Journal of Chromatography A (v.1216, #9)
Solid-phase microextraction on-fiber derivatization for the analysis of some polyphenols in wine and grapes using gas chromatography–mass spectrometry
by Pilar Viñas; Natalia Campillo; Nelson Martínez-Castillo; Manuel Hernández-Córdoba (pp. 1279-1284).
The present study describes a new environmentally friendly sample pretreatment system based on solid-phase microextraction (SPME) for the sensitive determination of polyphenols. A derivatization process was necessary to convert the polar non-volatile compounds into volatile derivatives. Direct immersion (DI) SPME was used for the adsorption of polyphenols, and then the fiber was placed in the headspace of the derivatizing reagent, bis(trimethylsilyl)trifluoroacetamide (BSTFA). The separation was carried out by coupling gas chromatography with mass spectrometry in the selected ion monitoring mode, after silylation. Optimal extraction conditions were 25°C for 10min under continuous stirring using DI and a polyacrylate fiber. After extraction, the fiber was inserted into the headspace of BSTFA (10μL) and the polyphenols were derivatized for 15min at 50°C. Desorption was carried out at 280°C for 5min. The method allowed the determination of both isomers cis- and trans-resveratrol, piceatannol, catechin and epicatechin in wine and grapes, and it was validated for linearity, detection and quantitation limits, selectivity, accuracy and precision. Detection limits ranged from 0.05 to 0.9ngmL−1 at a signal-to-noise ratio of 3, depending on the compound. Recoveries obtained for spiked samples were satisfactory for all compounds.
Keywords: Gas chromatography–mass spectrometry; Solid-phase microextraction; On-fiber derivatization; Polyphenols; Wine; Grapes
Application of an automatic thermal desorption–gas chromatography–mass spectrometry system for the analysis of polycyclic aromatic hydrocarbons in airborne particulate matter
by J. Gil-Moltó; M. Varea; N. Galindo; J. Crespo (pp. 1285-1289).
The application of the thermal desorption (TD) method coupled with gas chromatography–mass spectrometry (GC–MS) to the analysis of aerosol organics has been the focus of many studies in recent years. This technique overcomes the main drawbacks of the solvent extraction approach such as the use of large amounts of toxic organic solvents and long and laborious extraction processes. In this work, the application of an automatic TD–GC–MS instrument for the determination of particle-bound polycyclic aromatic hydrocarbons (PAHs) is evaluated. This device offers the advantage of allowing the analysis of either gaseous or particulate organics without any modification. Once the thermal desorption conditions for PAH extraction were optimised, the method was verified on NIST standard reference material (SRM) 1649a urban dust, showing good linearity, reproducibility and accuracy for all target PAHs. The method has been applied to PM10 and PM2.5 samples collected on quartz fibre filters with low volume samplers, demonstrating its capability to quantify PAHs when only a small amount of sample is available.
Keywords: Thermal desorption; GC–MS analysis; Atmospheric PM samples; PAHs; SRM1649a urban dust
Simple and commercial readily-available approach for the direct use of ionic liquid-based single-drop microextraction prior to gas chromatography
by Alberto Chisvert; Iván P. Román; Lorena Vidal; Antonio Canals (pp. 1290-1295).
A simple and commercial readily-available approach that enables the direct use of ionic liquid (IL)-based single-drop microextraction (SDME) prior to gas chromatography (GC) is presented. The approach is based on thermal desorption (TD) of the analytes from the IL droplet to the GC system, by using a robust and commercially-available thermodesorption system. For this purpose, a two-glass-tube concentrically disposed system was designed. The inner tube is a laboratory-cut Pyrex tube (20mm length) that houses the ionic liquid droplet from the SDME process, and the outer tube is a commercially-available TD glass tube (187mm length) commonly employed for stir-bar sorptive extractions (SBSE). In this way, the proposed device prevents IL from entering the GC system, as this could dirty the inlet or even block the column. The determination of 10 chlorobenzenes in water samples by GC coupled with mass spectrometric (MS) detection has been chosen as model analytical application, showing the feasibility of the proposed approach. The SDME process consists of a 5μL droplet of 1-hexyl-3-methylimidazolium hexafluorophosphate ([C6MIM][PF6]) suspended in the headspace (HS) of a 10mL stirred sample. After extracting for 37min at room temperature, the IL droplet is directly placed into the small inner tube, which is placed into the TD tube. The whole device is placed inside the TD unit, where desorption of the analytes is performed at 240°C for 5min with a helium flow rate of 100mLmin−1. The analytical figures of merit of the proposed IL-(HS)-SDME-TD-GC–MS approach are very suitable for the determination of chlorobenzenes at ultratrace levels, with relative standard deviation values ranging between 2% and 17%, and limits of detection ranging between 1 and 4ngL−1, showing the potential offered by the IL-based SDME process with GC.
Keywords: Chlorobenzenes; Ionic liquid; Gas chromatography–mass spectrometry; Thermal desorption; Single-drop microextraction (SDME); Water analysis
An experimental design approach employing artificial neural networks for the determination of potential endocrine disruptors in food using matrix solid-phase dispersion
by Vasiliki I. Boti; Vasilios A. Sakkas; Triantafyllos A. Albanis (pp. 1296-1304).
Matrix solid-phase dispersion (MSPD) as a sample preparation method for the determination of two potential endocrine disruptors, linuron and diuron and their common metabolites, 1-(3,4-dichlorophenyl)-3-methylurea (DCPMU), 1-(3,4-dichlorophenyl) urea (DCPU) and 3,4-dichloroaniline (3,4-DCA) in food commodities has been developed. The influence of the main factors on the extraction process yield was thoroughly evaluated. For that purpose, a 3(4–1) fractional factorial design in further combination with artificial neural networks (ANNs) was employed. The optimal networks found were afterwards used to identify the optimum region corresponding to the highest average recovery displaying at the same time the lowest standard deviation for all analytes. Under final optimal conditions, potato samples (0.5g) were mixed and dispersed on the same amount of Florisil. The blend was transferred on a polypropylene cartridge and analytes were eluted using 10ml of methanol. The extract was concentrated to 50μl of acetonitrile/water (50:50) and injected in a high performance liquid chromatography coupled to UV–diode array detector system (HPLC/UV–DAD). Recoveries ranging from 55 to 96% and quantification limits between 5.3 and 15.2ng/g were achieved. The method was also applied to other selected food commodities such as apple, carrot, cereals/wheat flour and orange juice demonstrating very good overall performance.
Keywords: Experimental design; Artificial neural networks; Matrix solid-phase dispersion; EDCs
Preparation of solid-phase microextraction fiber coated with single-walled carbon nanotubes by electrophoretic deposition and its application in extracting phenols from aqueous samples
by Quanlong Li; Xuefeng Wang; Dongxing Yuan (pp. 1305-1311).
A novel solid-phase microextraction (SPME) Pt fiber coated with single-walled carbon nanotubes (SWCNTs) was prepared by electrophoretic deposition (EPD) and applied to the determination of phenols in aqueous samples by direct immersion (DI)-SPME-HPLC-UV. The results revealed that EPD was a simple and reproducible technique for the preparation of SPME fibers coated with SWCNTs without the use of adhesive. The obtained SWCNT coating did not swell in organic solvents nor strip off from substrate, and possessed high mechanical strength due to the strong Van der Waals attractions between the surfaces of the SWCNTs. The prepared SPME fiber was conductive since both SWCNT coating and Pt wire were conductive. Using Pt wire as substrate, the fiber was unbreakable. Owing to the presence of oxygenated groups on SWCNTs and the high surface area of SWCNTs, the SWCNT fiber was similar to or superior to commercial PA fiber in extracting the studied phenols from aqueous sample. A durability of more than 80 analyses was achieved for one unique fiber. Under optimized conditions, the detection limits for the phenols varied between 0.9 and 3.8ng/mL, the precisions were in the range of 0.7–3.2% ( n=3), and linear ranges were within 10 and 300ng/mL. The method was successfully applied to the analysis of spiked seawater and tap water samples with the recoveries from 87.5 to 102.0%.
Keywords: Solid-phase microextraction; Electrophoretic deposition; Single-walled carbon nanotubes; Phenols
A sensitive post-column photochemical derivatization/fluorimetric detection system for HPLC determination of bisphosphonates
by Tomás Pérez-Ruiz; Carmen Martínez-Lozano; María Dolores García-Martínez (pp. 1312-1318).
A new reversed-phase ion-pair high-performance liquid chromatographic (HPLC) method has been developed for the determination of the following bisphosphonic acids: alendronic acid (ALEN), etidronic acid (ETID), ibandronic acid (IBAN) and risedronic acid (RISE). Separation was achieved on a C18 column using a mixture of 50mmolL−1 borate buffer pH 9.0 containing 0.25mmolL−1 tetrabutylammonium chloride and 0.5mmolL−1 EDTA and acetonitrile (97:3) as the mobile phase. The sensitive detection of the above bisphosphonic acids was based on their oxidation to orthophosphate by the on-line peroxydisulfate-assisted photolysis followed by post-column reaction with molybdate to yield phosphomolybdate. This subsequently reacted with thiamine to generate thiochrome and, finally, the fluorescence of thiochrome was measured at 440nm with excitation at 375nm. The developed method is precise with a mean relative standard deviation of 1.3%, sensitive (with a detection limit at the nmolL−1 level), accurate, specific, rapid (analysis time approximately 13min) and inexpensive because to the low cost of the reagents. The assay was applied to the analysis of the four bisphosphonic acids in commercial dosage formulations, in which the excipients did not interfere with the determination. The method was also applied to the determination of etidronate, risedronate and ibandronate in human urine. Sample preparation involves precipitation of the analytes from urine along with endogenous phosphates such as calcium salts by addition of calcium chloride at alkaline pH and dissolution of the precipitate in 0.05molL−1 ethylene glycol-bis(β-aminoethyl ether)- N, N, N′, N′-tetraacetic acid.
Keywords: Bisphosphonates; HPLC; On-line photo-oxidation; Molybdophosphoric acid reaction; Fluorescence detection; Pharmaceuticals; Urine
Characterization of fulvic acids by liquid chromatography-quadrupole time-of-flight mass spectrometry
by Douglas B. Mawhinney; Fernando L. Rosario-Ortiz; Seungyun Baik; Brett J. Vanderford; Shane A. Snyder (pp. 1319-1324).
Fulvic acid standards from Suwannee River, Pony Lake, Elliot Soil, Waskish Peat, and Nordic Reservoir were characterized by liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) operating in negative electrospray ionization mode. The method employed a commercially available stationary phase that resulted in a distinctive chromatographic peak for each of the fulvic acid samples that differed in width and retention time at peak maximum. The QTOF-MS, operating in TOF mode, revealed that the unique chromatographic peak shapes were the result of the relative fraction of hydrogen and oxygen contained in various fulvic acid components. Those species that contained larger amount of hydrogen displayed a larger mass defect and were retained longer on the LC column, indicating reduced polarity. This is supported by a reduction in the degree of fragmentation related to polar functional groups as the mass defect and retention time increased. Lastly, the analysis of even and odd mass (at m/ z 1 greater) ion intensity ratios revealed a correlation to the percent nitrogen of the various standards.
Keywords: Dissolved organic matter; Time-of-flight mass spectrometry; Humic substances; LC-QTOF-MS; Natural organic matter
Numerical and analytical solutions for the column length-dependent band broadening originating from axisymmetrical trans-column velocity gradients
by K. Broeckhoven; G. Desmet (pp. 1325-1337).
Trans-column velocity gradients arising from radial variations in packing density or mobile phase temperature lead to a plate height contribution that, in the case of for example a 4.6mm column, may increase over several tens of centimeters before it reaches a constant value. Considering a wide variety of different trans-column velocity profiles, including Giddings’ general polynomial expression and several simplified partially flat profiles, and performing a set of analytical calculations (to establish an expression for the long time-limit constant value H∞) and numerical simulations (to calculate the band broadening in the transient regime), it was found that the column length-dependent variation of this plate height contribution can be very closely approximated by a simple exponential-law expression. The availability of the latter will greatly simplify the experimental analysis of radial column heterogeneity effects, especially considering that this expression is independent of the radial dispersion, the column diameter, and the average velocity and maximum velocity difference. Surprisingly, the exponential-law expression is to a first approximation also independent of the shape of the velocity profile, provided the velocity profile does not become flat over a substantially large part of the cross-section. In the latter case, the transient curve obeys a more complex law, but can nevertheless still be approximated by an exponential-law expression, though with a different (larger) decay constant.
Keywords: Radial heterogeneity; Band broadening; Plate height model; Column packing; Numerical simulations
Comprehensive two-dimensional liquid chromatography separations of pharmaceutical samples using dual Fused-Core columns in the 2nd dimension
by Anthony J. Alexander; Lianjia Ma (pp. 1338-1345).
This paper focuses on the application of RPLC×RPLC to pharmaceutical analysis and addresses the specific problem of separating co-eluting impurities/degradation products that maybe “hidden” within the peak envelope of the active pharmaceutical ingredient (API) and thus may escape detection by conventional methods. A comprehensive two-dimensional liquid chromatograph (LC×LC) was constructed from commercially available HPLC equipment. This system utilizes two independently configurable 2nd dimension binary pumping systems to deliver independent flow rates, gradient profiles and mobile phase compositions to dual Fused-Core secondary columns. Very fast gradient separations (30s total cycle time) were achieved at ambient temperature without excessive backpressure and without compromising optimal 1st dimension sampling rates. The operation of the interface is demonstrated for the analysis of a 1mg/ml standard mixture containing 0.05% of a minor component. The practicality of using RPLC×RPLC for the analysis of actual co-eluting pharmaceutical degradation products, by exploiting pH-induced changes in selectivity, is also demonstrated using a three component mixture. This mixture (an API, an oxidation product of the API at 1.0%, w/w, and a photo degradant of the API at 0.5%, w/w) was used to assess the stability indicating nature of an established LC method for analysis of the API.
Keywords: Comprehensive two-dimensional; Pharmaceutical degradation products; Dual parallel 2nd dimension columns; Fused-Core
Effect of an open tube in series with a packed capillary column on liquid chromatographic performance
by Hongjuan Xu; Stephen G. Weber (pp. 1346-1352).
A postcolumn reactor or a simple open tube connecting a capillary column to, for example, a mass spectrometer affects the performance of a capillary liquid chromatography system in two ways: stealing pressure from the column and adding band-spreading. This effect is especially intolerable in fast separations. Our calculations show that in the presence of a 25μm radius postcolumn reactor, column (50μm radius) efficiency (number of theoretical plates) is severely reduced by more than 75% with a t0 of 10s and a particle diameter from 1 to 5μm for unretained solutes at room temperature. Therefore, it is necessary to minimize the reactor's effect and to improve the column efficiency by optimizing postcolumn conditions. We derived an equation that defines the observed number of theoretical plates ( Nobs) taking into account the two effects stated above, which is a function of the maximum pressure Pm, the particle diameter dp, the reactor radius ar, the column radius ac, the desired dead time t0, the column temperature T and zone capacity factor k″. Poppe plots were obtained by calculations using this equation. The results show that for a t0 shorter than 18s, a Pm of 4000psi, and a dp of 1.7μm, a 5μm radius reactor has to be used. Such a small reactor is difficult to fabricate. Fortunately, high temperature helps to minimize the reactor effect so that reactors with manageable radius (larger than 12.5μm) can be used in many practical conditions. Furthermore, solute retention diminishes the influence of a postcolumn reactor. Thus, a 12.5μm reactor supersedes a 5μm reactor for retained solutes even at a t0 of 5s ( k″>3.8, or k′>2.0).
Keywords: Nano-LC; Taylor–Aris dispersion; Band-spreading; Capillary HPLC; Poppe plot; HPLC
Optimization of the thermal environment of columns packed with very fine particles
by Fabrice Gritti; Georges Guiochon (pp. 1353-1362).
The apparent reduced HETP (height equivalent to a theoretical plate) of columns packed with very fine 1.7μm BEH-C18particles were measured under isocratic conditions, for different thermal conditions applied to the surface wall (column left in still-air at laboratory temperature, column placed in the oven of the Acquity UPLC chromatograph heated at different temperatures, or column immersed in a water stream at different controlled temperatures). The sample was the low-molecular weight, highly diffusive compound naphtho[2,3-a]pyrene. The mobile phase was either pure acetonitrile or a mixture of acetonitrile and water (85/15, v/v). The plot of the measured HETPs versus the mobile phase flow velocity begins to deviate from the classical isothermal van Deemter curve or the advantages of using very fine particles begins to disappear when the heat power released by the friction of the stream percolating through the packed bed exceeds 4W per unit length of column (m). These effects are minimum when (1) the temperature of the column wall is not controlled and the wall remains in contact with air; or (2) a suitable difference between the temperature of the column wall (hot) and the temperature of the entering liquid (cooler) is set by the analyst.
Keywords: Very-high-pressure liquid chromatography; Heat effects; Temperature gradients; BEH-C; 18; columns; Column efficiency; Naphtho[2,3-a]pyrene; Acetonitrile mobile phase
Approaches to comprehensive multidimensional liquid chromatography systems
by Jacob N. Fairchild; Krisztián Horváth; Georges Guiochon (pp. 1363-1371).
This work compares the performance of the three different schemes implementing two-dimensional liquid chromatography (2D-LC) in terms of the peak capacity that they can generate and of the time that they need to complete a two-dimensional analysis. We discuss in detail how time is spent in these two-dimensional liquidchromatography×liquid chromatography (LC×LC) schemes and how to compare them. Keeping constant the characteristics of the first-dimension separation, we systematically varied those of the second-dimension separation and of its coupling to the first-dimension. In the process, five systems were created, based on the principles of the three known implementations of comprehensive 2D-LC. This work demonstrates an original method for the selection of the best comprehensive 2D-LC approach, depending on the desired peak capacity and on time constraints. The decision to use a 2D-LC method arises from the need to achieve a given resolution (i.e., a target peak capacity) within as short a time as possible or to reach the highest possible resolution in a given analysis time. Using the most appropriate schemes, we suggest how it is realistically possible to generate peak capacities ranging from 266 in just over 20min or about 2800 in 2.3h. When the time available for a two-dimensional separation is very short and the desired peak capacity cannot be achieved in 1D-LC, an on-line 2D-LC approach is unquestionably best. However, if a longer analysis time is acceptable, a 10-fold increase in the peak capacity can be obtained at the cost of a mere 7-fold increase in total analysis time.
Keywords: Analysis time; Two-dimensional chromatography; Off-line 2D-LC; On-line 2D-LC; Stop-and-go 2D-LC; Optimization; Peak capacity
Separation of protein mixtures using pH-gradient cation-exchange chromatography
by Paul K. Ng; Jie He; Mark A. Snyder (pp. 1372-1376).
Historically, separation of a protein mixture after adsorption to a cation-exchange column is effected by alteration in ionic strength. An alternative separation method using pH induced gradient in the range of 4–7.5 was studied. A cation-exchange column with large particle beads containing excessive carboxyls was employed. A pH gradient across the column was generated by a step change at the column entrance using a non-retained buffer system. Consistency and accuracy of pH values in timed intervals were demonstrated in three different batches. In development of the application, we found a correlation coefficient of >0.9 between the elution pH values of six acidic proteins and their isoelectric points. One case study showed the resolution between a monoclonal antibody and non-retained protein species from a protein A column. Another case study showed the feasibility of separating polyethylene glycol conjugated protein from native protein.
Keywords: Cation-exchange; pH gradient; Monoclonal antibody; Pegylated proteins
Studying the mechanism of RNA separations using RNA chromatography and its application in the analysis of ribosomal RNA and RNA:RNA interactions
by Sakharam P. Waghmare; Petros Pousinis; David P. Hornby; Mark J. Dickman (pp. 1377-1382).
DNA/RNA chromatography presents a versatile platform for the analysis of nucleic acids. Although the mechanism of separation of double stranded (ds) DNA fragments is largely understood, the mechanism by which RNA is separated appears more complicated. To further understand the separation mechanisms of RNA using ion pair reverse phase liquid chromatography, we have analysed a number of dsRNA and single stranded (ss) RNA fragments. The high-resolution separation of dsRNA was observed, in a similar manner to dsDNA under non-denaturing conditions. Moreover, the high-resolution separation of ssRNA was observed at high temperatures (75°C) in contrast to ssDNA. It is proposed that the presence of duplex regions/secondary structures within the RNA remain at such temperatures, resulting in high-resolution RNA separations. The retention time of the nucleic acids reflects the relative hydrophobicity, through contributions of the nucleic sequence and the degree of secondary structure present. In addition, the analysis of RNA using such approaches was extended to enable the discrimination of bacterial 16S rRNA fragments and as an aid to conformational analysis of RNA. RNA:RNA interactions of the human telomerase RNA component (hTR) were analysed in conjunction with the incorporation of Mg2+ during chromatography. This novel chromatographic procedure permits analysis of the temperature dependent formation of dimeric RNA species.
Keywords: RNA/DNA chromatography; Ion pair reverse phase liquid chromatography; RNA conformation; RNA:RNA interactions
Reversed-phase liquid chromatography using mandelic acid as an eluent for the determination of uranium in presence of large amounts of thorium
by P.G. Jaison; Vijay M. Telmore; Pranaw Kumar; Suresh K. Aggarwal (pp. 1383-1389).
Studies were carried out for the separation of uranium (U) and thorium (Th) on reversed-phase (RP) C18 columns using mandelic acid as an eluent. Retention of thorium–mandelate on the unmodified stationary phase was found to be greater than that of uranyl–mandelate under the pH conditions employed. Th retention capacity of the stationary phase was determined as a function of pH and MeOH content of the mobile phase. The optimised parameters allowing U elution prior to Th were utilized for the determination of small amounts of U in the presence of large amounts of Th. The method has been used for the determination of U in synthetic samples with Th/U amount ratios up to 100,000 (10μg/g of U) without any pre-separation, employing a particulate C18 column. Effect of concentration of ion interaction reagents (IIRs) on the retention was studied to understand the mechanism of adsorption of their mandelate complexes onto the stationary phase. The experiments conducted unequivocally prove that thorium–mandelate complex is neutral whereas uranyl–mandelate complex is anionic in nature.
Keywords: HPLC; Reversed-phase; Mandelic acid; Thorium; Uranium
Centrifugal partition chromatography directly interfaced with mass spectrometry for the fast screening and fractionation of major xanthones in Garcina mangostana
by E. Destandau; A. Toribio; M. Lafosse; V. Pecher; C. Lamy; P. André (pp. 1390-1394).
Xanthones are well known for their interesting phytochemical properties, which make them attractive to the pharmaceutical and medicinal industry. We have therefore developed a method to analyse the major xanthones in Garcina mangostana. The xanthones were extracted by pressurized liquid extraction with ethanol and separated at the semi-preparative scale by centrifugal partition chromatography (CPC) with a biphasic solvent system consisting of heptane/ethyl acetate/methanol/water (2:1:2:1, v/v/v/v). A CPC-electrospray ionisation MS coupling was performed and used to simultaneously separate and identify the compounds. Thanks to a variable flow splitter and an additional stream of ethanol/1molL−1 ammonium acetate (95:5, v/v), all the compounds were ionised, detected and monitored whatever the solvents used in mobile phase for the CPC separation. The dual mode or elution–extrusion which are less solvent-consuming and faster than the elution mode were used without loss of ionisation and detection.
Keywords: Xanthones; Mangosteen; Centrigugal partition chromatography; Mass spectrometry
Characterization of weld ( Reseda luteola L.) and spurge flax ( Daphne gnidium L.) by high-performance liquid chromatography–diode array detection–mass spectrometry in Arraiolos historical textiles
by Rita Marques; Micaela M. Sousa; Maria C. Oliveira; Maria J. Melo (pp. 1395-1402).
The natural dyes, and dye sources, in two seventeenth century Arraiolos carpets from the National Museum of Machado de Castro were analysed by high-performance liquid chromatography with UV–vis diode array detection (HPLC–DAD) and HPLC–mass spectrometry (LC–MS). Weld ( Reseda luteola L.), indigo and spurge flax ( Daphne gnidium L.) were found to be the dye sources, in agreement with original dyeing recipes collected during the nineteenth century. In order to fully characterize the plant sources, LC–MS conditions were optimized with plant extracts and the chromatographic separation and mass detection were enhanced. Extraction of the dyes, in the Arraiolos carpet samples, was performed using mild conditions that avoid glycoside decomposition. For the blues a dimethylformamide solution proved to be efficient for indigotin recovery. For all the other colours, an improved mild extraction method (with oxalic acid, methanol, acetone and water) was used, enabling to obtain the full dye source fingerprint, namely the flavonoid glycosides in the yellow dyes.
Keywords: Arraiolos; Dyes; HPLC; LC–MS; Mild extraction; Weld; Spurge flax
Determination of proanthocyanidin A2 content in phenolic polymer isolates by reversed-phase high-performance liquid chromatography
by Jayma L. Koerner; Victor L. Hsu; Jungmin Lee; James A. Kennedy (pp. 1403-1409).
This article summarizes the development of an analytical method for the determination of proanthocyanidin (PAC) A2 in phenolic polymer isolates following acid-catalyzed degradation in the presence of excess phloroglucinol. Isolates from concentrated cranberry juice (CCJ) were extensively characterized and molar extinction coefficients were determined for the terminal A2 and phloroglucinol adduct of the extension A2 unit. Peanuts were also found to contain both extension and terminal A-type PACs and therefore a total peanut system (TPS) was chosen to test the effectiveness of the HPLC method that was developed with the CCJ system. Kinetic studies were conducted and reaction conditions were optimized for the A2 units in both CCJ and TPS. The optimized method provides quantitative and reproducible information on the A2 content of proanthocyanidin isolates.
Keywords: Proanthocyanidins; Condensed tannins; Flavan-3-ols; A-type; Phloroglucinolysis; Cranberry; Peanut
Application of ultra-high-pressure liquid chromatography–tandem mass spectrometry to the determination of multi-class pesticides in environmental and wastewater samples
by José M. Marín; Emma Gracia-Lor; Juan V. Sancho; Francisco J. López; Félix Hernández (pp. 1410-1420).
An ultra-high-pressure liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS) method for the determination of 37 pesticides (herbicides, insecticides and fungicides) in environmental and wastewater has been developed. To efficiently combine UHPLC with MS/MS, a fast-acquisition triple quadrupole mass analyzer was used. This analyzer (minimum dwell time, 5ms) allows acquiring up to three simultaneous transitions in the selected reaction monitoring mode for each compound assuring a reliable identification without resolution or sensitivity losses. A pre-concentration step based on solid-phase extraction using Waters Oasis HLB cartridges (0.2g) was applied with a 100-fold pre-concentration factor along the whole analytical procedure. The method was validated based on European SANCO guidelines using surface, ground, drinking and treated water (from an urban solid residues treatment plant) spiked at two concentration levels (0.025 and 0.1μg/L), the lowest having been established as the limit of quantification objective. The method showed excellent sensitivity, with instrumental limits of detection ranging from 0.1 to 7pg. It was applied to environmental water samples (ground and surface water) as well as to samples of urban solid waste leachates (raw leachate and treated leachate after applying reversed osmosis) collected from a municipal treatment plant. Matrix effects have been studied in the different types of water samples analyzed, and several isotope-labelled internal standards have been evaluated as a way to compensate the signal suppression observed for most of the compounds studied, especially in wastewater samples. As a general remark, only those pesticides which response was corrected using their own isotope-labelled molecule, could be satisfactorily corrected in all type of samples, assuring in this way the accurate quantification in all matrix samples.
Keywords: Pesticides; Ultra-high-pressure liquid chromatography; Tandem mass spectrometry; Confirmation; Matrix effects; Triple quadruple; Internal standard; Environmental and waste water
Liquid chromatography–tandem mass spectrometry method for the detection of marine lipophilic toxins under alkaline conditions
by Arjen Gerssen; Patrick P.J. Mulder; Mairead A. McElhinney; Jacob de Boer (pp. 1421-1430).
A new LC–MS/MS method for the separation and detection of the most prominent marine lipophilic toxin groups comprising okadaic acid, dinophysistoxins, yessotoxins, azaspiracids, pectenotoxins, spirolides and some okadaic acid fatty acid esters has been developed. With this method 28 different marine lipophilic biotoxins can be analysed in a single run. Separation was achieved with an acetonitrile/water gradient containing ammonium hydroxide (pH 11). All toxins were stable under these basic conditions. Compared to chromatography using an acidic gradient, the limit of detection (LODs) for okadaic acid, yessotoxin, gymnodimine and 13-desmethyl spirolide C were improved two- to three-fold, mainly due to better peak shapes. The azaspiracids and pectenotoxins-2 showed comparable LODs under acidic and basic conditions. A major advantage of the developed method is that toxins can be clustered in retention time windows separated for positively and negatively ionized molecular ions. Therefore, there is no need for rapid polarity switching or two separate runs for one sample. The new method showed good repeatability and reproducibility and is an important step in the development of alternatives to the animal tests currently in use for shellfish toxin analysis.
Keywords: Marine lipophilic toxins; LC–MS/MS; Liquid chromatography
Efficient isolation of the subunits of recombinant and pituitary glycoprotein hormones
by C.M. Carvalho; J.E. Oliveira; B.E. Almeida; E.K.M. Ueda; P.A. Torjesen; P. Bartolini; M.T.C.P. Ribela (pp. 1431-1438).
Complete dissociation into subunits was attained by incubating Chinese hamster ovary (CHO)-derived or native human thyrotropin, follitropin and lutropin overnight at 37°C in acetic acid. The α-and β-subunits of the pituitary glycoprotein hormones were rapidly and quantitatively isolated by reversed-phase high-performance liquid chromatography (RP-HPLC). A dissociation efficiency of >98% was obtained on the basis of mass determinations of the heterodimers and subunits carried out via mass spectrometry. CHO-derived or native subunits were isolated on a C4 column (80–90% total recovery) and characterized comparatively for purity, hydrophobicity, molecular mass and charge distribution by HPLC, mass spectrometry, sodium dodecylsulfate-polyacrylamide gel electrophoresis and isoelectric focusing. Thyrotropin was used as a model for showing that, after subunit reassociation, the in vivo bioactivity of the hormone was completely restored. The method described is mild, practical, flexible, and can be adapted to dissociate microgram amounts of native or recombinant glycoprotein hormones, allowing characterization of each subunit.
Keywords: α- and β-subunits; hFSH; hLH; hTSH; MALDI-TOF-MS; Isoelectric focusing; RP-HPLC
Combined column–mobile phase mixture statistical design optimization of high-performance liquid chromatographic analysis of multicomponent systems
by Márcia C. Breitkreitz; Isabel C.S.F. Jardim; Roy E. Bruns (pp. 1439-1449).
A statistical approach for the simultaneous optimization of the mobile and stationary phases used in reversed-phase liquid chromatography is presented. Mixture designs using aqueous mixtures of acetonitrile (ACN), methanol (MeOH) and tetrahydrofuran (THF) organic modifiers were performed simultaneously with column type optimization, according to a split-plot design, to achieve the best separation of compounds in two sample sets: one containing 10 neutral compounds with similar retention factors and another containing 11 pesticides. Combined models were obtained by multiplying a linear model for column type, C8 or C18, by quadratic or special cubic mixture models. Instead of using an objective response function, combined models were built for elementary chromatographic criteria (retention factors, resolution and relative retention) of each solute or pair of solutes and, after their validation, the global separation was accomplished by means of Derringer's desirability functions. For neutral compounds a 37:12:8:43 (v/v/v/v) percentage mixture of ACN:MeOH:THF:H2O with the C18 column and for pesticides a 15:15:70 (v/v/v) ACN:THF:H2O mixture with the C8 column provide excellent resolution of all peaks.
Keywords: HPLC; Split-plot designs; Mobile phase optimization; Derringer's desirability function; Response surface analysis
Analysis of fatty acids in sputum from patients with pulmonary tuberculosis using gas chromatography–mass spectrometry preceded by solid-phase microextraction and post-derivatization on the fiber
by Dongmei Cha; Dong’e Cheng; Mingming Liu; Zhaorui Zeng; Xiaowei Hu; Wenwu Guan (pp. 1450-1457).
A method based on solid-phase microextraction (SPME) and post-derivatization on the fiber coupled to gas chromatography–mass spectrometry (GC–MS) was developed for the analysis of fatty acids in sputum from patients with pulmonary tuberculosis. The sputum specimens were digested, hydrolyzed, extracted, derivertized, injected and analyzed without cultivation or isolation of the microorganism. Under optimized conditions, the relative standard deviations (RSD, n=5) for all analytes were below 17% and the limits of detection varied from 1.68 (C24:0) to 150.4μgL−1 (C12:0). Good linearity was observed for all the fatty acids studied except for C12:0 within a wide concentration range of three orders of magnitudes with the correlation coefficients ranging from 0.91 (C24:0) to 0.99 (C14:0). Fatty acids in sputum specimens from 21 persons were directly analyzed using the proposed method. The results show that in all the sputum specimens from patients, who were clinically diagnosed with tuberculosis (TB), tuberculosis stearic acid (TBSA) was detected, while in all the sputum samples from persons without TB, TBSA was not found. The possibility of using the proposed method to detect mycobacterium tuberculosis (MTB) via the identification of TBSA in sputum was discussed. The comparison with other methods including sputum culture and microscopy of direct smears indicated that the proposed method is fast and sensitive for the analysis of fatty acids in sputum and offers an alternative for the detection of MTB in sputum.
Keywords: Derivatization; Solid-phase microextraction; Gas chromatography–mass spectrometry; Fatty acids; Sputum; Tuberculosis
Traceability of honey origin based on volatiles pattern processing by artificial neural networks
by Tomas Cajka; Jana Hajslova; Frantisek Pudil; Katerina Riddellova (pp. 1458-1462).
Head-space solid-phase microextraction (HS-SPME)-based procedure, coupled to comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry (GC×GC–TOF-MS), was employed for fast characterisation of honey volatiles. In total, 374 samples were collected over two production seasons in Corsica ( n=219) and other European countries ( n=155) with the emphasis to confirm the authenticity of the honeys labelled as “Corsica” (protected denomination of origin region). For the chemometric analysis, artificial neural networks with multilayer perceptrons (ANN-MLP) were tested. The best prediction (94.5%) and classification (96.5%) abilities of the ANN-MLP model were obtained when the data from two honey harvests were aggregated in order to improve the model performance compared to separate year harvests.
Keywords: Honey; Traceability; Origin; Authenticity; Head-space solid-phase microextraction; Comprehensive two-dimensional gas chromatography; Time-of-flight mass spectrometry; Artificial neural networks
Mass spectrometric profiling of saturated fatty acid esters of steroids separated by high-temperature gas chromatography
by Hyun-Jin Jung; Won-Yong Lee; Bong Chul Chung; Man Ho Choi (pp. 1463-1468).
An efficient analytical method for simultaneous determination of 12 SFEs in serum is described. The method involves solid-phase extraction to isolate of SFEs from interfering species, especially cholesteryl esters, conversion to trimethylsilyl (TMS) ether derivatives for the direct analysis by gas chromatography–mass spectrometry (GC–MS) using a high temperature MXT-1 (Silcosteel-treated stainless steel) capillary column. All SFEs as their TMS derivatives were well separated with excellent peak shapes within 12min. Overall recoveries ranged from 88% to 119%, with a detection limits for SFEs ranged from 2 to 30μgL−1. The linearity as correlation coefficient was higher than 0.99 except for pregnenolone-3-arachidate ( r2=0.98) in the concentration range of 5–3000μgL−1. Ten serum samples obtained from volunteers were also analyzed and quantitatively determined of DHEA-3-palmitate and pregnenolone-3-stearate in 1.8–1195.8μgL−1 concentration. The devised high temperature GC–MS method could be useful for identification of SFEs in biological specimens including serum.
Keywords: Steroids; Fatty acids; Lipoidal conjugate; Gas chromatography; Mass spectrometry
High-throughput approach for analysis of multicomponent gas chromatographic–mass spectrometric signals
by Zhichao Liu; Wensheng Cai; Xueguang Shao (pp. 1469-1475).
Hyphenated techniques such as gas chromatography–mass spectrometry (GC–MS) or high-performance liquid chromatography–mass spectrometry (LC–MS) produce a large amount of data in a form of two-way data matrix. It has been a great challenge to furthest extract the useful information from the data. In this work, a chemometric approach based on a modification of adaptive immune algorithm (AIA) was proposed for a high-throughput analysis of the multicomponent overlapping GC–MS signals. With the proposed method, the chromatographic profile of each component in an overlapping signal can be extracted independently and sequentially along the retention time. In order to show the efficiency of the method, a stimulated GC–MS data of six components with background and an experimental GC–MS data of 40 pesticides were investigated. It was found that the multicomponent overlapping GC–MS signals could be fast and accurately resolved. Furthermore, the quantitative property of the extracted information was also investigated. The correlation coefficients ( r) between the peak area and the added volumes of the sample are in the range 0.9658–0.9953.
Keywords: High-throughput analysis; Multicomponent analysis; Chemometrics; Hyphenated techniques; Gas chromatography–mass spectrometry (GC–MS); Pesticide
Development of a screening method to determine the pattern of fermentation metabolites in faecal samples using on-line purge-and-trap gas chromatographic–mass spectrometric analysis
by Vicky De Preter; Greet Van Staeyen; Diederik Esser; Paul Rutgeerts; Kristin Verbeke (pp. 1476-1483).
An on-line screening method to analyse volatile organic compounds (VOCs) in faecal samples was developed. VOCs were isolated from a standard solution or faecal samples using a purge-and-trap system and identified and quantified by GC–MS. The experimental conditions were optimised and the performance of the system was evaluated. Linear calibration curves were obtained with correlation coefficients of at least 0.992. RSDs within and between days were less than 10%. The method was successfully applied to the analysis of faecal samples, yielding 135 different volatile organic compounds identified in 11 faecal samples. Of those, 22 VOCs were found in all volunteers, whereas 34 VOCs were person-specific.
Keywords: Volatile organic compounds; Purge-and-trap; GC-TOF-MS
Ultra-high concentration of amylose for chiral separations in capillary electrophoresis
by Wei-Li Wei; Bao-Yuan Guo; Jin-Ming Lin (pp. 1484-1489).
In the present study, a capillary electrophoresis method using high concentration of amylose solutions as separation medium has been developed with the aid of dimethyl sulfoxide (DMSO) as co-solvent. The best buffer conditions for primaquine, trihexyphenidyl (THP), sulconazole and cetirizine enantiomers were optimized as 20mM sodium phosphate buffer with DMSO/water (40/60, v/v) as solvent at a pH of 3.0, containing 10% (w/v) amylose. Partial-filling and semi-permanent coating techniques were used considering the influences of DMSO on UV detection. High chiral resolution for THP enantiomers was obtained showing good chiral separation capacity of this method. The method showed good linearity ( R2>0.998) over the concentration range of 0.50 and 2.00mgL−1 for all the enantiomers. The detection limits for the tested enantiomers were in the range from 0.05 to 0.12mgL−1. The linear calibration models were proven to be adequate for the experimental data by lack-of-fit test. The intra-assay precision, inter-day precision and accuracy were all evaluated to be acceptable. Separation and determination of THP enantiomers in rabbit blood were also carried out.
Keywords: Capillary electrophoresis; Chiral separation; Dimethyl sulfoxide; Ultra-high concentration of amylose
Online preconcentration of recombinant Arg-Gly-Asp-hirudin using dynamic pH junction for analysis in human urine samples by capillary electrophoresis-mass spectrometry
by Shengmin Su; Yunqiu Yu (pp. 1490-1495).
A sensitive and effort-saving method was established and validated for the quantitative determination of recombinant Arg-Gly-Asp-hirudin (rRGD-hirudin) in human urine samples. The assay was performed on a uncoated fused silica capillary of 70cm×50μm I.D. and a positive voltage of 30kV was applied. The sample was injected under pressure of 50mbar for 300s and the temperature of capillary was kept 25°C. Sheath liquid consisting of 30% methanol and 70% of 0.1% formic acid aqueous solution flowing at 7μL/min was supplied to the CE-electrospray interface. Utilizing the dynamic pH junction technique, a lower limit of quantitation of approximately 35nM was achieved (concentration coefficiency was about 100-fold) without complex sample preprocessing procedure. CE-MS conditions and parameters were also optimized to obtain better performance. The method has been successfully applied in clinical research of rRGD-hirudin.
Keywords: CE-MS; Online preconcentration; Dynamic pH junction; rRGD-hirudin; Human urine; Quantitative assay
Drop-to-drop microextraction across a supported liquid membrane by an electrical field under stagnant conditions
by Nickolaj Jacob Petersen; Henrik Jensen; Steen Honoré Hansen; Knut Einar Rasmussen; Stig Pedersen-Bjergaard (pp. 1496-1502).
Electromembrane extraction (EME) of basic drugs from 10μL sample volumes was performed through an organic solvent (2-nitrophenyl octyl ether) immobilized as a supported liquid membrane (SLM) in the pores of a flat polypropylene membrane (25μm thickness), and into 10μL 10mM HCl as the acceptor solution. The driving force for the extractions was 3–20V d.c. potential sustained over the SLM. The influence of the membrane thickness, extraction time, and voltage was investigated, and a theory for the extraction kinetics is proposed. Pethidine, nortriptyline, methadone, haloperidol, and loperamide were extracted from pure water samples with recoveries ranging between 33% and 47% after only 5min of operation under totally stagnant conditions. The extraction system was compatible with human urine and plasma samples and provided very efficient sample pretreatment, as acidic, neutral, and polar substances with no distribution into the organic SLM were not extracted across the membrane. Evaluation was performed for human urine, providing linearity in the range 1–20μg/mL, and repeatability (RSD) in average within 12%.
Keywords: Extraction; Sample preparation; Electromembrane extraction (EME); Supported liquid membrane (SLM)
High-sensitivity microchip electrophoresis determination of inorganic anions and oxalate in atmospheric aerosols with adjustable selectivity and conductivity detection
by Scott D. Noblitt; Florian M. Schwandner; Susanne V. Hering; Jeffrey L. Collett Jr.; Charles S. Henry (pp. 1503-1510).
A sensitive and selective separation of common anionic constituents of atmospheric aerosols, sulfate, nitrate, chloride, and oxalate, is presented using microchip electrophoresis. The optimized separation is achieved in under 1min and at low background electrolyte ionic strength (2.9mM) by combining a metal-binding electrolyte anion (17mM picolinic acid), a sulfate-binding electrolyte cation (19mM HEPBS), a zwitterionic surfactant with affinity towards weakly solvated anions (19mM N-tetradecyl,N,N-dimethyl-3-ammonio-1-propansulfonate), and operation in counter-electroosmotic flow (EOF) mode. The separation is performed at pH 4.7, permitting pH manipulation of oxalate's mobility. The majority of low-concentration organic acids are not observed at these conditions, allowing for rapid subsequent injections without the presence of interfering peaks. Because the mobilities of sulfate, nitrate, and oxalate are independently controlled, other minor constituents of aerosols can be analyzed, including nitrite, fluoride, and formate if desired using similar separation conditions. Contact conductivity detection is utilized, and the limit of detection for oxalate (S/N=3) is 180nM without stacking. Sensitivity can be increased with field-amplified sample stacking by injecting from dilute electrolyte with a detection limit of 19nM achieved. The high-sensitivity, counter-EOF operation, and short analysis time make this separation well-suited to continuous online monitoring of aerosol composition.
Keywords: Microchip electrophoresis; Atmospheric aerosol; Inorganic anion; Conductivity detection
Dispersive liquid–liquid microextraction combined with high-performance liquid chromatography-UV detection as a very simple, rapid and sensitive method for the determination of bisphenol A in water samples
by Mohammad Rezaee; Yadollah Yamini; Shahab Shariati; Ali Esrafili; Mojtaba Shamsipur (pp. 1511-1514).
Dispersive liquid–liquid microextraction (DLLME) coupled with high-performance liquid chromatography (HPLC)-UV detection was applied for the extraction and determination of bisphenol A (BPA) in water samples. An appropriate mixture of acetone (disperser solvent) and chloroform (extraction solvent) was injected rapidly into a water sample containing BPA. After extraction, sedimented phase was analyzed by HPLC-UV. Under the optimum conditions (extractant solvent: 142μL of chloroform, disperser solvent: 2.0mL of acetone, and without salt addition), the calibration graph was linear in the range of 0.5–100μgL−1 with the detection limit of 0.07μgL−1 for BPA. The relative standard deviation (RSD, n=5) for the extraction and determination of 100μgL−1 of BPA in the aqueous samples was 6.0%. The results showed that DLLME is a very simple, rapid, sensitive and efficient analytical method for the determination of trace amount of BPA in water samples and suitable results were obtained.
Keywords: Dispersive liquid–liquid microextraction; Preconcentration; Bisphenol A; Water samples; HPLC
Improved determination of milk oligosaccharides using a single derivatization with anthranilic acid and separation by reversed-phase high-performance liquid chromatography
by Fiame Leo; Sadaki Asakuma; Tadashi Nakamura; Kenji Fukuda; Akitsugu Senda; Tadasu Urashima (pp. 1520-1523).
An improved analytical scheme for human milk neutral oligosaccharides determination was developed, in which, the oligosaccharides were pooled in two fractions (pools 1 and 2) after gel filtration, and then were quantitatively derivatized with a single fluorescent reagent, 2-anthranilic acid. Separation was by reversed-phase HPLC on an ODS-100Z column with a mobile phase of 50mM ammonium acetate pH 4.0 and 150mM citrate buffer pH 4.5 and monitored by a fluorescence detector at 360nm excitation and 425nm emission wavelengths. The method improved on the separation of neutral tetra- and hexa-saccharide isomers, namely, lacto-N-tetraose (LNT) and lacto-N-neotetraose (LNnT) as well as of lacto-N-difucohexaose I (LNDFH I) and lacto-N-difucohexaose II (LNDFH II). The separation of trisacccharide isomers, 3-fucosyllactose (3-FL) and 2′-fucosyllactose (2′-FL) was also successful. Limits of detection and quantification were in the range of 1–10ng/l and 2–30ng/l, respectively. The methods’ accuracy was good with its precision at <20% RSD and <1% RSD, respectively, for oligosaccharide concentration and retention time. The recoveries were in the range of 80–100%. This method was successfully applied to the separation and determination of representative neutral oligosaccharide contents in Samoa women milk.
Keywords: Neutral oligosaccharides; Anthranilic acid; Derivatization; HPLC; Lacto-N-fucopentaose III; 2′-Fucosyllactose
Detailed analysis of petroleum hydrocarbon attenuation in biopiles by high-performance liquid chromatography followed by comprehensive two-dimensional gas chromatography
by Debin Mao; Richard Lookman; Hendrik Van De Weghe; Dirk Van Look; Guido Vanermen; Nicole De Brucker; Ludo Diels (pp. 1524-1527).
Enhanced bioremediation of petroleum hydrocarbons in two biopiles was quantified by high-performance liquid chromatography (HPLC) followed by comprehensive two-dimensional gas chromatography (GCXGC). The attenuation of 34 defined hydrocarbon classes was calculated by HPLC–GCXGC analysis of representative biopile samples at start-up and after 18 weeks of biopile operation. In general, a-cyclic alkanes were most efficiently removed from the biopiles, followed by monoaromatic hydrocarbons. Cycloalkanes and polycyclic aromatic hydrocarbons (PAHs) were more resistant to degradation. A-cyclic biomarkers farnesane, trimethyl-C13, norpristane, pristane and phytane dropped to only about 10% of their initial concentrations. On the other hand, C29–C31 hopane concentrations remained almost unaltered after 18 weeks of biopile operation, confirming their resistance to biodegradation. They are thus reliable indicators to estimate attenuation potential of petroleum hydrocarbons in biopile processed soils.
Keywords: Petroleum hydrocarbons; Soil; HPLC–GCXGC; Attenuation; Biodegradation; Biomarkers