Electroanalytical procedure and sorption studies for imazaquin in different soils

The objective of the present work is to determine sorption coefficients of the herbicide imazaquin using the differential pulse polarography in the major soil classes occurring in the State of São Paulo, Brazil. This study contributes to the predictions of pesticide fate and transport mechanisms in the environment as well as its exposure and interactions with different soil materials. Imazaquin was analysed directly in soil samples (scan rate 2 mV s^–1, mercury drop size 0.37 mm, and pulse height 50 mV) and the detection limits varied from 42 to 58 g L^–1 for different soils. Imazaquin showed the K_F values varying from 0.8 (for the sandy soil) to 35.5 L kg^–1 (for the medium textured soil), with a significant dependence on the soil pH, organic matter content, and clay minerals. The study demonstrates the practical utilisation of the electroanalytical methodology to determine the imazaquin adsorption in soil and consequently assess the impact of this herbicide in the environment, especially for the evaluation of the potential risk of surface and groundwater contamination.     

An observation of unusual temperature effects for enantioselective CZE employing highly sulfated-beta-cyclodextrin

In this paper data are presented suggesting that for enantiomers of basic and neutral analytes, the concentrations of highly sulfated CDs typically used are above the optimum since lower concentrations result in unacceptable migration times. This situation arises because of the high binding affinities often obtained with sulphated CDs. In a system being over the optimum CD concentration increasing the temperature of the capillary offers a capability to improve selectivity and reduce migration times.     

高效液相色谱手性拆分药物对映体机理研究

于Whelk-O1(R,R)手性固定相上直接拆分药物萘普生和丙卡特罗。两药物的对映体在该手性固定相上均可以实现基线分离,分离因子达1.4以上。根据相关手性色谱分离热力学数据,进行了手性识别机理研究,并据此成功预测了药物克仑特罗对映体在Whelk-O1(R,R)手性柱上的拆分。     

Enantioselectivity of basic analytes in CZE enantioseparation under reversed-polarity mode using sulfated beta-cyclodextrins as chiral selectors: An unusual temperature effect

Temperature effects on the enantioselectivity of basic analytes in CZE enantioseparation were studied under reversed-polarity mode using randomly sulfate-substituted beta-CDs (MI-S-beta-CD) as chiral seletors. Two catecholamines (epinephrine and isoproterenol) and two structurally related compounds (octopamine and norephedrine) were selected as test compounds in an electrophoretic system at low pH. The mobility differences between the (+)-enantiomers and the (-)-enantiomers of the two catecholamines and dopamine at 40 degrees C are greater than those at 25 degrees C with MI-S-beta-CD, even at a concentration as low as 0.3% w/v. Thus the enantioselectivity of these three basic analytes increases with increasing temperature. This phenomenon results from the inequality of the temperature effect on the mobility of the two enantiomers. In contrast, norephedrine behaves differently. The (+)-enantiomers of these basic analytes were found to migrate faster than the (-)-enantiomers. Consequently, the unusual temperature effect on the enantioselectivity can be observed when the mobility difference of the (+)-enantiomer between 40 and 25 degrees C is greater than that of the (-)-enantiomer using MI-S-beta-CD at a concentration greater than about 0.7% w/v for enantioseparation of isoproterenol, 0.4% w/v for epinephrine, and 0.3% w/v for octopamine. This unusual temperature effect offers the advantages to enhance enantioselectivity, to improve enantioseparation, and to reduce migration times.     

Determination of imazaquin residues in soil by solid-phase extraction and high-performance liquid chromatography

A method has been developed for the quantitation of imazaquin residues in soil. The herbicide was extracted from soil with methanol-water (2 + 1, v/v) and cleaned up by strong anion-exchange solid-phase extraction cartridges. Analysis was performed by using high-performance liquid chromatography with ultraviolet detection. Average recoveries through the method ranged from 90.7 to 100.6%, with relative standard deviation equal to or lower than 6.6%. The limit of detection was estimated to be 0.0015 mg/kg, and the minimum quantitation concentration of imazaquin in soil was 0.005 mg/kg. This method was successfully applied to evaluate imazaquin residue levels in soil and its dissipation rates in a soybean field in the Xisanqi District of Beijing, People's Republic of China. The dissipation study showed that the half life of imazaquin in soil was 10.37 +/- 0.0135 days at 3 different application rates.     

Separation of multiphosphorylated peptide isomers by CZE

A separation of mono, doubly and triply phosphorylated isomers was developed with CZE with an aqueous electrolyte containing 3.9 mol/L formic acid and 30% v/v trifluoroethanol. Thus a mixture of ten phosphopeptides corresponding to the human tau sequence 226-240 was separated within 70 min. Although peptides with different phosphorylation degrees, i.e. 0-3 phosphate groups, were well separated, some of the phosphopeptide isomers containing one or two phosphate groups were only partially separated. The electrolyte system is compatible with both MALDI- and ESI-MS, allowing a direct coupling, and thus could have some interesting applications in proteomics.     

Effect of alkali metals and metal-ammonia complexes on electroosmosis,effective field strength,and resolution in the separation of diuretics by CZE

The counter ion in CZE separation systems affects resolution, effective field strength and electroosmosis. Alkali metals (lithium, sodium, potassium, and cesium), the ammonium ion, and several complexes of metals with ammonia ([Ag(NH₃)₂]⁺, [Cu(NH₃)₄]²⁺, [Zn(NH₃)₄]²⁺, [Cd(NH₃)₄]²⁺, [Ni(NH₃)₆]²⁺, and [Co(NH₃)₆]²⁺) have been studied for their effect on the separation of diuretics. With the alkali metals the electroosmotic flow velocity decreased and the effective field strength and resolution increased as the hydrated radius of the alkali metal decreased. All the metal-ammonia complexes except that with silver greatly reduced the electroosmotic flow velocity (V_eo) and had only a slight effect on the effective field strength (E_eff). Because these complexes had a negligible effect on the ionic strength of the buffer, they enabled high separating power to be maintained during the separation, and hence the use of more energy in the separation system. This yielded better resolution of the compounds, but the analysis time was then compromised. A simultaneous reduction in capillary length and V_eo while maintaining the high voltage enabled increased resolution without an increase in analysis time. The ability to control V_eo by adding small concentrations (< 100 μM ) of metal complexes to the buffer solution makes it possible to adjust the analysis time and capillary length independently while employing high separation power.     

Influencing of the migration time in CZE

For selective influencing of the ion mobility in CZE several electrolyte additives were used. With acetone as organic solvent the migration times of inorganic cations are changed. The separation of Cl^– and I^– is optimized by adding -cyclodextrin to the electrolyte. By adding 18-crown-6 it is possible to slow down the mobility of K⁺. In this way the disturbing effect of matrix ions can be prevented.     

Advances in the enantioseparation of second-generation antidepressant drugs by electrodriven methods

Stereochemistry is steadily increasing in importance in the development of new drugs, and the availability of pure enantiomer drugs can make therapy safer and more efficacious. In particular, almost all second-generation antidepressant drugs possess one or more chiral centres; however, only some of them are administered as single enantiomers. A fundamental part of the quality control of pharmaceutical formulations is the determination of enantiomeric excess and enantiomeric purity; this is also important for the therapeutic drug monitoring of depressed patients. For this purpose, efficient and reliable analytical methods are needed and electrodriven techniques (most of all CE, CEC and MEKC) are very efficient and inexpensive candidates for the role. In this review, the enantioselective electrodriven methods available for the analysis of second-generation antidepressant are presented and discussed. In particular, the following pharmacological classes of antidepressants will be considered: selective serotonin reuptake inhibitors (fluoxetine, citalopram, paroxetine, sertraline); norepinephrine reuptake inhibitors (reboxetine); serotonin and norepinephrine reuptake inhibitors (venlafaxine, milnacipran, duloxetine); and noradrenergic and specific serotonergic antidepressants (mirtazapine).     

Comparison of chromium speciation by CZE and ion exchange followed by AAS

The hydrogen chromate anion (HCrO4-), which is the predominant species in acidic solutions and solutions with low chromium concentration, was determined by capillary zone electrophoresis (CZE) using UV detection on-column at 200 nm. A fused-silica capillary (55 cm x 50 microm i.d.) was employed with a high negative voltage of 20 kV. Total chromium was determined after reduction by H2O2 and its complexation by EDTA. The use of H2O2 as reducing agent is advantageous, as it does not increase the conductivity of the solution. Detection limits achieved (for 200 s injection time) were 30 and 8 microg/L for Cr(VI) and Cr(III), respectively. The CZE results obtained for Cr(III) and Cr(VI) were compared with those obtained by ion exchange with subsequent AAS.     

Determination of Melamine in Food by SPE and CZE with UV Detection

A novel method for the determination of melamine residue in food was developed using solid-phase extraction and capillary zone electrophoresis with UV detection. Spiked samples were extracted with 1% trichloroacetic acid while 0.03 g sodium deoxycholate was used to precipitate protein in the real samples. After centrifuging and clean-up by solid-phase extraction cartridge, the extract was directly analyzed by CZE–UV. The method was validated and good results were obtained with respect to precision, repeatability and spiked recovery. The limit of detection for melamine varied between 0.25 and 0.5 mg kg^?1. The proposed method was successfully applied for the analysis of melamine in food with total recoveries ranging from 94 to 102% in the spiked range of 0.5–5 mg kg^?1, and the relative standard deviations were between 1.5 and 4.1%.     

CZE and ESI-MS of Borate-Sugar Complexes

Capillary zone electrophoresis (CZE) with electrospray ionization (ESI) mass spectrometry (MS) was used to study borate (B^?1) and sugar (L) complexes (L _x B^?1). Boric acid was adjusted to pH 10 with ammonium hydroxide to create an ESI-MS compatible CZE background electrolyte. We show for the first time that the electrophoretic peaks for each injected sugar contained both the substrates (i.e., sugar and/or multimers) and products (i.e., L _x B^?1). The effects of sheath liquid, temperature, and borate concentration were studied. The molecular mass information obtained from the ESI-MS provided new evidence on the mechanisms of borate-sugar complexation. Direct infusion ESI-MS and CZE-ESI-MS experiments strongly suggest that the formation of L _x B^?1 was from the direct reaction of a sugar or sugar multimer (L _x ) and B^?1. Larger L _x B^?1, where x > 2 were observed. Separation in the CZE dimension allows for the simultaneous analysis of a sugar mixture and simplified the ESI-MS analysis of sugars of the same molecular mass. The increase in sugar electrophoretic mobility caused by the increase in borate concentration was discussed in terms of the formation of L _x B^?1 complexes. In addition, the separation of five nucleosides by CZE using a borate electrolyte and detection using ESI-MS is demonstrated.     

Comparison of chromium speciation by CZE and ion exchange followed by AAS

The hydrogen chromate anion (HCrO₄ ^–), which is the predominant species in acidic solutions and solutions with low chromium concentration, was determined by capillary zone electrophoresis (CZE) using UV detection on-column at 200 nm. A fused-silica capillary (55 cm × 50 μm i.d.) was employed with a high negative voltage of 20 kV. Total chromium was determined after reduction by H₂O₂ and its complexation by EDTA. The use of H₂O₂ as reducing agent is advantageous, as it does not increase the conductivity of the solution. Detection limits achieved (for 200 s injection time) were 30 and 8 μg/L for Cr(VI) and Cr(III), respectively. The CZE results obtained for Cr(III) and Cr(VI) were compared with those obtained by ion exchange with subsequent AAS.     

Study of soils by thermal analysis

The study of soils is very important in the geological and geological engineering researches. A study of ten samples of soils was carried out by thermal analysis, and X-Ray Fluorescence Spectrometry to understand soil evolution in Angra dos Reis region, Rio de Janeiro State, Brazil. The sample collection sites were chosen based on geological characteristics, the soil layer thickness, the soil composition pattern, and whether or not it was moved either by erosion or by gravitational shifts. Because of the humid tropical climatic condition, natural soils tend to show great thickness of weathered mantles with formation of saprolites and saprolite soils. Kaolinite is an important secondary mineral which can be formed from many different minerals, like k-mica and k-feldspar and can be weathered to gibbsite. The results from TG/DTG and DTA indicated which soils had more weathering, and the same results were obtained by XRF, when silica/aluminum ratios from samples are compared with thermal analysis results.     

Temperature and enantioseparation by macrocyclic glycopeptide chiral stationary phases

Seventy-one chiral compounds were separated on four macrocyclic glycopeptide chiral selectors: teicoplanin, its aglycone, ristocetin A and vancomycin, using three possible separation modes: reversed phase with methanol/buffer mobile phases, normal phase with hexane/ethanol mobile phases and polar ionic mode (PIM) with 100% methanol mobile phase with trace amounts of acid and/or base. These 148 separations were studied in a 5-45 degrees C temperature range. Peak efficiencies always increased with temperature, but in only 17% of the separations studied a small increase of the enantioresolution factor was observed. In the majority (83%) of the cases, the enantioresolution decreased or even vanished when temperature increased. All 148 Van't Hoff plots were linear showing that the selector did not change in the temperature range studied. The calculated enthalpy and entropy variations showed that the interaction of the solute with the stationary phase was always enthalpy driven with normal and reversed mobile phases. It could be enthalpy as well as entropy driven with PIM mobile phases strongly dependent on the solute. The plots of delta(deltaH) versus delta(deltaS) were linear in most cases (enthalpy entropy compensation). This observation cannot be used to give clear information on chiral recognition mechanisms, but it allowed identifying specific stationary phase-solute interactions because the points corresponding to the respective thermodynamic parameters were clearly delineated from the general compensation lines.     

Simultaneous determination of tetracyclines in pharmaceuticals by CZE using experimental design

An optimized capillary zone electrophoresis (CZE) method for the analysis of tetracycline (TC), chlortetracycline (CTC), oxytetracycline (OTC) and doxycycline (DXC) is described. Using fused-silica capillaries, the influence of the electrolyte composition, pH and concentration, as well as temperature and applied voltage were investigated. A factorial and central composite design was performed to optimize the method in a simple way. The optimal separation conditions were 50 mmol L⁻¹ sodium carbonate + 1 mmol L⁻¹ EDTA, pH 10; voltage 13 kV and temperature 23 °C. The method was validated for TC determination in pharmaceuticals through the following performance criteria: linearity and linear range, sensitivity, selectivity, intra-assay and inter-assay precision, detectability, accuracy and ruggedness. In comparison with the recommended HPLC method in the United States Pharmacopeia, this CZE-method exhibited the same performance as the official method, with the advantage that the same method could be used for the simultaneous determination of the different tetracyclines in pharmaceutical formulations.     

Determination of phosphate in seawater by CZE with on-line transient ITP

We developed CZE with indirect UV detection for the determination of phosphate in seawater using transient ITP as an on-line concentration procedure. The following optimum conditions were established: BGE, 5 mM 2,6-pyridinedicarboxylic acid (PDC) containing 0.01% hydroxypropylmethylcellulose (HPMC) adjusted to pH 3.5; detection wavelength, 200 nm; vacuum injection period of sample, 3 s (45 nL); terminating ion solution, 500 mM MES adjusted to pH 4.0; vacuum injection period of the terminating ion solution, 30 s (450 nL); applied voltage, 30 kV with the sample inlet side as the cathode. The LOD for phosphate was 16 microg/L (PO(3-)(4) -P) at S/N of 3. The respective values of the RSD of the peak area, peak height, and migration time for phosphate were 2.6, 2.3, and 0.34%. The proposed method was applied to the determination of phosphate in a seawater certified reference material for nutrients, MOOS-1, distributed by the National Research Council of Canada (NRC). The results were very similar to certified values. The method was also applied to the determination of phosphate in coastal seawaters. The results agreed with those obtained using a conventional spectrophotometric method.     

Assessment of protein-incorporated arginine methylation in biological specimens by CZE UV-detection

Protein arginine methyltransferases methylate post-translationally arginine residues in proteins to synthesize monomethylarginine (MMA), asymmetric dimethylarginine (ADMA), or symmetric dimethylarginine. Protein arginine methylation is involved in the regulation of signal transduction, RNA export, and cell proliferation. Moreover, upon proteolysis, arginines are released into the cytosol in which they exert important biological effects. Both MMA and ADMA are inhibitors of nitric oxide synthase and especially elevated levels of ADMA are associated with endothelial dysfunction and cardiovascular disease. Quantification of these analytes is commonly performed by HPLC after sample cleanup and derivatization. We propose a CE method in which these steps have been avoided and the procedure for sample preparation has been simplified. After acidic hydrolysis of proteins, samples were dried, resuspended in water, and directly injected in CE. A baseline separation of analytes was reached in a 60 cm x 75 microm id uncoated silica capillary, by using a Tris-phosphate run buffer at pH 2.15. This method allows an accurate assessment of protein arginine methylation degree in different biological samples such as whole blood, plasma, red blood cells, cultured cells, and tissue. Moreover, its good sensitivity permits to evaluate the methylation of a single protein type after the opportune purification steps. A method applicability concerns both clinical laboratories, where the evaluation of blood protein from numerous samples could be rapidly performed, and research laboratories where the factors affecting the arginine protein methylation degree could be easily studied.     

Effects of lactate and acetate on the determination of serum ethyl glucuronide by CZE

The analysis of ethyl glucuronide (EtG), a marker of recent alcohol consumption, in serum with an optimized CZE assay is reported. The method uses a 0.1-mm id fused-silica capillary of 50 cm effective length that is coated with linear polyacrylamide, a pH 4.4 nicotinic acid/epsilon-aminocaproic acid (EACA) BGE, reversed polarity and indirect analyte detection. The assay is based on a 1:1 dilution of serum with deionized water and has LODs for EtG, lactate and acetate of 3.8 x 10(-7) M, 2.60 x 10(-6 )M and 2.18 x 10(-6 )M, respectively. Separation of EtG from endogenous macro- and microcomponents (anionic serum components of high and low concentration, respectively) and its quantification are shown to be possible for a wide range of lactate (stacker) and acetate (destacker) concentrations, macrocomponents that have an impact on the CZE behavior of EtG and that change after intake of ethanol. The assay has been successfully applied to the analysis of EtG, lactate and acetate in (i) sera of volunteers that ingested known amounts of alcohol and (ii) samples of patients that were classified (teetotalers and social drinkers vs. alcohol abusers) via analysis of carbohydrate-deficient transferrin.     

Determination of caffeine in coffee products by dynamic complexation with 3,4-dimethoxycinnamate and separation by CZE

A method based on the formation of pi-complexes with chlorogenate-like species was proposed for the determination of caffeine in regular (nondecaffeinated) and decaffeinated coffee. Both caffeate and 3,4-dimethoxycinnamate were able to transform caffeine--a neutral species in aqueous solutions--into an anionic species. The usage of 3,4-dimethoxycinnamate in the running electrolyte is advantageous, because of its greater chemical stability and the improved resolution of the peaks of caffeine, theobromine, and theophylline. Negative peaks were registered with a capacitively coupled contactless conductivity detector when solutions of these alkylxanthines were analyzed with a BGE composed of 20 mmol/L 3,4-dimethoxycinnamic acid and pH adjusted to 8.5 with Tris. This behavior was expected, because the complex is larger and thus should move slower than the free anion. Caffeine was determined in ground and instant coffee with precision and accuracy that meet Brazilian norms about such products. The LOD was estimated as 33 mg/L, which corresponds to 0.8 and 0.3 mg of caffeine per gram of dry instant coffee and ground coffee, respectively. For the case of decaffeinated coffee, ten times preconcentration with dichloromethane was carried out to allow the quantitation of caffeine, which should not exceed the concentration of 1 mg/g in dry matter.