=3). The LOQ were 0.1 and 10 µg/mL for (1) and (2), respectively. Mean recovery was 99.7 % for (1) and 98.0 % for (2).

J Chromatogr A, 1619, 460945 (2020). Samples were lamotrigin as standard, or extracted with an oil-in-water microemulsion (10 µL butyl acetate, 4 mL n-butanol, 925 mg sodium dodecyl sulphate, 8.6 mL water) either from patients’ raw plasma (for separation from blood proteins) after spiking, or from commercial tablets dissolved in methanol. TLC on silica gel with a water-in-oil microemulsion of 9 mL butyl acetate, 1 mL n-butanol, 250 mg sodium dodecyl sulphate, 250 µL water. Both optimal microemulsions were predicted using Taguchi orthogonal array and Plackett-Burman design. Evaluation in UV 254 nm, quantification from the digital picture using four image processing software programs. For lamotrigin (hRF 24), limits of quantification were 170 ng for pure drug and 10 ng for spiked plasma. Linearity (in range 20–200 ng/spot) was directly obtained for the calibration curve in spiked plasma; however, for pure drug, linearity was obtained only when using log values of the calculated densities (300–3000 ng/spot).

J. Chromatogr. Sci. 60 (3), 267-273 (2022). HPTLC for the selective detection of the diuretic drug triamterene in pure form, tablets and human plasma, on silica gel with ethyl acetate - dimethylformamide - ammonia 70:27:3. Quantitative determination by fluorescence measurement at 440 nm improved the method sensitivity 250-fold compared with previously reported studies, and enabled the detection of triamterene in the linear concentration range of 0.8 to 60 ng/band for the pure drug and 1.0 to 60 ng/band for biological samples (human plasma).

J. Planar Chromatogr. 34, 411-418 (2021). HPTLC of sphingomyelin in erythrocyte membranes of patients on silica gel with chloroform - methanol - acetic acid - water 60:50:1:4. Detection by exposure to iodine vapor for 30 min. Quantitative determination by densitometric measurement of the intensity of individual zones and the red, green and blue values of the component colors. The hRF value for sphingomyelin was 86. Linearity was between 0.25 and 10 μg/zone. LOD and LOQ were 140 and 410 ng/zone, respectively. Intermediate precisions were below 2 % (n=3). Recovery was between 85 and 97 %.

Pharm. Res. 38, 127-140 (2021). HPTLC of [11C]metoclopramide in plasma, kidney, urine and liver extracts on silica gel with ethyl acetate - ethanol - 25 % ammonium hydroxide 16:4:1. Detection using a multisensitive phosphor screen. The hRF value for [11C]metoclopramide was 60. The method allowed kinetic analysis in different organs after radiotracer injection in mice.

J. Liq. Chromatogr. Relat. Technol. 44, 33-51 (2021). Review of analytical techniques for the determination of haloperidol, including TLC and HPTLC. Methods for the quantification of haloperidol in plasma samples and dosage forms using reverse phase TLC and silica gel HPTLC plates were discussed. In addition, methods for the study of lipophilicity of haloperidol were described. 

J. of Chromatogr. Sci. 58 (5), 411 - 417 (2020). Analysis of a binary mixture of silymarin (SR) and vitamin E (VE) acetate in their pure forms, pharmaceutical formulation and spiked human plasma, by HPTLC on silica gel with hexane - acetone - formic acid 140:60:3, detection at UV 215 nm, and quantification by densitometry. The linearity was 0.2 - 2.5 and 0.2 - 4.5 μg/band for SR and VE, respectively. Accuracy was 99.9 ± 1.2 % and 100.2 ± 1.6 % for SR and VE, respectively. The method was successfullly used for the determination of the studied drugs in their pharmaceutical formulation without any interference from excipients, and in spiked plasma samples. Statistical comparison of the results obtained by this HPTLC method showed no significant difference to the results obtained by the reported HPLC method.