Solid-phase extraction of phenols

Sample preparation for phenol analysis using solid-phase extraction (SPE) is reviewed. The scope of the review has been restricted to the literature dealing with the analysis of phenols as the main objective. The use, advantages and disadvantages of silica sorbents, polymeric, functionalized, carbon-based and mixed available sorbents, when applied to the separation and preconcentration of phenols, as well as the available experimental devices, are discussed. Other aspects such as phenol derivatisation prior to SPE, solid-phase microextraction, matrix effects and the storage of phenols in SPE cartridges, have been also discussed.

Synthesis of ecteinascidin ET-743 and phthalascidin Pt-650 from cyanosafracin B

An efficient new process is described for the synthesis of ecteinascidin ET-743 (1) and phthalascidin (2), starting from readily available cyanosafracin B (3).

Cis-regulation of achaete and scute: shared enhancer-like elements drive their coexpression in proneural clusters of the imaginal discs

The pattern of bristles and other sensory organs on the adult cuticle of Drosophila is prefigured in the imaginal discs by the pattern of expression of the proneural achaete (ac) and scute (sc) genes, two members of the ac-sc complex (AS-C). These genes are simultaneously expressed by groups of cells (the proneural clusters) located at constant positions in discs. Their products (transcription factors of the basic-helix-loop-helix family) allow cells to become sensory organ mother cells (SMCs), a fate normally realized by only one or a few cells per cluster. Here we show that the highly complex pattern of proneural clusters is constructed piecemeal, by the action on ac and sc of site-specific, enhancer-like elements distributed along most of the AS-C (approximately 90 kb). Fragments of AS-C DNA containing these enhancers drive reporter lacZ genes in only one or a few proneural clusters. This expression is independent of the ac and sc endogenous genes, indicating that the enhancers respond to local combinations of factors (prepattern). We show further that the cross-activation between ac and sc, discovered by means of transgenes containing either ac or sc promoter fragments linked to lacZ and thought to explain the almost identical patterns of ac and sc expression, does not occur detectably between the endogenous ac and sc genes in most proneural clusters. Our data indicate that coexpression is accomplished by activation of both ac and sc by the same set of position-specific enhancers.

Competence to develop sensory organs is temporally and spatially regulated in Drosophila epidermal primordia

The Drosophila adult cuticle displays a stereotyped pattern of sensory organs (SOs). Its deployment requires the expression of the achaete (ac) and scute (sc) genes. Their products confer to cells of epidermal primordia (imaginal discs and histoblasts) the ability to become SO precursors (SOPs). In imaginal discs, ac and sc expression is spatially restricted to cell clusters within which one or a few cells become SOP(s). With the help of ubiquitous sc expression provided at different developmental times by a heat shock-sc (HSSC) chimeric gene, we have analyzed the response of epidermal primordia to the proneural action of the sc product, and have tested whether the patterned distribution of ac/sc products is necessary to position SOs correctly within the epidermis. Each primordium responds to HSSC expression by developing SOs only during a characteristic developmental period. In the absence of the endogenous ac and sc genes, most SOs induced by HSSC are of the correct type and are located in wild type positions. These results indicate that the capacity of primordia to respond to sc is temporally and spatially regulated, that specification of the type of SO does not depend on ac/sc, and that SO positioning utilizes topological information independent of the spatially restricted distribution of ac/sc products.

Determination of acidic drugs in sewage water by gas chromatography-mass spectrometry as tert.-butyldimethylsilyl derivatives

A procedure is described for the determination of five acidic non-steroidal anti-inflammatory pharmaceuticals (ibuprofen, naproxen, ketoprofen, tolfenamic acid and diclofenac) in sewage water. The analytical method involves the concentration of water samples using a solid-phase extraction polymeric sorbent, functionalized with N-vinylpyrrolidone. Analytes were eluted with ethyl acetate. derivatized using N-methyl-N-(tert.-butyldimethylsilyl)trifluoroacetamide (MTBSTFA) and analyzed by GC-MS. Influence of time, temperature and volume of MTBSTFA in the yield of the derivatization step were studied in detail using a factorial central composite design. Quantification limits of the analytical procedure for 500 ml of sewage water ranged from 20 to 50 ng/l. Recoveries from 90 to 115% were found for sewage water samples spiked with the studied compounds at the low ng/ml level. Results obtained for real samples show the presence of ibuprofen and naproxen in both influent and effluent of a sewage water treatment plant.

Optimisation of a solid-phase microextraction method for the determination of parabens in water samples at the low ng per litre level

A procedure for the determination of five esters of p-hydroxybenzoic acid (parabens) in water samples is presented. Analytes (methyl, ethyl, propyl, butyl and benzyl paraben) are concentrated on a solid-phase microextraction (SPME) fibre, converted on their tert-butyldimethylsilyl derivatives and selectively determined using gas chromatography in combination with tandem mass spectrometry (GC-MS/MS). Influence of different factors on the efficiency of extraction and on-fibre derivatization steps is described in detail. For all species, the highest enrichment factors were achieved using a polyacrylate (PA) fibre exposed directly to stirred water samples, containing 150 mg/ml of sodium chloride, at room temperature. Performance of the further on-fibre derivatization reaction was also maximum at room temperature, considering a short exposition period of the SPME fibre to vapours of the silylation reagent. Under optimised conditions, the proposed method achieved quantification limits from 0.001 to 0.025 ng/ml and it was free of matrix effects; therefore, external calibration can be used as the quantification technique. From our knowledge, this work describes the first application of SPME and gas chromatography to the determination of parabens in water. The analysis of a limited number of real samples revealed the presence of parabens in raw sewage water at concentrations up to 3 ng/ml.

Precision Measurement of the Proton Flux in Primary Cosmic Rays from Rigidity 1 GV to 1.8 TV with the Alpha Magnetic Spectrometer on the International Space Station

A precise measurement of the proton flux in primary cosmic rays with rigidity (momentum/charge) from 1 GV to 1.8 TV is presented based on 300 million events. Knowledge of the rigidity dependence of the proton flux is important in understanding the origin, acceleration, and propagation of cosmic rays. We present the detailed variation with rigidity of the flux spectral index for the first time. The spectral index progressively hardens at high rigidities.

Determination of natural and synthetic estrogens in water by gas chromatography with mass spectrometric detection

A procedure for the determination of six natural and synthetic estrogens (diethylstilbestrol, estrone, 17beta-estradiol, mestranol, 17alpha-ethinylestradiol and estriol) in water samples is described. Samples, up to 2000 ml, were concentrated using Oasis HLB solid-phase extraction cartridges. Analytes were derivatized with N-methyl-N-(trimethylsilyl)trifluoroacetamide and determined by GC-MS or GC-MS-MS. The reactivity of several silylation reagents versus aliphatic and aromatic hydroxyl groups contained in the structure of the selected analytes was evaluated. Influence of parameters such as sample pH, nature of the water samples and derivatization conditions on the performance of the whole analytical procedure was systematically studied. Under optimal conditions, quantification limits between 1 and 3 ng/l were achieved for the determination of the considered estrogens in sewage water.

First result from the Alpha Magnetic Spectrometer on the International Space Station: precision measurement of the positron fraction in primary cosmic rays of 0.5-350 GeV

A precision measurement by the Alpha Magnetic Spectrometer on the International Space Station of the positron fraction in primary cosmic rays in the energy range from 0.5 to 350 GeV based on 6.8 × 10(6) positron and electron events is presented. The very accurate data show that the positron fraction is steadily increasing from 10 to ∼ 250  GeV, but, from 20 to 250 GeV, the slope decreases by an order of magnitude. The positron fraction spectrum shows no fine structure, and the positron to electron ratio shows no observable anisotropy. Together, these features show the existence of new physical phenomena.

Determination of Parabens and Triclosan in Indoor Dust Using Matrix Solid-Phase Dispersion and Gas Chromatography with Tandem Mass Spectrometry

A simple sample preparation method for the determination of four parabens and triclosan in indoor dust is presented. Analytes were extracted from the sample and isolated from interfering species using the matrix solid-phase dispersion technique. After that, they were silylated and determined by gas chromatography combined to tandem mass spectrometry (GC/MS/MS). The influence of several factors on the yield and selectivity of the extraction was evaluated in detail. Under final working conditions, samples (0.5 g) were mixed with the same amount of anhydrous sodium sulfate and dispersed on 1.25 g of C18. This blend was transferred to the top of a polypropylene cartridge containing 2 g of Florisil. After removing less polar species with 10 mL of dichloromethane, analytes were recovered using 10 mL of acetonitrile. This extract was concentrated to 1 mL, derivatized, and injected in the GC/MS/MS system. Derivatization was carried out at 45 degrees C in 5 min using 100 microL of N-methyl-N-(tert-butyldimethylsilyl) trifluoroacetamide. Quantification limits from 0.6 to 2.6 ng/g and absolute recoveries between 80 and 114% were achieved. Analysis of dust samples demonstrated the presence of the target species in indoor dust from private houses. The highest average concentration (702 ng/g) corresponded to triclosan.

Immune response of zebrafish (Danio rerio) against a newly isolated bacterial pathogen Aeromonas hydrophila

A strain of Aeromonas hydrophila associated with unusual mortalities in zebrafish (Danio rerio) culture facilities was isolated, identified and characterized. In challenge experiments, adult zebrafish were susceptible to infection by intraperitoneal (i.p.) injection with viable bacteria and its extracellular products (ECPs) reaching very high mortalities in a few hours. The infection, by the viable bacteria or the ECPs, caused cell death in kidney, due to the cytotoxic and haemolytic activities of the bacterial ECPs. Moreover, the infection affected the release of oxygen (ROS) and nitrogen (NO) reactive free radicals. To determine if this A. hydrophila infection induces an inflammatory response, mRNA expression levels of tumour necrosis factor-alpha (TNFalpha), interleukin-1beta (IL-1beta), interferon-gamma (IFNgamma) and inducible nitric oxide (iNOS) were assessed by real time PCR. The expression levels of TNFalpha, IL-1beta and IFNgamma were upregulated in the kidneys of infected zebrafish with viable bacteria, heat-killed bacteria and ECPs. Expression levels of iNOS were upregulated by ECPs. Mortality rate (LD(50)) and histopathology were also determined.

Aquatic degradation of triclosan and formation of toxic chlorophenols in presence of low concentrations of free chlorine

The degradation of 2-(2,4-dichlorophenoxy)-5-chlorophenol (triclosan) in chlorinated water samples was investigated. Sensitive determination of the parent compound and its transformation products was achieved by gas chromatography with mass spectrometry detection after sample concentration, using a solid-phase extraction sorbent and silylation of the target compounds. Experiments were accomplished using ultrapure water spiked with chlorine and triclosan concentrations in the low mg/l and ng/ml ranges respectively. Chlorination of the phenolic ring and cleavage of the ether bond were identified as the main triclosan degradation pathways. Both processes led to the production of two tetra- and a penta-chlorinated hydroxylated diphenyl ether, as well as 2,4-dichlorophenol. The formation of 2,3,4-trichlorophenol was not detected in any experiment; however, significant amounts of 2,4,6-trichlorophenol were noticed. All of these five compounds were also identified when triclosan was added to tap-water samples with free chlorine concentrations below 1 mg/l. Minor amounts of three di-hydroxylated phenols, containing from one to three atoms of chlorine in their structures, were also identified as unstable triclosan chlorination by-products. The analysis of several raw wastewater samples showed the co-existence of important concentrations of triclosan and its most stable by-products (2,4-dichlorophenol and 2,4,6-trichlorophenol), reinforcing the potential occurrence of the described transformations when products containing triclosan are mixed with chlorinated tap water.

Formation of halogenated by-products of parabens in chlorinated water

Chemical transformations of four alkyl esters of p-hydroxybenzoic acid, parabens, in chlorinated water samples are investigated. Quantification of the parent species and identification of their reaction by-products were performed using gas chromatography in combination with mass spectrometry. Experiments were accomplished considering free chlorine and paraben concentrations at the mg L(-1) and microg L(-1) level, respectively. Concentration of water samples, using solid-phase extraction, and silylation of the target species were carried out in order to improve the detectability of parent species and their possible transformation products, achieving quantification limits at the low ng L(-1) level. Under employed experimental conditions, the decrease in the concentrations of parabens followed pseudo-first-order kinetics. Half-lives values obtained for model ultrapure water solutions were in good agreement with those observed in tap water samples. For the first type of sample, only two by-products were detected for each paraben. They corresponded to chlorination of the aromatic ring in one or two carbons situated in ortho-positions to the hydroxyl group. Both species were also generated after the addition of parabens to chlorinated tap water. Moreover, three new transformation products were noticed for each parent compound. They were identified as bromo- and bromochloro-parabens, formed due to the existence of traces of bromide in tap water sources. Experiments carried out by mixing paraben-containing personal care products with tap water, containing free chlorine, confirmed the formation of all above described halogenated by-products. In addition, the presence of the di-chlorinated forms of methyl and propyl paraben has been detected for first time in raw sewage water samples.

Suitability of solid-phase microextraction for the determination of organophosphate flame retardants and plasticizers in water samples

The feasibility of solid-phase microextraction (SPME) for the determination of several organophosphorus flame retardants and plastizicers in water samples by gas chromatography-nitrogen phosphorous detection (GC-NPD) is evaluated. These compounds have a wide range of polarities and volatilities and require a thorough optimisation of the different SPME parameters. Considering also possible contamination and carryover sources, the best compromise microextraction conditions were found to be direct extraction of 22 ml samples, containing 300 mg/ml of NaCl, with a PDMS-DVB coated fibre at room temperature. Although equilibrium was not achieved, an extraction time of 40 min allowed obtaining a good sensitivity (quantification limits between 0.010 and 0.025 ng/ml), comparable to that achieved by solid-phase extraction (SPE) of 1l samples, producing both similar values of precision and accuracy. Furthermore, the SPME method has shown to be free of matrix effects, avoiding the need of employing the standard addition procedure for quantification, and was suitable for the determination of eight of the nine considered compounds. Only tris-(2-ethylhexyl)-phosphate was neither determinable by SPME nor by SPE. Finally, the application of the developed methodology to the analysis of wastewater samples, showed that important concentrations of these compounds (up to 10 ng/ml) have been detected in treated sewage water, being discharged into the aquatic environment.

Development of a dispersive liquid–liquid microextraction method for organophosphorus flame retardants and plasticizers determination in water samples

A fast, inexpensive and efficient sample preparation method for the determination of 10 organophosphorus compounds in water samples is presented. Analytes were extracted using the dispersive liquid-liquid microextraction (DLLME) technique and determined by gas chromatography with nitrogen-phosphorus detection (GC-NPD). The influence of several variables (e.g. type and volume of dispersant and extraction solvents, ionic strength, shaking time and mode, etc.) on the performance of the sample preparation step was carefully evaluated. Under final working conditions, 1 mL of acetone containing a 2% of 1,1,1-trichloroethane (20 microL) was added to 10 mL of water with 20% of sodium chloride. The ternary mixture was centrifuged at 3500 rpm to allow phase separation. After removing the aqueous supernatant, an aliquot of the settled extract was injected in the GC-NPD system. Under the above conditions, the method provided enrichment factors between 190 and 830 times (depending on the considered compound), relative standard deviations below 10%, except for tris(2-ethylhexyl) phosphate (TEHP), and quantification limits between 0.01 and 0.08 ng/mL. Matrix effects were assessed using different water samples, and accuracy was evaluated by comparison with solid-phase microextraction.

Microwave-assisted extraction of organophosphate flame retardants and plasticizers from indoor dust samples

A procedure for the determination of eight organophosphate flame retardants and plasticizers in dust samples is presented. Microwave-assisted extraction and gas chromatography (GC) with nitrogen-phosphorus detection (NPD) were used for sample preparation and analytes quantification, respectively. Influence of different variables (type and volume of organic solvent, temperature, time, agitation, etc.) on the yield of the extraction step was evaluated. The most important factor was the type of solvent, with the highest efficiencies corresponding to acetone. Under final conditions 10 mL of this solvent were employed. The extraction was carried out at 130 degrees C and satisfactory yields, similar to those obtained with the Soxhlet technique, were achieved. Due to the high content of organic carbon in dust samples, primary acetone extracts had to be subjected to intensive clean-up. Dilution with ultrapure water followed by concentration on a reversed-phase sorbent and further purification using silica, allowed a significant reduction of co-extracted interferences. Application of the developed methodology to indoor dust from private houses showed important concentrations of several organophosphate esters. The highest levels, up to 19 microg/g, corresponded to tris(butoxyethyl) phosphate; moreover, average values of two chlorinated compounds, used as flame retardants and considered as the most concerning species in the group, exceeded the 1 microg/g level.

Helium-3 MRI diffusion coefficient: correlation to morphometry in a model of mild emphysema

Hyperpolarised gases have been most recently used in magnetic resonance imaging to demonstrate new image-derived pulmonary function parameters. One of these parameters is the apparent diffusion coefficient, which reflects the sizes of the structures that compartmentalise gas within the lung (i.e. alveolar space). In the present study, noninvasive parameters were compared to microscopic measurements (mean linear intercept and mean alveolar internal area). Nonselective helium-3 gas density coronal ex vivo images and apparent diffusion maps were acquired in control and elastase-induced panacinar emphysema rats. Total lung capacity was considered the reference for both imaging experiments and lung fixation. A mild degree of emphysema was found based on mean linear intercept (134 +/- 25 microm) versus control (85 +/- 14 microm). The apparent diffusion coefficients were significantly different between the two groups (0.18 +/- 0.02 and 0.15 +/- 0.01 cm2 x s(-1) for elastase and control, respectively). A significant correlation between the apparent diffusion coefficient and corresponding morphometric parameters in mild emphysema was demonstrated for the first time. This study opens the possibility of estimating absolute airspace size using noninvasive techniques.

Solid-phase microextraction with on-fiber derivatization for the analysis of anti-inflammatory drugs in water samples

A sensitive and solvent-free procedure for the determination of non-steroidal acidic anti-inflammatory drugs in water samples was optimized using solid-phase microextraction (SPME) followed by on-fiber silylation of the acidic compounds and gas chromatography-mass spectrometry (GC-MS) determination. Microextraction was carried out directly over the filtered water samples using a polyacrylate fiber. Derivatization was performed placing the SPME fiber, loaded with the extracted analytes, in the headspace of a vial containing 50 microl of N-methyl-N-(tert-butyldimethylsilyl)-trifluoroacetamide (MTBSTFA). Derivatives were desorbed for 3 min in the GC injector. Influence of several parameters in the efficiency of microextraction (volume of sample, time, pH, type of fiber coating, etc.) and derivatization steps (time, temperature and volume of MTBSTFA) was systematically investigated. In the optimal conditions an excellent linearity over three orders of magnitude and quantification limits at the ng/l level (from 12 to 40 ng/l) were achieved. The proposed method was applied to the determination of acidic compounds in sewage water and results compared to those obtained using solid-phase extraction (SPE) followed by the derivatization of the compounds in the organic extract of the solid-phase extraction cartridge.

Identification of fatty acids in edible wild plants by gas chromatography

The total lipidic content and the distribution of fatty acids in twenty edible wild plants in S.E. Spain was determined by GC. The lipidic content was higher than usual in the common vegetables. The high ratio of the omega 3 series of unsaturated fatty acids relative to the omega 6 series demonstrates the good nutritional qualities of these plants.

Disposition of fluvoxamine in humans is determined by the polymorphic CYP2D6 and also by the CYP1A2 activity

BACKGROUND

Fluvoxamine is a selective serotonin reuptake inhibitor used widely in the treatment of depression and other psychiatric diseases, but little is known about the specific isozymes involved in its metabolism. This study investigated the relationship between fluvoxamine disposition and the polymorphic CYP2D6 and the polycyclic aromatic hydrocarbon (as contained in cigarette smoke) inducible CYP1A2.

METHODS

Fluvoxamine (50 mg orally) was given to 10 extensive metabolizers and four poor metabolizers of debrisoquin, and concentrations were assessed in plasma by high performance liquid chromatography. Five of the extensive metabolizers and one of the poor metabolizers were smokers of more than 10 cigarettes per day. The CYP1A2 activity was determined by means of a urinary caffeine test.

RESULTS

Compared with nonsmoking extensive metabolizers, nonsmoking poor metabolizers had a statistically significant (p = 0.02, Mann-Whitney U test) about twofold higher maximum plasma concentration, longer half-life, and fivefold lower oral clearance of fluvoxamine. The oral clearance of fluvoxamine correlated to the CYP1A2 index in the 14 subjects (rs = 0.58; p < 0.05; Spearman rank correlation).

CONCLUSION

The disposition of fluvoxamine in humans is associated with the polymorphic CYP2D6 activity, but CYP1A2 also seems to be involved.

Pressurized liquid extraction with in-cell clean-up followed by gas chromatography–tandem mass spectrometry for the selective determination of parabens and triclosan in indoor dust

A sample preparation method based on the use of pressurized liquid extraction is proposed for the determination of four alkyl parabens and triclosan in indoor dust. Extraction of analytes and removal of interfering species were achieved in the same step, by placing an appropriate sorbent in the extraction cell and by choosing a right combination of washing and elution solvents. Compounds, as silylated derivatives, were determined by gas chromatography in combination with tandem mass spectrometry (GC-MS/MS). Factors affecting the yield and selectivity of the sample preparation procedure were carefully evaluated. Under final conditions, dried samples (0.5 g of dust and 1g of sodium sulphate) were dispersed with 3g of Florisil and loaded into an 11 mL stainless-steel extraction cell containing 1g of the same material as clean-up sorbent. Non-polar species were removed with n-hexane under mild conditions (40 degrees C, 3.4 MPa) and then analytes were extracted with ethyl acetate. The best compromise extraction conditions were 103 degrees C, 13.8 MPa and 3 static extraction cycles of 1 min. The proposed method provided recoveries from 76 to 98%, relative standard deviations under 11% (operating under reproducibility conditions) and quantification limits from 1 to 4 ng/g. The analysis of dust samples from private houses and office buildings confirmed the ubiquitous presence of target bacteriocides in these environments.

Microwave assisted extraction followed by gas chromatography with tandem mass spectrometry for the determination of triclosan and two related chlorophenols in sludge and sediments

A procedure for the determination of 2-(2,4-dichlorophenoxy)-5-chlorophenol (Triclosan) and two possible transformation compounds, 2,4-dichlorophenol (2,4-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP), in sludge from sewage treatment plants (STP) and sediments is presented. Extraction was performed using an acetone:methanol (1:1) mixture under the action of a microwave field. The centrifuged supernatant was diluted with a NaOH aqueous solution and twice extracted with n-hexane for removing neutral and basic interferences. The aqueous layer was acidified and processed as a waste water sample. After concentration analytes were silylated and determined by gas chromatography with tandem mass spectrometry (GC-MS/MS). Influence of experimental conditions on the yield of the extraction process and on the efficiency of the further clean-up step was thoroughly evaluated. Performance of MS/MS detection in comparison to single MS is described. Under final working conditions quantification limits between 0.4 and 0.8 ng/g and recoveries from 78% to 106% were obtained. The method was applied to the analysis of several sludge and sediment samples. Only low levels of TCS were detected in some of the sediments; however, all three compounds were found in sludge samples at concentrations ranging from 7 to 316 ng/g, in the case of chlorophenols, and from 420 to 5400 ng/g, for Triclosan.

Precision Measurement of the Helium Flux in Primary Cosmic Rays of Rigidities 1.9 GV to 3 TV with the Alpha Magnetic Spectrometer on the International Space Station

Knowledge of the precise rigidity dependence of the helium flux is important in understanding the origin, acceleration, and propagation of cosmic rays. A precise measurement of the helium flux in primary cosmic rays with rigidity (momentum/charge) from 1.9 GV to 3 TV based on 50 million events is presented and compared to the proton flux. The detailed variation with rigidity of the helium flux spectral index is presented for the first time. The spectral index progressively hardens at rigidities larger than 100 GV. The rigidity dependence of the helium flux spectral index is similar to that of the proton spectral index though the magnitudes are different. Remarkably, the spectral index of the proton to helium flux ratio increases with rigidity up to 45 GV and then becomes constant; the flux ratio above 45 GV is well described by a single power law.

Electron and positron fluxes in primary cosmic rays measured with the alpha magnetic spectrometer on the international space station

Precision measurements by the Alpha Magnetic Spectrometer on the International Space Station of the primary cosmic-ray electron flux in the range 0.5 to 700 GeV and the positron flux in the range 0.5 to 500 GeV are presented. The electron flux and the positron flux each require a description beyond a single power-law spectrum. Both the electron flux and the positron flux change their behavior at ∼30  GeV but the fluxes are significantly different in their magnitude and energy dependence. Between 20 and 200 GeV the positron spectral index is significantly harder than the electron spectral index. The determination of the differing behavior of the spectral indices versus energy is a new observation and provides important information on the origins of cosmic-ray electrons and positrons.

High-speed chiral separations on microchip electrophoresis devices

High-speed electrophoretic chiral separations have been successfully performed in a microfabricated device by employing cyclodextrin-modified micellar electrokinetic chromatography (CD-MEKC). Utilizing short separation channels and relatively high field strengths in combination with small volume-defined injection plugs, and operating in counter-electroosmotic flow conditions, fast and efficient separations of fluorescein insothiocyanate (FITC)-labeled amino acid enantiomers were obtained. Analysis time ranged from 75 s for the most basic amino acids to 160 s for the most acidic ones with associated efficiencies from 7000 up to 28 000 effective plates (100 000 to 395 000 plates/m). Buffer parameters were varied in order to study the effect on chiral resolution. A buffer system consisting of 100 mM borate (pH 9.4), 30 mM of SDS, and 10 mM gamma-CD as chiral selector provided adequate resolution of the majority of FITC-amino acid enantiomers tested.