Development of a novel electrochemical cell for slab optical waveguide spectroscopy for in situ observation of methylene blue and anions on an electrode/electrolyte interface

A new spectroelectrochemical cell for slab optical waveguide (SOWG) spectroscopy was developed in order to observe in situ an electrode/electrolyte interface for bulk electrolysis. The new SOWG spectroelectrochemical cell has been evaluated by simultaneous electrochemical-absorption experiments of methylene blue (MB) using cyclic voltammetry (CV) and SOWG spectrometry. CV was performed in the SOWG spectroelectrochemical cell using indium tin oxide (ITO) coated glass as the working electrode, platinum wire as the counter electrode and a silver/silver chloride electrode (Ag/AgCl) as the reference electrode. Based on the CV and SOWG spectrometric data, it was found that the SOWG spectra showed the MB spectra on the electrode surface selectively and that SOWG with the cell would be useful as a tool for in situ study of an electrode/electrolyte interface. Using this cell, the effects of the supporting electrolytes, NaNO₃, KNO₃, CH₃COONa, and CH₃COOK on the absorbance of MB were examined at the potential of +0.8 V versus Ag/AgCl. The decrease in MB absorbance by nitrate ions was greater than that of acetate ions. Therefore the competitive adsorption of nitrate ions was stronger than that of acetate ions. Thus, the decrease in absorbance of MB in the presence of anions demonstrates the competitive adsorption of anions. These results show that the extent of specific adsorption of electrolytes was observed by measuring the SOWG absorbance intensity of MB.     

Assessment of the surfactant-dye binding degree method as an alternative to the methylene blue method for the determination of anionic surfactants in aqueous environmental samples

The surfactant to dye binding degree (SDBD) method is proposed for the routine monitoring of anionic surfactants in aqueous environmental samples and their analytical features compared with those provided by the standard methylene blue (MB) method. This new analytical approach is based on the effect that anionic surfactants exert on the binding degree of the cationic surfactant didodecyldimethylammonium bromide (DDABr) to the anionic dye Coomassie Brilliant Blue G (CBBG). The formation of DDABr-CBBG aggregates is monitored photometrically. The analytical applicability of the proposed method was demonstrated by determining anionic surfactants in tap, river and swamp water, and raw and treated sewage. The mean recoveries obtained ranged between 99 and 101%. The SDBD method offers important advantages over the classical MB method: it is more sensitive, selective, precise, simple and rapid; the analytical response is independent of the molecular structure of the anionic surfactants, and the volume of sample required for analysis and the consumption of organic solvents are significantly reduced.     

A sub-second, time-resolved, linear dichroism measurement system for visible attenuated total reflection spectroscopy with a slab optical waveguide

A sub-second, time-resolved, linear dichroism (LD) measurement system was constructed, fitted with a slab optical waveguide (SOWG), and utilized to observe the adsorption process of methylene blue (MB) onto silica surfaces. In the system, a semiconductor laser (670 nm) was used as the light source and the out-coupled beam from the SOWG was split by a polarizing beam splitter into two polarized beams (TE and TM modes) to allow sequential linear dichroic ratio data to be obtained; the acquisition rate was 11 data sets per second. For an MB solution that contained no sodium dodecylbenzenesulfonate (DBS), in contact with a bare silica surface, a clear decrease occurred in the average orientation angle of adsorbed MB in the initial stages of the adsorption process. This result may correspond to a change in the chemical form of MB from monomer to dimer.     

Study of adsorption of methylene blue and new methylene blue in liquid-solid interface by slab optical waveguide spectroscopy

A slab optical waveguide (SOWG) has been used for study of adsorption of both methylene blue (MB) and new methylene blue (NMB) in liquid–solid interface. Adsorption characteristics of MB and NMB on both bare SOWG and silanized SOWG by octadecyltrichlorosilane (ODS) were compared. Effect of pH on adsorption on MB and NMB was investigated. Binding rate constant analysis showed that both MB and NMB on bare SOWG demonstrates larger association constants than those on ODS-SOWG. Interactions of MB and NMB on bare SOWG and ODS-SOWG were analyzed by molecular mechanics calculation method. The binding energy change was in the following order: E_NMB–bare > E_MB–bare > E_NMB–ODS > E_MB–ODS.     

Simultaneous determination of methylene blue and new methylene blue by slab optical waveguide spectroscopy and artificial neural networks

A slab optical waveguide (SOWG) has been used for study of adsorption of both methylene blue (MB) and new methylene blue (NMB) in liquid-solid interface. Adsorption characteristics of MB and NMB on both bare SOWG and silanized SOWG by octadecyltrichlorosilane (ODS) were compared. The simultaneous determinations of both MB and NMB were explored by flow injection SOWG spectrophotometric analysis and artificial neural networks (ANNs) for the first time. Concentrations of MB and NMB were estimated simultaneously with the ANNs. Results obtained with SOWG were compared with those got by conventional UV-visible spectrophotometry.     

Aggregation‐Induced Emission Active Probe for Light‐Up Detection of Anionic Surfactants and Wash‐Free Bacterial Imaging

Anionic surfactants are widely used in daily life and industries, but their residues can cause serious damage to the environment. The current detection methods for anionic surfactants suffer from various limitations and a new detection strategy is highly desirable. Based on 2‐(2‐hydroxyphenyl)benzothiazole fluorogen with aggregation‐induced emission characteristics, we have developed a fluorescent probe HBT‐C₁₈ for selective and sensitive detection of anionic surfactants. By in situ formation of catanionic aggregates or micelles with anionic surfactants, the emission intensity of the HBT‐C₁₈ probe can increase with increasing keto/enol emission ratio through restriction of intramolecular motion and excited‐state intramolecular proton‐transfer mechanisms. The probe can also be used for wash‐free imaging of bacteria enveloped by a negatively charged outer membrane. The results of this study provide a new strategy for sensitive detection of anionic surfactants and wash‐free bacterial imaging.     

几种表面活性剂与DNA的相互作用

用循环伏安、紫外－可见光谱和交流阻抗等方法，以电活性小分子亚甲基蓝（ MB）为探针，研究了几种表面活性剂与DNA的相互作用。研究发现，阴离子、阳离 子和非离子表面活性剂均可通过疏水和静电作用与固定在电极表面的DNA分子结合 ，改变电极表面DNA的状态，进而影响电活性小分子的电化学行为。阴离子表面活 性剂与DNA之间以静电排斥为主，也有部分疏水性结合，它使MB的氧化还原峰峰电 流减小。阳离子表面活性剂十六烷基三甲基溴化铵、十二烷基三甲基氯化铵均在一 定浓度范围内对MB的电化学响应有增敏作用，而代十六烷基吡啶、溴代十八烷基吡 啶表现出抑制效应，它们与DNA间既有疏水性作用，也有静电吸引。非离子表面活 性剂与DNA的结合较弱，其主要是通过改变溶液的性质（如粘度、极性和介电常数 等）影响DNA的构象，从而导致MB电化学参数的微弱变化。此外，表面活性剂疏水 链的长短及极性头基的大小对作用过程也有一定影响。     

Optical sensor of anionic surfactants using solid-phase extraction with a lactone-form rhodamine B membrane.

An optical sensor for the detection of anionic surfactants was developed. The optical sensing membrane is a 2-nitrophenyloctyl ether-plasticized poly(vinyl chloride) membrane incorporating a lactone-form Rhodamine B (L-RB). The response of the optical membrane to anionic surfactants was a result of the ion-pair coextraction of an anionic surfactant and a proton into the PVC membrane. The L-RB forms an ion associate with the extracted anionic surfactant; simultaneously, the formed L-RB ion associate is accompanied by a spectral change. Namely, the extracted anionic surfactant changes the color of the membrane from light pink to dark pink (absorption maximum; 558 nm). The optical membrane responds to anionic surfactants, such as dodecylbenzenesulfonate, dodecylsulfate and di-2-ethylhexyl sulfosuccinate in the concentration range from 1 to 50 microM.     

Voltammetric Determination of Folic Acid Using Adsorption of Methylene Blue onto Electrodeposited of Reduced Graphene Oxide Film Modified Glassy Carbon Electrode

This work presents a sensitive voltammetric method for determination of folic acid by adsorbing methylene blue onto electrodeposited reduced graphene oxide film modified glassy carbon electrode (MB/ERGO/GCE) in 100 mM KCl‐10 mM sodium phosphate buffer solution (pH 7.40). The surface morphology of the MB/ERGO/GCE modified electrode was characterized using scanning electron microscopy, displays that both MB and ERGO distributed homogeneously on the surface of GCE. The MB/ERGO/GCE modified electrode shows more favorable electron transfer kinetics for potassium ferricyanide and potassium ferrocyanide probe molecules, which are important electroactive compounds, compared with bare GCE, MB/GCE, and ERGO/GCE. The electrochemical behaviors of folic acid at MB/ERGO/GCE were investigated by cyclic voltammetry, suggesting that the modified electrode exhibited excellent electrocatalytic activity towards folic acid compared with other electrodes. Under physiological condition, the MB/ERGO/GCE modified electrode showed a linear voltammetric response from 4.0 μM to 167 μM for folic acid, and with the detection limit of 0.5 μM (S/N=3). The stability, reproducibility and anti‐interference ability of the modified electrode were examined. The developed method has been successfully applied to determination of FA in tablets with a satisfactory recovery from 96 % to 100 %. The work demonstrated that the electroactive MB adsorbing onto graphene modified electrode showed an enhanced electron transfer property and a high resolution capacity to FA.     

Spectrophotometric determination of anionic surfactants by conversion of the leuco-bases of triphenylmethane dyes

A one-phase, one-reagent, spectrophotometric technique is reported for the detection and determination of anionic surfactants of the sulfonate and sulfate types. Both applications are based on conversion of the colorless leuco-bases of triphenylmethane dyes (Brilliant Green and methyl violet) to colored (quinoid) forms by the anionic surfactants. The quantitative method, in the absorption and reflectance modes, is applicable to anionic surfactants in the 0–1500 ppm range; the spectrophotometric procedure can be automated. Residual surfactant can be detected at the 0.01% level on the surface of cellulosic products.     

Hydrophobically Modified Polyelectrolytes: V. Interaction of Fluorocarbon Modified Poly (acrylic acid) with Various Added Surfactants

The interactions between fluorocarbon‐modified poly (sodium acrylate) and various kinds of added surfactants have been studied by means of viscometric measurement. Association behavior was found in both hydrogenated and fluorinated anionic, nonionic and cationic surfactants. Among them, the interactions between fluorocarbon‐modified poly (sodium acrylate) and cationic surfactants are the strongest, owing to the cooperation of both electrostatic attractions and hydrophobic associations. The anionic surfactants have the weakest effects on the solution properties because of the existence of unfavorable electrostatic repulsion. The hydrophobic interactions between copolymers and fluorinated surfactants are much stronger than those between copolymers and hydrogenated surfactants.     

盐酸氯丙嗪作探针共振瑞利散射法测定环境水样中某些阴离子表面活性剂

在pH 3.0～5.0的HAc-NaAc缓冲溶液中, 盐酸氯丙嗪与十二烷基苯磺酸钠(SDBS)、十二烷基硫酸钠(SDS)和十二烷基磺酸钠(SLS)等阴离子表面活性剂反应形成离子缔合物时, 能导致共振瑞利散射(RRS)的显著增强并产生新的RRS光谱, 最大RRS峰分别位于277, 369和277 nm处, 方法对SDBS, SDS和SLS的检出限分别为0.018, 0.046和0.200 μg/mL, 其线性范围分别为0.09~10.0, 0.15~15.0 和0.67~12.5 μg/mL. 研究了适宜的反应条件及分析化学性质, 提出了一种用RRS技术灵敏、简便并快速测定阴离子表面活性剂的新方法.     

Amperometric Ethanol Biosensor Based on Integration of Alcohol Dehydrogenase with Meldola's Blue/Ordered Mesoporous Carbon Electrode

An amperometric ethanol biosensor was fabricated by integration of alcohol dehydrogenase (ADH) with meldola's blue (MB)/ordered mesoporous carbon (OMC) composite modified glassy carbon electrode (MB/OMC/GCE). The MB/OMC/GCE was highly sensitive for nicotinamide adenine dinucleotide (NADH) measurement (9.1±0.25 μA/mM) and gave a low detection limit of 0.21±0.02 μM. The ethanol biosensor exhibited a wide linear range up to 6 mM with a lower detection limit of 19.1±0.58 μM as well as a high sensitivity of 34.58±2.43 nA/mM without suffering any interference from some common electroactive compounds.     

Determination of the aggregation threshold of non-UV-absorbing, neutral or charged surfactants by frontal- and vacancy-frontal analysis continuous capillary electrophoresis

Supplementing our recent work on UV-absorbing anionic surfactants, new protocols based on frontal analysis continuous capillary electrophoresis (FACCE) were developed for the investigation of the aggregation threshold of non-UV absorbing anionic, cationic and neutral surfactants, and exemplified with sodium dodecyl sulfate (SDS), tetradecyltrimethylammonium bromide (TTABr) and Brij 35. Contrary to UV-absorbing surfactants, the critical micelle concentration (CMC) determination of non-UV absorbing surfactants requires the use of a marker providing adequate detection capabilities. UV-absorbing markers were selected, according to the charge of the studied surfactant (neutral for SDS and TTABr, anionic for Brij 35). In all cases, the free marker concentration was quantified as a function of the total surfactant concentration. In addition, a modified implementation of FACCE, that we called vacancy FACCE (VFACCE), was employed for the case of the neutral surfactant. VFACCE entails first filling the capillary with the system components to be studied in the background electrolyte, next continuously introducing the plain BGE electrokinetically. The salient theoretical features of FACCE and VFACCE were compared. These new protocols were successfully applied to yield reliable CMC values within short operational time and with low sample consumption.     

Sorption of a fluorescent whitening agent (Tinopal CBS) onto modified cellulose fibers in the presence of surfactants and salt

The combined effect of salt (10 mmol L(-1)) and surfactants on the sorption of the fluorescent brightener 4,4'-distyrylbiphenyl sodium sulfonate (Tinopal CBS) onto modified cellulose fibers was studied. Sorption efficiencies with both cationic and anionic surfactants were evaluated. Emission spectroscopy was used for quantitative analysis since Tinopal has an intense fluorescence. The sorption efficiency of the brightener is greater for solutions containing a cationic surfactant (DTAC) below the critical micelle concentration (cmc), while for an anionic surfactant (SDS) above its cmc the efficiency is greater. The profile of the sorption isotherms were interpreted in terms of the evolution of surfactant aggregation at the fiber/solution interface. Salt influences the efficiency of the Tinopal sorption on the modified cellulose fibers either because it decreases the cmc of the surfactants or because the ions screen the surface charges of the fiber which decreases the electrostatic interaction among the charged headgroup of the surfactant and the charged fiber surface.     

Anionic groups on cellulosic fiber surfaces investigated by XPS, FTIR-ATR, and different sorption methods

Anionic groups (AGs) on different cellulosic fiber surfaces were investigated by methylene blue (MB) and polyelectrolyte (PE) sorption, X-ray photoelectron spectroscopy (XPS), and total attenuated reflectance infrared spectrometry (FTIR-ATR). The MB sorption isotherms fitted well the Langmuir equation that gave consistent estimations of sorption capacities. FTIR-ATR showed that MB molecules had extensive accessibility to the fiber wall pores. Estimation of surface AGs by PE sorption gave much higher values than a new method combining MB sorption and XPS measurements (MB-XPS). The surface AGs in different cellulosic fibers accounted for 1-3% of the total AG content as revealed by MB-XPS. It was suggested that PE molecules can penetrate the fiber wall and form loops or unattached segments at external fiber surfaces that disrupt the PE sorption stoichiometry. The competition of MB and PE for the anionic sites in papermaking was assessed and it was shown that MB ions have a much stronger affinity to AGs than PE molecules.     

盐酸氯丙嗪作探针二级散射和倍频散射法测定环境水样中某些阴离子表面活性剂

在pH3.0~5.0的HAc-NaAc缓冲溶液中,盐酸氯丙嗪与十二烷基苯磺酸钠、十二烷基磺酸钠和十二烷基硫酸钠等阴离子表面活性剂反应形成离子缔合物时,仅能引起吸收光谱和荧光光谱的微小变化,但却能导致二级散射(SOS)和倍频散射(FDS)的显著增强。最大SOS峰均在552nm附近,最大FDS峰均在390nm附近。其中SOS法灵敏度更高,它对十二烷基苯磺酸钠、十二烷基硫酸钠和十二烷基磺酸钠的检出限分别为0.047、0.106和0.117mg/L,而其线性范围分别为0.2~12、0.4~15和0.4~20.0mg/L。研究了反应产物的吸收、荧光、SOS和FDS光谱特征、适宜的反应条件及分析化学性质,据此发展了一种用SOS技术灵敏、简便、快速测定阴离子表面活性剂的环境友好型新方法。     

多巴胺在聚亚甲基蓝/石墨烯修饰电极上的电化学行为研究

利用电聚合方法在石墨烯修饰的玻碳电极表面制备了聚亚甲基蓝/石墨烯修饰电极(PMB/GH/GCE)。采用循环伏安法(CV)和差分脉冲伏安法(DPV)研究了多巴胺(DA)和抗坏血酸(AA)在该修饰电极上的电化学行为。在pH 6.9的磷酸盐缓冲溶液中,DA和AA分别在0.208 V和-0.108 V处产生灵敏的氧化峰,与其在聚亚甲基蓝和石墨烯单层修饰电极上的电化学行为相比,两者的峰电流明显增加,峰电位差达316 mV。研究表明,电聚合方法使亚甲基蓝牢固地非共价修饰到石墨烯上,并产生协同增效作用,较好地提高了电极的灵敏度和分子识别性能,有利于在大量AA存在下实现对DA的选择性测定。在1.00×10-3mol/L AA的存在下,DA的差分脉冲伏安法峰电流与其浓度在1.00×10-7～5.00×10-3mol/L范围内呈良好的线性关系,检出限达1.00×10-8mol/L。将该方法用于盐酸多巴胺注射液的测定,结果满意。     

催化动力学光度法测定阴离子表面活性剂

基于在H2SO4介质中,阴离子表面活性剂对高碘酸钠氧化罗丹明B褪色的反应具有较强的催化作用,建立了测定阴离子表面活性剂的催化动力学光度法.本文以十二烷基硫酸钠为标准品进行实验,线性范围为0.08～0.20 mg/L,检出限为0.0193 mg/L.用于水样中阴离子表面活性剂总量的测定,测定结果的相对标准偏差为1.3%～1.4%,回收率为104%～106%.     

Interaction between β‐Cyclodextrin and Mixed Cationic‐Anionic Surfactants (1): Thermodynamic Study

The interactions between β‐cyclodextrin (β‐CD) and the mixtures of cationic‐anionic surfactants in aqueous solution were investigated by surface tension and ¹H NMR measurements. It was shown that the critical micelle concentration (cmc) increased linearly with the increase of β‐CD concentration. Furthermore, β‐CD formed 1∶1 inclusion complex with both cationic and anionic surfactants in the mixed surfactant systems, and no significant selective inclusion was observed. The thermodynamic parameters of the inclusion process of β‐CD to mixed cationic‐anionic surfactants were calculated by a numerical method based on the surface tension measurements, and it was found that the inclusion process was both enthalpy and entropy favorable.