Liquid Chromatography System For Analysis Research Articles

Development of an On-Line Two-dimensional Normal Phase Liquid Chromatography System for Analysis of Weakly Polar Samples

In this study, a novel on-line two-dimensional (2D) normal phase × normal phase liquid chromatography (NPLC × NPLC) was developed for the separation of weakly polar samples. The 2D NPLC was integrated by a unique designed solvent evaporation (SE) interface, including a 6-port 2-position valve and a 10-port 2-position valve in conjunction with two silica gel-packed enrichment columns. The enrichment columns played a pivotal role in evaporating normal phase (NP) solvent from the first dimensional NPLC under vacuum and elevated temperature condition. The working parameters of the interface were evaluated comprehensively. To demonstrate the resolving powerful 2D system, we analyzed three natural-sourced weakly polar compounds from the extracts of toad venom, dammar resin, and propolis. To this end, we studied the effects of mobile phase combinations, the second dimensional column length for separation of the extracts from toad venom, and propolis, respectively. In general, we have found that excellent separation can be obtained with diversity of NP solvent combinations and longer NPLC column (150 mm long). Moreover, compared with the generally used 2D reversed-phase liquid chromatography (RPLC × RPLC), the NPLC × NPLC method exhibited better separation orthogonality. In conclusion, the new NPLC × NPLC separation method provides potential advantages for analysis of weakly polar samples.

Application of dispersive liquid-liquid microextraction for the preconcentration of eight parabens in real samples and their determination by high-performance liquid chromatography.

A simple and sensitive method for the simultaneous determination of eight parabens in human plasma and urine samples was developed. The samples were preconcentrated using dispersive liquid-liquid microextraction based on the solidification of floating organic drops and determined by high-performance liquid chromatography with ultraviolet detection. The influence of variables affecting the extraction efficiency was investigated and optimized using Placket-Burman design and Box-Behnken design. The optimized values were: 58 μL of 1-decanol (as extraction solvent), 0.65mL methanol (as disperser solvent), 1.5% w/v NaCl in 5.0mL of sample solution, pH 10.6, and 4.0min centrifugation at 4000rpm. The extract was injected into the high-performance liquid chromatography system for analysis. Under the optimum conditions, the linear ranges for eight parabens in plasma and urine were 1.0-1000ng/mL, with correlation coefficients above 0.994. The limit of detection was 0.2-0.4 and 0.1-0.4ng/mL for plasma and urine samples, respectively. Relative recoveries were between 80.3 and 110.7%, while relative standard deviations were less than 5.4%. Finally, the method was applied to analyze the parabens in 98 patients of primary breast cancer. Results showed that parabens existed widely, at least one paraben detected in 96.9% (95/98) of plasma samples and 98.0% (96/98) of urine samples.

Analysis of global components in Ganoderma using liquid chromatography system with multiple columns and detectors

In present study, a multiple columns and detectors liquid chromatography system for analysis of global components in traditional Chinese medicines was developed. The liquid chromatography system was consist of three columns, including size exclusion chromatography column, hydrophilic interaction chromatography column, and reversed phase chromatography column, and three detectors, such as diode array detector, evaporative light scattering detector, and mass spectrometry detector, based on column switching technique. The developed multiple columns and detectors liquid chromatography system was successfully applied to the analysis of global components, including macromolecular (polysaccharides), high (nucleosides and sugars)-, and low (triterpenes)-polarity small molecular compounds in Ganoderma, a well-known Chinese medicinal mushroom. As a result, one macromolecular chromatographic peak was found in two Ganoderma species, 19 components were identified in Ganoderma lucidum (two sugars, three nucleosides, and 14 triterpenes), and four components (two sugars and two nucleosides) were identified in Ganoderma sinense. The developed multiple columns and detectors liquid chromatography system was helpful to understand comprehensive chemical characters in TCMs.

In-situ metathesis reaction combined with ultrasound-assisted ionic liquid dispersive liquid–liquid microextraction method for the determination of phenylurea pesticides in water samples

A novel microextraction technique, named in-situ metathesis reaction, combined with ultrasound-assisted ionic liquid dispersive liquid–liquid microextraction was developed for the determination of five phenylurea pesticides (i.e., diuron, diflubenzuron, teflubenzuron, flufenoxuron, and chlorfluazuron) in environmental water samples. In the developed method, 360μL LiNTf2 aqueous solution (0.162g/mL) was added to the sample solution containing a small amount of [C6MIM]Cl (0.034g) to form a water-immiscible ionic liquid, [C6MIM]NTf2, as extraction solution. The mixed solutions were placed in an ultrasonic water bath at 150W for 4min and centrifuged at 3500rpm for 10min to achieve phase separation. After centrifugation, fine droplets of the extractant phase settled to the bottom of the centrifuge tube and were directly injected into the high-performance liquid chromatography system for analysis. The quantity of [C6MIM]Cl, the molar ratio of [C6MIM]Cl and LiNTf2, ionic strength, ultrasound time, and centrifugation time, were optimized using a Plackett–Burman design. Significant factors obtained were optimized by employing a central composite design. The optimized technique provides good repeatability (RSD 2.4 to 3.5%), linearity (0.5μg/L to 500μg/L), low LODs (0.06μg/L to 0.08μg/L) and great enrichment factor (244 to 268). The developed method can be applied in routine analysis for the determining of phenylurea pesticides in environmental samples.

A Low-pH Reverse-Phase High-Performance Liquid Chromatography System for Analysis of the Phenylthiohydantoins of S-Carboxymethylcysteine and S-Carboxyamidomethylcysteine

A Low-pH Reverse-Phase High-Performance Liquid Chromatography System for Analysis of the Phenylthiohydantoins of S-Carboxymethylcysteine and S-Carboxyamidomethylcysteine