Uncoated Capillary Research Articles

Parallel coupling of gas chromatography to mass spectrometry and solid deposition Fourier transform infrared spectroscopy: an innovative approach to address challenging identifications.

The request for novel hyphenated instruments and techniques, capable of affording exhaustive information and results, is a focus continuously watched out. In this context, the present work aimed at the development of an integrated system combining gas chromatographic (GC) separation with mass spectrometry (MS) and (solid deposition) Fourier transform infrared spectroscopy (FTIR) detection. An external transfer line was designed inthelab for the parallel coupling of the two detectors, in such a way toobtain complementary analytical information consisting of anMS spectrum, anIR spectrum and linear retention indices (LRI), within a single analysis. The instrument performance was demonstrated for the analysis of a commercial mixture consisting of 139 hydrocarbons, comprising linear, branched, unsaturated and aromatic compounds. A 100-m poly(dimethylsiloxane) column was employed for the separation, and the outlet flow was split 95:5 between the IR and MS detectors using two uncoated capillaries. The IR spectra were acquired from solid deposits on a zinc selenide disc (-90 °C), over a spot (detector area) of about 0.1 mm2, in the range of 4000-700 cm-1 and at a resolution of 4 cm-1. Final identification of the separated compounds by alibrary search was achieved by excluding incorrect results, sequentially using a three-filter approach (85% similarity against reference MS and IR library spectra and ±10 LRI unit tolerance). Based on these preliminary results, the GC-MS/sd-FTIR system is a promising tool for the characterization of complex matrix constituents, for which identification is cumbersome, by using only one detection technique.

Experimental Observation of Space-Charge Field Screening of a Relativistic Particle Bunch in Plasma.

The space-charge field of a relativistic charged bunch propagating in plasma is screened due to the presence of mobile charge carriers. We experimentally investigate such screening by measuring the effect of dielectric wakefields driven by the bunch in a uncoated dielectric capillary where the plasma is confined. We show that the plasma screens the space-charge field and therefore suppresses the dielectric wakefields when the distance between the bunch and the dielectric surface is much larger than the plasma skin depth. Before full screening is reached, the effects of dielectric and plasma wakefields are present simultaneously.

Sensitive and rapid analysis of plasmid DNA topology isoforms by capillary gel electrophoresis with laser induced fluorescence in uncoated capillary.

The work describes the use of SYBR Gold to improve the detection sensitivity of plasmid DNA topoisomers by capillary gel electrophoresis with laser induced fluorescence in an uncoated capillary. The impact of different dyes, including ethidium bromide, SYBR Green and SYBR Gold, was compared based on detection and separation of DNA plasmid topoisomers. Use of SYBR Gold enabled improvement of detection sensitivity by 15-fold while maintaining good separation resolution of the different topoisomers. The baseline dropped with the use SYBR Gold but was overcome by the employment of a capillary with longer ineffective length (40 vs. 20cm). Separation resolution and reproducibility were impacted by the concentration of SYBR Gold and hydroxypropyl methylcellulose. With the use of a short capillary (10cm effective length and 50cm total length), fast separations of supercoiled, linear, open circular, and other isoforms were accomplished within 8min. Appropriate capillary cleaning with 0.1M sodium hydroxide/0.1M hydrochloric acid and capillary storage with 0.1M hydrochloric acid ensured good separation reproducibility of 217 runs during an extended period of use.

Zero-Degree Celsius Capillary Electrophoresis Electrospray Ionization for Hydrogen Exchange Mass Spectrometry

Currently, fast liquid chromatographic separations at low temperatures are exclusively used for the separation of peptides generated in hydrogen deuterium exchange (HDX) workflows. However, it has been suggested that capillary electrophoresis may be a better option for use with HDX. We performed in solution HDX on peptides and bovine hemoglobin (Hb) followed by quenching, pepsin digestion, and cold capillary electrophoretic separation coupled with mass spectrometry (MS) detection for benchmarking a laboratory-built HDX-MS platform. We found that capillaries with a neutral coating to eliminate electroosmotic flow and adsorptive processes provided fast separations with upper limit peak capacities surpassing 170. In contrast, uncoated capillaries achieved 30% higher deuterium retention for an angiotensin II peptide standard owing to faster separations but with only half the peak capacity of coated capillaries. Data obtained using two different separation conditions on peptic digests of Hb showed strong agreement of the relative deuterium uptake between methods. Processed data for denatured versus native Hb after deuterium labeling for the longest timepoint in this study (50,000 s) also showed agreement with subunit interaction sites determined by crystallographic methods. All proteomic data are available under DOI: 10.6019/PXD034245.

Short-End Injection Capillary Electrophoresis and Multivariate Analysis for Simultaneous Determination of Heavy Metals in Passiflora incarnata Tea.

An ultra-fast method for the simultaneous determination of heavy metals in Passiflora incarnata tea by capillary electrophoresis (CE) using a short-end injection combined with multivariate analysis was proposed. Separation was conducted by hydrodynamic injection (5 s at 0.5 psi) using the short-end injection procedure in a fused uncoated silica capillary (50 cm total length, 10.2 cm effective length, 50 µm i.d.) with separation time less than 2 min. An indirect UV detection at 214 nm was employed by using imidazole as a chromophore. The buffer used was 6 mmol/L hydroxybutyric acid (HIBA). The optimum conditions by full factorial with a central point were achieved by 18-crown-6 concentration (23.3 mmol L−1), voltage (+11.4 kV), methanol concentration (3.8%), and temperature (20 °C). The method showed good linearity (R2 > 0.998) for both Cd and Pb, inter-day precision of less than 14.49%, and an adequate limit of quantification only for Cd (LOQ < 0.5 µg mL−1 for Cd) based on the US Pharmacopeial Convention limit requirements for elemental impurities. After method validation, the method was applied to Passiflora incarnata tea samples from a local market. Furthermore, the developed method showed great potential for the determination of metals in other samples with proper sample preparation procedures.

Enantioselective analysis of the methamphetamine precursors ephedrine and pseudoephedrine by capillary electrokinetic chromatography using cyclodextrins as chiral selectors

Ephedrine and pseudoephedrine can be used as precursors for the illicit synthesis of stimulant drugs, such as methamphetamine and methcathinone. For this reason, an enantioselective capillary electrokinetic chromatography method was developed for the separation of ephedrine and pseudoephedrine enantiomers. After testing two different charged or chargeable cyclodextrins (β-cyclodextrin sulphate and carboxymethyl-β-cyclodextrin) and a few mixtures as possible chiral selectors, a mixture of 3 mM carboxymethyl-β-cyclodextrin and 3 mM heptakis(2,6-di-O-methyl)-β-cyclodextrin in pH 3.4 acetate buffer was used as the enantioselective background electrolyte and the separation was carried out in an uncoated silica capillary (75 µm internal diameter, 48.6 cm total length, 40.0 cm effective length). Analytical method performance was then evaluated in terms of linearity, precision, selectivity and accuracy with good results. Proof of concept application to mixtures simulating illicit methamphetamine (containing small amounts of ephedrine and pseudoephedrine as possible residual synthesis impurities) provided satisfactory results for the identification and quantitation of the four analyte diastereomers.

Cationic electrophoretic focusing on inverse electromigration dispersion profile with ESI-MS detection. New capillary electrophoretic method for high-sensitivity analysis of 2-hydroxy-s-triazines in waters

Electrophoretic focusing on an inverse electromigration dispersion profile is a relatively new electrophoretic separation method for the analysis of ionisable analytes. Although it offers alternative selectivity, powerful concentration capability and high sensitivity, so far only several systems for the analysis of anionic compounds were reported. This work describes for the first time a functional electrolyte system for the separation of cationic analytes by this method. Based on computer simulations and calculations, a functional electrolyte system was designed, based on 1-ethylpiperazine and pivalic acid. It is suitable for the analysis of weak bases with pKa values between 4.5 and 6 and due to the volatility of both components, it can be operated in combination with ESI-MS detection. Its practical applicability is demonstrated on direct analysis of four 2-hydroxy-s-triazines in waters. Separation in an uncoated capillary with application of negative pressure at the inlet provides very satisfactory results with good reproducibility of peak areas, peak heights and detection times, and with LODs at the 0.5–1 nM (100 ngL−1) level. The robustness of the method is shown on analyses of real tap and river water samples used without any pretreatment.

Simultaneous determination of mitotane, its metabolite, and five steroid hormones in urine samples by capillary electrophoresis using β-CD2 SDS1 complexes as hydrophobic compounds solubilizers.

Mitotane is a cytotoxic drug used in the treatment of inoperable adrenocortical carcinoma, it inhibits steroidogenesis as well, and therefore monitoring the level of steroid hormones in patients treated with mitotane is a crucial point of therapy. Hence, we have developed a simple, fast, and efficient electrophoretic method combined with reverse polarity sweeping as online preconcentration technique and dispersive liquid-liquid microextraction for the simultaneous determination of mitotane, its main metabolite DDA, and five steroid hormones (progesterone, testosterone, epitestosterone, cortisol, and corticosterone) in urine samples. In addition, a new sample matrix consisting of β-CD2 SDS1 complexes for a high hydrophobic compounds solubilization was developed. Approach based on the application of β-cyclodextrin and SDS complex of a ratio 2:1 allowed for hydrodynamic injection into the capillary of a solution containing both mitotane and other analytes. The detection limits of the analytes for the reverse polarity sweeping-dispersive liquid-liquid microextraction method were found to be in the range of 1.5-3ng/mL, which were approximately 1000 times lower than in the conventional hydrodynamic injection (5 s, 0.5psi) without any preconcentration procedure. All analytes were completely resolved in less than 13 min by uncoated silica capillary with an inner diameter of 75μm (ID) × 60cm. Electrophoretic separation was performed in reverse polarity with a voltage of -25kV with a background electrolyte (BGE) consisting of 100mM SDS, 25% ACN, 25mM phosphate buffer (pH 2.5), and 7 mMβ-cyclodextrin.

Microscale thermophoresis for studying protein-small molecule affinity: Application to hyaluronidase

Studying the binding affinity between large biomolecules (i.e. enzyme) and small molecules (molecular weight less than 1000 Da) is an extremely challenging task when using conventional techniques because of the difficulty associated with the detection of the minuscule variations caused by the binding. Microscale thermophoresis (MST) is a sensitive novel emerging biophysical tool allowing a rapid and accurate determination of the dissociation constant (Kd) of enzyme - small molecule system. For the first time, a systematic MST study was carried out to evaluate Kd between hyaluronidase (Hyal), a model enzyme, and two small flavonoid compounds known as potent Hyal's inhibitors, epigallocatechin gallate (EGCG) and apigenin-7-glucoside. In the optimized conditions, hyaluronidase fluorescent labelling (Hyal*) was achieved by direct labelling with RED-NHS NT647 dye using a phosphate ammonia buffer (20 mM NaH2PO4 + 50 mM NH3) + 77 mM NaCl at pH 6.6. This latter ensured a high labelling efficiency while preventing Hyal* precipitation (pI of hyaluronidase is equal to 8.6). Pre-capillary CE/UV enzymatic assays of Hyal* demonstrated the preservation of its enzymatic activity even though the tested concentration was very low (50-fold times lower than control enzymatic assay). Fluorescence signal intensity and shape as well as MST traces have shown that phosphate ammonia buffer required the addition of surfactant, Tween-20 at 0.05%, to efficiently improve the protein solubility and limited aggregate formation using standard uncoated capillaries. MST results revealed the absence of affinity between Hyal* and the tested flavonoids regardless of the incubation time and the tested inhibitory concentration range unless the hyaluronidase substrate, hyaluronic acid (HA) is added to the preparation. Kd values were estimated to be 163 µM for Hyal*/HA/EGCG and 157 µM for Hyal*/HA/apigenin-7-glucoside. The repeatability of the assays was excellent as confirmed by the very low standard deviation on Kd values.

Comparative study of atenolol in human plasma by high performance liquid chromatography and capillary zone electrophoresis

Atenolol is a beta-blocker that is cardioselective, meaning it only affects beta receptors. It is used to treat angina pectoris and high blood pressure. The HPLC and Capillary Zone Electrophoresis analytical technique was developed for the purpose of detecting and quantifying Atenolol in human plasma, according to the study paper you're reading right now. The internal standard and atenolol were recovered from the solution after being extracted from plasma using the Liquid-Liquid Extraction method. A mobile phase of 10mM sodium hydrogen phosphate, 7.3mM Sodium Lauryl sulphate (pH=3), methanol, and acetonitrile (40:57:3, v:v:v) is used, with a flow rate of 1.0ml/min. A fluorescence detector was used to detect the isolated materials, which had an excitation wavelength of 229 nm and an emission wavelength of 298 nm. With this in view, Atenolol's and the internal norm's survival times are observed to be 5.4 and 8.3 minutes, respectively. The linear correlation coefficient (R20.9992) was found in the Atenolol calibration curve. The recovery rate for atenolol and an internal norm was estimated to be between 76 and 87 percent. Solid-phase extraction was performed on an uncoated silica capillary with a diameter of 58.5 cm 75 m, and detection was performed at 194 nm in the Capillary Zone Electrophoresis procedure. For an electrolyte solution containing 50mM H3BO3 and 50mM Na2B4O7 (50:50 V/V), atenolol was determined to be present in the solution in less than 3 minutes. Energized with a voltage of 25kV and injected with a hydrodynamic configuration for 4S. Under various conditions, this method was used to assess the stability and capability of measuring Atenolol in human plasma.

Investigation of lipase-ligand interactions in porcine pancreatic extracts by microscale thermophoresis.

The evaluation of binding affinities between large biomolecules and small ligands is challenging and requires highly sensitive techniques. Microscale thermophoresis (MST) is an emerging biophysical technique used to overcome this limitation. This work describes the first MST binding method to evaluate binding affinities of small ligands to lipases from crude porcine pancreatic extracts. The conditions of the MST assay were thoroughly optimized to successfully evaluate the dissociation constant (Kd) between pancreatic lipases (PL) and triterpenoid compounds purified from oakwood. More precisely, the fluorescent labeling of PL (PL*) using RED-NHS dye was achieved via a buffer exchange procedure. The MST buffer was composed of 20mM NaH2PO4 + 77mM NaCl (pH6.6) with 0.05% Triton-X added to efficiently prevent protein aggregation and adsorption, even when using only standard, uncoated MST capillaries. Storage at -20°C ensured stability of PL* and its fluorescent signal. MST results showed that crude pancreatic extracts were suitable as a source of PL for the evaluation of binding affinities of small ligands. Quercotriterpenoside-I (QTT-I) demonstrated high PL* binding affinity (31nM) followed by 3-O-galloylbarrinic acid (3-GBA) (500nM) and bartogenic acid (BA) (1327nM). To enrich the 50 kDa lipase responsible for the majority of hydrolysis activity in the crude pancreatic extracts, ammonium sulfate precipitation was attempted and its efficiency confirmed using capillary electrophoresis (CE)-based activity assays and HRMS. Moreover, to accurately explain enzyme modulation mechanism, it is imperative to complement binding assays with catalytic activity ones.

Analysis of three antipyretic analgesic drugs by open-tubular capillary electrochromatography

The advantages of capillary electrophoresis, such as small sample consumption, high separation efficiency, and multiple separation modes, have been known for decades. However, exploring unique capillary electrophoresis techniques for the analysis of fluid drugs in living bio-systems remains an important and urgent task. Owing to the similar structures and mass-to-charge ratios of antipyretic analgesic drugs, efficient baseline separation of these analytes by capillary zone electrophoresis method cannot be easily achieved. Micellar electrokinetic chromatography can improve the baseline separation of these drugs, but the substantial amounts of non-volatile surfactants (such as sodium dodecyl sulfate, sodium dodecyl sulfonate, sodium deoxycholate and cetylammonium bromide) in running buffer solutions would pollute the ion source during mass spectrometric analysis. For this reason, it is difficult to analyze unknown drugs by capillary electrophoresis-electrospray ionization-mass spectrometry. To overcome these drawbacks, much attention has been paid to capillary electrochromatography (CEC) because combines the high separation efficiency of capillary electrophoresis with the high selectivity of high performance liquid chromatography (HPLC). Recent challenges encountered in open-tubular capillary electrochromatography (OT-CEC) expanding the range of suitable functional polymer monomers and improvement of the separation efficiency by tuning the characteristics of the polymer coatings without using any organic solvent additives. In this study, a protocol based on OT-CEC using a block co-polymer coating is proposed for the analysis of three test antipyretic analgesic drugs (4-aminoantipyrine, antipyrine and phenacetin), without adding organic solvents and surfactants in the running buffer solutions. First, an amphiphilic block co-poly(styrene-co-glycidyl methacrylate) (P(St-GMA)), was synthesized by reversible addition-fragmentation chain transfer polymerization under mild conditions. Then, P(St-GMA) was coated onto the capillary surface, and an OT-CEC analysis was performed. Next, the effect of some key factors, including the polymerization time for obtaining P(St-GMA) with different molecular weights, coating concentrations of the block copolymer, the species of the running buffer solutions, pH and concentrations of the running buffer solutions, and organic solvent additives, on the OT-CEC separation efficiency were investigated. Under the optimized conditions with 50.0 mmol/L NaAc-HAc as the running buffer solution at pH 5.7, the three test antipyretic analgesic drugs were base-line separated by the constructed OT-CEC system. Good linear relationships between peak area and concentration of the test analytes in the range of 8.0-2.5×103 μmol/L were obtained (R2 ≥ 0.995). The limits of detection (LODs) were 1.0-2.5 μmol/L. Furthermore, the reason for the OT-CEC separation efficiency was clarified based on the decreased electro-osmotic flow in the coated capillary compared with that in the uncoated capillary. Finally, the proposed OT-CEC assay without using any organic solvents and surfactants as additives was applied for analysis of the three test antipyretic analgesic drugs in rat serum samples. Importantly, it was found that despite peak tailing, the OT-CEC separation efficiency of the drugs was dramatically enhanced because the block co-polymer could self-assemble in the solution and form pseudo-micelles, which further increased the interactions between the P(St-GMA) and these drugs. Our results not only reveal the great potential of block co-polymer coatings in OT-CEC for the analysis of drugs in real biological samples, but also serve asa platform for the preparation of diverse block co-polymers to be used in OT-CEC analysis. We believe that in the near future, the peak tailing problem in OT-CEC analysis can be resolved by using the designed unique block co-polymers, which possess a greater number of functional sites, as coatings and by appropriately tuning the interactions between the analytes and the coatings.

Determination of seven pueraria constituents by high performance liquid chromatography and capillary electrophoresis

Puerariae Radix is a commonly used Chinese herbal medicine derived from the dried root of the legume plant, which contains a series of isoflavones as its chief pharmacologically active constituents. Using 7 pueraria constituents as marker substances, a high performance liquid chromatography (HPLC and a capillary electrophoresis (CE) method were developed to assay the quality of Puerariae Radix within 65 and 50 min, respectively. Extracted samples were analyzed with a Cosmosil 5C18-MS column and eluted with a mixture of potassium dihydrogenphosphate (30 mM, adjusted to pH 3.0 with phosphoric acid) and aqueous acetonitrile solution, or an uncoated capillary (75 μm I.D.) and carried with an aqueous solution containing 10 mM sodium dihydrogenphosphate and 40 mM sodium dodecyl sulphate. The relative standard deviation of the marker substances, on the basis of peak-area ratios for 6 replicate injections, was 0.50∼0.97% (intraday) and 0.48∼0.97% (interday) for HPLC, and 0.88∼1.25% (intraday) and 0.85∼1.38% (interday) for CE. Both methods yielded accurate results differing by only 5% when applied to the analysis of practical samples of Puerariae Radix.

Enantioseparation and quantitative determination of ibuprofen using vancomycin-mediated capillary electrophoresis combined with molybdenum disulfide-assisted dispersive solid-phase extraction: optimization using experimental design

A dispersive solid-phase extraction procedure using molybdenum disulfide as an adsorbent was developed for pretreatment and preconcentration of low quantity of ibuprofen in natural samples prior to enantioseparation. The chiral separation was carried out by vancomycin-mediated capillary electrophoresis coupled with UV detector. The effect of the main factors on the extraction recovery and enantioselective resolution was investigated using a central composite design. The best enantioseparation of ibuprofen was achieved on an uncoated capillary at 20 °C using phosphate buffer (pH 6.5) containing 1 mM vancomycin and 20 kV applied voltage. The optimum condition of the dispersive solid-phase extraction was obtained at the sample solution with pH 4.0 containing 1.4 M NaCl, 0.12 g adsorbent, 10 min adsorption time, 25 °C adsorption temperature, 1 mL the elution solvent (acetone-0.25 M NaOH (aq) (2:1 (v v−1)), 5 min desorption time, 50 °C desorption temperature, and the stirring speed of 900 rpm for adsorption and desorption steps. Good values of linearity range (0.125–5 µg mL−1, R2 = 0.999), preconcentration factor (33.4), precision (less than 2.3%), and recovery (93.2%) were achieved. The limit of detection and quantification of, respectively, 0.025 and 0.070 μg mL−1 was provided, which enabled a satisfactory trace determination of ibuprofen in urban water and human urine samples.

Maltodextrin-modified graphene oxide for improved enantiomeric separation of six basic chiral drugs by open-tubular capillary electrochromatography.

An electrochromatographic capillary was modified with graphene oxide (GO), and the coating was characterized by scanning electron microscopy, energy dispersive X-ray spectrometry, and Fourier transform infrared spectra. By utilizing maltodextrin (MD) as the chiral selector, the basic chiral drugs nefopam (NEF), amlodipine (AML), citalopram hydrobromide (CIT), econazole (ECO), ketoconazole (KET) and cetirizine hydrochloride (CET) can be enantiomerically separated on this CEC. Compared with an uncoated silica capillary, the resolutions are markedly improved (AML: 0.32 → 1.45; ECO: 0.55 → 1.89; KET: 0.88 → 4.77; CET: 0.81 → 2.46; NEF: 1.46 → 2.83; CIT: 1.77 → 4.38). Molecular modeling was applied to demonstrate the mechanism of enantioseparation, which showed a good agreement with the experimental results. Graphical abstractSchematic representation of the preparation of graphene oxide-modified capillary (GO@capillary) for enantioseparation of drug enantiomers. The monolayered GO was used as the coating of theGO@capillary. Then the capillary was applied to construct capillary electrochromatography system with maltodextrin for separation of basic chiral drugs.

Capillary electrophoresis‐based enzyme assays for β‐lactamase enzymes

Generic in-capillary as well as offline CE-based enzyme assays were developed for serine-β-lactamases and metallo-β-lactamases. The hydrolysis of benzylpenicillin to benzylpenicilloic acid was analyzed using 100mM sodium phosphate solution, pH6.0, as a background electrolyte. In-capillary assays employed an uncoated as well as a polyethylene oxide-coated capillary, while the offline assays employing long end and short end injection were performed in an uncoated capillary. Using procaine hydrochloride or 4-hydroxybenzoic acid as internal standard, the respective assays were validated with regard to linearity, LOD and LOQ, repeatability, precision, and accuracy. The assays were applied to the determination of the Michaelis-Menten parameters Km and Vmax of Bacillus cereus penicillinase as well as New Delhi metallo-β-lactamase 1 and Verona integrin-encoded metallo-β-lactamase 2. Furthermore, the inhibition of the enzymes by irreversible and competitive inhibitors was evaluated. Comparable data were obtained with all assays. The use of a simple substrate ensured broad applicability to the various types of β-lactamases.

Separations of antifungal compounds in capillary electrophoresis with two anionic cyclodextrins.

CD-CZE methods were developed for complete stereoisomeric separations of a series of six γ-lactam analogues, of which some were neutral, or cationic depending on the background electrolyte nature. The tested cyclodextrin was the versatile sulfobutylether-β-CD, used either in a phosphate buffer using capillaries dynamically coated with polyethylene oxide or in a borate buffer using uncoated capillaries. Long-end and short-end modes and concentration variations of chiral selectors allowed finding conditions of complete separation of four out of the six derivatives (i.e., 1, 2, 3, and 4) in short run times, confirming their broad range of applications. To separate the two last compounds, the highly sulfated-γ-CD was examined as chiral selector in acidic phosphate conditions. The enantiomers of the γ-lactam analogues 5 and 6 were baseline resolved with 5.5 and 4%, respectively as concentration in the buffer.

Use of a recently developed thermal modulator within the context of comprehensive two-dimensional gas chromatography combined with time-of-flight mass spectrometry: Gas flow optimization aspects.

The present research is based on the use of a recently developed comprehensive two-dimensional gas chromatography thermal modulator, which is defined as solid-state modulator. The transfer device was installed on top of a single gas chromatography oven, while benchtop low-resolution time-of-flight mass spectrometry was used to monitor the compounds exiting the second analytical column. The solid-state modulator was first described by Luong etal. in 2016, and it is a moving modulator that does not require heating and cooling gases to generate comprehensive two-dimensional gas chromatography data. The accumulation and remobilization steps occur on a trapping capillary, this being subjected to thermoelectric cooling and micathermic heating. In this study, the effects of the gas linear velocity on the modulation performance were evaluated by using two different uncoated trapping capillaries, viz., 0.8m × 0.25mm id and 0.8m × 0.20mm id. Solid-state modulator applications were carried out on a standard solution containing n-alkanes (C9, C10, C12 ), and on a sample of diesel fuel. The results indicated that the type of trapping capillary and gas velocity have a profound effect on modulation efficiency.

A two-step method for rapid characterization of electroosmotic flows in capillary electrophoresis.

The measurement of electroosmotic flow (EOF) is important in a capillary electrophoresis (CE) experiment in terms of performance optimization and stability improvement. Although several methods exist, there are demanding needs to accurately characterize ultra-low electroosmotic flow rates (EOF rates), such as in coated capillaries used in protein separations. In this work, a new method, called the two-step method, was developed to accurately and rapidly measure EOF rates in a capillary, especially for measuring the ultra-low EOF rates in coated capillaries. In this two-step method, the EOF rates were calculated by measuring the migration time difference of a neutral marker in two consecutive experiments, in which a pressure driven was introduced to accelerate the migration and the DC voltage was reversed to switch the EOF direction. Uncoated capillaries were first characterized by both this two-step method and a conventional method to confirm the validity of this new method. Then this new method was applied in the study of coated capillaries. Results show that this new method is not only fast in speed, but also better in accuracy.

The use of experimental design for the development of a capillary zone electrophoresis method for the quantitation of captopril.

A capillary zone electrophoresis (CZE) method for the quantitation of captopril (CPT) using UV detection was developed. Influence of electrolyte concentration and system variables on electrophoretic separation was evaluated and a central composite design (CCD) was used to optimize the method. Variables investigated were pH, molarity, applied voltage and capillary length. The influence of sodium metabisulphite on the stability of test solutions was also investigated. The use of sodium metabisulphite prevented degradation of CPT over 24 hours. A fused uncoated silica capillary of 67.5cm total and 57.5 cm effective length was used for analysis. The applied voltage and capillary length affected the migration time of CPT significantly. A 20 mM phosphate buffer adjusted to pH 7.0 was used as running buffer and an applied voltage of 23.90 kV was suitable to effect a separation. The optimized electrophoretic conditions produced sharp, well-resolved peaks for CPT and sodium metabisulphite. Linear regression analysis of the response for CPT standards revealed the method was linear (R2 = 0.9995) over the range 5-70 μg/mL. The limits of quantitation and detection were 5 and 1.5 μg/mL. A simple, rapid and reliable CZE method has been developed and successfully applied to the analysis of commercially available CPT products.