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J Chromatogr A [journal]
- Recent development and applications of dispersive liquid-liquid microextraction. [JOURNAL ARTICLE]
- J Chromatogr A 2013 Apr 22.
Dispersive liquid-liquid microextraction (DLLME) is a modern sample pretreatment technique that is regarded as consilient with the current trends of modern analytical chemistry. DLLME is simple, inexpensive, environmentally friendly, and could offer high enrichment factors from a wide gap between acceptor and donor phases. As a consequence, DLLME has attracted considerable attention from researchers and, based on the numerous publications concerning DLLME, has been generally accepted in separation science since the technique's invention in 2006. However, several innate weaknesses of DLLME, which restrict the technique's use in certain fields, have led to various attempts or suggestions to improve this technique. The present review focuses on the recent advances made in DLLME; the selected papers that are discussed in this work represent modifications that fall into three main categories (exploration of new extraction solvents, disperser solvents and combination with other techniques). The recent applications of DLLME in environmental, food and biological samples are also summarised, covering almost all of the publications related to the technology from the beginning. In addition, the feasibility of future trends of DLLME is discussed.
- In situ derivatization of metals and organometallics using borate reagents in gas chromatographic speciation studies. [JOURNAL ARTICLE]
- J Chromatogr A 2013 Apr 27.
Development of sensitive and selective analytical methods is required for trace metal and metalloids speciation analysis, including their alkyl-, phenyl- or other organometallic species. Gas chromatography is one of the most suitable techniques for effective separation of the above compounds however it requires that the analytes are volatile or semi-volatile. Today very popular derivatization methods make use of borate reagents for in situ derivatization of elements like Hg, Pb, Sn, Se, As, etc. Tetrahydroborates are suitable for hydride generation and alkylborates for alkylation of the inorganic ions of the above elements, as well as of several partially alkylated ones. This almost immediate reaction can be done in aqueous solutions and produces fully alkylated products of higher volatility suitable for separation by gas chromatography and measured by various detectors. The number of papers published in this field is constantly high, including many applications to various types of matrices, like biological, environmental, industrial, food, polymers, etc. For this reason, many articles of the last two decades are reviewed in this paper and emphasis is given to the use of borate reagents and the relative microreactions for selected elements.
- Quantification of selected synthetic cannabinoids and Δ(9)-tetrahydrocannabinol in oral fluid by liquid chromatography-tandem mass spectrometry. [JOURNAL ARTICLE]
- J Chromatogr A 2013 Apr 22.
An LC-MS/MS method for the quantification of the synthetic cannabinoids JWH-200, JWH-250, JWH-073, JWH-018, HU-211, CP 47,497 and CP 47,497-C8, and THC in oral fluid was developed and validated. Samples (0.5mL) were extracted using Strata X cartridges (Phenomenex). Chromatographic separation was achieved with a Sunfire™ IS column (20×2.1mm, 3.5μm) (Waters Corp.), with formic acid 0.1% and acetonitrile as mobile phase. A different chromatographic gradient was applied for the separation of the analytes depending on the ionization mode employed, with a total chromatographic run of 14min. Detection was performed in a Quattro Micro™ API ESCI (Waters Corp.), using electrospray in the positive mode (ESI+) for JWH-200, JWH-250, JWH-073, JWH-018 and THC, and ESI- for HU-211, CP 47,497, and CP 47,497-C8. Validation of the method included the assessment of selectivity, linearity (0.1-2.5 to 200ng/mL), limits of detection (0.025-1ng/mL) and quantification (0.1-2.5ng/mL), imprecision (%CV≤14.4%), accuracy (91.8-109.7% of target concentration), extraction recovery (65.4-105.6%) and Quantisal recovery (56.1-66.7%), and matrix effect (neat oral fluid: -56.0% to 38.5%; oral fluid in Quantisal buffer: -15.1% to -71.7%). The application of this method to oral fluid samples from roadside testing will provide unique information on the use of these new synthetic drugs by Spanish drivers.
- Limit of the speed-resolution properties in adiabatic supercritical fluid chromatography. [JOURNAL ARTICLE]
- J Chromatogr A 2013 Apr 24.
Kinetic Poppe plots for small retained compounds were calculated in HPLC (using pure acetonitrile) and SFC (using pure carbon dioxide) for columns having twenty one different lengths (between 3cm and 30m), operated under strict adiabatic conditions (no heat exchange was allowed between the column and the external environment), with a constant pressure drop of 200bar. The outlet pressures were set at 1 and 160bar in HPLC and SFC, respectively. The eluent inlet temperature was set at 312K. The hold-up time t0 and the apparent column efficiency 〈N〉 were calculated by taking into account the longitudinal variations of the eluent pressure, its temperature, density, viscosity, heat capacity, thermal expansion coefficient, equilibrium constant, and diffusion coefficient along the column length. Three different classes of stationary phase were considered: fully porous particles and core-shell particles of different diameter and structure, and silica monolithic columns of the second generation. The reduced plate heights of these stationary phases were taken from experimental data obtained with liquid eluents (acetonitrile/water mixtures). The columns were assumed to be radially homogeneous. The Henry's constant of the compound was fixed at Ka=2.0 at the column inlet. The results demonstrate the potential advantage of using sub-3μm core-shell particles for fast analysis in both LC and SFC, regardless of the intra-particle diffusivity through the stationary phase. In RPLC conditions, the contribution of surface diffusion to intra-particle diffusivity is important and the 4.6 μm core-shell particles can perform as well as sub-2 μm fully porous particles and silica monolithic columns of the second generation. In the absence of surface diffusion or for localized adsorption onto the stationary phase, sub-2 μm particles and silica monolithic column of the second generation outperform the 4.6 μm core-shell particles because the solid-liquid mass transfer resistance controls the column efficiency at high speeds. Eventually, for the same stationary phase and speed of analysis, SFC methods using pure CO2 may provide at least a twice column efficiency than LC methods using pure acetonitrile. For a constant pressure drop and resolution power, SFC methods may generate four times faster analyses than LC methods. Ultimately, a standard commercial 4.6mm × 50mm long column packed with 2.6μm core-shell particles, operated with an inlet flow rate of 25mL/min in fast SFC (200bar back pressure, 40°C) may provide a hold-up time of about 1s requiring data acquisition at a frequency of 400Hz, with a variance of 0.35μL(2). This performance will require the use of new, ultra-low dispersion SFC system.
- New sample preparation approach for mass spectrometry-based profiling of plasma results in improved coverage of metabolome. [JOURNAL ARTICLE]
- J Chromatogr A 2013 Apr 18.
Sample preparation remains a challenge in untargeted metabolomics studies and no method currently results in complete extraction of all metabolite classes in human plasma. Because a large variety of molecules, with vast differences in dynamic range, could be involved in human disease, there is an urgent need to develop analytical techniques that result in comprehensive coverage of metabolites. Furthermore, analysis of more focused molecular classes could be necessary to more fully interrogate markers of human disease. However, such techniques, which generally involve multiple steps, often result in high variability. We have optimized a combined liquid-liquid and solid phase extraction method for plasma and have compared that to traditional methanol precipitation using spiked internal standards as controls. This method, based largely on previously published methods, results in 5 separate fractions enriched for aqueous species, phospholipids, fatty acids, neutral lipids, and hydrophobic lipids. Using liquid chromatography mass spectrometry as the analytical method, we detect over 3806 metabolites using the new method versus 1851 metabolites using methanol alone. Qualitative analysis and quantitative analysis of both internal standards (ISTDs) and endogenous metabolites demonstrate excellent reproducibility with CV's below 15% for the combined method compared to 30% using the methanol method. While both methods have applications for clinical metabolomics, fractionation resulted in greater overall coverage and can be used for initial classification of molecular species.
- Development of a simultaneous multiple solid-phase microextraction-single shot-gas chromatography/mass spectrometry method and application to aroma profile analysis of commercial coffee. [JOURNAL ARTICLE]
- J Chromatogr A 2013 Apr 24.
A simultaneous multiple solid-phase microextraction-single shot-gas chromatography mass spectrometry (smSPME-ss-GC/MS) method has been developed for headspace analysis. Up to four fibers (50/30μm DVB/CAR/PDMS) were used simultaneously for the extraction of aroma components from the headspace of a single sample chamber in order to increase sensitivity of aroma extraction. To avoid peak broadening and to maximize resolution, a simple cryofocusing technique was adopted during sequential thermal desorption of multiple SPME fibers prior to a 'single shot' chromatographic run. The method was developed and validated on a model flavor mixture, containing 81 known pure components. With the conditions of 10min of incubation and 30min of extraction at 50°C, single, dual, triple and quadruple SPME extractions were compared. The increase in total peak area with increase in the number of fibers showed good linearity (R(2)=0.9917) and the mean precision was 12.0% (RSD) for the total peak sum, with quadruple simultaneous SPME extraction. Using a real sample such as commercial coffee granules, aroma profile analysis was conducted using single, dual, triple and quadruple SPME fibers. The increase in total peak intensity again showed good linearity with increase in the number of SPME fibers used (R(2)=0.9992) and the precision of quadruple SPME extraction was 9.9% (RSD) for the total peak sum.
- Study of the peak variance in isocratic and gradient liquid chromatography using the transport model. [JOURNAL ARTICLE]
- J Chromatogr A 2013 Apr 22.
The expressions accounting for the peak variance in isocratic and gradient liquid chromatography is derived from the transport model. In mathematical treatments, the dwelling time is taken into account, and the type of solvent strength, gradient profile and the variation of plate height (H) with mobile phase composition (φ) is not specified. By applying a coordinate transformation, the transport model is solved by using the Laplace transform approach. A plate height equation that is suited for both isocratic and gradient elution is obtained. Based on this equation, the plate height equations for any combination of stepwise and linear gradients are derived. These equations will be algebraic when the solvent strength is linear and the H-φ plot is parabolic. The plate height equations for single stepwise, single linear and the ladder-like gradients are also given.
- Sensitive analysis of aminoglycoside antibiotics via hyphenation of transient moving substitution boundary with field-enhanced sample injection in capillary electrophoresis. [JOURNAL ARTICLE]
- J Chromatogr A 2013 Apr 22.
A novel field-enhanced sample injection coupled with transient moving substitution boundary method in capillary electrophoresis was developed for aminoglycoside antibiotic (AG) analysis using 18-crown-6-tetracarboxylic acid (18C6H4) as a pseudostationary phase. Results indicated that the stacking mechanism of moving substitution boundary relied on the substitution reaction between 18C6H4-bonded AG complexes and Na(+) at the substitution boundary. The stacking mechanism as well as important parameters governing pre-concentration and separation have been investigated in order to obtain maximum resolution and sensitivity. Under optimized conditions, using a sample prepared in a low-conductivity matrix, the limits of detection for streptomycin, neomycin, and kanamycin were 0.62, 5.9 and 8.6nM (S/N=3), respectively, and the detection sensitivities were improved 940-, 692-, and 415-fold, respectively. The method also gave accurate and reliable results in the analysis of AGs in river water samples.
- Water stable metal-organic framework packed microcolumn for online sorptive extraction and direct analysis of naproxen and its metabolite from urine sample. [JOURNAL ARTICLE]
- J Chromatogr A 2013 Apr 18.
The metal-organic framework MIL-101 was fabricated in a polyetheretherketone (PEEK) tube as micro-trapping device, and applied to sorptive extraction of naproxen and its metabolite in urine samples. The remarkable water stability of the MIL-101 characterizes the material as being different from other moisture sensitive metal-organic framework. It is therefore suitable for extraction of pharmaceuticals from biological fluids. The adsorption isotherms in aqueous solution showed that the adsorption of naproxen on MIL-101 is endothermic. Additionally, MIL-101 exhibited higher extraction capacity to naproxen than that of C18-bonded silica and multi-walled nanotube. A specially designed in-tube sorptive extraction (ITSE) device endows the extraction process with the characteristic of rapidness, convenience, and easy of conjunction with high performance liquid chromatography (HPLC). Finally the MIL-101 based ITSE method coupled with HPLC and fluorescence detection was applied to analysis of naproxen and 6-O-desmethylnaproxen in urine samples. Parameters that influence the online extraction procedure, including pH of the sample solution, flow rate of extraction, sample volume, desorption solvents and time were investigated. The method is proved to be highly sensitive with the linear range of 0.05-6.0μgL(-1) and the limits of detection of 0.034 and 0.011μgL(-1) for naproxen and 6-O-desmethylnaproxen, respectively. The recoveries in urine samples were 85.3-98.3% for naproxen and 94.0-97.3% for 6-O-desmethylnaproxen with intra- and inter-day RSDs of 2.7-5.2% and 7.1-8.1%, respectively. Urine samples could be directly subjected to analysis without any additional sample pretreatment. The proposed method was demonstrated an efficient, flexible and versatile extraction tool which is ideally suitable for online conjunction with chromatographic methods.
- Determination of gamma-hydroxybutyric acid in biofluids using a one-step procedure with "in-vial" derivatization and headspace-trap gas chromatography-mass spectrometry. [JOURNAL ARTICLE]
- J Chromatogr A 2013 Apr 17.
A headspace-trap gas chromatography-mass spectrometry (HS-trap GC-MS) method was developed to determine GHB, a low molecular weight compound and drug of abuse, in various biological fluids. Combining this relatively novel and fully automated headspace technique with "in-vial" methylation of GHB allowed for a straightforward approach. One single method could be used for all biofluids (urine, plasma, serum, whole blood or lyzed blood), requiring only 100μl of sample. Moreover, our approach involves mere addition of all reagents and sample into one vial. Following optimization of headspace conditions and trap settings, validation was performed. Although sample preparation only consists of the addition of salt and derivatization reagents directly to a 100μl-sample in a HS-vial, adequate method sensitivity and selectivity was obtained. Calibration curves ranged from 5 to 150μg/ml GHB for urine, from 2 to 150μg/ml for plasma, and from 3.5 to 200μg/ml for whole blood. Acceptable precision and accuracy (<13% bias and imprecision) were seen for all quality controls (QC's) (LLOQ-level, low, medium, high), including for the supplementary serum- and lyzed blood-based QC's, using calibration curves prepared in plasma or whole blood, respectively. Incurred sample reanalysis demonstrated assay reproducibility, while cross-validation with another GC-MS method demonstrated that our method is a valuable alternative for GHB determination in toxicological samples, with the advantage of requiring only 100μl and minimal hands-on time, as sample preparation is easy and injection automated.