Showing papers in "Journal of Separation Science in 2004"

Applications of silica-based monolithic HPLC columns

Abstract: The recent invention and successive commercial introduction of monolithic silica columns has motivated many scientists from both academia and industry to study their use in HPLC. The first paper on monolithic silica columns appeared in 1996. Currently about 200 papers have been published relating to applications and characterization of monolithic silica columns, including monolithic capillaries. This review attempts to give an overview covering various aspects of this new column type in the field of high throughput analysis of drugs and metabolites, chiral separations, analysis of pollutants and food-relevant compounds, as well as in bioanalytical separations such as in proteomics. Some of the applications are described in greater detail. The numerous publications dealing with the physicochemical and chromatographic characterization of monolithic silica columns are briefly summarized.

Preparation and HPLC applications of rigid macroporous organic polymer monoliths

Abstract: Rigid porous polymer monoliths are a new class of materials that emerged in the early 1990s. These monolithic materials are typically prepared using a simple molding process carried out within the confines of a closed mold. For example, polymerization of a mixture comprising monomers, free-radical initiator, and porogenic solvent affords macroporous materials with large through-pores that enable applications in a rapid flow-through mode. The versatility of the preparation technique is demonstrated by its use with hydrophobic, hydrophilic, ionizable, and zwitterionic monomers. Several system variables can be used to control the porous properties of the monolith over a broad range and to mediate the hydrodynamic properties of the monolithic devices. A variety of methods such as direct copolymerization of functional monomers, chemical modification of reactive groups, and grafting of pore surface with selected polymer chains is available for the control of surface chemistry. Since all the mobile phase must flow through the monolith, the convection considerably accelerates mass transport within the molded material, and the monolithic devices perform well, even at very high flow rates. The applications of polymeric monolithic materials are demonstrated mostly on the separations in the HPLC mode, although CEC, gas chromatography, enzyme immobilization, molecular recognition, advanced detection systems, and microfluidic devices are also mentioned.

Organic polymer monoliths as stationary phases for capillary HPLC.

Abstract: Modern rigid porous polymer monoliths were conceived as a new class of stationary phases in classical columns in the early 1990s and later extended to the capillary format. These monolithic materials are typically prepared using a simple molding process carried out within the confines of the capillary. Polymerization of a mixture comprising monomers, initiator, and porogenic solvent affords macroporous materials with large through-pores that enable applications in a rapid flow-through mode. Since all the mobile phase must flow through the monolith, convection considerably accelerates mass transport within the monolithic separation medium and improves the separations. As a result, monolithic columns perform well even at very high flow rates. Various mechanisms including thermally and UV initiated free radical polymerization as well as ring opening metathesis copolymerizations were demonstrated for the preparation of monolithic capillary columns. The versatility of these preparation techniques was demonstrated by their use with hydrophobic (styrene, divinylbenzene, butyl methacrylate, ethylene dimethacrylate), hydrophilic (2-hydroxyethyl methacrylate, methacrylamide, methylenebisacrylamide), ionizable (vinylsulfonic acid, 2-acrylamido-2-methyl-propanesulfonic acid), and tailor-made (norborn-2-ene, 1,4,4a,5,8,8a-hexahydro-1,4,5,8-exo,endo-dimethanonaphthalene) monomers. Variation of polymerization conditions enables control of the porous properties of the monolith over a broad range and mediates the hydrodynamic properties of the monolithic columns. The applications of polymer-based monolithic capillary columns are demonstrated for numerous separations in the μHPLC mode.

Monoliths for fast bioseparation and bioconversion and their applications in biotechnology

Abstract: Monoliths have consolidated their position in bioseparation. More than 200 different applications have been reported in the past two decades and their advantages compared to conventional chromatography demonstrated. These include the high mass transfer efficiency due to the convective flow enabled by the macroporous character of the matrix. Recently plasmid DNA and viruses were separated with high efficiency and cryogels and monolithic superporous agarose were developed for capture of proteins from crude homogenates and separation of microorganisms or lymphocytes. Currently four companies manufacture monoliths mainly for analytical applications although monoliths with a volume of 0.8 liter are commercially available and 8 L are available as prototypes. A book entitled "Monolithic materials: preparation, properties and applications" was published in 2003 and became standard reference of the status of this area. This review focuses on the progress in monoliths that goes beyond the scope of this reference book. Less progress has been made in the field of bioconversions in spite of the fact that monolithic supports exhibit better performance than beads in enzymatic processing of macromolecules. It appears that the scientific community has not yet realized that supports for these applications are readily available. In addition, monoliths will further substantially advance bioseparations of both small and large molecules in the future.

The evolution of comprehensive two-dimensional gas chromatography (GC x GC).

Abstract: For a technology little over a decade old, comprehensive two-dimensional gas chromatography (GC x GC) has quickly reached the status of one of the most powerful analytical tools for volatile organic compounds. At the heart of any GC x GC system is an interface, which physically connects the primary and the secondary columns and acts to preserve the separation obtained in the first dimension (first column) while allowing additional separation in the second dimension. The paper presents a review of the technology, including fundamental principles of the technique, data processing and interpretation and a timeline of inventive contributions to interface design. In addition, applications of the technique are presented, with a more detailed discussion of selected examples.

Characterization of polyacrylamide based monolithic columns.

Abstract: Supermacroporous monolithic polyacrylamide (pAAm)-based columns have been prepared by radical cryo-copolymerization (copolymerization in the moderately frozen system) of acrylamide with functional co-monomer, allyl glycidyl ether (AGE), and cross-linker N,N'-methylene-bis-acrylamide (MBAAm) directly in glass columns (ID 10 mm). The monolithic columns have uniform supermacroporous sponge-like structure with interconnected supermacropores of pore size 5-100 microm. The monoliths can be dried and stored in the dry state. High mechanical stability of the monoliths allowed sterilization by autoclaving. Column-to-column reproducibility of pAAm-monoliths was demonstrated on 5 monolithic columns from different batches prepared under the same cryostructuration conditions.

Determination of hydrolyzable tannins in the fruit of Terminalia chebula Retz. by high-performance liquid chromatography and capillary electrophoresis.

Abstract: A RP-HPLC method for determining fourteen components (gallic acid, chebulic acid, 1,6-di-O-galloyl-D-glucose, punicalagin, 3,4,6-tri-O-galloyl-D-glucose, casuarinin, chebulanin, corilagin, neochebulinic acid, terchebulin, ellagic acid, chebulagic acid, chebulinic acid, and 1,2,3,4,6-penta-O-galloyl-D-glucose) in the fruit of Terminalia chebula Retz. is described. The separation was achieved within 80 min using a binary gradient with mobile phases consisting of a pH 2.7 phosphoric acid solution and an 80% CH3CN solution. Capillary electrophoretic analyses were also attempted, and it was found that CZE (25 mM Na2B4O7, 5 mM NaH2PO4, pH 7.0) was an efficient method for the separation of gallotannins, while an MEKC method (25 mM Na2B4O7, 5 mM NaH2PO4, 20 mM SDS, pH 7.0, and 10% acetonitrile) provided a better separation for most of the tannins examined. The HPLC and CE methods developed were both successfully applied to the assay of tannins in commercial samples of Chebulae Fructus.

Investigating the history of prehistoric glues by gas chromatography–mass spectrometry

Abstract: Although organic materials are very sensitive to biochemical alteration processes, they may be preserved for millennia in various archaeological contexts. Remains of adhesives made during prehistory were discovered at different sites, in the form of residues adhering to flint tools and ceramic vessels or as free lumps in sediment. To characterise the natural substances exploited for adhesive production during late prehistory, we undertook GC and GC/MS analysis of 90 samples from 8 sites dating from the Neolithic to Iron Age periods. This paper discusses our approach to the study of organic adhesives preserved in archaeological contexts, with a particular focus on the presentation of the various categories of organic adhesives that we analysed and the choice of chromatographic conditions adapted to the specificity of such samples. The results obtained show that birch bark tar, a triterpenoid adhesive made by destructive distillation of white birch bark, was predominantly used during the neolithic period even though other materials such as various barks or organic fossil substance were also used. During the Bronze and Iron ages, which follow the Neolithic period, adhesive production is evolving through the expansion of the range of the natural substances used (identification of diterpenoid pine resin) and the addition of beeswax as a plasticiser to birch bark tar. By combining chromatographic analysis and archaeological data, it was thus possible to follow the evolution of adhesive making at the end of prehistory, testifying to the inventiveness of the craftsmen whatever the period considered.

Development of a validated HPLC method for the determination of B-complex vitamins in pharmaceuticals and biological fluids after solid phase extraction.

Abstract: An HPLC method was developed for the simultaneous determination of seven water-soluble vitamins, viz. thiamine, riboflavin, nicotinic acid, nicotinamide, pyridoxine, cyanocobalamin, and folic acid, in multivitamin pharmaceutical formulations and biological fluids (blood serum and urine). Separation was achieved at ambient temperature on a Phenomenex Luna C18 (150 x 4.6 mm) analytical column. Gradient elution was performed starting at a 99:1 A:B v/v composition, where A: 0.05 M CH3COONH4/CH3OH (99/1) and B: H2O/CH3OH (50/50), at a flow rate of 0.8 mL/min. After a 4-min isocratic elution the composition was changed to 100% of B in 18 min and elution continued isocratically for 8 min. Detection was performed with a photodiode array detector at 280 nm. Each vitamin was quantitatively determined at its maximum wavelength. Spectral comparison was used for peak identification in real samples. Detection limits were in the range of 1.6-3.4 ng, per 20-microL injection, while linearity held up to 25 ng/microL. Accuracy, intra-day repeatability (n = 6), and inter-day precision (n = 7) were found to be satisfactory. Theobromine (2 ng/microL) was used as internal standard. Sample preparation of biological fluids was performed by SPE on Supelclean LC-18 cartridges with methanol-water 85/15 v/v as eluent. Extraction recoveries from biological matrices ranged from 84.6% to 103.0%.

Characterization of monolithic columns for HPLC.

Abstract: Monolithic stationary phases and columns have rapidly become highly popular separation media for liquid chromatography, in spite of their recent discovery. However, their most important features have not yet been completely clarified. A complete understanding of their performance and of their intrinsic characteristics will require the systematic acquisition of many series of reliable experimental data and their consistent analysis from different points of view. Progress in their design and production requires now that the chromatographic behavior of monolithic columns be studied in close connection with their physico-chemical and structural properties. The main goal of this review is to summarize fundamental information on some physico-chemical and chromatographic characteristics of monolithic stationary phases and columns for RPLC. The material reviewed deals only with silica-based monolithic columns. First, structural information on the porosities and the size of the pores in monolithic columns is reported. Second, results of chromatographic studies that deal with the characterization of monolithic columns are summarized. Third, results of detailed studies made on the adsorption equilibrium and the surface heterogeneity of monolithic stationary phases are presented. Finally, results on the mass transfer kinetics in monolithic columns derived from the applications of the classical random-walk model and of the moment theory to a new model of the monolith are discussed.

Structural formation of hybrid siloxane-based polymer monolith in confined spaces.

Abstract: Structural deformation of phase-separated methylsiloxane gel under the influence of a surface has been studied. Competitive wetting of siloxane gel phase on a surface during phase formation is found to significantly affect the final morphology in a confined space. When the spinodal wavelength is sufficiently shorter than the size of the available space, a uniform bicontinuous structure forms in confined geometry. However, gel skeletons in the vicinity of a surface are elongated with decreasing size of the space, and finally when the size of the space becomes shorter than the spinodal wavelength, all the gel phase wets on a surface, showing a "wetting transition". Homogeneous bicontinuous methylsiloxane gels were successfully prepared, avoiding such structural deformation, in a long cylindrical fused silica capillary and used for capillary HPLC. The capillary gels exhibited excellent separation efficiency of nitrobenzenes and it was found that the surface character can be altered by incorporating surfactants, which will enable more advanced and extended control of surface character, depending on the analytes.

Effects of traditional processing methods of linseed oil on the composition of its triacylglycerols.

Abstract: Different oil processing methods were performed, which included washing with water and treatment with lead-based driers, with and without heating to different temperatures, giving a set of 7 oils to be investigated. The effects of the traditional processing methods of linseed oil on its triacylglycerol (TAG) composition were studied, using the following analytical methods: high performance size exclusion chromatography (HPSEC), Fourier transform infrared spectroscopy (FTIR), high-performance liquid chromatography-atmospheric pressure chemical ionisation-mass spectrometry (HPLC-APCI-MS), direct temperature resolved mass spectrometry (DTMS), matrix assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF-MS), and electrospray ionisation Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS). A decrease of the initial cis-double bonds and the formation of trans-double bonds upon heating of the oils was observed. Heating a lead and oil mixture to 150°C, or heating the oil alone to 300°C led to the highest degree of oxidation. A difference was observed for the oxidation patterns for oils with and without the addition of lead. Furthermore, levels of oxygen incorporation were higher when lead was added to the oil. High temperature treatment of the oils resulted in an increased average molecular weight. The changes in the initial conformation of the double bond systems observed with FTIR were supported by HPLC-APCI-MS measurements that showed the formation of a number of new isomeric TAGs in the heated oil compared to freshly pressed, untreated oil. Oligomerisation up to hexamers was observed with HPSEC, and MALDI-TOF-MS. The formation of oligomers up to trimers only, however, was observed with ESI-FTICR-MS. Incorporation of oxygen was mainly observed with MALDI-TOF-MS and ESI-FTICR-MS whereas with DTMS and FTIR hardly any evidence was found for this.

Characterisation of proteinaceous binders in artistic paintings by chromatographic techniques

Abstract: This review discusses the application of chromatographic techniques (GC, HPLC and Py-GC) for the characterisation of proteinaceous materials in artistic paintings. The focus is on the various analytical steps that are needed to determine these natural materials in paint samples, from sampling and sample pre-treatment, including various methods of hydrolysis and derivatisation for GC and HPLC, to approaches for data evaluation.

Capillary columns in liquid chromatography: between conventional columns and microchips.

Abstract: Liquid chromatography on columns with small internal diameters has been reviewed as the intermediate technique between conventional liquid chromatography and microchip separations The development of micro column separations in the early years has been described, starting with the papers of Horvath and co-workers and Ishii and co-workers, continuing into the first part of the eighties, then making a leap in time to recent innovations with small-bore columns Based on internal diameters a classification of the different analytical HPLC columns has been suggested The advantages of small-bore columns have been discussed, with particular emphasis on the advantage of coupling to concentration sensitive detectors when the sample amount is limited Open tubular columns are treated as a part of the historic background The recent developments include a brief look into the current status of monolithic columns, the use of packed nano columns and micro columns with electrospray mass spectrometry, and the potential of two-dimensional comprehensive liquid chromatography Finally, the coupling of sample preparation to analytical columns and the future applications of the novel technological improvements to the microchip separation methods have been discussed

Characterization of methacrylate monoliths for purification of DNA molecules.

Abstract: The suitability of methacrylate based anion exchange monolithic supports for the separation and purification of plasmid and genomic DNA has been explored. The effect of the size of the channels, ionic strength of the solution, and ligand density on the dynamic binding capacity has been investigated. The dynamic binding capacity was found to be flow independent, at least up to a linear velocity of 700 cm h(-1), and exceeded 9 mg mL(-1) for all types of DNA. The recovery depends on the pH value of the mobile phase and its ionic strength as well as on the density of the active groups. Under optimal conditions recoveries exceeding 80% were obtained even for genomic DNA. Finally, the suitability of this approach is demonstrated by purification of a real-life sample.

Analysis of sulfur-containing compounds in crude oils by comprehensive two-dimensional gas chromatography with sulfur chemiluminescence detection.

Abstract: This paper reports an analytical method for separating, identifying, and quantifying sulfur-containing compounds in crude oil fraction (IBP-360 degrees C) samples based on comprehensive two-dimensional gas chromatography coupled with a sulfur chemiluminescence detector. Various sulfur-containing compounds and their groups were analyzed with one direct injection. 3620 peaks were detected including 1722 thiols/thioethers/ disulfides/1-ring thiophenes, 953 benzothiophenes, 704 dibenzothiophenes, and 241 benzonaphthothiophenes. The target sulfur compounds and their groups were identified based on the group separation feature and structured retention of comprehensive two-dimensional gas chromatography as well as standard substances. The quantitative analysis of major sulfur-containing compounds and total sulfur was based on the linear response of the sulfur chemiluminescence detector using the internal standard method. The sulfur contents of target sulfur compounds and their groups in 4 crude oil fractions were also determined. The recoveries for standard sulfur-containing compounds were in the range of 90-102%. The quantitative result of total sulfur in the Oman crude oil fraction sample was compared with those from ASTM D 4294 standard method (total S by X-ray fluorescence spectrometry), the relative deviation (RD%) was 4.2% and the precision of the method satisfactory.

Application of comprehensive multidimensional gas chromatography combined with time-of-flight mass spectrometry (GC×GC-TOFMS) for high resolution analysis of hop essential oil

Abstract: The selection and quality of hops is a major determinant in beer flavour. Brewers acknowledge that distinctive characteristics of different hop varieties can be traced to the composition of their essential oils. The difficulty in characterising complex mixtures such as hop oil using 1-D chromatography is that many compounds co-elute. With the introduction of comprehensive multidimensional capillary gas chromatography (GC x GC), there is a tremendous improvement in the separation power or peak capacity. Recent work using GC x GC with flame ionisation detection has suggested that there may be over 1,000 compounds in hop oil. This work describes the use of GC x GC combined with TOFMS detection (Leco Pegasus 4D instrument) to analyse Target hop oil. The TOFMS spectral acquisition rate of 60 Hz provided sufficient spectra per peak (2-D peak base width of 0.1-0.2 s) for identification (119 components were identified with 45 previously unreported compounds). When analysing results, an advantage of GC x GC coupled to TOFMS is that 2-D chromatograms can be viewed for individual masses that are characteristic of particular functional groups. This allows the analyst to view the various homologous series of compounds although in certain cases coelution may still be present as shown by the esters with mass 75.

Sequential injection chromatographic determination of paracetamol, caffeine, and acetylsalicylic acid in pharmaceutical tablets.

Abstract: In this contribution, a new separation method for simultaneous determination of paracetamol, caffeine, acetylsalicylic acid, and internal standard benzoic acid was developed based on a novel reversed-phase sequential injection chromatography (SIC) technique with UV detection. A Chromolith Flash RP-18e, 25-4.6mm column (Merck, Germany) and a FIAlab 3000 system (USA) with an 8-port selection valve and a 5 mL syringe were used for sequential injection chromatographic separations in our study. The mobile phase used was acetonitrile-(0.01 M) phosphate buffer (10:90, v/v) pH 4.05, flow rate 0.6 mL min(-1). UV detection was at 210 and 230 nm. The validation parameters showed good results: linearity (r >0.999) for all compounds, detection limits in the range 0.3-0.8 microg mL(-1), repeatability (RSD) of peak heights between runs in the range 1.10-4.30% at three concentration levels and intra-day repeatability of the retention times in the range 0.28-0.43%. The analysis time was <6 min. The method was found to be applicable for the routine analysis of the active compounds paracetamol, caffeine, and acetylsalicylic acid in pharmaceutical tablets.

Monolithic columns with a gradient of functionalities prepared via photoinitiated grafting for separations using capillary electrochromatography.

Abstract: Stationary phases for capillary electrochromatography with a longitudinal gradient of functionalities have been prepared via photoinitiated grafting of polymer chains onto the pore surface of a porous polymer monolith. In order to achieve the desired retention and electroosmotic flow, the hydrophobic poly(butyl methacrylate-co-ethylene dimethacrylate) monolith with optimized porous properties was grafted with a layer of ionizable polymer, poly(2-acrylamido-2-methyl-1-propanesulfonic acid). A moving shutter and a neutral density filter were used to control the dose of UV light received at different locations along the monolith in order to create the longitudinal gradient of functionalities. Formation of the desired gradients was confirmed using electron probe microanalysis of different locations along the column. The preparation technique significantly affects performance in the CEC mode as demonstrated on the separations of a model mixture using columns both with homogeneous distribution of grafts and with a gradient of functionality. Columns grafted with the gradient of functionalities were found superior to those functionalized uniformly. A comparison of the performance of the gradient column with another containing evenly distributed functionalities showed the performance benefits of the "gradient" column.

Pesticide analysis by capillary electrophoresis

Abstract: In this work, a critical and updated revision of the current situation of the analysis of pesticides by Capillary Electrophoresis (CE) is presented. The review has been written in two main sections. The first one presents a thorough revision of the various offline and on-line sample preconcentration procedures that have been used in conjunction with CE to analyze these compounds. The second part reviews the various detection strategies (i.e., UV, LIF, MS, and electrochemical) and CE modes that have been applied to the analysis of pesticides. Future trends that can be expected from this hot research area are also discussed.

Simple 2D‐HPLC using a monolithic silica column for peptide separation

Abstract: Separation of peptides by fast and simple two-dimensional (2D)-HPLC was studied using a monolithic silica column as a second-dimension (2nd-D) column. Every fraction from the first column, 5 cm long (2.1 mm ID) packed with polymer-based cation exchange beads, was subjected to separation in the 2nd-D using an octadecylsilylated (C18) monolithic sillica column (4.6 mm ID, 2.5 cm). A capillary-type monolithic silica C18column (0.1 mm ID, 10 cm) was also employed as a 2nd-D column with split flow/injection. Effluentof the first dimension (1st-D) was directly loaded into an injector loop of 2nd-D HPLC. UV and MS detection were successfully carried out at high linear velocity of mobile phase at 2nd-D using flow splitting for the 4.6 mm ID 2nd-D column, or with directconnection of the capillary column to the MS interface. Two-minute fractionation inthe 1st-D, 118-second loading, and 2-second injection by the 2nd-D injector, allowed one minute for gradient separation in the 2nd-D, resulting in a maximum peak capacity of about 700 within 40 min. The use of a capillary column in solvent consumption and better MS detectability compared to a larger-sized column. This kind of fast and simple 2D-HPLC utilizing monolithic silica columns will be useful for the separation of complex mixtures in a short time.

Optimization of the extraction of paclitaxel from Taxus baccata L. by the use of microwave energy

Abstract: A simple and rapid microwave-assisted extraction (MAE) procedure was developed and optimized for the extraction of paclitaxel (Taxol) from the needles of yew trees Taxus baccata L. grown in Iranian habitats. The samples, immersed in a methanol-water mixture, were irradiated with microwaves in a closed-vessel system. The method was evaluated using a factorial design approach based on parameters such as extraction time, temperature, methanol concentration in water (v/v), and the ratio of grams of sample to 10 mL of solvent. Statistical treatment of the results revealed that the selected parameters were all significant except the extraction time. Optimum conditions would be 1.5 g samples in 10 mL solvent (90% methanol), an extraction temperature of 95 degrees C, and an extraction time of 7 min. The extracts has been analyzed by reverse-phase high-performance liquid chromatography with UV detection (LC/UV) at 227 nm for quantification. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used for confirmation. The main advantage of the proposed MAE method versus conventional solvent extraction (CSE) are the considerable reductions in time (7 min versus 16 h) and in solvent consumption (20 mL versus 150 mL). The MAE procedure yielded extracts that could be analyzed directly without any preliminary clean-up or solvent exchange steps. Both extraction methods show RSDs lower than 10% and lead to comparable recoveries of paclitaxel (87-92%).

High-performance liquid chromatographic enantioseparations on capillary columns containing monolithic silica modified with cellulose tris(3,5-dimethylphenylcarbamate)

Abstract: Monolithic capillary columns containing native silica gel were modified with cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC) and used for enantioseparations in capillary liquid chromatography. The method adopted for in situ enantioselective modification of monolithic fused silica capillary columns by coating with CDPMC appears to be fairly simple and fast. High efficiency enantioseparations of test racemic compounds and several chiral drugs were achieved in a short time. It was possible to increase the amount of chiral selector present by multiple coating of monoliths with CDMPC. The baseline enantioseparation of 2,2,2-trifluoro-1-(9-anthryl)ethanol was achieved in an analysis time less than 30 s with this capillary column. In addition, reproducible enantioseparations were obtained when the chiral selector was removed from the monolithic column by flushing it with appropriate solvent and the column recoated.

Structural elucidation of catechin and epicatechin in sorrel leaf extracts using liquid-chromatography coupled to diode array-, fluorescence-, and mass spectrometric detection.

Abstract: Flavonoids are natural compounds in medicinal herbs and posses several biological activities important in plant drug design. Especially strong antioxidant effects play an important role against radical oxidative stress causing pathological processes, such as arteriosclerosis or cancer. The aim of this work was to investigate unknown analytes found in sorrel leaf (Rumex acetosa) extracts in order to discover new leading compounds to enable quality control in phytopharmaceuticals made thereof. Therefore compounds of interest were separated after methanolic extraction by reversed-phase liquid chromatography (RP-LC) employing silica-C18 as stationary phase using gradient elution with water (10 mM H3PO4) and acetonitrile as mobile phase. Structural elucidation was carried out by diode array, fluorescence, and mass spectroscopic detection. Photodiode-array detection allowed the extraction of UV-absorbance spectra from the peaks of interest. Absorbance maxima were found at 203 and 279 nm with a shoulder at 230 nm. Additionally fluorescence emission and excitation spectra were recorded from the analytes using a fluorescence detector (FLD) after stop flow (lambdaex = 279 nm, lambdaem = 307 nm). The chromatographic reversed-phase system was coupled to an ion-trap mass spectrometer (LC-MS) by using an electrospray ionization interface (ESI). After optimization processes the separation was carried out using an ammonium acetate buffer at pH 5.5. Mass spectrometric detection turned out to be more sensitive in negative mode. Collisionally induced dissociation (CID) was used to obtain fragment ions of structural relevance (LC-MS/MS). Finally, compounds of interest coming from sorrel leaf (Rumex acetosa) eluting at low acetonitrile concentrations were confirmed to be catechin and epicatechin.

Separation and determination of active components in Radix Salviae miltiorrhizae and its medicinal preparations by nonaqueous capillary electrophoresis.

Abstract: A nonaqueous capillary electrophoresis (NACE) method was developed for simultaneous assay of three bioactive components (1: cryptotanshinone; 2: tanshinone IIA, and 3: tanshinone I) in Radix Salviae miltiorrhizae and in its herbal preparations for the first time. After optimization of separation conditions, a buffer of 250 mmol L–1 ammonium acetate containing 30% acetonitrile and 1.0% acetic acid (V : V) in methanol was selected for separating the three analytes, but baseline separation of tanshinon I and tanshinone IIA was not obtained. Therefore second-order derivative electropherograms were applied for resolving overlapping peaks. Regression equations revealed good linear relationships (correlation coefficients 0.9943–0.9991) between peak heights in second-order derivative electropherograms and concentrations of the three analytes. The relative standard deviations (RSD) of the migration times and the peak height of the three constituents were in the range of 0.81–0.88% and 0.34–1.13% (intra-day), 1.57–1.86% and 3.05–5.52% (inter-day), respectively. The recoveries of three constituents ranged from 90.2 to 108.5%. The results indicated that baseline separation of the analytes was sometimes hard to obtain and second-order derivative electropherograms were applicable for the resolving and analysis of overlapping peaks.

Speciation of nitrogen‐containing compounds in diesel fuel by comprehensive two‐dimensional gas chromatography

Abstract: Nitrogen-containing compounds in diesel fuel have been speciated by comprehensive two-dimensional gas chromatography with nitrogen chemiluminescence detector (GC x GC-NCD). The speciation of nitrogen-containing compounds in diesel is difficult because of low concentration and complexity. The advantages of GC x GC are improved resolution and enhanced sensitivity. GC x GC-NCD can achieve the type and class separation of nitrogen-containing compounds with an appropriate separation column combination. Diesel contains both neutral (indoles and carbazoles) and basic (pyridines and quinolines) nitrogen-containing compounds. Relative concentrations of each class as well as each carbon number family can be quantified by integrating their peak volumes. This study demonstrates the capability of GC x GC-NCD for speciation of nitrogen-containing compound classes.

Mass transfer characteristics of plasmids in monoliths

Abstract: The hydrodynamic properties and pore-structure of monoliths based on functionalized poly(glycidyl methacrylate-ethylene dimethacrylate) were characterised by pulse response experiments using different probes representing a wide range of molecular mass. On a small scale, band spreading was found to be caused to the extent of more than 90% by extra-column effects. These monoliths have large channel diameters, providing a suitable chromatography adsorbent for processing of large molecules. Dynamic and static binding capacity for plasmid DNA was investigated. For our model plasmid, consisting of 4.9 kbp, a capacity of 7 mg/mL was observed in comparison to 0.3 mg/mL for a conventional medium designed for protein separation. When plasmids were loaded on the monolith a gradual increase in pressure drop was observed. The channels filled up and the cross-sectional area available for liquid flow decreased. Therefore, a higher pressure drop was observed during elution. This is caused by (i) shrinking of the channels as effect of the high salt concentration, (ii) high viscosity of the mobile phase due to high concentration of plasmids, and (iii) an increase of the hydrodynamic radius of the plasmid with salt concentration from 45 nm at 150 mM to 70 nm at 2 M NaCl, as measured by dynamic light scattering. These types of monoliths are considered to be the preferred adsorbents for plasmid separation.

Enzyme immobilization on epoxy‐ and 1,1′‐carbonyldiimidazole‐activated methacrylate‐based monoliths

Abstract: Monolithic Convective Interaction Media (CIM) have been activated with epoxide and imidazole carbamate functionalities and used as supports for covalent immobilization of protein A, deoxyribonuclease I, and trypsin. The efficiency of immobilization for these proteins was determined from the amount of bound IgG, degradation of DNA, and hydrolysis of Nalpha-benzoyl-L-arginine ethyl ester, respectively. The respective biological activities of trypsin and the binding capacity of protein A immobilized via imidazole carbamate groups were 11.45 and 2.25 times higher than those obtained for epoxide matrix while they were practically equal for deoxyribonuclease I. The kinetics of immobilization was studied in detail for trypsin under dynamic conditions and revealed that the enzyme immobilized via imidazole carbamate groups already reached its highest activity in 5 min. In contrast, a much longer time was required for immobilization via epoxy groups.

Automated on-line comprehensive two-dimensional LC×GC and LC×GC–ToF MS: Instrument design and application to edible oil and fat analysis

Abstract: After a successful off-line feasibility study, the automation of comprehensively coupled liquid chromatography and gas chromatography (LC x GC) has been studied. Important aspects to consider when developing automated LG x GC include the relative speeds of the two dimensions, the compatibility of the LC eluent (type and flow rate) with the GC dimension, and the column loadabilities. Because the GC separation is relatively slow, the LC instrument has to be operated in the stop-flow mode. Two interfaces for transferring large numbers of subsequent LC fractions to the GC were constructed: one based on a six-port switching valve, and one which uses a dual side-port syringe. Both interfaces were found to perform fully acceptably. The actual transfer of the LC fraction to the GC was realised using a standard split injector to vaporise the compounds and LC eluent. Gas phase splitting was applied to match LC mass load and GC column loadability. The standard deviations of the peak areas obtained in this way were better than 7% (n = 6). The reliability of the system was demonstrated by the problem-free analysis of large series of oil and fat samples, with the focus on both intact triglycerides and their fatty acid methyl esters (FAMEs). Finally, the hyphenation of the automated LC x GC system to a sensitive and rapid-scanning time-of-flight mass spectrometer was realised. By using LC x GC-ToF MS, the information density of the chromatograms could be improved even further, which allowed easy identification of individual compounds as well as compound groups.

Comprehensive multidimensional GC for the characterization of roasted coffee beans

Abstract: The present investigation is based on the separation of one of the most complex food matrices: the roasted coffee bean volatile fraction. Analysis of the two main species of coffee (Arabica/Robusta) was achieved through an effective and simple sampling procedure, headspace solid-phase microextraction (SPME), and the unprecedented resolving power of comprehensive gas chromatography (GC x GC). The combination of these two techniques proved to be a powerful tool for the extraction and separation of coffee volatiles. In fact, thousands of compounds that play various roles in the constitution of coffee aroma profile were resolved in the 2-D contour plot, each occupying a specific position pinpointed by two retention time coordinates. The potential use of this method for the assessment of coffee quality and the detection of commercial fraud is discussed. The potential of GC x GC for identification and classification of unknowns was also demonstrated, as the formation of characteristic patterns for structurally related compounds was observed in the bidimensional chromatogram. Moreover, reproducibility results were supported by the use of an autosampler for SPME applications that allowed any inaccuracy arising from manual handling to be avoided.