On-line monitoring of pH junctions in capillary electrophoresis using Fourier transform infrared spectrometry

Fourier transform mid-infrared spectroscopic detection is proposed as an on-line detection technique for the study of on-line preconcentration processes in capillary electrophoresis (CE). The molecule-specific information contained in mid-IR spectra can be used to directly determine the chemical compositions of individual zones and their boundaries. This paper reports on pH junctions employed in myoglobin analysis. On-line mid-IR detection allowed the shape of the sample peak to be monitored as well as the chemical compositions of the surrounding zones. From this information it was possible to obtain detailed insights into the actual chemical compositions of the individual zones governing the efficiency of the preconcentration technique applied. The principle of measurement outlined here can therefore also be regarded as a promising one for investigating other on-line preconcentration techniques, like stacking, sweeping, and pH junction-sweeping among others. Fourier transform mid-infrared spectroscopic detection has been employed in pH junction experiments. This approach can be used to measure the chemical compositions of the phase boundaries formed, as well as the relative positions of the analyte in the zones. The principle of this technique is demonstrated by measuring myoglobin (acetate buffer, pH 4.5) in an ammonium BGE (pH 9.25)     

Stopped flow and merging zones — a new approach to enzymatic assay by flow injection analysis

Four alternative flow injection methods based on the concept of merging zones have been developed for the assay of glucose in serum with glucose dehydrogenase. Special attention has been paid to the dispersion and synchronization of the merging zones and to methods of measuring the blank value of serum. The optimal procedure, based on rate measurements, allows the assay of glucose to be done at a rate of 100 determinations per hour, with the analytical readout available 30 s after sample injection. The assay requires less than one unit of enzyme per sample.     

应力对低合金钢焊接接头相电化学行为的影响

采用微区相电化学测试技术,测量和研究了１６Ｍｎ钢焊接接头上不同热经历区在硝酸盐溶液中的微区相电化学行为（包括自腐蚀电位、自腐蚀电流密度和极化曲线）以及外加载荷（应力）的影响。此外,还分别测量了各区中铁素体和珠光体的电化学行为,尤其是加载状态下的行为。结果表明,加载后各热经历区以及各区中铁素体和珠光体的自腐蚀电位均比未加载前负移,相应的自腐蚀电流密度增大,铁素体和珠光体之间电位差明显减小。加载后各热     

Properties of moving boundaries in electrophoretic systems with multivalent weak electrolytes: principles of non-Kohlrausch concentration adjustment

This paper describes the properties of electrophoretic moving boundaries in systems containing multivalent weak electrolytes where the Kohlrausch regulating law is not valid. It is shown that zones of unexpected properties can be formed in such systems and that the adjusted concentrations in these zones cannot be predicted using present knowledge. A theoretical approach to the properties of such "non-Kohlrausch" systems is presented that allows the explanation and prediction of their properties. The theory based on velocity diagrams describes the electrophoretic evolution of a concentration boundary between a pair of zones (differing only in the concentration ratio of their components) as the formation of two moving boundaries migrating in opposite directions. The concentration profiles and velocities of these moving boundaries, that can be either sharp or broadening by electromigration dispersion, as well as the adjusted concentrations in the formed intermediate zones can be predicted from calculated velocity diagrams. Such zones differ from normal systems in that their adjusted concentrations are a function of the composition of both zones that formed the original boundary. The theory is illustrated and verified by both computer simulations and experiments.     

Electric detection of DNA with PDMS microgap electrodes and silver nanoparticles

In this work a novel microdevice sensor has been developed by plating gold on the PDMS surface to generate a sandwich-type gap electrode for DNA detection. The microdevice utilizes a gold band electrode-PDMS-gold band electrode configuration and the minimum detectable volume could be as low as 5 μL. The 20 μm PDMS-based gap was chemically modified with DNA capture probes and DNA sandwich hybrids were formed with the addition of DNA target and silver nanoparticle probes. To increase detection sensitivity, parallel detection zones have been developed in which the relevant resistances decrease substantially upon hybridyzation. By measuring the change in electrical conductivity, the DNA target in the concentration range of 1000-0.1 nM can be assayed and the limit of lowest detectable concentration was achieved at 0.01 nM.     

Isotachophoresis of proteins in a networked microfluidic chip: experiment and 2-D simulation

This paper reports both the experimental application and 2-D simulation of ITP of proteins in a networked microfluidic chip. Experiments demonstrate that a mixture of three fluorescent proteins can be concentrated and stacked into adjacent zones of pure protein under a constant voltage of 100 V over a 2 cm long microchannel. Measurements of the isotachophoretic velocity of the moving zones demonstrates that, during ITP under a constant voltage, the zone velocity decreases as more of the channel is occupied by the terminating electrolyte. A 2-D ITP model based on the Nernst-Planck equations illustrates the stacking and separation features of ITP using simulations of three virtual proteins. The self-sharpening behavior of ITP zones dispersed by a T-junction is clearly demonstrated both by experiment and by simulation. Comparison of 2-D simulations of ITP and zone electrophoresis (ZE) confirms that ZE lacks the ability to resharpen protein zones after they pass through a T-junction.     

Peak deformation in cationic analysis caused by system zones.

In electrophoretic processes, often zones migrate through the separation compartment, with a composition different from that of the background electrolyte (BGE) but which do not contain, however, any component of the sample mixture. These zones migrate with a mobility mainly determined by the composition of the BGE and are called system zones (SZs). If these SZs are visible in electropherograms they are called system peaks (SPs). If sample components have a mobility close to that of a SZ, the separation process can be disturbed and the sample peak shapes are deformed. SZs can appear applying BGEs containing more co-ionic species or if BGEs are used at high or low pH. Recently, the existence of SZs has been described applying BGEs containing weak multivalent anionic species. In this paper, the diverse kinds of system zones, are discussed for cationic systems and the effect of invisible SZs on separations is shown. As an example of a weak multivalent cation, the behavior of the divalent cation histamine is studied, which can be used as co-ion in BGEs for the separation of cations in the indirect UV mode. Applying BGEs containing histamine, SZs are visible in the electropherograms and there existence could also be established theoretically by the use of SystCharts. A mathematical model for the calculation of the mobility of SZs is verified and it has been shown that an unsafe region with a mobility window of msp +/- 10% can be indicated, for the separation of fully ionized sample components.     

Dual stacking of unbuffered saline samples,transient isotachophoresis plus induced pH junction focusing

A dual stacking mechanism based on transient isotachophoresis (TITP) and induced pH junction focusing is demonstrated as a means to increase the concentration sensitivity in capillary electrophoresis of highly saline samples. When stacking was carried out with an unbuffered saline sample of fluorescein between two zones of low mobility background electrolyte at high pH under an electric field of reverse polarity, two transient peaks at both boundaries of the sample zone were observed. One peak at the rear boundary could be inferred as a transient isotachophoretic stacked zone. Through computer simulations of an unbuffered sample with a high concentration of sodium chloride, we showed that the fast moving zones of sodium and chloride ions induced pH changes at both boundaries to satisfy the electroneutrality condition and that the peak at the front boundary was due to the induced pH junction. To verify the pH changes, an indicator, thymol blue, was added to an NaCl solution and the color changes under an electric field were observed. The proposed mechanism was supported by observing the dual stacking procedure for an unbuffered sample of 4-nitrophenol and measuring additional sensitivity enhancements by dual stacking for ten weakly acidic compounds. For the ten analytes including nucleoside phosphates, every dual stacking of an unbuffered sample exhibited an additional enhancement up to 86% larger than that of usual transient isotachophoresis of the corresponding buffered sample without loss of separation efficiency and reproducibility. Therefore, it would be useful to skip over buffering in sample preparation for TITP, contrary to the general recommendation.     

Development of a microfluidic paper-based analytical device for the determination of salivary aldehydes

A low cost, disposable and easy to use microfluidic paper-based analytical device (μPAD) was developed for simple and non-invasive determination of total aldehydes in saliva with a potential to be used in epidemiological studies to assess oral cancer risk. The μPAD is based on the colour reaction between aldehydes (e.g. acetaldehyde, formaldehyde), 3-methyl-2-benzothiazolinone hydrazone (MBTH) and iron(III) to form an intense blue coloured formazan dye. The newly developed μPAD has a 3D design with two overlapping paper layers. The first layer comprises 15 circular detection zones (8 mm in diameter), each impregnated with 8 μL of MBTH, while the second layer contains 15 reagent zones (4 mm in diameter). Two μL of iron(III) chloride are added to each one of the second layer zones after the addition of sample to the detection zones in the first layer. All hydrophilic zones of the μPAD are defined by wax printing using a commercial wax printer.     

Development and validation of a novel rheological test device and measurement system for determining the influence of humidity on viscosity

Although a strong impact of humidity on polymers and the formation of their molecular network is known, the complex interactions between humidity, temperature, diffusion, reaction kinetics, rheological behaviour and mechanical properties are not fully understood yet. Most current approaches solely analyse the relationships between environmental conditions in a solidified or crosslinked state and the mechanical properties. In contrast, this work focusses on measuring changes in rheological properties depending on relative humidity in the liquid state. A custom designed novel measuring geometry is introduced and validated. It enables for the first time to rheometrically investigate the influence of relative humidity on reactive systems during their cross-linking process. Our results significantly depict the influence of humidity on the cross-linking process and the gel time. The potential of the introduced measuring geometry for improving reactive systems, adapting these precisely to environmental boundary conditions or assuring product performance is hereby demonstrated. This is especially important for industrial manufacturing processes running at different production sites around the world in different climatic zones or repair processes being performed outdoor, e.g. for wind energy plants.     

Composition and antibacterial activity of essential oil from Scutellaria grossa Wall ex Benth

The chemical composition of the steam volatile oil of the whole aerial part of Scutellaria grossa Wall ex Benth. (Lamiaceae), obtained by steam distillation, has been analysed by capillary GC and GC-MS. The oil was found to be rich in oxygenated monoterpenes (88.6%). A total of 50 constituents were identified, representing 94.4% of the total oil composition. Linalool (37.0%) and 1-octen-3-ol (32.0%) were found to be the principal constituents. The antibacterial activity of the oil was determined against 10 bacterial strains by measuring the growth inhibitory zones. The oil showed significant antibacterial activity against Gram-positive bacteria, Bacillus subtilis and Enterococcus faecalis, and the Gram-negative, Klebsiella pneumoniae and Salmonella enterica enterica. A minimum inhibitory concentration of 31.25?μL mL(-1) was observed against E. faecalis.     

System zones in capillary zone electrophoresis

When working with capillary zone electrophoresis (CZE), the analyst has to be aware that the separation system is not homogeneous anymore as soon as a sample is brought into the background electrolyte (BGE). Upon injection, the analyte creates a disturbance in the concentration of the BGE, and the system retains a kind of memory for this inhomogeneity, which is propagated with time and leads to so-called system zones (or system eigenzones) migrating in an electric field with a certain eigenmobility. If recordable by the detector, they appear in the electropherogram as system peaks (or system eigenpeaks). However, although their appearance can not be forecasted and explained easily, they are inherent for the separation system. The progress in the theory of electromigration (accompanied by development of computer software) allows to treat the phenomenon of system zones and system peaks now also in very complex BGE systems, consisting of several multivalent weak electrolytes, and at all pH ranges. It also allows to predict the existence of BGEs having no stationary injection zone (or water zone, EO zone, gap, dip). Our paper reviews the theoretical background of the origin of the system zones (system peaks, system eigenpeaks), discusses the validity of the Kohlrausch regulating function, and gives practical hints for preparing BGEs with good separation ability not deteriorated by the occurrence of system peaks and by excessive peak-broadening.     

Electro-static discharge method of zone location for paper chromatographs

This paper presents an entirely new application of static discharge current for the localization of zones or spots on paper chromatographs Electroscope and neon-tube methods of location are described Both methods can be carried out by the same instrument, which is inexpensive to construct, takes up little space, and is portable Used in conjunction with Blake's titrimeter quantitative measurements are made     

Forming architectured paper by printing a starch patterned grid: a new low-cost approach for lightweighting packaging

To meet the environmental challenges, the use of plastic packaging must be drastically reduced. Paper-based solutions may be a credible alternative provided that their production cost is reduced. One way may be to improve the paper stiffness to weight ratio. In this work, a simple and low-cost approach is proposed, which consists in printing a patterned grid of starch at the paper surface by using a widespread printing process. With only a small quantity of starch (7 g/m²), the bending stiffness of a packaging paper of 60 g/m² was multiplied by more than a factor three. This improvement originates from the permanent 3D shape the paper unexpectedly took after printing. The printed lines formed “valleys” whereas the unprinted zones were raised, forming “mountains”. Drying shrinkage of the starch is assumed to play a major role, in particular by inducing local buckling of the unprinted zones. In addition, the resulting 3D shape could be interestingly tuned by adjusting the grid pattern. Even if a better understanding is necessary to be able to well control the phenomena, this approach appears relevant to form “architectured” papers with improved bending resistance to weight ratio.

     

Visualization of charge-carrier propagation in water

The electrical properties of water in the region between parallel electrodes were investigated using pH indicator dyes. Different pH values corresponded to different colors, which could be registered by a video camera. Imposition of electrical current was able to produce zones of constant pH around, and well beyond each electrode: extremely low pH around the positive electrode and extremely high pH around the negative electrode. The border between alkaline and acid zones was jagged and separated by only a narrow layer of water with neutral pH. When the water was replaced by various salt solutions, similar zones were observed. Again, passage of current produced large zones of extreme pH values near and beyond each electrode. Alkaline zones appeared to propagate from the negative to the positive electrode in narrow channels through the neutral solution. When the power supply was disconnected from the electrodes and replaced by a resistive load, a potential difference was registered, and current flowed through the resistor for some period of time. Hence, the acid and alkaline zones appear to carry opposite charges throughout their volume.     

Calorimetric measurements of the heat of solution and immersion of minerals in water using a new calorimetric vessel

The paper describes a new calorimetric measuring vessel for the commercial precision calorimetry system LKB 8700. The vessel was tested by measuring the enthalpy of solution of CaF₂ in water and the enthalpies of immersion of different minerals in water. The results of these experiments are comparable to previously published data. The vessel is suitable for accurately measuring enthalpies greater than 50 mJ. The results are discussed in relation to the heat treatment of the minerals.It can be assumed that this calorimetric vessel will allow us to measure enthalpies of displacement. Thus it should be possible to investigate in future experiments the selective adsorption in the liquid phase on a solid surface which has been immersed in the liquid before starting the adsorption experiment. These measurements may afford a reliable approach to the investigation of the flotation process.     

Liquid crystal nose,chiral case: towards increased selectivity and low detection limits

In this paper, we describe a simple prototype of an olfaction system based on chiral liquid crystals (LCs) and suitable for sensing volatile organic compounds (VOCs). The detection of small concentrations of VOCs is based on measuring weak colour fluctuations on the surface of the LC droplet. Detection of larger concentrations is based on measuring colour changes (or shift of the selective reflection band) and isotropisation transition of the whole droplet. Thus, a broad range of VOC concentrations can be detected by this LC nose.     

Immobilized enzymes - A simple calorimetric method for the determination of the catalytic activity

The results communicated in this paper show that rapid and reliable information about the activity of immobilized enzymes follows from calorimetric measurements. The study was done using spherical and plain carriers as well as different enzymes (urease, glucose-oxidase, invertase). The enzyme thermistor developed by Danielsson et al. was used as a measuring system. This measuring system was applied to investigate the activity of enzyme carrier complexes produced by the sol-gel technique. The influence of processing parameters could be pointed out at complexes of different forms (xerogel, gel on ceramic carrier, thin gel layers on foil, etc.). With the described calorimetric method, a fast and reliable technique for comparative determination of the activity of immobilized enzymes is available. A special advantage of this method is its variability in carriers and the generally applicable thermal measuring principle. Therefore, it seems useful for the development of new immobilization techniques.     

Detection of antibiotics in muscle tissue with microbiological inhibition tests: effects of the matrix.

The effects of the tissue matrix on detection limits of antibiotics with microbiological inhibition tests, intended for muscle tissue, were measured. Pieces of frozen meat were laid directly on top of paper disks impregnated with aqueous antibiotic solutions. Inhibition zones were compared with those obtained by the same standard solution without tissue. Only tetracyclines were detected as efficiently with as without muscle tissue. Inhibition zones of the beta-lactam antibiotics ampicillin and penicillin G, and the fluoroquinolone antibiotics enrofloxacin and ciprofloxacin were smaller when muscle tissue was added to low levels of standard solution. At higher levels the differences were not substantial. Inhibition zones of tylosin were smaller and irregular or had disappeared completely, while ceftiofur, sulfadimidine, erythromycin, lincomycin, and streptomycin were not detected in spiked muscle tissue at concentrations fivefold higher than the detection limits without tissue. These results indicate that ceftiofur, sulfonamides, streptomycin and some macrolide antibiotics cannot be detected in intact meat with the plates and bacterial strains prescribed in the European Four Plate Test, a test which was initially intended as a multi-residue method for muscle tissue. Two plates of this system are not suitable for screening purposes; a third one detects tetracyclines and beta-lactam antibiotics in spiked tissue; the fourth one is sensitive for beta-lactam antibiotics and for some but not all macrolides. Samples spiked with the fluoroquinolones enrofloxacin and ciprofloxacin can be detected with an additional plate, not included in the Four Plate Test.     

Colorimetric determination of acidity constant using a paper-based microfluidic analytical device

Acid dissociation constant is an important chemical characteristic of organic and inorganic compounds and it affects both chemical properties and biological activities of the molecules. Herein, a very simple, fast and cost-effective method based on microfluidic technology has been reported for colorimetric determination of acidity constants. The designed device works based on pH-metric titration of colorful indicators followed by colorimetric measurements by a smart phone mobile device or a flatbed scanner. So, it does not need sophisticated instrumentation and is accomplished in a very short time (about 1 min). All titration steps are transferred on a star-like designed µPAD device: (1) spotting 0.3 µL buffers of different pHs at the end of the channels (reaction zones), (2) spotting a 30 µL portion of the indicator on the center of µPAD followed by movement of indicator solution toward the reaction zone by capillary action of the paper. The measured color change of the indicators at the reaction zone is fitted to the Henderson–Hasselbalch equation, through which acidity constants are calculated. The performance of the device was evaluated by measuring acidity constant of 4 indicators including bromothymol blue, bromocresol green, bromocresol purple and phenolphthalein. A very close agreement was achieved between those measured by the suggested device here and the previously reported values. The reproducibility of this method was lower than 5% for relative standard deviation of three replicate measurements.