Identification and interaction of amino acids with leucine-anthracene reagent by TLC and spectrophotometry: experimental and theoretical studies

A new reagent has been synthesized by coupling anthracene moiety to L-leucine. The reagent is characterized by different analytical techniques. It is capable for easy identification of various amino acids on thin-layer chromatography plates by developing distinguishable colors (detection limit between 0.1-0.5 μg at cold condition and 0.1-0.4 μg after heating). This reagent also binds with different amino acids very strongly in solution (methanol). Estimation of equilibrium binding constants of this new reagent with different amino acids has also been carried out. The values of the binding constants are lowest for L-Tyrosine (6.86 × 103 dm3 mol(-1)) and highest for L-Arginine monohydrochloride (8.86 × 10? dm3 mol(-1)) at 25°C. A theoretical study (Hartree-Fock) has been performed to investigate the interaction of the reagent with a representative amino acid, glycine.     

新型安培检测毛细管电泳微系统

将电极、６ｃｍ分离毛细管、缓冲池、检测池集成于８．４×５．０ｃｍ有机玻璃片上,制作了一个毛细管电泳微系统。以碳纤维微盘电极作为工作电极,采用三电极体系柱端检测了１×１０－４ｍｏｌ／Ｌ多巴胺（ＤＡ）,具有良好的重现性,检测限３．６×１０－８ ｍｏｌ／Ｌ,线性范围５×１０－７～１×１０－４ｍｏｌ／Ｌ,并在该系统上分离了邻苯二酚（ＣＡ）和多巴胺的混合物。     

Rapid and sensitive analysis of three polyphenols in tobacco by CE using homemade C(4) D with a mini detection cell

A rapid, sensitive, and practical CE with C(4) D detection was developed for the analysis of three polyphenols (rutin, scopoletin, and chlorogenic acid) in tobacco samples. The constructed mini detection cell (12 mm × 10 mm × 10 mm) of C(4) D featured with small inner cell volume (～2 nL), smaller noise (<0.9 mV), repeatability, high strength and durableness. Three polyphenols were ultrasonically extracted with methanol-water (70:30, v/v) solution following SPE cleanup. The CE method was optimized with the running buffer of 150 mmol L(-1) 2-amino-2-methyl-1-propanol (pH 11.2), and the applied separation voltage of +20 kV over a capillary of 50 μm id × 375 μm od × 50 cm (38 cm to the C(4) D window, 41.5 cm to the UV detector window), which gave a baseline separation of three polyphenols within ca. 6 min. The method provided the limits of quantification (S/N = 10) at about 0.08-0.15 μg g(-1) for three polyphenols, whereas the overall recoveries ranged from 82% to 88%. The proposed method has been successfully applied to measure three polyphenols in the actual tobacco samples, and their contents were calculated and evaluated.     

Determination of azide in gastric fluid and urine by flow-injection electrospray ionization tandem mass spectrometry

A rapid method was developed to identify and quantify the azide ion (N(3)(-)) in gastric fluid and urine. N(3)(-) in diluted biological fluids was reacted with NaAuCl(4) to produce Au(N(3))(2)(-), which was extracted with octanol. Five microliters of the extract were flow-injected into an electrospray ionization tandem mass spectrometric instrument. Quantification of N(3)(-) was performed by selected reaction monitoring of the product ion Au(N)(N(3))(-) at m/z 253, which was derived from the precursor ion Au(N(3))(2)(-) at m/z 281, using 50 μL of aqueous solution within 10 min. This method was found to be linear up to 10(-5) M, to have a limit of quantification of 10(-7) M, a limit of detection of 3.0?×?10(-8) M, and a coefficient of variation of ≦10% at 10(-7) M. In the case of urine, 50 μL of urine were spiked with N(3)(-), this was diluted 10-fold and passed through 1 mL of a resin, and finally diluted to 100-fold of the original. This method was linear up to 10(-3) M, had a limit of quantification of 10(-5) M, a limit of detection of 3.0?×?10(-6) M, and coefficient of variation of ≦8.8% for an original urine concentration of 10(-5) M. The practical applicability of this method was checked by diluting 1 μL of a suspected suicide victim's gastric fluid 20,000-fold and 1 μL of the victim's urine 5,000-fold and then measuring the N(3)(-) levels. These levels were found to be (7.5?±?1.0)?×?10(-2) M and (3.2?±?0.4)?×?10(-3) M, respectively.     

Polyester-toner electrophoresis microchips with improved analytical performance and extended lifetime

This paper reports the fabrication of polyester-toner (PT) electrophoresis microchips with improved analytical performance and extended lifetime. This has been achieved with a better understanding about the EOF generation and the influence of some parameters including the channel dimensions (width and depth), the injection mode, and the addition of organic solvent to the running buffer. The analytical performance of the PT devices was investigated using a capacitively coupled contactless conductivity detector and inorganic cations as model analytes. The proposed devices have exhibited EOF values of (3.4 ± 0.2) × 10(-4) cm(2) V(-1) s(-1) with good stability over 25 consecutive runs. It has been found that the EOF magnitude depends on the channel dimension, i.e. the wider the channel, the higher the EOF value. The separation efficiency for inorganic cations ranged from 13 000 to 50 000 plates/m. The LOD found for K(+) , Na(+) , and Li(+) were 4.2, 7.3, and 23 μM, respectively. In addition, the same PT device has been used by three consecutive days. Lately, due to improved analytical performance, it was carried out by the first time the detection of inorganic cations in real samples such as energetic drinks and pharmaceutical formulations.     

微流蒸发光散射检测器的研制及评价

构建了适用于纳升级到微升级流量的毛细管分离体系的微流蒸发光散射检测器(μELSD),实现了其与毛细管液相色谱(eLC)的联用.对雾化器孔径和雾化毛细管内径、蒸发管内径和长度、光散射池尺寸、雾化毛细管位置和辅助载气流量等参数进行了优化.在最优条件下,微流蒸发光散射检测器检出限为直接进样葡萄糖1 ng(S/N＞ 10),线性范围0.01～1.0 μg,重复性好,峰面积RSD(n=6)为0.4％,峰高RSD(n=6)为0.3％.本检测器已成功应用cLC-μELSD平台,使用C18毛细管色谱柱(内径250 μm),0.1％甲酸铵溶液(pH 4.5)-甲醇(60∶40,V/V)为流动相,分离检测了3种常用甜味剂,表明本研究构建的系统可以应用于实际分离检测中,具有分析时间快、溶剂消耗量少、样品需求量小的优点.     

Determination of 1-hydroxypyrene in human urine by HPLC with electrochemical detection at a boron-doped diamond film electrode

A high-performance liquid chromatographic method with electrochemical detection (HPLC-ED) at a boron-doped diamond film electrode with preliminary separation and preconcentration by solid-phase extraction (SPE) has been developed for the determination of 1-hydroxypyrene (1-HP) in human urine. 1-HP is among the most widely used biomarkers of exposure to polycyclic aromatic hydrocarbons. Optimal HPLC-ED conditions have been found: mobile phase methanol-0.05 mol L(-1) phosphate buffer pH 5.0 (80:20, v/v), detection potential +1,000 mV versus Ag/AgCl (3 mol L(-1) KCl), and flow rate 0.8 mL min(-1). For SPE, LiChrolut(?) RP-18 E cartridges were used. The extraction yield was (87.0 ± 5.8)% (n = 5). The concentration dependence of 1-HP was measured in the concentration range from 0.01 to 10 μmol L(-1) (2.18-2,180 μg L(-1)) using methanolic solutions resulting from the SPE pretreatment of spiked human urine samples. The limit of detection (signal-to-noise ratio 3) and the limit of quantification (signal-to-noise ratio 10) of the biomarker were 0.013 μmol L(-1) (2.84 μg L(-1)) and 0.043 μmol L(-1) (9.39 μg L(-1)), respectively, which is sufficient for its determination in the urine of persons exposed to polycyclic aromatic hydrocarbons.     

A Simple Contactless Conductivity Detector Employing a Medium Wave Radio Integrated Circuit for the Signal Treatment

A new procedure has been tested for the treatment of the alternating signal coming from a contactless conductivity detection cell. The cell consists of a polyethylene (2 mm o.d., 1.5 mm i.d.) or polytetrafluoroethylene (1.6 mm o.d., 0.8 mm i.d.) tubing, with 5 mm wide tubular electrodes placed over the tubing and separated by a 5 mm gap. An unmodulated or an amplitude‐modulated AC voltage is applied to the cell and the AC current passing through the cell is treated by a TDA 1072A integrated circuit, obtaining a signal depending on the conductivity of the quiescent or flowing solution inside the cell. Under optimized conditions, the solution conductance can be measured within a range from ca. 10 to 700 μS cm^?1, corresponding to ca. 9×10^?5 to 5×10^?3 M KCl. The detector was used to measure the conductivities of various drinking waters and the values obtained were in a good agreement with those provided by a commercial contact conductometer. It has been found that the use of unmodulated input voltage is advantageous both experimentally, and from the point of view of the quality of the analytical characteristics. The integrated circuit tested is not, however, sufficiently sensitive for application to capillary detection cells with diameters of a few tens of μm, employed in microseparation procedures.     

Cooperative use of cytochrome cd1 nitrite reductase and its redox partner cytochrome c552 to improve the selectivity of nitrite biosensing

In this work, a novel enzymatic biosensor for determination of nitrites constructed on an electrochemical transducing platform is proposed. The sensor is based on cytochrome-cd(1) (cyt-cd(1)) nitrite reductase from Marinobacter hydrocarbonoclasticus strain 617 as biological recognition element, and its putative physiological redox partner cytochrome-c(552) (cyt-c(552)), as electron mediator. The proteins were co-immobilized using a photopolymerizable polyvinyl alcohol (PVA) derivative, onto carbon paste screen printed electrodes (CPSPEs); the optimal modification conditions were 100 μM cyt-cd(1)/100 μM cyt-c(552) and 50% PVA, after a 48 h polymerization time. Electrochemical characterization of the mediator was carried out by cyclic voltammetry. The one-electron exchange between cyt-c(552) and the working electrode is a quasi-reversible process, without mass transport limitations. The formal potential of the mediator is 254±2 mV vs NHE and the intermolecular electron transfer rate constant between cytochromes c(552) and cd(1) is 9.9×10(3)M(-1)s(-1). The analytical parameters of the biosensor response to nitrite as assessed by amperometric measurements were: linear range from 10 to 200 μM; detection and quantification limits of 7 and 24 μM, respectively; sensitivity of 2.49±0.08 Amol(-1)cm(2) μM(-1). Catalytic profiles in the presence of possible interfering species were also investigated. The interference from competitive enzymatic reduction of dissolved oxygen could be overcome by tuning the cyclic voltammograms for faster sweep rates.     

Determination of microcystin-LR in waters in the subnanomolar range by sol-gel imprinted polymers on solid contact electrodes

The present work reports new sensors for the direct determination of Microcystin-LR (MC-LR) in environmental waters. Both selective membrane and solid contact were optimized to ensure suitable analytical features in potentiometric transduction. The sensing layer consisted of Imprinted Sol-Gel (ISG) materials capable of establishing surface interactions with MC-LR. Non-Imprinted Sol-Gel (NISG) membranes were used as negative control. The effects of an ionic lipophilic additive, time of sol-gel polymerization, time of extraction of MC-LR from the sensitive layer, and pH were also studied. The solid contact was made of carbon, aluminium, titanium, copper or nickel/chromium alloys (80 : 20 or 90 : 10). The best ISG sensor had a carbon solid contact and displayed average slopes of 211.3 mV per decade, with detection limits of 7.3 × 10(-10) M, corresponding to 0.75 μg L(-1). It showed linear responses in the range of 7.7 × 10(-10) to 1.9 × 10(-9) M of MC-LR (corresponding to 0.77-2.00 μg L(-1)), thus including the limiting value for MC-LR in waters (1.0 μg L(-1)). The potentiometric-selectivity coefficients were assessed by the matched potential method for ionic species regularly found in waters up to their limiting levels. Chloride (Cl(-)) showed limited interference while aluminium (Al(3+)), ammonium (NH(4)(+)), magnesium (Mg(2+)), manganese (Mn(2+)), sodium (Na(+)), and sulfate (SO(4)(2-)) were unable to cause the required potential change. Spiked solutions were tested with the proposed sensor. The relative errors and standard deviation obtained confirmed the accuracy and precision of the method. It also offered the advantages of low cost, portability, easy operation and suitability for adaptation to flow methods.     

在线固相萃取/高效液相色谱法测定环境水样中的4种痕量邻苯二甲酸酯

建立了一种在线固相萃取/高效液相色谱测定水样中4种痕量邻苯二甲酸酯(邻苯二甲酸甲酯、邻苯二甲酸乙酯、邻苯二甲酸丁酯和邻苯二甲酸(2-乙基)己酯)的新方法.样品由外加泵注入一根固相萃取小柱上进行富集,再将富集柱切换至高效液相色谱系统中,将富集在固相萃取小柱的邻苯二甲酸酯洗脱至分析柱进行分析.在线固相萃取柱为IonPac(...     

The novel assay method for nicotine metabolism to cotinine using high performance liquid chromatography

Nicotine is the primary psychoactive component in tobacco. It is taken into the body by tobacco smoking, and mainly metabolized to cotinine in the hepatic cytochrme P450 (CYP) 2A6. The objective of this study was to develop a sensitive method for the determination of nicotine metabolism to cotinine using HPLC. The internal standard, trans-4'-carboxycotinine methyl ester was synthesized with a simple method. The nicotine and cotinine were separated completely and detected by C(18) 5-μm analytical column (L-column Octa decyl silyl (ODS), 150 mm × 4.6 mm i.d.) equipped with a C(18) 5-μm guard column (L-column ODS, 10 mm × 4.6 mm i.d.) and ultraviolet detection at 260 nm. The detection limit of the assay was 0.05 μM for cotinine (n=5, R.S.D) and 0.1 μM for nicotine. Thus the present results provided a sensitive and useful method for the determination of nicotine metabolism catalyzed by CYP2A6.     

Probing the binding kinetics of proinflammatory cytokine-antibody interactions using dual color fluorescence cross correlation spectroscopy

Dual color fluorescence cross correlation spectroscopy (FCCS) was used to investigate quantitatively the binding kinetics of tumor necrosis factor (TNFα) with TNFα antibody (anti-TNFα) following fluorescent labeling. Through the analysis of the auto correlation curves of fluorescence correlation spectroscopy (FCS), diffusion coefficients of 100.06 ± 4.9 μm(2) s(-1) and 48.96 ± 2.52 μm(2) s(-1) for Alexa488-TNFα and Atto647N-anti-TNFα were obtained. In addition, the calculated hydrodynamic diameters of the Alexa488-TNFα and Atto647N-anti-TNFα were approximately 4.89 ± 0.24 nm and 9.99 ± 0.52 nm, respectively, which agrees with the values of 5.20 ± 1.23 nm and 9.28 ± 0.86 nm for the native TNFα and the anti-TNFα as determined from dynamic light scattering measurements. For the binding kinetics, association (k(on)) and dissociation (k(off)) rate constants were (1.13 ± 0.08) × 10(4) M(-1) s(-1) and (1.53 ± 0.19) × 10(-3) s(-1) while the corresponding dissociation constant (K(d)) at 25 °C was (1.36 ± 0.10) × 10(-7) M. We believe this is the first report on the binding kinetics for TNFα-antibody recognition in the homogeneous phase. Using this technology, we have shown that controlled experiments can be performed to gain insight into molecular mechanisms involved in the immune response.     

Rapid ultraviolet monitoring of multiple psychotropic drugs with a renewable microfluidic device

A rapid method for sensitive ultraviolet detection of multiple psychotropic drugs in human plasma was developed on a low-cost and expediently fabricated hybrid microfluidic device. The device was composed of one fused-silica capillary with a sampling fracture, a poly(methyl methacrylate) board with four reservoirs, and a printed circuit board. At the optimal separation and detection conditions, the baseline separation of three kinds of psychotropic drugs including barbiturates (phenobarbital and barbital), benzodiazepines (nitrazepam, clonazepam, chlordiazepoxide, alprazolam and diazepam) and tricyclic antidepressant drugs (amitriptyline) was achieved within 200 s with separation efficiency up to 3.80 × 10(5) plates m(-1). The linear ranges for ultraviolet detection were from 2.0 to 1000.0 μg mL(-1) for chlordiazepoxide and 1.0 to 1000.0 μg mL(-1) for other seven drugs. Combining with solid-phase extraction, this novel protocol could successfully be used to screen naturally existing psychotropic drugs in a known human plasma sample. The minimum detectable concentration was down to 27 ng mL(-1) for phenobarbital spiked in plasma. This work provided a promising way to initially screen different psychotropic drugs with high resolution, rapid separation and low-cost.     

Blood separation on microfluidic paper-based analytical devices

A microfluidic paper-based analytical device (μPAD) for the separation of blood plasma from whole blood is described. The device can separate plasma from whole blood and quantify plasma proteins in a single step. The μPAD was fabricated using the wax dipping method, and the final device was composed of a blood separation membrane combined with patterned Whatman No.1 paper. Blood separation membranes, LF1, MF1, VF1 and VF2 were tested for blood separation on the μPAD. The LF1 membrane was found to be the most suitable for blood separations when fabricating the μPAD by wax dipping. For blood separation, the blood cells (both red and white) were trapped on blood separation membrane allowing pure plasma to flow to the detection zone by capillary force. The LF1-μPAD was shown to be functional with human whole blood of 24-55% hematocrit without dilution, and effectively separated blood cells from plasma within 2 min when blood volumes of between 15-22 μL were added to the device. Microscopy was used to confirm that the device isolated plasma with high purity with no blood cells or cell hemolysis in the detection zone. The efficiency of blood separation on the μPAD was studied by plasma protein detection using the bromocresol green (BCG) colorimetric assay. The results revealed that protein detection on the μPAD was not significantly different from the conventional method (p > 0.05, pair t-test). The colorimetric measurement reproducibility on the μPAD was 2.62% (n = 10) and 5.84% (n = 30) for within-day and between day precision, respectively. Our proposed blood separation on μPAD has the potential for reducing turnaround time, sample volume, sample preparation and detection processes for clinical diagnosis and point-of care testing.     

Analysis of carbofuran, carbosulfan, isoprocarb, 3-hydroxycarbofuran, and 3-ketocarbofuran by micellar electrokinetic chromatography

We developed an analytical method for the detection and quantitation of five pesticides and some of their metabolites - 3-hydroxycarbofuran, 3-ketocarbofuran, carbofuran, carbosulfan, and isoprocarb - using micellar electrokinetic chromatography coupled with a UV-Vis detector. The optimum separation conditions were 20 mM phosphate buffer (pH 8.0) containing 15 mM sodium dodecyl sulfate. The detection wavelength was set at 200 nm and the applied voltage was 12.5 kV. Under these conditions, baseline separation of five pesticides was achieved in 15 min, and the detection limits (S/N = 3) of 3-hydroxycarbofuran, 3-ketocarbofuran, carbofuran, carbosulfan, and isoprocarb were 0.3, 0.3, 0.3, 4.0, and 0.3 μM, respectively. The linear ranges for 3-hydroxycarbofuran, 3-ketocarbofuran, carbofuran, and isoprocarb were between 1.0 and 50.0 μM and that for carbosulfan was between 10.0 and 100.0 μM, with R(2) larger than 0.995. When applied to the analysis of a carbofuran-spiked rice sample, this approach yielded results with excellent repeatability (3.3%, n = 5), reproducibility (4.5%, n = 5), separation efficiency (>2.1 × 10(4) theoretical plates), and recovery (95.5 ± 1.4%, n = 5).     

Fabrication of high-aspect-ratio poly(2-hydroxyethyl methacrylate) brushes patterned on silica surfaces by very-large-scale integration process

We used a novel fabricated process including electron beam and isotropic oxygen plasma to generate signal line patterns of polymerized 2-hydroxyethyl methacrylate (HEMA) on patterned Si(1 0 0) surfaces. Isotropic oxygen plasma was introduced to enhance the resolutions of the line and dots patterns of the PHEMA brush are approached to 350 nm and 2 μm, respectively. We established the surface grafting polymerization kinetics of the PHEMA chains on silicon surface by to fit the thickness and number-average molecular weight (M(n)). The propagation rate (k(p)) and active grafting specie deactivation rate (k(d)) lies in the range of ~3.6 × 10(-2) s(-1) M(-1) and 4.8 × 10(-5) s(-1), respectively. The measured thicknesses by ellipsometer and analyzed M(n) of "free" PHEMA by gel permeation chromatography (GPC) are fitted well by the polymerization kinetic model. In addition, aspect-ratios (height/width) are used to define the shape of patterned PHEMA brushes. The high-aspect-ratio of the PHEMA brush line with width of 350 nm is 0.27. We use a graft polymerization/solvent immersion method for generating various patterns of polymer brushes to investigate the deformation of the PHEMA brush through aspect-ratios.     

Simultaneous determination of copper, mercury and zinc in water with a tailored fluorescent bipyridine ligand entrapped in silica sol-gel

A novel fluorescent ligand, (4-[(E)-2-(4'-methyl-2,2'-bipyridin-4-yl)vinyl]phenol) (abbreviated BSOH), has been designed and prepared for simultaneous determination of heavy metals in water. Its photophysical and photochemical properties in the absence and in the presence of Cd(II), Cu(II), Hg(II), Ni(II) and Zn(II) were determined, and the respective complexation constants (7.4 × 10(3)-2.8 × 10(8) l mol(-1)) and stoichiometries were extracted thereof. The Stern-Volmer emission intensity and lifetime plots indicate an efficient static quenching of the indicator dye with the heavy metals. The BSOH fluorescent reagent has been successfully immobilised in a silica sol-gel matrix for automation of the analytical method, and the sensing phase demonstrated a reversible response to Cu(II), Hg(II) and Zn(II) but not to Cd(II) and Ni(II). Characterisation of the sensor showed that its response to those heavy metals is linear in the 2.5 to 50 μmol l(-1) range, with a response time (t (90)) on the order of 100 min, providing detection limits of 9.0 × 10(-7), 4.7 × 10(-7) and 2.9 × 10(-7) mol l (-1) for Zn(II), Cu(II) and Hg(II), respectively. Due to the stability of the immobilised ligand, which presented no leaching from the sol-gel matrix, the simultaneous determination of the three cations in water was feasible by employing multivariate calibration techniques coupled to fluorescence quenching measurements. The sensor was validated with recovery tests by addition of Cu(II) and Hg(II) ions to spring waters, providing results with standard errors lower than 4.1 μmol l (-1).     

Integration of single cell injection, cell lysis, separation and detection of intracellular constituents on a microfluidic chip

A microfluidic system was developed for the analysis of single biological cells, with functional integration of cell sampling, single cell loading, docking, lysing, and capillary electrophoretic (CE) separation with laser induced fluorescence (LIF) detection in microfabricated channels of a single glass chip. Channels were 12 microm deep and 48 microm wide, with a simple crossed-channel design. The effective separation channel length was 35 mm. During sampling with a cell suspension (cell population 1.2 x 10(5) cells per mL in physiological salt solution), differential hydrostatic pressure (created by adjusting liquid levels in the four reservoirs) was used to control cell flow exclusively through the channel crossing. Single cell loading into the separation channel was achieved by electrophoretic means by applying a set of potentials at the four reservoirs, counteracting the hydrostatic flow. A special docking (adhering) procedure for the loaded cell was applied before lysis by repeatedly connecting and disconnecting a set of low potentials, allowing precise positioning of the cell within the separation channel. Cell lysis was then effected within 40 ms under an applied CE separation voltage of 1.4 kV (280 V cm(-1)) within the working electrolyte (pH 9.2 borate buffer) without additional lysates. The docked lysing approach reduced dispersion of released intracellular constituents, and significantly improved the reproducibility of CE separations. Glutathione (GSH) was used as a model intracellular component in single human erythrocyte cells. NDA derivatized GSH was detected using LIF. A throughput of 15 samples h(-1), a retention time precision of 2.4% RSD was obtained for 14 consecutively injected cells. The average cellular concentration of GSH in human erythrocytes was found to be 7.2 [times] 10(-4)+/- 3.3 x 10(-4) M (63 +/- 29 amol per cell). The average separation efficiency for GSH in lysed cells was 2.13 x 10(6)+/- 0.4 x 10(6) plates per m, and was about a factor of 5 higher than those obtained with GSH standards using pinched injection.     

A thin-layer contactless conductivity cell for detection in flowing liquids

The design is described of a thin-layer contactless conductivity detector suitable for liquid chromatography and flow-injection analysis. Its principal analytical parameters have been determined using a potassium chloride solution: the linear dynamic range extends from 7.5 × 10⁻⁶ to 1.5 × 10⁻² S m⁻¹, corresponding to the KCl concentration range from 0.5 to 1000 μM, the limit of detection equals 3.5 × 10⁻⁶ S m⁻¹ (0.2 μM KCl), the detection repeatability, expressed in terms of the relative standard deviation, amounts to 1.13% and the detection volume is 0.6 μL. The detector was applied to detection of ionic compounds, benzoic, lactic and octanesulfonic acids, and sodium capronate, after their separation by liquid chromatography in a Biospher PSI 100C 18 columns using a 60% aqueous acetonitrile mobile phase. The frequency characteristics of the detector are reasonably theoretically described on the basis of a simple model which is commonly used in the field of contactless impedance detectors.