Fused silica capillary tube isotachophoresis using a multichannel photodiode array detector

Isotachophoresis carried out in a 0.25 mm i.d. fused-silica capillary tube yielded high resolution, compared with that in a fluorinated ethylene-propylene polymer tube. The use of an ultraviolet-visible multichannel spectrophotometer with photodiode array as detector together with a cross flow cell (volume 0.01 μl) was investigated. The system was successfully applied to the analysis of cationic dyes such as neutral red, bismarck brown, and basic fuchsine.     

Poly(methacrylic acid-ethylene glycol dimethacrylate) monolith in-tube solid-phase microextraction applied to simultaneous analysis of some amphetamine derivatives in urine by capillary zone electrophoresis

A method based on in-tube solid-phase microextraction and capillary zone electrophoresis (CZE) was proposed for simultaneously determining four amphetamines (amphetamine, methamphetamine, 3,4-methylenedioxyamphetamine, and 3,4-methylenedioxymethamphetamine) in urine. A poly(methacrylic acid-ethylene glycol dimethacrylate) monolithic capillary column, which can provide sufficient extraction efficiency, was introduced for the extraction of amphetamines from urine samples. The hydrophobic main chains and acidic pendant groups of the monolithic column make it a superior material for extraction of basic analytes from aqueous matrix. After extraction, the samples were analyzed by CZE. The best separation was achieved using a buffer composed of 0.1 M disodium hydrogen phosphate (adjusted to pH 4.5 with 1 M hydrochloric acid) and 20% methanol v/v, with a temperature and voltage of 25 degrees C and 20 kV, respectively. By applying electrokinetic injection with field-amplified sample stacking, detection limits of 25-34 microg/L were achieved. Excellent method of reproducibility was found over a linear range of 0.1-5 mg/L. Determination of these analytes from abusers' urine sample was also demonstrated.     

Ultra-fast essential oil characterization by capillary GC on a 50 microm ID column

A 5 m x 50 microm capillary column with 0.05 microm stationary phase film thickness, with a calculated efficiency of almost 20,000 plates per metre (under optimum conditions), was used for very fasthigh resolution GC analysis of lime essential oil. The total analysis time of this volatile essential oil was less than 90 s. Fast GC is shown to be appropriate for essential oil quality assurance analysis, and quantitative results of key components are comparable with those obtained by using conventional GC analysis. The fast GC analysis is approximately 33 times faster than the conventional GC method.     

Electrochemical Preparation of Poly(Malachite Green) Film Modified Nafion‐Coated Glassy Carbon Electrode and Its Electrocatalytic Behavior Towards NADH,Dopamine and Ascorbic Acid

Poly(malachite green) film modified Nafion‐coated glassy carbon electrodes have been prepared by potentiodynamic cycling in malachite green solution. The pH of polymerisation solution has only minor effect on film formation. Electrochemical quartz crystal microbalance (EQCM) was used to monitor the growth of the poly(malachite green) film. Cyclic voltammogram of the poly(malachite green) film shows a redox couple with well‐defined peaks. The redox response of the modified electrode was found to be depending on the pH of the contacting solution. The peak potentials were shifted to a less positive region with increasing pH and the dependence of the peak potential was found to be 56 mV per pH unit. The electrocatalytic behavior of poly(malachite green) film modified Nafion‐coated glassy carbon electrodes was tested towards oxidation of NADH, dopamine, and ascorbic acid. The oxidation of dopamine and ascorbic acid occurred at less positive potential on poly(malachite green) film compared to bare glassy carbon electrode. In the case of NADH, the overpotential was reduced substantially on modified electrode. Finally, the feasibility of utilizing poly(malachite green) film electrode in analytical estimation of ascorbic acid was demonstrated in flow injection analysis.     

聚吡咯水杨酸修饰电极的电化学行为及水杨酸含量测定

本用电化学方法制备了聚吡咯－水杨酸修饰电极；并进行了电化学行为的研究，经电化学处理该是电极对水杨酸根具有选择性响应，响应线性范围在１．０×１０＾－＾５－１．０×１０＾－＾３ｍｏｌ／Ｌ之间。电极斜率为４０ｍＶ／ｐＣ，该电极具有较好的稳定性，响应时间在１８０－３００ｓ之间；电极寿命可达６０ｄ。     

异咯嗪蒙脱石修饰电极的电化学行为

应用十六烷基三甲基溴化铵对蒙脱石进行改性，成功地制备稳定性良好的异咯嗪蒙脱石修饰电采，用循环伏安法对此修饰电极的电化学行为进行了研究。测定了异咯嗪在蒙脱石膜内的化学扩散系数，对异咯嗪在改性蒙脱石中电极反应机制进行了探讨。     

三正辛胺修饰电极伏安测定痕量金的研究

用化学修饰电极伏安测定痕量金,Kalcher K等曾采用阴离子交换剂碳糊修饰电极及打萨宗碳糊修饰电极检测100～300μg/L的金。本文采用三正辛胺(TOA)修饰玻碳电极,在1.5 mol/L介质中,Au(Ⅲ)在+0.16 V(vs SCE)处有一灵敏的不可逆还原峰。检出限为0.1μg/L。灵敏度比文献方法高千倍。Au(Ⅲ)浓度在5×10~(-7)～5×10~(-9)mol/L范围内峰高与浓度     

Sample-stacking techniques in non-aqueous capillary electrophoresis

In sample-stacking techniques, the detection limit cannot be improved by simply increasing the length of the sample solution, because the individual electrophoretic parameters must be optimized. In an attempt to increase the amount of sample injected, as well as to focus them onto a small zone, two novel methods are proposed. One of these employs an "ultra-high conductivity zone", which was inserted between the sample zone and background solution to build an unequal conductivity gradient. The other employs a "low temperature bath". A portion of the capillary (near the junction between the sample solution and the background solution) was immersed in a low temperature bath, which served as a "pseudo-high-conductivity zone" due to the fact that conductivity would increases when the temperature is decreased. As a result, a large volume of sample injection can be achieved. Using 3,4-methylenedioxymethamphetamine as a model compound, the detection limit was determined to be 1.6 x 10(-6) M (S/N = 3) by means of normal non-aqueous capillary electrophoresis (NACE). This could be improved to 3.0 x 10(-8) M, 4.8 x 10(-9) M and 5.0 x 10(-9) M, respectively, when the normal stacking, ultra-high conductivity zone NACE-stacking and the low-temperature zone NACE-stacking methods were applied.     

Fused silica capillary micro-packed columns in gas chromatography

Summary Flexibility, strength and adsorption inertness of fused-silica capillaries permits their extensive application for the preparation of micro-packed columns in gas chromatography. Decreasing the column diameter (from 0.5 to 0.15 mm) and the diameter of the sorbent particles (from 100 to 5 μm) results in a marked reduction of the height equivalent to a theoretical plate (HETP), as well as in diminishing the dependence of the HETP on the carrier gas flow rate. The chromatographic characteristics of fused-silica capillary micro-packed columns and open-tubular columns are compared. The fused-silica capillary micro-packed column can be used to advantage for performing rapid and trace analyses and have been shown to be adapted for application in gas-solid chromatography. Separation of organic and inorganic compounds on fused-silica capillary micro-packed columns is illustrated by practical examples. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

Determination of imazalil by on-line coupled capillary isotachophoresis with capillary zone electrophoresis

A simple, rapid and reproducible capillary isotachophoretic on-line coupled with capillary zone electrophoresis (CITP-CZE) method for the determination of IMz in food packaging extracts and its residues in apples is described. A good separation of the IMZ from other sample constituents was achieved within 15 minutes without any sample clean up. Method characteristics (linearity, accuracy, intra-assay and detection limit) were determined. Less amount of time involved, sufficient sensitivity and low running cost are the important attributes of CITP-CZE method.