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Thin layer chromatography–flame ionization detection (TLC–FID) is a versatile analytical technique that can be used for fast analysis of organic compounds. It has been implemented in past decades for the analysis of lipids and petrochemical products, but rarely in other fields. Despite the improvement in the latest Iatroscan model and the introduction of an automatic programmable sample spotter, this system is still struggling to gain acceptance in universities and major research laboratories. The reason behind this might be a lack of awareness on the potential application of this system to other fields of analytical chemistry. This review presents TLC–FID as a mature and reliable, state of the art technique that combines the separation power of TLC with FID as a universal detector, which can be applied to the analysis of a wide variety of organic compounds. Basic operational procedures and previous literature, including its potential for ultrafast analysis of commercial samples, are discussed in order to create awareness on the potentials of this piece of equipment to other fields.

In this study, a simple and robust capillary electrophoresis method with capacitively coupled contactless conductivity detection (C4D) is developed for the determination of the tetracycline antibiotics (1) tetracycline, (2) chlortetracycline and (3) oxytetracycline. An uncoated, fused silica capillary (60.2 cm long, 75 µm i.d.) and a solution of 50 mM tris(hydroxymethyl) aminomethane, 50 mM l-histidine and 5 mM methyl-β-cyclodextrin, without pH adjustment (pH 8.76), was used as background electrolyte. Electrophoresis at + 25 kV showed a rapid analysis with sufficient resolution among the three antibiotics in the order of tetracycline, chlortetracycline and oxytetracycline. Successive inter-injection rinsing (20 psi) of the capillary ensured intra- and inter-day repeatability (0.9–2.2% RSD and 2.0–4.5% RSD, respectively, for relative peak areas). The method showed satisfactory performance in terms of selectivity, accuracy (99.3–101.4%) and linearity (R2 = 0.999). Finally, the method was applied to commercial samples of tetracycline, oxytetracycline and chlortetracycline. This method can be applied for rapid quality control in developing countries in particular, and across the globe in general.

The present study explores the potential of 10-day-old zebrafish (Danio rerio) as a predictive blood-brain-barrier model using a set of 7 pharmaceutical agents. For this purpose, zebrafish were incubated with each of these 7 drugs separately via the route of immersion and the concentration reaching the brain was determined by applying a brain extraction procedure allowing isolation of the intact brain from the head of the zebrafish larvae. Sample analysis was performed utilizing capillary ultra-high performance liquid chromatography (cap-UHPLC) on a Pepmap RSLC C18 capillary column (150 mm × 300 μm, dp = 2 μm) coupled to a variable wavelength UV detector. Gradient separation was performed in 28 min at a flow rate of 5 μL/min and the optimal injection volume was determined to be 1 μL. The brain extraction procedure was established for the zebrafish strain TG898 exhibiting red fluorescence of the brain, allowing control of the integrity of the extracted parts. Quantitative experiments carried out on pooled samples of six zebrafish (n = 6) demonstrated the selective semipermeable nature of the blood-brain barrier after incubating the zebrafish at the maximum tolerated concentration for the investigated pharmaceuticals. The obtained brain-to-trunk ratios ranged between 0.3 for the most excluded compound and 1.2 for the pharmaceutical agent being most accumulated in the brain of the fish.

A robust, specific, precise and sensitive high-performance liquid chromatographic method has been described for purity control of temocillin. Chromatographic separation was achieved using a Symmetry C18 (150 × 4.6 mm, 5 µm) column kept at 30 °C. The mobile phase consisted of a gradient mixture of mobile phases A (5 g/L solution of Na2HPO4·2H2O, pH 7) and B (ACN-MeOH-H2O, 50:10:40 v/v/v) pumped at a flow rate of 1.0 mL/min. UV detection was performed at 235 nm. The developed method was validated according to the ICH guidelines for its robustness, selectivity, sensitivity, precision and linearity. An experimental design was applied for the robustness study. Linearity was assessed both at impurity level in the range from LOQ to 10 % and assay level from 25 % to 150 % (0.6 mg/mL = 100 %). It is the first liquid chromatographic method described for the separation of temocillin and its potential impurities. It was possible to identify four degradation products from the forced degradation studies. The degradants do not interfere with the main peak and other known impurities showing that the method is specific and stability-indicating.

The aim of the study was to develop a new, simple and cost-effective liquid chromatography–ultraviolet (LC–UV) method for determination of the peptide product from an enzymatic in vitro reaction. The method permits monitoring of the process of Abl1 tyrosine kinase inhibition by different inhibitors. Chromatographic separation was achieved on an Alltima C18 5 μm, 250 × 4.6 mm column using acetonitrile–water (22:78, v/v) with 0.05 % trifluoroacetic acid as mobile phase. The signal was monitored at 210 nm. The calibration curve was plotted after data transformation and the residual plot indicated a good fit of the transformed data with a linear model. The determination coefficient was 0.997. Repeatability and intermediate precision RSD were less than 10 % and accuracy was from −1.6 to +5.3 %. The stability of the sample was acceptable for 3 days in the autosampler. The validated LC–UV method was applied to study inhibitors of Abl1 tyrosine kinase. The measured inhibitory activity of model inhibitors (imatinib and nilotinib) was consistent with previous reports. Three natural products (quercetin, chrysophanol and resveratrol) were tested in this system and the inhibition potency ranking was quercetin > chrysophanol > resveratrol when their concentrations were set at 1 and 10 μM. However, the ranking for the three natural products reversed to quercetin < chrysophanol < resveratrol when their concentrations were 0.1 μM. The developed method is characterized by a widespread detection mode, easy operation and low cost for enzyme activity study or peptide analysis.

The development of a simple reversed phase ion pair liquid chromatographic method for the assay of kanamycin A has been described. Because of the lack of a UV chromophore in the structure of kanamycin A, borate complexation was used to allow direct UV detection at 205 nm. Three columns were evaluated in this study: Zorbax Extend C18 (4.6 mm × 250 mm; 5 μm), XBridge C18 (4.6 mm × 250 mm; 5 μm) and apHera C18 (4.6 mm × 250 mm; 5 μm). The mobile phase was a mixture of 0.1 M disodium tetraborate (pH 9.0) and water (20:80, v/v) supplemented with 0.5 g L−1 sodium octanesulphonate. Final chromatographic conditions were achieved on the XBridge column at 50 °C. The method was validated according to ICH guidelines and applied to a commercially available sample. It is much faster and more specific than the current microbiological assay prescribed in the European Pharmacopoeia. No expensive equipment is necessary to perform this assay making it a viable replacement.

A gradient liquid chromatographic (LC) method for control of emtricitabine (FTC) was validated for the analysis of FTC formulations (capsules and oral solution) and fixed-dose-combination tablets containing FTC [FTC combined with tenofovir disoproxil fumarate (TDF) and FTC combined with TDF and efavirenz (EFV)]. The method is based on the purity test recently prescribed in the International Pharmacopoeia and uses a Hypersil BDS C18 column (25 cm × 4.6 mm i.d.), 5 μm kept at a temperature of 35 °C. Other reversed-phase columns were also investigated. The mobile phases for gradient elution consist of acetonitrile, phosphate buffer and water. The flow rate is 1.0 mL min−1 and UV detection is performed at 280 nm. The method is capable of separating the main components from one another, from the inactive ingredients and from the main degradation products. The method was validated with respect to accuracy, precision, sensitivity and linearity for each component and the solution media were optimized. Finally, commercial FTC capsules, FTC oral solution, FTC/TDF tablets and FTC/TDF/EFV tablets were examined.

Several gentamicin bulk samples from different origins were investigated using an LC/MS method. LC equipped with ion trap MS with positive ionization was performed on a Capcell Pak C18 (AQ) column with the mobile phase containing 50 mM trifluoroacetic (TFA) and methanol. Impurities present in batches of gentamicin bulk samples were elucidated and compared according to their fragmentation behavior. In total seventeen impurities present in samples, five impurities were not elucidated and two compounds were identified preliminarily. It was observed that the impurity profiles were different in samples from different origins which indicate necessity in the quality control of gentamicin.

A liquid chromatographic method with UV detection was developed for the assay of a tablet for HIV (human immunodeficiency virus) treatment containing three active components, which are emtricitabine, tenofovir disoproxil fumarate and rilpivirine. A Hypersil BDS-C18 column was used as stationary phase and the assay was performed with gradient elution using mobile phases containing acetonitrile, 0.2 M potassium dihydrogen phosphate and water. Dimethyl sulfoxide–distilled water (1:1) was used as solvent for the active components. The method proved to be selective, linear, repeatable, sensitive and easy to perform.

The application of liquid chromatography–ion trap mass spectrometry for the characterization of linear and cyclic polypeptide antibiotics was investigated. The aim was on-line identification of impurities in those antibiotic complexes without recourse to time-consuming isolation and purification procedures. Hyphenated techniques, such as liquid chromatography coupled to mass spectrometry, are ideally suited for this purpose. Characterization was performed with an ion trap mass spectrometer offering MS n capability; this enables more structural information to be obtained. Liquid chromatography in combination with ion trap mass spectrometry was successfully applied for the characterization of impurities in gramicidin, polymyxin B, polymyxin E, and bacitracin and the study of the degradation products of polymyxins B and E.