Current Chromatography - Volume 4, Issue 1, 2017

Background: Recently, graphene as a special class of carbon-based nanomaterial, has attracted great attention of chromatographers due to its exceptional material properties, high mechanical strength, excellent thermal conductivity, and ultra-larger surface area. Methods: In this review, applications of graphene-based materials in chromatography have been summarized. For better clarification, these applications are divided into two categories of employing graphene for sample preparation for chromatography uses, and its application as robust stationary phases, mainly for high performance liquid chromatography. Results: Graphene-based materials as an adsorbent, due to their exceptional material properties and ultra-larger surface area, were used for preconcentration of many kinds of compounds such as antibiotics, estrogens, dyes and pesticides, in different samples before introduction to chromatographic instruments. As a stationary phase, modified graphene has been employed in almost all types of the column chromatography nowadays. Conclusion: Graphene based materials are excellent selective adsorbents for many kinds of compounds and are very suitable for both chromatographic separations and sample pretreatment.

Background: Air pollutants, such as inorganic compounds (e.g. nitrogen and sulphur oxides, metals, metalloids, respirable particulate matter), as well as organic (e.g. volatile organic compounds, polyaromatic hydrocarbons) have adverse influence on human health. Usually analysis of ionic substances in gaseous samples is preceded by absorption of the gaseous analytes in a liquid or on a solid sorbent. The second option is direct chemical analysis of aerosols, particulate matter, or wet precipitations. Objective: In order to understand the health effects and mutual interactions between components present in gases and aerosols, several analytical techniques are applied. One of them is ion chromatography which is use to analyse inorganic and organic ionic substances in the air samples. Method: The paper presents the possibility of application of ion chromatography in air analysis, with particular focus on international standards methods. Results: Since its introduction in the middle of 70ies of 20th century, ion chromatography has been one of the versatile and powerful techniques for the analysis of anions and cations mainly in water and wastewater. The introduction of new sample preparation methods, more selective stationary phases and detection modes, allows its application for more complex matrices, such as gaseous and solid samples. Conclusion: Recently, its application in air analysis has increased significantly. The limitation is connected with the appropriate selectivity, and the need to conduct analytes into ionic forms.

Background: B vitamins are a group of water-soluble vitamins which have an important role in cell metabolism and, therefore, they are regularly added to foods and beverages. Determination of vitamins in these products for quality control purposes is of interest. However, due to the complex matrixes of foods and beverages, one or more pretreatment steps are usually used to increase sensitivity and selectivity of the available instruments. The goal of sample preparation is sample cleanup, sample enrichment, and signal enhancement. Methods: In the present study, MEPS have been used for extraction of B vitamins (B1, B2, B3, B5 and B6) from energy beverage matrixes prior to liquid chromatography-electrospray ionization tandem mass spectrometry assay. Various important factors affecting MEPS performance including the type of sorbent, type of preconditioning and washing solvent, type and volume of eluent, sample and eluent ow rates were optimized. Results: Under the optimized condition, five linear calibration curves in the concentration range of 1-300 ! g mL-1 were obtained. The repeatability and accuracy of the method were evaluated by determination of three quality control samples using the developed method, and the results (coefficients of variation (CV%) values were between 1% and 14%, relative recoveries ranged between 86-119%) confirm that a powerful alternative method has been developed for the extraction and determination of the investigated vitamins in energy beverage matrixes. MEPS sorbent was used for 100 extractions before it was discarded. Conclusions: In summary, MEPS can be used as a powerful sample preparation technique prior to liquid chromatography-electrospray ionization tandem mass spectrometry assay for daily quality control analysis of B vitamins in energy drinks as a cheap, fast, simple, and at the same time accurate and precise method.

Background: Monitoring of uric acid levels is of significant importance for the prevention of conditions such as gout and kidney disease. Likewise, the metabolites produced from reaction of uric acid with reactive oxygen species are indicative of the level of oxidative stress. Quantitative methods are therefore needed for measuring these compounds in biological sample matrices. Objective: To investigate the use of silica hydride-based HPLC columns operating in aqueous normal phase mode to retain and separate uric acid from its metabolites in both reference standard solutions and urine samples. Method: LC-MS instrumentation operating in positive ion mode was used for the detection of the analyte peaks. An internal standard of tyrosine was chosen in order to normalize the detector response. Two stationary phases based on silica hydride were investigated. Results: The diol-based silica hydride column showed superior chromatographic resolution of the four analyte peaks. As polar molecules, all four were readily retained in the aqueous normal phase mode. Another metabolite, triuret, was also possibly observed, although lack of an available standard precluded definitive confirmation. Quantitative data demonstrated uric acid linearity in the range 0.2–1.6 mg/dL. Conclusion: The diol functional groups appeared to impart beneficial secondary selectivity to the separation, which was not observed using the other silica hydride-based column. The preliminary quantitative data showed that the developed method approach could be suitable for the analyses of uric acid and its metabolites in biological samples.

Background: A rapid methodology has been developed and applied successfully for the determination of trace levels of four naphthalene sulfonate (NSs) in seawater. Objective: The aim of this research was finding a rapid, interference-free and easy to operate extraction technique for isolation and preconcentration of NSs from seawater. Method: This technique is based on coupling of in-syringe dispersive liquid-liquid microextraction to high-performance liquid chromatography. Naphthalene sulfonate (NSs) forms ion-pair species with tetrabutylammonium (TBA) and then were microextracted to an organic phase by IS-DLLME followed with high-performance liquid chromatography (HPLC) analysis. The effects of different parameters on the extraction efficiency such as pH, type and volume of extraction solvent, the type and volume of dispersive solvent, the effects of multiple extractions, sample volume, and amount of tetrabutylammonium (ion pair in reagent) were studied and optimized. Results: The effects of different parameters on the extraction efficiency such as pH, type and volume of extraction solvent, the type and volume of dispersive solvent, the effects of multiple extractions, sample volume, and amount of tetrabutylammonium (ion pair in reagent) were studied and optimized. Under the optimized condition, the linear ranges were found to be between 0.1-100.0 μg L-1 for all NSs with the detection limits better that 0.32 μg L-1. The enrichment factors of NSs were calculated to be between 172 and 280 folds. The mean recoveries of NSs were 80.2-104.5 % with mean RSD of 2.6-6.6 %. Conclusion: The technique has been successfully applied for the analysis of trace amount of four naphthalene sulfonates in seawater of Chabahar Bay.

Background: The effective separation of wood pulp components to produce high-quality, high-yield cellulose products is of high economic interest for global market players in the pulp and paper industry. Technological advances offer the opportunity to generate value out of currently unutilized wood constituents, which are normally combusted for power generation. In particular, hardwood xylan shows enormous potential, as it remains almost unaffected during alkaline Kraft cooks and can be separated from cellulose by a simple process-integrated alkaline post-extraction step. Objective: To obtain a valuable xylan product with high purity, the selective extraction of xylan without impurities is sought. Yet, residual lignin is co-extracted with xylan under alkaline conditions. To define strategies for the removal of this lignin, its solution behavior in extraction lyes should be clarified. Method: In this project, experiments including enzymatic xylan digests coupled with size exclusion chromatography (SEC) were conducted to explore the effects of lignin-xylan complexes. Results: The simultaneous decline of UV and RI signal intensities in size exclusion chromatograms after enzymatic xylan digest indicated the presence of linkages between hardwood xylan and residual technical lignin. Conclusion: The indication of linkages between xylan and lignin allows for defining bleaching strategies for the production of a high purity xylan product.