On‐line sample preconcentration by polarity switching in floating electrode‐integrated microchannel

In this study, we found that the polarity switching was effective to enrich and separate fluorescent analytes which have weakly‐dissociated groups in a floating platinum electrode (width, 50 µm; thickness, 2.5 µm)‐integrated straight‐channel in microchip electrophoresis (MCE). In the straight channel filled with an Alexa Flour 488 (AF488) solution, a sharp peak was observed after the polarity inversion with a 530‐fold enhancement of the sensitivity relative to the conventional MCE analysis. By using a fluorescent pH indicator, we verified that a sharp high‐pH zone was generated nearby the floating electrode and moved toward the anode with maintaining the high pH, which induced the sample enrichment like a dynamic pH junction mechanism. In the floating electrode‐embedded channel, the mixture of AF488‐labeled proteins was also well concentrated and separated within 100 s.     

Laser and electrochemical complex machining of micro-stent with on-machine three-dimensional measurement

In the micro-fabrication, small installation misalignment and deformation of the workpiece cause fatal damage. On-machine measurement is one of the efficient methods to prevent this damage. Our system performs the laser machining and the three-dimensional measurement of the workpiece position using only one laser. Based on the measurement result, the position error of the workpiece is automatically corrected and laser-machined. Electrochemical machining (ECM) is also done on the same machining system. In this paper, the configuration of the system is explained. Measurement and error correcting techniques are described in detail. And the experimental results that made stent shape using the micro-tube of diameter 120 μm and 210 μm are shown.     

Quantitative on‐line concentration for capillary electrophoresis with inkjet sample introduction technique

A quantitative sample introduction method based upon inkjet injection was applied to capillary electrophoresis coupled with stacking and sweeping on‐line concentration techniques. Methylxanthines were used as model compounds for the proof‐of‐concept of the method. The volume of injected sample could be easily manipulated by controlling the number of ejected droplets in the injection procedure. Under optimized conditions, a linear relationship between the ejected droplet number and peak area was obtained when the droplet number introduced into the capillary was less than 100. Under optimized quantitative on‐line concentration conditions, the limits of detection for theobromine, caffeine, and theophylline were 1.0, 2.0, and 1.0 μM, respectively. The inkjet injection system was evaluated by comparing it with conventional injection methods. The electropherogram of the inkjet injection mode was the same as that for hydrodynamic injection mode, and no sample discrimination was observed compared with the electrokinetic injection mode. The established method was applied to the determination of methylxanthines in bottled green tea. The recoveries of theobromine, caffeine, and theophylline were 94.1, 110.6, and 86.8%, respectively. We conclude that proposed method can be used for quantitative concentration for capillary electrophoresis, thus resulting in an improved accuracy.     

加速溶剂萃取-在线净化-气相色谱-质谱法测定土壤中多氯烃类化合物

以土壤中六氯环戊二烯、六氯丁二烯、六氯乙烷为研究对象,采用加速溶剂萃取法进行在线净化和萃取,用气相色谱-质谱法测定。将土壤样品10g与石英砂20g混合均匀后,加入到装有氟罗里硅土粉1g和石墨炭黑粉0.2g的萃取池中,以二氯甲烷-丙酮(4+1)混合液为萃取剂进行萃取。考察了萃取温度、萃取剂、分散剂和土壤pH、TOC等因素的影响,分析了在线净化和离线净化的差异以及复合净化的优势。应用该方法对3个不同土壤样品进行测定,回收率在72.3%~89.0%之间,相对标准偏差(n=7)为7.4%~13%。     

On-line automatic SPE-CE coupling for the determination of biological markers in urine

Automatic SPE has been coupled on-line to CE by a transfer tube and the replenishment system of the CE instrument. The approach allows the target analytes (viz. creatinine, creatine, xanthine, hypoxanthine, uric acid, p-aminohippuric acid and ascorbic acid in urine samples) to be removed from the sample matrix, cleaned up, preconcentrated and injected into the capillary. The detection limits range between 0.14 and 4.50 microg/mL, the quantification limits between 0.45 and 15.0 microg/mL, and linear dynamic ranges - which include the reference healthy human values - from the quantification limits to 1332 microg/mL. The precision, expressed as RSD, ranges between 0.38 and 2.22% for repeatability and between 1.79 and 7.61% for within-laboratory reproducibility. The errors, expressed as RSD for all compounds, range between 0.20 and 6.90%. The time for automatic SPE and that necessary for the individual separation-detection of the target analytes are 13 and 12 min, respectively; the analysis frequency is 5 h(-1). The accuracy of the method and potential matrix effects were studied by using spiked samples and recoveries between 96.00 and 103.07 % were obtained. The proposed method was applied to samples from healthy young students.     

On-line preconcentration of weak electrolytes by electrokinetic accumulation in CE: experiment and simulation

A new on-line preconcentration technique was developed that makes possible to determine nanomolar concentrations of weak acidic analytes in CE. The method consists of long-running electrokinetic sample injection and stacking (electrokinetic immobilization) of the analytes at a boundary of two electrolytes with different pH values (pH 9.5 and 2.5) and consequent mobilization of the stacked uncharged analytes in a micellar system (containing SDS micelles). Several factors including buffer concentration, pH, applied voltage, time of preconcentration, and SDS concentration were tested to optimize the analysis method. An about 4600-fold increase of the sample concentration (in comparison with the standard CZE) can be achieved during the preconcentration step. Two preservatives applied in food industry -- benzoic acid and sorbic acid were used as model samples. The applicability of the proposed method in food analysis was demonstrated by determination of nanomolar concentrations of benzoic acid in sunflower oil. An extended version of the computer program Simul was used for modeling both the preconcentration and mobilization processes taking place in the capillary.     

填充毛细管液相色谱-高温毛细管气相色谱在线联用分析重油

重油的组成分析一直是个难题,它的沸点高,族组分种类多,各族内组分的异构体又极为繁多.最好的分析方法是用高效液相色谱(HPLC)做族分离,馏分收集后再用CGC分析.但HPLC的族馏分体积比CGC进样量大100倍.本文采用填充毛细管液相色谱(μHPLC)与高温毛细管气相色谱(HTGC)在线联用技术[1]分析重油.正相μHPLC将样品按族分离,μHPLC的柱效高,族分离能力强,而小的馏分体积(<100μL)可避免GC分流进样.在一次LC进样后,多位储存型联用接口将分离后的各族组分切割、存储并分别无损失转入HTGC分析,利用FID对高于C10的有机物的响应值相…     

On Free Boundary Problem for the Non-Newtonian Shear Thickening Fluids

The aim of this paper is to explore the free boundary problem for the NonNewtonian shear thickening fluids. These fluids not only have vacuum, but also have strong nonlinear properties. In this paper, a class of approximate solutions is first constructed, and some uniform estimates are obtained for these approximate solutions. Finally, the existence of free boundary problem solutions is proved by these uniform estimates.     

流动注射在线萃取—石墨炉原子吸收光谱法测定地质样品痕量钯

应用流动注射在线萃取技术将ＰｄＣｌ＾２－６萃入２－巯基苯并噻唑－甲基异丁基酮直接进行石墨炉原子吸收测定。研究了流动注射在线萃取－石墨炉原子吸收光谱法测定地质样品中钯的实验条件、流路参数等。采样速率为２０样／ｈ,ＲＳＤ（ｎ＝１０）为４．８％,测定Ｐｄ的特征质量为２．６＊１０＾－１１。