Influence of a stacking phenomenon on the results of Hadamard transform capillary electrophoresis

Advantageous features (enhanced sensitivity and low baseline noise) of the multiplex measuring procedure, the Hadamard transform capillary electrophoresis (HT-CE), are experimentally demonstrated and critically discussed. To perform a perfect multiplex experiment in CE, sample species need to be dissolved in the background electrolyte medium and have very low concentration. The mismatch of electric conductivity resulting from a sample dissolved in water or in a separation buffer diluted with water will lead to sample stacking and corrupting the anticipated outcome. The multiplex measurements were carried out with benzyltriethylammonium bromide, resorcinol and 3,5-dihydroxybenzoic acid in the phosphate buffer, 511 sample/buffer injections were performed into the capillary according to the pseudorandom binary sequence. The averaged electropherogram of the single injection was calculated from the detection signal with the aid of the Fourier transform. The results illustrate the detrimental effect of sample matrix dilution with water and the effect of increased initial sample concentration on the multiplex measurement in CE. Multiplex advantage, in theory possible in the HT-CE, can be obtained at low concentration levels feasible with laser induced fluorescence and optically gated sampling. To achieve successful multiplex measurements with the UV detector, the single injection signal should be approximately at the baseline noise level.     

The LIF Excitation Spectrum of Jet-Cooled 2,6-Dicyano-3, 5-Dimethylaniline

The laser-induced fluorescence (LIF) excitation spectrum of jet-cooled 2, 6-dicyano-3,5-dimethylaniline (DCDMA) has been measured in the spectral range of 29,750–32,250cm^–1. The band origin at 29,860.8 cm^–1 and as many as 250 vibrational bands have been identified in the excitation spectrum. The analysis of the excitation spectrum of DCDMA gives more than 28 vibrational modes involving aromatic ring oscillations and oscillations related to the substituent groups. DCDMA is nonplanar in the ground state, with the NH₂ plane at about 9° with respect to the molecular plane (RHF/6-31G*). The singlet excited molecule is planar (CIS/6-31G*). Both CIS/6-31G* and CASPT2 calculations predict that the lowest excited state of DCDMA involves a dominant HOMO-LUMO excited configuration. The characteristic feature of the excitation spectrum of DCDMA is the presence of progressions in the low-frequency mode, 112 cm^–1. The calculations suggest that this mode and some other active modes involve motions of the amino group and strongly interacting adjacent cyano substituents.     

免疫毛细管电泳-激光诱导荧光分析DNA加合物的方法学研究

DNA加合物是一类重要的生物标志物,可应用于人体致癌物暴露监测、癌症风险评价和人群易感性研究。DNA加合物作为生物标志物的应用需要安全、灵敏、快速的先进分析技术。我们利用免疫毛细管电泳-激光诱导荧光分析,发展了高灵敏的DNA加合物分析方法和技术。本文主要介绍了相关的仪器研制及方法学研究。方法学研究涉及DNA加合物荧光探针的合成和表征、抗体与DNA加合物的相互作用及其结合计量学、抗原-抗体复合物的稳定化和DNA驱动电泳聚焦技术。     

水体中溶解有机物激光诱导荧光光谱分析方法

讨论了用激光诱导荧光(LIF)的方法分析水体中溶解有机物(DOM)的含量,利用拉曼散射信号对荧光光谱进行归一化处理,消除激发光强度和水体对荧光的二次吸收和接收条件等因素的影响,并给出了理论依据,由此依据得出了非线性浓度校准的数学模型。利用这个数学模型对实验数据进行非线性拟合,拟合的相关系数高于0.99。该浓度校准的数学模型,考虑到了水体对荧光信号的二次吸收以及溶液浓度的变化对二次吸收的影响,结果表明它可作为不同水体的通用浓度校准的数学模型对水体中的DOM进行定量分析。     

Analysis of low‐molecular mass aldehydes in drinking waters through capillary electrophoresis with laser‐induced fluorescence detection

The potential of CZE with LIF detection in the separation and determination of low‐molecular mass aldehydes involving precolumn derivatization with fluorescein 5‐thiosemicarbazide was investigated. Different variables that affect derivatization (pH, fluorescein 5‐thiosemicarbazide concentration, time and temperature) and separation (pH and concentration of the BGE, kind and concentration of surfactants at levels higher and lower than CMC, and applied voltage) were studied. The separation was conducted within 16 min by using borate buffer (60 mM; pH 10) with 10 μM polyethylene glycol tert‐octylphenyl ether as modifier. Good linearity relationships (correlation coefficients ranged from 0.9978 to 0.9994 for aldehydes) were obtained between the peak areas and concentration of the analytes (0.5–100 μg/L). The LODs for aldehydes were achieved at submicrogram‐per‐liter level (0.15–0.35 μg/L), which indicated that the proposed method surpassed other electrophoretric alternatives in terms of LOD, in many cases even at ca. 1000‐fold. The inter‐day precision (RSD, %) of the aldehydes ranged from 5.2 to 8.3%. Finally, the method was successfully applied to bottled drinking‐water samples, and the aldehydes were readily detected at 0.6–4.4 μg/L levels with average recoveries ranging from 99.1 to 103.5%.     

HPLC-fluorescence detection and MEKC-LIF detection for the study of amino acids and catecholamines labelled with naphthalene-2,3-dicarboxyaldehyde

Naphthalene-2,3-dicarboxyaldehyde (NDA) is commonly used for detection of primary amines in conjunction with their separation with HPLC and CE. The fluorescence of the derivatives can be measured by a conventional fluorometer or via LIF. NDA is a reactive dye, which can replace o-phthaldehyde (OPA) and provides for derivatives which are considerably more stable than OPA derivatives. In addition, NDA can be used to derivatize primary amines at concentrations as low as 100 pM. In this work, HPLC/fluorescence and MEKC/LIF experiments were performed to separate/detect six neuroactive compounds, the amino acids, Gly, Glu, Asp, gamma-aminobutyric acid (GABA) and the catecholamines, dopamine and noradrenaline. The two methods were compared in terms of performance of separation. The amino acids can be separated in HPLC in less than 30 min and an identical separation is obtained in CE using MEKC and lithium salts with greater resolution (the number of theoretical plates was approximately 5000 for HPLC and 200 000 for MEKC). The lowest detected concentration was in the range of 0.1 nM for CE/LIF. The presence of a high salt concentration does not affect the separation of the samples. Examples of the analysis of microdialysate samples as well as amino acids in Ringer's solution are presented.     

一种便携式激光诱导荧光检测器的研制

基于共聚焦检测原理,自组装了一台便携式激光诱导光检测器,用于微型液相流动系统。精巧的目视观察校准装置使光学校准非常容易。以亚甲基蓝试剂作为检测物质对该系统性能进行了评价,在检测池直径0.25mm时,检测下限为0.2nmol/L,线性范围为10^3,性能达到了文献报道的水平。     

Identification of new bands in the red system of CoO

The laser-induced fluorescence excitation spectrum of jet-cooled CoO molecules has been studied in the range of 540-725 nm. Beside all the parallel-polarized and perpendicular bands observed previously by Barnes and co-workers [M. Barnes, D.J. Clouthier, P.G. Hajigeorgiou, G. Huang, C.T. Kingston, A.J. Merer, G.F. Metha, J.R.D. Peers, S.J. Rixon, J. Mol. Spectrosc. 186 (1997) 374-402], 59 new bands have been recorded. Rotational constants have been derived and three new vibrational progressions identified. These three new band systems have been designated [13.99]⁴Π_5/2-X⁴Δ_7/2, [14.20]⁴Π_5/2-X⁴Δ_7/2 and [15.85]⁴Π_5/2-X⁴Δ_7/2. In addition, lifetime measurements have been carried out for most of the bands under collision-free conditions.     

A weak cation-exchange phase for the separation of biogenic amines by open tubular liquid chromatography

Summary The preparation and performance of a weak cation-exchange stationary phase for Open Tubular Liquid Chromatography (OT-LC) was investigated. The stationary phase was prepared in 5.4 μm I.D. fused silica capillaries byin situ photopolymerization of a mixture of silicon acrylate and acrylic acid. The influence of pH, counter ion concentration and organic modifier concentration of the mobile phase on the retention was studied with catecholamines as test solutes using LIF detection. Other biological amines like amino acids, small peptides and nucleic acid derivatives could be separated on this stationary phase as well. The kinetic performance of the stationary phase was studied with several cations and neutral solutes.     

Determination of ζ‐potential,charge, and number of organic ligands on the surface of water soluble quantum dots by capillary electrophoresis

The number of charges and/or organic ligands covalently attached to the surface of CdTe quantum dot nanoparticles has been determined from their electrophoretic mobilities measured in capillaries filled with free electrolyte buffers. Three sizes of water soluble CdTe quantum dots with 3‐mercaptopropionic and thioglycolic acids as surface ligands were prepared. Their electrophoretic mobilities in different pH and ionic strength values of separation buffers were measured by capillary electrophoresis with laser induced fluorescence detection. The ζ‐potentials determined from electrophoretic mobilities using analytical solution of Henry function proposed by Ohshima were in the range from ?30 to ?100 mV. Charges of QDs were calculated from ζ‐potentials. As a result, numbers of organic ligands bonded to QDs surface were determined to be 13, 14, and 15 for the sizes of 3.1, 3.5, and 3.9 nm, respectively. The dissociation constants of organic ligands bonded on QDs surfaces estimated from the dependence of QDs charge on pH of the separation buffer were 7.8 and 7.9 for 3‐mercaptopropionic acid and 6.9 for thioglycolic acid.