Micellar liquid chromatography (MLC) is a simple well-established branch of high-performance liquid chromatography. The applications of MLC for the determination of numerous compounds in pharmaceutical formulations, biological samples, food, and environmental samples have been growing very rapidly. MLC technique has several advantages over other techniques, such as simultaneous separation of charged and uncharged solutes, rapid gradient capability, direct on-column injection of physiological fluids, unique separation selectivity, high reproducibility, robustness, enhanced luminescence detection, low cost, and safety. This review is devoted to the evaluation of the agreement of MLC with the principles of green chemistry which recently represents a universal trend. Also, it provides an overview on the basics of MLC, in addition to a survey of MLC methods published in the past five years for the assay of various compounds in different matrices.

The first stability-indicating HPLC method was developed and validated for azelastine HCl (AZL). The separation of AZL from its degradation products was achieved on a C18 column using acetonitrile-0.04 M phosphate buffer of pH 3.5 (32:68, v/v) as a mobile phase with UV-detection at 210 nm and naftazone as an internal standard. The method was rectilinear over the range of 0.2 -20.0 μg mL -1 with a detection limit of 7.05 ng mL -1 . The degradation behavior of AZL was studied under different ICH-recommended stress conditions along with a kinetic investigation; also, degradation products were identified by mass spectrometry. The method was applied for the quality control and stability assessment of AZL in eye drops and nasal spray. The obtained results were favorably compared with those obtained by a comparison method.

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A highly sensitive and simple spectrofluorimetric method was developed for the determination of loratadine (LRT) and desloratadine (DSL) in their pharmaceutical formulations. The proposed method is based on investigation of the fluorescence spectral behaviour of LRT and DSL in a sodium dodecyl sulphate (SDS) micellar system. In aqueous solution of acetate buffer of pH 4.5, the fluorescence intensities of both LRT and DSL were greatly enhanced (240%) in the presence of SDS. The fluorescence intensity was measured at 438 nm after excitation at 290 nm for both drugs. The fluorescence-concentration plots were rectilinear over the range 0.05-2.0 µg/mL for both LRT and DSL, with lower detection limits of 5.13 × 10(-3) and 6.35 × 10(-3) µg/mL for LRT and DSL, respectively. The method was successfully applied to the analysis of the two drugs in their commercial tablets, capsules and syrups, and the results were in good agreement with those obtained with the official or comparison methods. The proposed method is specific for the determination of LRT in the presence of other co-formulated drugs, such as pseudoephedrine. The application of the proposed method was extended to stability studies of LRT and DSL after exposure to different forced degradation conditions, such as acidic, alkaline and oxidative conditions, according to ICH guidelines.

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BackgroundAlendronate (ALD) is a member of the bisphosphonate family which is used for the treatment of osteoporosis, bone metastasis, Paget's disease, hypocalcaemia associated with malignancy and other conditions that feature bone fragility. ALD is a non-chromophoric compound so its determination by conventional spectrophotometric methods is not possible. So two derivatization reactions were proposed for determination of ALD through the reaction with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) and 2,4-dinitrofluorobenzene (DNFB) as chromogenic derivatizing reagents.ResultsThree simple and sensitive spectrophotometric methods are described for the determination of ALD. Method I is based on the reaction of ALD with NBD-Cl. Method II involved heat-catalyzed derivatization of ALD with DNFB, while, Method III is based on micellar-catalyzed reaction of the studied drug with DNFB at room temperature. The reactions products were measured at 472, 378 and 374 nm, for methods I, II and III, respectively. Beer's law was obeyed over the concentration ranges of 1.0-20.0, 4.0-40.0 and 1.5-30.0 μg/mL with lower limits of detection of 0.09, 1.06 and 0.06 μg/mL for Methods I, II and III, respectively. The proposed methods were applied for quantitation of the studied drug in its pure form with mean percentage recoveries of 100.47 ± 1.12, 100.17 ± 1.21 and 99.23 ± 1.26 for Methods I, II and III, respectively. Moreover the proposed methods were successfully applied for determination of ALD in different tablets. Proposals of the reactions pathways have been postulated.ConclusionThe proposed spectrophotometric methods provided sensitive, specific and inexpensive analytical procedures for determination of the non-chromophoric drug alendronate either per se or in its tablet dosage forms without interference from common excipients.Graphical abstract

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A simple and highly sensitive stability-indicating HPLC method was developed and validated for the determination of the new antidepressant agent, agomelatine (AGM). Separation of AGM from its stress-induced degradation products was achieved on a BDS Hypersil phenyl column (250 mm × 4.6 mm i.d., 5 µm particle size) using methanol-0.05 M phosphate buffer of pH 2.5 (35: 65, v/v) as a mobile phase with fluorescence detection at 230/370 nm. Naproxen was used as an internal standard. The method satisfied all the validation requirements, as evidenced by good linearity (correlation coefficient of 0.9999, over the concentration range 0.4-40.0 ng/mL), accuracy (recovery average 99.55 ± 0.90%), precision (intra-day RSD 0.54-1.35% and inter-day RSD 0.93-1.26%), robustness and specificity. The stability of AGM was investigated under different ICH recommended stress conditions including acidic, alkaline, neutral, oxidative and photolytic. AGM was found to be labile to acidic and alkaline degradation and a kinetic study was conducted to explore its degradation behavior. First-order degradation rate constants and half-life times were calculated in each case. The proposed method was applied for the determination of AGM in tablets and spiked human plasma with mean percentage recoveries of 99.87 ± 0.31 (n = 3) and 102.09 ± 5.01 (n = 5), respectively. Hence, the proposed method was successfully applied for the determination of AGM in human volunteer plasma. The results were compared statistically with those obtained by a comparison HPLC method revealing no significant differences between the two methods regarding accuracy and precision.