Capillary electrophoretic determination of ammonia using headspace single-drop microextraction

A new method involving headspace single-drop microextraction (SDME) and capillary electrophoresis (CE) is developed for the preconcentration and determination of ammonia (as dissolved NH₃ and ammonium ion). An aqueous microdrop (5 μL) containing 1 mmol/L H₃PO₄ and 0.5 mmol/L KH₂PO₄ (as internal standard) was used as the acceptor phase. Common experimental parameters (sample and acceptor phase pH, extraction temperature, extraction time) affecting the extraction efficiency were investigated. Proposed SDME-CE method provided about 14-fold enrichment in about 20 min. The calibration curve was linear for concentrations of NH₄⁺ in the range from 5 to 100 μmol/L (R² = 0.996). The LOD (S / N = 3) was estimated to be 1.5 μmol/L of NH₄⁺. Such detection sensitivity is high enough for ammonia determination in common environmental and biological samples. Finally, headspace SDME was applied to determine ammonia in human blood, seawater and milk samples with spiked recoveries in the range of 96-107%.     

Capillary zone electrophoretic determination of phenolic compounds in chess (Bromus inermis L.) plant extracts

A simple CZE method for quantification of phenolic compounds (vanillin, cinnamic, sinapic, chlorogenic, syringic, ferulic, benzoic, p-coumaric, vanillic, p-hydroxybenzoic, rosmarinic, caffeic, gallic and protocatechuic acids) in less than 10 min using 20 mM sodium tetraborate (pH 9.2) with 5% v/v methanol as a BGE and with UV detection at 254 nm is described. The LODs (3 S/N) ranged between 0.02 and 0.12 microg/ mL. Repeatabilities (RSDs) were 0.66-1.8 and 1.56-4.23% for migration times and peak areas (n = 5), respectively. The method was applied to the determination of phenolic compounds in chess (Bromus inermis L.) after Soxhlet extraction and purification of the crude extracts with SPE procedures. The results compared well with those obtained by liquid chromatographic method. B. inermis was found as a suitable model plant containing a broad spectrum of phenolic compounds in easily detectable concentrations and as a potential source of antioxidants.     

Capillary zone electrophoretic determination of tosufloxacin and trovafloxacin in urine

Summary A simple and rapid capillary zone electrophoretic method with UV detection has been developed for determination of tosufloxacin and trovafloxacin. The separation was performed in fused-silica capillaries (57 cm length × 75μm i.d.); the running buffer was 35mm borate + 35mm phosphate buffer solution, pH 8.6, containing 6% (v/v) acetonitrile. The applied potential was 15 kV, the temperature 30°C, and detection was at 262 nm. Piromidic acid was used as the internal standard. Response was linearly dependent on concentration in the range 1.0–120.0 μg mL⁻¹ and the detection limit was 0.2 μg mL⁻¹ for both compounds. The analysis was highly reproducible (RSD between 3.41 and 1.25%). The method was applied to the determination of tosufloxacin and trovafloxacin in human and rat urine. The method was validated by using HPLC as a reference method. Recovery was between 96.8 and 102%.     

硫代硫酸盐浸金过程中连多硫酸根的高效毛细管电泳法分析

采用高效毛细管电泳对硫代硫酸盐提金浸出液中的S3O62-和S4O62-进行分析研究,对缓冲溶液,电压、和检测波长对分析的影响进行了探讨。适宜的分离条件为:5 mmol/L(NH4)2SO4、5 mmol/L NaH2PO4,pH 6的缓冲溶液;重力进样5s,电压-20kV,波长214nm,有效长度为30 cm。在0.1～6 mmol/L和0.05～4mmol/L范围内S3O62-和S4O62-浓度与峰面积呈线性关系,在此进样条件下,S3O62-与S4O62-浓度高于80与50 mmol/L时信噪比大于2。实际浸金液用缓冲溶液稀释100倍后,S3O62-与S4O62-可实现基线分离,其它离子几乎不干扰检测。     

Capillary electrophoretic determination of oxalate in amniotic fluid

A capillary electrophoretic (CE) assay for oxalate has been applied to the quantitative determination of free oxalate in amniotic fluid. Indirect absorbance detection of oxalate is accomplished with a chromate-based background electrolyte modified with ethylenediaminetetraacetic acid (EDTA). Detection interference due to the presence of high levels (≈4 mg/ml) of inorganic chloride is eliminated through a direct sample clean-up procedure based on cation (Ag⁺-form) resins. Separation interference from amniotic fluid proteins is prevented through the use of a simple aqueous-based dilution procedure. This method for the determination of oxalate in amniotic fluid provides precision of ≈5% relative standard deviation (RSD). Within-day precisions for the oxalate response and migration time are better than 3% RSD and 1% RSD, respectively. Between-day precisions for the oxalate response and migration time are better than 6% RSD and 3% RSD, respectively. The analytical recovery of oxalate (1000 ng/ml) spiked into amniotic fluid was better than 96%. The limit of detection (LOD) for the method is ≈100 ng/ml oxalate. This method also shows promising results for the determination of oxalate in human blood plasma samples.     

On-line hyphenation of capillary electrophoresis with flame-heated furnace atomic absorption spectrometry for trace mercury speciation

Capillary electrophoresis (CE) was directly interfaced to flame-heated furnace atomic absorption spectrometry (FHF-AAS) via a laboratory-made thermospray interface for nanoliter trace element speciation. The CE-FHF-AAS interface integrated the superiorities of stable CE separation, complete sample introduction, and continuous vaporization for AAS detection without the need of extra external heat sources and any post-column derivation steps. To demonstrate the usefulness of the developed hybrid technique for speciation analysis, three environmentally significant and toxic forms of methylmercury (MeHg), phenylmercury (PhHg), and inorganic mercury (Hg(II)) were taken as model analytes. Baseline separation of the three mercury species was achieved by CE in a 60 cm long x 75 microm inner diameter fused-silica capillary at 20 kV and using a mixture of 100 mM boric acid and 10% v/v methanol (pH 8.30) as running electrolyte. The precision (relative standard deviation, RSD, n = 7) of migration time, peak area and peak height for the mercury species at 500 microg x L(-1) (as Hg) level were in the range of 0.9-1.2%, 1.5-1.9%, and 1.4-2.0%, respectively. The detection limit (S/N = 3) of three mercury species was 3.0 +/- 0.15 pg (as Hg), corresponding to 50.8 +/- 2.4 microg x L(-1) (as Hg) for 60 nL sample injection, which was almost independent on specific mercury species. The developed hybrid technique was successfully applied to the speciation analysis of mercury in a certified reference material (DORM-2, dogfish muscle).     

Capillary electrophoretic determination of lignin degradation products obtained by permanganate oxidation

A new capillary electrophoretic (CE) technique was developed for the separation of lignin degradation products after permanganate oxidation, yielding information about quality and quantity of various linkages in the lignin molecule. This CE method is a promising alternative to existing gas chromatographic (GC) methods. An advantage in comparison with GC is the short separation time and the fact that the oxidation products (aromatic acids) can be analyzed without derivatization. The selectivity and sensitivity of CE combined with UV detection is adequate and makes it suited for fast routine characterization of lignins. If necessary, the CE method can be coupled with electrospray ionization mass spectrometry in order to make a clear assignment of the peaks.     

Capillary electrophoretic analysis of dimethylsulfoniopropionate in sugarcane and marine algal extracts

A simple and high-resolution analytical method for the determination of dimethylsulfoniopropionate (DMSP) in sugarcane and marine algae is described. Effective extraction of DMSP from plant samples was also investigated using organic solvents, 5% perchloric acid or deionised water. To increase the sensitivity, DMSP in the extracts was first converted to a phenacyl ester, and the reaction mixture was applied directly to capillary electrophoresis without any pretreatment. Water extraction followed by esterification in a pH 4 reaction buffer was found most suitable for the measurement of alkaline-labile DMSP. This method was applied to the determination of DMSP levels in marine algae samples collected from the seashore of Nagasaki, Japan. An increase in DMSP content in Ulva pertusa in the winter period was observed.     

Capillary zone electrophoretic separation of isomeric benzoic acids using cyclodextrin

A method using capillary zone electrophoresis has been developed for separation of a series of isomeric benzene polycarboxylic acids. The separation was found to depend largely on the geometry of the acids and their degree of ionization as well as on the buffer pH and composition. The presence of additives to the buffer such as cyclodextrin and cationic surfactants was found necessary for complete resolution of all the isomers.     

Capillary electrophoresis-based methods for the determination of lipids--a review

Capillary electrophoresis (CE) is a high-resolution technique for the separation of complex biological and chemical mixtures. CE continues to emerge as a powerful tool in the determination of lipids. Here we review the analytical potential of CE for the determination of a wide range of lipids. The different classes of lipids are introduced, and the different modes of CE and optimization methods for the separation of lipids are described. The advantages and disadvantages of the different modes of CE compared to traditional methods like gas chromatography (GC) and liquid chromatography (LC) in the determination of lipids are discussed. Finally, the potential of CE in the determination of lipids in the future is illustrated.     

Capillary electrophoresis speciation analysis of various arsenical compounds

Separation of seven organic and inorganic arsenical species, i.e., inorganic arsenite (As III) and arsenate (As V), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), arsenobetaine (AsBet), arsenocholine (AsCh) and p-arsanilic acid (pAs) was carried out by capillary electrophoresis (CE) equipped with one of two different optical path cells, i.e., either the standard detection interface (SDI) or the high sensitive detection cell (HSDC). Separation, identification and quantification of the As species were performed by means of a capillary silica column with an alkaline borate buffer at pH 9.3 and direct UV detection at 192 nm. This methodological approach was tested with the abovementioned types of cells, and the results of the two modes were compared. In both cases, good separation was obtained, and also, repeatability in terms of migration times and peak areas was rather satisfactory. With regard to sensitivity, the HSDC allowed peak areas to be obtained, which were ca. 50 times greater than those afforded by the former cell. This also led to a substantial improvement in the limits of detection (LoDs); by a factor of 9 in the case of AsCh.     

Capillary electrophoretic analysis of anions in a multi-anion background electrolyte: Interference of system peaks

Summary This study deals with the simultaneous analysis of UV-transparent anions by capillary electrophoresis with indirect UV-detection. With a background electrolyte (BGE) based on UV-absorbing chromate and UV-transparent borate, the interference of system peaks with those of sample anions (chloride, sulfate, citrate, phosphate) is shown. The existence of such system peaks, and their position in relation to the peaks of the sample anions, are explained on the basis of the eigenpeak theory proposed by Poppe [1]. With this BGE the system peaks were manifested as a negative peak followed by a positive peak. Their shapes depended on the relative mobilities of the analyte and BGE anions and their areas depended on the amount of sample. The mobility of the system peak depends on the borate/boric acid mobility, which was adjusted by slight variation of the pH close to its pK _a-pH is the key factor governing system-peak mobility. When the locations of the system peaks are optimized, the quantification of citrate can be achieved; this was successfully used for determination of anions in milk.     

Capillary electrophoretic separation of inorganic sulfur-sulfide, polysulfides, and sulfur-oxygen species

A CE protocol was developed for the identification and separation of inorganic polysulfides simultaneously with other inorganic sulfur-bearing species coexisting in aqueous hydrosulfide/sulfur solutions. The electrophoretic separation of thiosulfate, sulfate, hydrosulfide, sulfite, tetrathionate, and polysulfides was achieved at pH values between 8.2 and 12.2. The peaks attributed to the polysulfide species were strongly sensitive to pH. CE analysis of hydrosulfide/sulfur solutions at different pH values permitted possible identification of two forms of polysulfides: S4(2-) and S3(2-). Upon exposure to air at ambient temperature, thiosulfate was the main oxidation product of hydrosulfide/sulfur solutions mainly in the first 60 min, when hydrosulfide was rapidly consumed. Analysis of the oxidation reaction products provided retrospectively tentative evidence that the peaks separated and identified as tri- and tetrasulfide may be ascribed to polysulfides.     

Capillary electrophoretic system incorporating an UV/CL dual detector

We developed a capillary electrophoretic system incorporating an ultra-violet absorption (UV)/chemiluminescence (CL) dual detector, taking advantage of the CL reaction of luminol-hydrogen peroxide and the batch-type CL detection cell. UV detection was carried out using the on-capillary method while CL detection was performed using the end-capillary method. Examination of isoluminol isothiocyanate (ILITC) as a model sample revealed two main peaks with UV detection and one main peak with CL detection. The first peak in the UV detection data corresponded to the main peak in the CL detection data. We then determined that the ILITC sample included natural ILITC as well as an impurity that had absorption behavior but did not have CL properties and labeling ability. Furthermore, the components of a mixture containing glycine, glycylglycine and glycylglycylglycine, all labeled with ILITC, were well separated and detected using the present system. The present system easily, rapidly, and simultaneously produces useful information due to the presence of both UV and CL detectors.     

Capillary electrophoretic separation of toxic drugs using a polyacrylamide-coated capillary

Summary Capillary electrophoresis (CE) has recently become an attractive approach for the analysis of pharmaceuticals. In this study, capillary electrophoretic separation of anxiolytic drugs, including barbiturates and benzodiazepines, was carried out using polyacrylamide (PAA)-coated capillaries. The surface of the capillary inner wall was coated with a neutral layer, and separation was performed in the absence of electroosmotic flow (EOF). Both charged and neutral solutes were separated in the presence of sodium dodecyl sulfate (SDS) above its critical micelle concentration (CMC) in the running buffer. This kind of CE method provided fast and efficient separation of a total of 24 kinds of toxic drugs in a mixture. In addition, the analysis of toxic drugs in body fluids was attempted after the sample preparation using liquid-liquid extraction or solid-phase microextraction (SPME).     

Capillary electrophoresis-chemiluminescence determination of norfloxacin and prulifloxacin

A capillary electrophoresis (CE)–chemiluminescence (CL) method for determining norfloxacin (NFLX) and prulifloxacin (PFLX) was developed based on the enhanced CL intensity of the cerium(IV)–sulfite–fluoroquinolone (FQ) reaction sensitized by terbium(III). The separation was conducted in buffer composed of 20 mM sodium citrate, 4 mM citric acid and 10 mM sodium sulfite at pH 6.1. The CL reagent solution consisted of 2 mM cerium(IV), 4 mM terbium(III) and 1.1 mM hydrochloric acid. NFLX and PFLX were baseline separated within 11 min with detection limits (S/N = 3) of 0.057 and 0.084 μg mL⁻¹, respectively. The maximum intra- and inter-day relative standard deviations (R.S.D.s) of migration time of the analytes were less than 4.0% and 4.2%, respectively. The proposed method was applied to detect NFLX and PFLX in fortified urine sample and the results were comparable to high-performance liquid chromatography (HPLC)–UV method. Moreover, the high selectivity of the CL detection and the high-separation efficiency of CE render the method the potential of quick analyzing fluoroquinolones in real complex matrix.     

毛细管电泳紫外吸收法分离检测海洋生物样品中不同形态的砷化合物

本研究建立了对亚砷酸盐As(Ⅲ)、二甲基砷(DMA)、对甲基苯砷酸(p-As)、一甲基砷(MMA)、砷酸盐(As(Ⅴ)) 5种不同形态的砷化合物的毛细管区带电泳(CZE)分离紫外检测方法,研究了检测波长、缓冲体系种类、pH值及其浓度、分离电压、温度、进样时间等因素对5种形态砷化合物的分离度、灵敏度、重现性等的影响.结果表明,在25 ℃、195 nm、20 mmol/L NaH2PO4-5 mmol/L Na2B4O7(pH=6.25)缓冲溶液、20 kV运行电压、3.0 kPa压力进样10 s条件下,5种不同形态砷化合物在11 min内取得完全分离,5种不同形态砷化合物的迁移时间和峰面积的RSD为0.50%～1.51%和1.65%～3.36%,检出限(3S/N)为0.004～0.30 mg/L.本法成功地应用于虾米中不同砷形态含量的测定,其回收率在93%～106%之间.     

Capillary electrophoretic separation of cationic constituents of imidazolium ionic liquids

A capillary electrophoretic method for resolving selected imidazolium ionic liquid cations is reported. The method, in which citric buffer is used as the running electrolyte, is simple and reproducible. The separation of a standard mixture is in linear accordance with the relative molecular mass (M(r)) of solutes regardless of the type of substitution (alkyl or aryl). The theoretical prediction of compounds as yet not analyzed is therefore possible; however, cations with identical molecular masses are inseparable with this method. Nevertheless, the method's quantitative analytical performance was excellent. The paper also discusses the applicability of a method for tracking the photodegradation kinetics of an exemplary ionic liquid.     

Capillary zone electrophoresis for simultaneous determination of seven nonsteroidal anti-inflammatory drugs in pharmaceuticals

A simple capillary zone electrophoresis (CZE) method has been developed for analyzing seven nonsteroidal anti-inflammatory drugs (NSAIDs)—sulindac (SU), ketoprofen (KE), indomethacin (IN), piroxicam (PI), nimesulide (NI), ibuprofen (IB), and naproxen (NA). The separation was run using borate buffer (60 mmol L^–1, pH 8.5) containing 13% (v/v) methanol at 20 kV, and detected at 200 nm. Several conditions were studied, including concentration and pH of borate buffer, methanol percentage, and separation voltage. In method validation, the calibration plots were linear over the range 40.0–500.0 mol L^–1. In intra-day and inter-day analysis, relative standard deviations (RSD) and relative errors (RE) were all less than 5%. The limits of detection were 10 mol L^–1 for SU, IN, PI, and 20 mol L^–1 for KE, NI, IB, NA (S/N = 3, sampling 6 s by pressure). All recoveries were greater than 95%. This method was applied to the quality control of six NSAIDs in pharmaceuticals using NI as internal standard (IS). The assay results were within the labeled amount required by USP 25.