Analysis of nitrophenols in cloud water with a miniaturized light-phase rotary perforator and HPLC-MS

An all-glass miniaturized light-phase rotary perforator for the enrichment of polar compounds has been modified/miniaturized and applied. Its application is demonstrated here for the analysis of nitrophenols and dinitrophenols from low-concentration/low-volume samples. For the method development of high-performance liquid chromatography–mass spectrometry (MS) four eluents were tested: (1) water–methanol, (2) acetic acid–methanol, (3) trifluoroacetic acid–methanol and (4) water–acetonitrile. The last eluent mentioned was used for the subsequent investigation of samples from field experiments. Detection limits varied between 1 ng and 50 pg. The relative standard deviation in repeated measurements was below 15%, corresponding to a good reproducibility. Recoveries ranged between 31 and 100%, showing a significant dependence on the extraction time and the final volume of the sample after evaporation. Quantification was carried out by using deuterated 4-nitrophenol and 2,4-dinitrophenol as standards and applying previously determined response factors. Structure determination of further substances under atmospheric pressure chemical ionization was performed by a first screening with a source collision-induced dissociation, followed by the definite analysis by MS ⁿ . The first results are shown for cloud water, fog water and rainwater samples from different locations.     

Qualitative and quantitative analyses of three bioactive compounds in different parts of Forsythia suspensa by high-performance liquid chromatography-electrospray ionization-mass spectrometry

A high-performance liquid chromatography-electrospray ionization-mass spectrometry (HPLC-ESI-MS) analytical method was developed to simultaneously detect and quantify three main distinctive compounds (forsythiaside, rutin and forsythin) in different parts of Forsythia suspensa (F. suspensa), an herbal medicine. This was the first report on the quantification of bioactive constituents in different parts of F. suspensa by HPLC-ESI-MS analytical method. The calibration curves of the three compounds showed good linearity (R² > 0.9994). The method was reproducible with intra- and inter-day variation less than 1.35% and 2.00%, respectively. The recovery of the assay was in the range of 98.27–101.07%. The results indicated that the developed assay could be considered as a suitable quality control method for this commonly used herbal medicine.     

Simultaneous determination of amiodarone and its metabolite desethylamiodarone by high-performance liquid chromatography with chemiluminescent detection

A novel method was developed for the determination of amiodarone and desethylamiodarone by high-performance liquid chromatography (HPLC) coupled with chemiluminescent (CL) detection. The procedure is based on the post-column photolysis of the analytes into photoproducts which are active in the tris(2,2′-bipyridyl)ruthenium(III) [Ru(bpy)₃³⁺] CL system. Ru(bpy)₃³⁺ was on-line generated by photo-oxidation of the Ru(II) complex in the presence of peroxydisulfate. The separation was carried out on a Mediterranea C₁₈ column with isocratic elution using a mixture of methanol and 0.017 mol L⁻¹ ammonium sulfate buffer of pH 6.8. Under the optimum conditions, analytical curves, based on standard solutions, were linear over the range 0.1-50 μg mL⁻¹ for amiodarone and 0.5-25 μg mL⁻¹ for desethylamiodarone. The detection limits of amiodarone and desethylamiodarone were 0.02 and 0.11 μg mL⁻¹, respectively. Intra- and inter-day precision values of 0.9% relative standard deviation (R.S.D.) (n = 10) and 1.6% R.S.D. (n = 15), respectively, were obtained. The method was applied successfully to the determination of these compounds in serum and pharmaceutical formulations.     

Application of dispersive liquid-liquid microextraction and high-performance liquid chromatography for the determination of three phthalate esters in water samples

A novel method, dispersive liquid-liquid microextraction (DLLME) coupled with high-performance liquid chromatography-variable wavelength detector (HPLC-VWD), has been developed for the determination of three phthalate esters (dimethyl phthalate (DMP), diethyl phthalate (DEP), and di-n-butyl phthalate (DnBP)) in water samples. A mixture of extraction solvent (41 μL carbon tetrachloride) and dispersive solvent (0.75 mL acetonitrile) were rapidly injected into 5.0 mL aqueous sample for the formation of cloudy solution, the analytes in the sample were extracted into the fine droplets of CCl₄. After extraction, phase separation was performed by centrifugation and the enriched analytes in the sedimented phase were determined by HPLC-VWD. Some important parameters, such as the kind and volume of extraction solvent and dispersive solvent, extraction time and salt effect were investigated and optimized. Under the optimum extraction condition, the method yields a linear calibration curve in the concentration range from 5 to 5000 ng mL⁻¹ for target analytes. The enrichment factors for DMP, DEP and DnBP were 45, 92 and 196, respectively, and the limits of detection were 1.8, 0.88 and 0.64 ng mL⁻¹, respectively. The relative standard deviations (R.S.D.) for the extraction of 10 ng mL⁻¹ of phthalate esters were in the range of 4.3-5.9% (n = 7). Lake water, tap water and bottled mineral water samples were successfully analyzed using the proposed method.     

Simultaneous HPTLC Determination of Escitalopram Oxalate and Clonazepam in Combined Tablets

A new, simple high-performance thin-layer chromatographic method has been established and validated for simultaneous determination of escitalopram oxalate and clonazepam in a combined tablet dosage form. The drugs were separated on aluminum plates precoated with silica gel 60 F₂₅₄; toluene–ethyl acetate–triethylamine 7:3.5:3 (v/v) was used as mobile phase. Quantitative analysis was performed by densitometric scanning at 258 nm. The method was validated for linearity, accuracy, precision, and robustness. The calibration plot was linear over the ranges 250–2,500 and 50–500 ng band⁻¹ for escitalopram oxalate and clonazepam, respectively. The method was successfully applied to the analysis of drugs in a pharmaceutical formulation.     

Magnetic ionic liquids as non-conventional extraction solvents for the determination of polycyclic aromatic hydrocarbons

This work describes the applicability of magnetic ionic liquids (MILs) in the analytical determination of a group of heavy polycyclic aromatic hydrocarbons. Three different MILs, namely, benzyltrioctylammonium bromotrichloroferrate (III) (MIL A), methoxybenzyltrioctylammonium bromotrichloroferrate (III) (MIL B), and 1,12-di(3-benzylbenzimidazolium) dodecane bis[(trifluoromethyl)sulfonyl)]imide bromotrichloroferrate (III) (MIL C), were designed to exhibit hydrophobic properties, and their performance examined in a microextraction method for hydrophobic analytes. The magnet-assisted approach with these MILs was performed in combination with high performance liquid chromatography and fluorescence detection. The study of the extraction performance showed that MIL A was the most suitable solvent for the extraction of polycyclic aromatic hydrocarbons and under optimum conditions the fast extraction step required ∼20 μL of MIL A for 10 mL of aqueous sample, 24 mmol L⁻¹ NaOH, high ionic strength content of NaCl (25% (w/v)), 500 μL of acetone as dispersive solvent, and 5 min of vortex. The desorption step required the aid of an external magnetic field with a strong NdFeB magnet (the separation requires few seconds), two back-extraction steps for polycyclic aromatic hydrocarbons retained in the MIL droplet with n-hexane, evaporation and reconstitution with acetonitrile. The overall method presented limits of detection down to 5 ng L⁻¹, relative recoveries ranging from 91.5 to 119%, and inter-day reproducibility values (expressed as relative standard derivation) lower than 16.4% for a spiked level of 0.4 μg L⁻¹ (n = 9). The method was also applied for the analysis of real samples, including tap water, wastewater, and tea infusion.     

Development and validation of a high-throughput high-performance liquid chromatographic assay for the determination of caffeine in food samples using a monolithic column

The present study reports the development and validation of a high-throughput high-performance liquid chromatographic (HPLC) assay for the determination of caffeine in food samples. The analyte was separated rapidly from sample matrix using a short monolithic column (50 mm × 4.6 mm i.d.). The flow rate was 3.0 mL min⁻¹, while the mobile phase consisted of ACN/water (10:90, v/v). Caffeine was detected directly at 274 nm. Under the optimal HPLC conditions, the sampling rate was 60 h⁻¹. The assay was validated for linearity, LOD and LOQ, precision, selectivity and ruggedness. The case of external calibration versus standard addition for the analysis of real samples was also examined. The proposed assay was applied to the analysis of beverages and coffee samples.     

Determination of kynurenine levels in rat plasma by high-performance liquid chromatography with pre-column fluorescence derivatization

Kynurenine (KYN), a tryptophan metabolite, is a crucial compound for modulating neurotransmission because it can be metabolized in vivo into both quinolinic acid and kynurenic acid, which are the agonist and antagonist, respectively, of N-methyl-d-aspartate receptor. For the highly sensitive detection of KYN by high-performance liquid chromatography (HPLC), a fluorescence derivatization of KYN with a benzofurazan-type fluorogenic reagent, 4-N,N-dimethylaminosulfonyl-7-fluoro-2,1,3-benzoxadiazole (DBD-F) was investigated in the present study. KYN was derivatized with DBD-F (DBD-KYN) at 60 °C for 30 min, and separated on an octadecylsilica column with a gradient elution of the mobile phase, which consists of 0.1% formic acid in acetonitrile/methanol/water. DBD-KYN was detected fluorimetrically at 553 nm with an excitation wavelength of 431 nm. The limits of detection and quantification were approximately 0.30 pmol [signal-to-noise ratio (S/N) 3] and 1.0 pmol (S/N, 10) on column, respectively. Plasma KYN levels were successfully determined using 10 μL of rat plasma with satisfactory precision and accuracy. Intra- and inter-day precisions and accuracies were 1.7-6.8%, and −10 to 9.6%, respectively. KYN levels in plasma of male Sprague-Dawley rats (7 weeks old) were approximately 2.4 ± 0.32 μmol L⁻¹ (n = 4). The proposed HPLC method was applied to determine KYN levels in the plasma of ketamine-treated rats—the animal model of schizophrenia.     

Analysis of berberine and total alkaloid content in cortex phellodendri by near infrared spectroscopy (NIRS) compared with high-performance liquid chromatography coupled with ultra-visible spectrometric detection

This paper developed a rapid method using near infrared spectroscopy (NIRS) to differentiate two species of Cortex Phellodendri (CP), Cortex Phellodendri Chinensis (PCS) and Cortex Phellodendri Amurensis (PAR), and to predict quantitatively the content of berberine and total alkaloid content in all Cortex Phellodendri samples. Three alkaloids, berberine, jatrorrhizine and palmatine were analyzed simultaneously with a Thermo ODS Hypersil column by gradient elution with a new mobile phase under high-performance liquid chromatography-diode array detection (HPLC-DAD). Berberine content determined by HPLC-DAD was exploited as a critical parameter for successful discrimination between them. Multiplicative scatter correction (MSC), second derivative and Savitsky-Golay (S.G.) were utilized together to correct the scattering effect and eliminate the baseline shift in all near infrared diffuse reflectance spectra as well as to enhance spectral features in order to give a better correlation with the results obtained by HPLC-DAD. With the use of principal component analysis (PCA), samples datasets were separated successfully into two different clusters corresponding to two species. Furthermore, a partial least squares (PLS) regression method was built on the correlation model. The results showed that the correlation coefficients of the prediction models were R = 0.996 for the berberine and R = 0.994 for total alkaloid content. The influences of water absorption bands present in the NIR spectra on the models were also investigated in order to explore the practicability of NIRS in routine use. The outcome showed that NIRS possibly acts as routine screening in the quality control of Chinese herbal medicine.     

Sensitive determination of nitric oxide in some rat tissues using polymer monolith microextraction coupled to high-performance liquid chromatography with fluorescence detection

A simple, sensitive, selective, and low-cost method is proposed for rapidly determining nitric oxide (NO) in some rat tissues. Polymer monolith microextraction (PMME) using a poly(methacrylic acid–ethylene glycol dimethacrylate) (MAA-EGDMA) monolithic column was combined with derivatization of NO using 1,3,5,7-tetramethyl-8-(3′,4′-diaminophenyl)-difluoroboradiaza-s-indacene (TMDABODIPY), and this was used to analyze the derivatives of NO by high-performance liquid chromatography (HPLC) with fluorescence detection at λ _ex/λ _em = 498/507 nm. The baseline separation of TMDABODIPY and its NO derivative is performed under simple conditions in which a C₁₈ column is used and eluted with 50 mmol L⁻¹ ethanolamine and methanol. The conditions for the extraction of NO derivatives were optimized. The limit of detection of NO was 2 × 10⁻¹² mol L⁻¹ (S/N = 3). The linearity range of the method was 9 × 10⁻¹¹−4.5 × 10⁻⁸ mol L⁻¹. The interday and intraday relative standard deviations were less than 5%. The proposed method was successfully applied to the determination of NO levels in some rat tissue samples including heart, kidney, and liver with recoveries varying from 87.1 to 95.2%.