Carbon nanotubes as solid-phase extraction sorbents prior to atomic spectrometric determination of metal species: A review

New materials have significant impact on the development of new methods and instrumentation for chemical analysis. From the discovery of carbon nanotubes in 1991, single and multi-walled carbon nanotubes – due to their high adsorption and desorption capacities – have been employed as sorption substrates in solid-phase extraction for the preconcentration of metal species from diverse matrices. Looking for successive improvements in sensitivity and selectivity, in the past few years, carbon nanotubes have been utilized as sorbents for solid phase extraction in three different ways: like as-grown, oxidized and functionalized nanotubes. In the present paper, an overview of the recent trends in the use of carbon nanotubes for solid phase extraction of metal species in environmental, biological and food samples is presented. The determination procedures involved the adsorption of metals on the nanotube surface, their quantitative desorption and subsequent measurement by means of atomic spectrometric techniques such as flame atomic absorption spectrometry, electrothermal atomic absorption spectrometry or inductively coupled plasma atomic emission spectrometry/mass spectrometry, among others. Synthesis, purification and types of carbon nanotubes, as well as the diverse chemical and physical strategies for their functionalization are described. Based on 140 references, the performance and general properties of the applications of solid phase extraction based on carbon nanotubes for metal species atomic spectrometric determination are discussed.     

Sample sonication after trichloroacetic acid precipitation increases protein recovery from cultured hippocampal neurons, and improves resolution and reproducibility in two-dimensional gel electrophoresis

Protein precipitation with TCA followed by acetone washing is frequently used to clean samples before 2-DE. However, the difficulty in solubilizing TCA-precipitated proteins causes some variability in 2-D gels and makes it difficult to detect some proteins. In this work we show that sonication of the samples, after TCA precipitation followed by elution in sample buffer, increases total protein recovery, and improves reproducibility and matching ratios between gels when analyzed by specialized software.     

Automated protein analysis by online detection of laser-induced fluorescence in slab gels and 3-D geometry gels

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) still remains the most reliable and comprehensive analytical method for the evaluation of protein extracts. However, conventional SDS-PAGE is time-consuming and, thus, unpractical if several tens or hundreds of samples must be examined. We show that SDS-PAGE protein analysis can be automated using slab gel DNA sequencers and compare the instrument's performance with conventional SDS-PAGE in terms of resolution, sensitivity and sample capacity. Labeled protein bands are detected online by laser-induced fluorescence (LIF) and the acquired signals are electronically stored for further processing, avoiding gel staining and scanning. Appropriate software allows immediate display of recorded data and convenient evaluation. The method provides a higher sensitivity and dynamic range than conventional Coomassie-stained gels and the resolution of proteins with different masses is independent of the polyacrylamide concentration. Internal markers can also be used for direct quantification and assignment of the molecular masses. Additionally, we present a novel electrophoresis instrument for the simultaneous separation and online LIF detection of all samples of a microtiterplate in parallel lanes in a 3-D geometry gel cylinder. The specific gel thermostatting concept prevents irregular sample migration (smiling) and improves the reproducibility and comparability of individual separation patterns. In combination with the expected large capacity of 384 or 1,536 samples, this makes the instrument a valuable tool for high-throughput comparative screening applications.     

Improved disc SDS‐PAGE for extraction of low molecular weight proteins from serum

The low molecular weight proteins can provide a lot of valuable information of biomarkers. To study these proteins, the high abundance and high molecular weight proteins must be removed prior to analysis. In this work, a simple and inexpensive disc SDS‐PAGE to extract low molecular weight proteins from human serum and cutoff proteins larger than 30 kDa was developed. Some experimental conditions were examined. The experimental results obtained by plate SDS‐PAGE and MALDI‐TOF MS showed that the molecular weight of extracted proteins was about in the range from 0.3 to 28 kDa. Some experiments, including precipitation of proteins in organic solvents, SPE and cytochrome C test, were carried out and the experimental results demonstrated successful recovery of proteins/peptides with molecular weight from several hundreds of dalton to about 30 kDa. The experimental results obtained by plate SDS‐PAGE indicated the repeatability was satisfactory.     

SDS存在下肌红蛋白在乙炔黑电极上的电化学行为研究

基于十二烷基磺酸钠(SDS)存在下,研究肌红蛋白(Mb)在乙炔黑电极上的电化学行为,建立了一种简便灵敏的肌红蛋白电化学分析方法.采用循环伏安法(CV)和差分脉冲伏安法(DPV)进行分析,SDS能显著提高肌红蛋白在乙炔黑电极上的还原峰电流.在最佳实验条件下,峰电流与肌红蛋白浓度在5.6×10-10 mol/L～2.8×10-7mol/L范围内有良好的线性关系,检出限为4.5×10-10 mol/L.方法用于合成样品中肌红蛋白含量的测定.乙炔黑电极可以作为传感器,用于样品中Mb的舍量测定.     

碱金属硫酸盐-十二烷基硫酸钠-聚乙二醇三元复合体系的束缚胶束特性

采用表面张力、稳态荧光猝灭和荧光分子探针技术研究了部分碱金属(锂、钠、钾)硫酸盐-十二烷基硫酸钠(Sod ium Dodecyl Su lfate SDS)-聚乙二醇(PEG)三元复合体系的聚集特性,发现加入碱金属硫酸盐后SDS仍以束缚胶束(bound m icelle)形式与PEG发生团簇化作用.表面张力实验表明,外加碱金属硫酸盐浓度c_e增加,体系的第一临界浓度c₁渐次降低,而第二临界浓度c₂略有增大,因而形成束缚胶束的浓度区间增宽;比饱和簇集量[Γ_∞]随之增大,如加入50 mmol/L硫酸锂时,[Γ_∞]增大了40%.稳态荧光猝灭实验表明,束缚胶束聚集数N_b随PEG浓度c_p线性减小,却随SDS浓度c线性增大,并呈c_e的单增函数关系;碱金属离子使N_b增大的能力按Li⁺++顺序增加,与碱金属水合离子半径减小的顺序相同.芘分子探针的荧光特性反映了束缚胶束的微环境极性随c和c_e增加而减小,随c_p增加而增大.     

SDS增溶DCM水溶液的荧光特性研究

研究了十二烷基硫酸钠(SDS) 增溶DCM水溶液的荧光光谱特性。随着SDS浓度的增加, DCM在水中的溶解度大大增加,荧光强度增强;当SDS浓度从0.025 mol·L-1增加到0.5 mol·L-1时,荧光峰值相对强度增强95倍。用532 nm激光激发SDS增溶DCM水溶液获得648 nm的强染料激光输出, 其波长相对于由DCM乙醇溶液获得的635 nm染料激光红移13 nm。利用该溶液荧光对苯的受激拉曼散射(SRS)Stokes波长选择增强。作为对比,用DCM乙醇溶液的荧光对苯受激拉曼散射进行选择增强,结果显示出二者对苯的二、三、四阶Stokes波均可产生放大,但前者最大放大波长位于第三阶Stokes线(632 nm)处,放大因子8.5,后者最大放大波长位于第二阶Stokes线(595 nm)处,放大因子为2.5。另外分析讨论了SDS增溶DCM水溶液和荧光增强的机制及其应用前景。     

甲苯胺蓝在SDS胶束中的电化学行为研究

在玻碳电极上研究了甲苯胺蓝(TB)及其在SDS胶束中的电化学行为,并与其直接电化学行为进行了比较。研究结果表明,TB在玻碳电极上的电极反应为2电子可逆氧化还原反应过程。通过介质pH对TB电极反应过程影响的研究,确定在pH<4.2,4.25.9时,参与电极过程的质子数分别为3,2和1,同时给出了TB解离常数K1与K2分别为1.68×10-5和1.93×10-6。在浓度分别为0.05mol.dm-3和0.1mol.dm-3PBS缓冲溶液中,TB在SDS浓度接近其临界胶束浓度(CMC)附近时,其还原峰电流(Ipc)和还原峰电位(Epc)随SDS浓度的增加而降低和负移。在大于CMC浓度时,其还原峰电流(Ipc)和还原峰电位(Epc)随SDS浓度的增加而上升和正移,之后出现了一个平台段。同时还测定了TB及其在胶束体系中的扩散系数D及电极反应速率常数Kf,并对SDS胶束对TB电化学行为的影响因素给出了合理的理论解释。     

用弱电解质理论研究水溶液中SDS胶团的电离行为

在临界胶团浓度以上,十二烷基硫酸钠(SDS)在溶液中形成聚集态的胶团,从而表现出不同于一般强电解质的电导行为.针对这一特点提出了一种胶团电离模型,即将胶团作为一种弱电解质,用弱电解质电导理论来描述其溶液电导的变化规律,导出SDS胶团电离度的计算式,并得到该溶液电导实测数据的验证.