Mode-filtered light methane gas sensor based on cryptophane A

A mode-filtered light sensor has been developed for methane (CH₄) gas determination at ambient conditions. The proposed chemosensor consisted of an annular column which was constructed by inserting an optical fiber coated with a thin silicone cladding of cryptophane A into a fused-silica capillary. When CH₄ was introduced to the sensor, selective inclusion of CH₄ into the silicone layer would cause a change in the local refractive index of the cladding, resulting in the change of mode-filtered light that emanated from the fiber. Three detection windows were set alongside the capillary to propagate the light to a charge-coupled device (CCD). The changes of mode-filtered light on exposure to various concentrations of CH₄ were thus simultaneously monitored. The mode-filtered light intensity decreased with the increase in concentration of CH₄. The dynamic concentration range of the sensor for CH₄ was 0.0-16.0% v/v with a detection limit of 0.15% v/v. The highest sensitivity was found at the channel furthest away from the excitation light source. The response time (t_95%) was about 5 min. The reproducibility was good with a relative standard deviation (RSD) of less than 7% from evaluating six cryptophane A-coated fibers. Oxygen, hydrogen and carbon dioxide showed very little interference on detection but interferences from dichloromethane and carbon tetrachloride were observed. The proposed mode-filtered light sensor has been successfully applied to determine CH₄ samples and the accuracy was good. Our work offers a promising approach for CH₄ detection.     

Synchronization of separation and determination based on multichannel mode-filtered light detection with capillary electrophoresis.

A novel method for the synchronization of separation and determination is described, in which a mode-filtered light detector is used as an online detector in capillary electrophoresis. An instrument is described which has been developed for this purpose. The round capillary used in conventional capillary electrophoresis is replaced by an annular column, which is constructed from a naked optical fibre inserted into a fused-silica capillary. In fact, the annular electrophoresis column itself forms part of the mode-filtered light sensor. Along the side of the annular column are several detection channels for gathering and transmitting the mode-filtered light to a charge-coupled device (CCD). Every channel provides information on the sample from the point at which it is located. Using capillary isotachophoresis incorporating the annular column, the analytes in a sample containing alanine (10.0 mM) and glycine (9.7 mM) were simultaneously separated and determined using multichannel mode-filtered light detection with a detection limit of 1.5 mM.     

Study on mode-filtered light sensor for methane detection

A novel mode-filtered light gas sensor has been reported.It was constructed by inserting an optical fiber deposited by a thin silicone cladding of cryptophane A into a fused-silica capillary.When different concentration of methane gas was introduced to the sensor,the phenomenon that mode-filtered light intensity decreased with the increasing concentration of methane was observed. And a linear relationship was obtained within the methane concentration range of 0.0-16.0%(v/v).The detection limit was 0.06% ...     

A novel sensor of potassium ions based on mode-filtered light detection

<正>A novel potassium ions sensor based on mode-filtered light detection was reported.The analyzer was consisting of an optical fiber immobilized with a dye of bromocresol green and a fused-silica capillary.It was found that mode-filtered light intensity decreased with the concentration of potassium ions and a linear detection range of 0.25-20 mmol/L(R~2 = 0.9977) was obtained with a detection limit of 9×10~(-5) mol/L as well as fast response,good reproducibility and reversibility in the working concentration range.     

Fiber-Optic Sucrose Sensor Based on Mode-Filtered Light Detection

A mode-filtered light fiber-optic sucrose sensor was constructed from an annular column consisting of a bare optical fiber inserted into a capillary tube. A series of standard solutions with different concentrations of sucrose were measured by the sensor. The response range of the sucrose solution is 0%–60% (w/w). A linear relationship was found between the strength of the mode-filtered light and the sucrose concentration, with a correlation coefficient of 0.9994. The sensor exhibits good reproducibility and reversibility, as well as good standardized recovery for real samples. Thus, a real-time, fast, and sensitive determination method for sucrose concentration has been established.     

Non-aqueous capillary electrophoresis with red light emitting diode absorbance detection for the analysis of basic dyes

Non-aqueous capillary electrophoresis was evaluated for the separation of five hydrophobic basic blue dyes for application in forensic dye analysis. The use of a red light emitting diode as a high intensity, low-noise light source provided sensitive detection of the blue dyes while also allowing the evaluation of solvents that absorb strongly in the UV region. Excellent peak shapes and separation selectivity were obtained in methanol, ethanol, acetonitrile and dimethylsulfoxide, however water, tetrahydrofuran, dimethylformamide and acetone were unsuitable as solvents due to poor peak shapes and a lack of sensitivity, most likely due to adsorption onto the capillary wall. Due to the known compatibility of methanol with capillary electrophoresis–mass spectrometry, this solvent was examined further with the relative acidity/basicity of the electrolyte being optimised with an artificial neural network. The optimised method was examined for the separation of ink samples from 6 fibre tip and 2 ball point blue or black pens and showed that a unique migration time for the main dye component in seven of the eight pens could be obtained.     

Residue Analysis of Oxytetracycline in Water and Sediment Samples by High-Performance Liquid Chromatography and Immunochemical Techniques

A simple photochemical method for the determination of ethanol using a flow-injection system is proposed. The method is based on the photo-oxidation of ethanol in the presence of UO₂²⁺ and Fe³⁺ upon irradiation with visible light. The Fe²⁺ produced in the photochemical process was monitored by measuring the absorbance after complexation with ferrozine. The range of measurements depended on the length of the irradiation time. The sample throughput was 60 samples h^–1. The usefulness of the method was demonstrated by determining ethanol levels in different beverages.     

Development of headspace solid-phase microextraction-gas chromatography-mass spectrometry methodology for analysis of terpenoids in Madeira wines

A dynamic headspace solid-phase microextraction methodology was developed for analysis of varietal aroma compounds in must and Madeira wine samples, a spirit wine with an ethanol content of 18% (v/v). The factors with influence in the headspace solid-phase microextraction efficiency such as: fibre coating, extraction time and temperature, pH, ionic strength, ethanol content, desorption time and temperature, were optimised and the method validated. The best results were obtained for a 85 μm polyacrylate fibre, with a 60 min headspace for must and 120 min for wine samples, in a 2.4 ml sample at 40 °C with 30% of NaCl. The extract is injected in the splitless mode in a GC-MS Varian system, Saturn III, and separated on a Stabilwax capillary column. The linear dynamic range of the method covers the normal range of occurrence of analytes in wine with typical r² between 0.985 (β-ionone) and 0.998 (linalool) for musts and between 0.980 (α-terpineol) and 0.999 (linalool) for must and wine samples, respectively. For must samples the reproducibility ranges from 2.5% (citronellol) to 14.4% (nerolidol) (as R.S.D.), and from 4.8% (citronellol) to 14.2% (nerolidol) for wine samples. The analysis of spiked samples has shown that matrix effects do not significantly affect method performance. Limits of detection obtained are in low μg l⁻¹ range for all compounds analysed in this study.     

Automatic flow procedure for the determination of ethanol in wine exploiting multicommutation and enzymatic reaction with detection by chemiluminescence

An automatic procedure for the determination of ethanol in wines using a flow system based on multicommutation and enzymatic reaction is described. Alcohol oxidase was immobilized on aminopropyl glass beads and packed in an acrylic column. The peroxide due to enzymatic reaction with ethanol reacted with luminol and generated the chemiluminescence radiation that was monitored by using a laboratory-made detector based on photodiodes. The system manifold comprised a set of 3-way solenoid valves controlled by a microcomputer furnished with electronic interfaces, which ran on software written in Quick BASIC 4.5 to provide facilities to perform on-line sample dilution, reagent addition, and data acquisition. After system parameters optimization, ethanol samples were processed without prior pretreatment. The following suitable features were achieved: linear response ranging from 2.5 to 25% (v/v) ethanol, relative standard deviation of 1.8% (n = 10), detection limit of 0.3% (v/v) ethanol, sampling rate of 23 determinations per hour, and low reagent consumption of 0.23 mg luminol and 7 mg hexacyanoferrate (III) per determination. When the results were compared with those obtained using the AOAC Official Method, no significant difference at the 90% confidence level was observed.     

Isotachophoretic separation of cetyltrimethylammonium bromide

Capillary isotachophoresis (ITP), equipped with the conductivity detection, was tested for the separation of cetyltrimethylamonium (CTMA) bromide. To prevent adsorption of CTMA to the capillary walls, several neutral polymers and ethanol were added into the leading electrolytes. Unlike polymer additives, the CTMA free monomers and micelles, created as a result of the isotachophoretic concentration effect, were recognised in the presence of ethanol from 10 to 25% (v/v). At 30% of ethanol, only a single zone of CTMA monomer was registered because the micellization process did not take place under this condition.Employing an ITP apparatus in the column-coupling configuration, the operational system with 30% of ethanol was tested for the determination of CTMA in hair conditioners. The achieved detection limits were about 0.02 mM. Both model solutions and real samples of hair conditioners were analysed with the precision about R.S.D. = 3%. One analysis in the column-coupled system takes circa 15 min.     

Some factors affecting enantiomeric impurity determination by capillary electrophoresis using ultraviolet and laser-induced fluorescence detection.

The key factors influencing enantiomer trace determination were investigated; these include resolution capillary diameter, limit of detection, linear range and type of detection. Chiral reagents, (+)- and (-)-1-(9-fluorenyl)ethyl chloroformate (FLEC), were employed as probes to demonstrate the influence of the variables. In order to find the best resolution, separation variables were optimized in both capillary zone electrophoresis (CZE) and micellar electrokinetic capillary chromatography (MEKC) modes by the application of factorial design experiments. A highly efficient chiral separation of the (+/-)-FLEC, derivatized with nonchiral amino acids, was achieved when using gamma-cyclodextrin as the chiral selector. The benefits of using a small diameter capillary for direct determination of both (+) and (-)-FLEC impurity (0.05-0.1% area/area) were demonstrated using UV detection and applying a sample stacking condition. A frequency-doubled argon ion laser (244 nm) was used as light source for laser-induced fluorescence (LIF) detection. Excitation light was provided by means of an optical fiber directed into the Hewlett Packard 3D capillary cartridge. The signals from UV and LIF were monitored simultaneously. The application of LIF detection greatly improved sensitivity and linear range. Further, as a consequence of the increased sensitivity, sample loading could be decreased, which led to an improvement of separation efficiency. Direct determination of 0.005% impurity could be achieved within the linear range.     

Separation and quantitation of milk whey proteins of close isoelectric points by on-line capillary isoelectric focusing--electrospray ionization mass spectrometry in glycerol-water media

On-line coupling between CIEF and ESI/MS based on the use of bare fused-silica capillaries and glycerol-water media, recently developed in our laboratory, has been investigated for the separation of milk whey proteins that present close pI values. First, a new rinsing procedure, compatible with MS detection, has been developed to desorb these rather hydrophobic proteins (α-casein (α-CN), bovine serum albumin (BSA), lactoferrin (LF)) from the inner capillary wall and to avoid capillary blockages. Common hydrochloric acid washing solution was replaced by a multi-step sequence based on the use of TFA, ammonia and ethanol. To achieve the separation of major whey proteins (β-lactoglobulin A (β-LG A), β-lactoglobulin B (β-LG B), α-lactalbumin (α-LA) and BSA, which possess close pI values (4.5-5.35), CIEF parameters i.e. carrier ampholyte nature, capillary partial filling length with ampholyte/protein mixture and focusing time, have been optimized with respect to total analysis time, sensitivity and precision on pI determination. After optimization of sheath liquid composition (80:20 (v/v) methanol-water+1% HCOOH), quantitation of β-LG A, β-LG B, α-LA and BSA was performed. The limits of detection obtained from extracted ion current (EIC) and single ion monitoring (SIM) modes were in the 57-136 nM and 11-68 nM range, respectively. Finally, first results obtained from biological samples demonstrated the suitability of CIEF-MS as a potential alternative methodology to 2D-PAGE to diagnose milk protein allergies.     

Gas-diffusion dilution flow-injection method for the determination of ethanol in beverages without sample pretreatment

The combination of immobilized alcohol oxidase (AOD) with a gas-diffusion membrane in a flow-injection system greatly enhanced the specificity of ethanol determination. This gas-diffusion flow-injection system with amperometric detection of hydrogen peroxide had a linear range of analysis from 0.0006 up to 60% (v/v) ethanol. Silicone-modified polypropylene membranes of different thickness were used. Undiluted samples of beer, wine, spirits and medicine could be investigated with excellent correlation with standard methods (r > 0.997). The frequency of analysis was 120–180 samples h^?1 and the operational half-life of the immobilized enzyme was 8000 injections within 44 h.     

In-column fiber-optic laser-induced fluorescence detection for CE

A highly sensitive in-column fiber-optic LIF detector for CE has been constructed and evaluated. In this detection system, a 457-nm diode-pumped solid-state blue laser was used as the excitation light source and an optical fiber (40 mum od) was used to transmit the excitation light. One end of the optical fiber was inserted into the separation capillary and was in situ positioned at the detection window. The other end of the fiber was protruded from the capillary to capture the excitation light beam from the blue laser. Fluorescence emission was collected by a 40 x microscope objective, focused on a spatial filter, and passed through a yellow color filter before reaching the photomultiplier tube. The present CE-fluorescence detection is a simple and compact optical system. It reduces the laser scattering effect from the capillary and fiber as compared to the conventional LIF detection for CE. Its utility was successfully demonstrated by the separation and determination of D-penicillamine labeled with naphthalene-2,3-dicarboxaldehyde. The detection limit was 0.8 nM (S/N = 3). The present detection scheme has been proven to be attractive for sensitive fluorescence detection for CE.     

Development of miniaturized multi-channel high-performance liquid chromatography for high-throughput analysis

We have developed miniaturized multi-channel high-performance liquid chromatography (HPLC) system. With this system, we can simultaneously separate multiple samples, using a single high-pressure gradient pump, a chip-based sample injection unit, a monolithic silica capillary column array, and a multi-channel UV detection unit based on fiber optics. The injection unit has a simplified structure composed of brass housing and a quartz microchip having microchannels and access ports, which enable a direct injection of sample to multi-channel by commercial multichannel micropipette. Moreover, that possesses a function of microvalve, and on-chip definition of sample injection plugs achieved with a cross channel injection method, providing each column of monolithic silica capillary array. The substances in channels were simultaneously detected with UV having multiple cells. Standard samples were analyzed for characterizing newly developed system, and sharp peaks were obtained with reproducibility data of < 0.9% (R.S.D.). Analysis of tryptic digestion of casein was also employed. These results show that the novel multi-channel HPLC system has the benefits for the high-throughput analysis in the post-genomic analysis/combinatorial chemistry.     

Ionic liquids as selectors for the enhanced detection of proteins

Herein, we report an approach for protein detection enhanced by ionic liquid (IL) selectors in capillary electrophoresis (CE), with avidin as a model protein. Hydrophilic ILs were added into the running buffer of CE and acted as selectors for sample injection, enriching the positive target and excluding the negative from the capillary. When using 3 % (v/v) IL selector, the detection sensitivity of avidin was improved by over one order of magnitude, while the interference from protein adsorption was effectively avoided, even in an uncoated capillary. The electrochemiluminescence method was initially used for IL-based CE with low noise that was independent of the IL concentration, making ILs almost transparent as additives in the electrophoresis buffer.     

Gas chromatographic sensing on an optical fiber by mode-filtered light detection

A chemical sensor for gas phase measurements is reported which combines the principles of chemical separation and fiber optic detection. The analyzer incorporates an annular column Chromatographic sensor, constructed by inserting a polymer-clad optical fiber into a silica capillary. Light from a helium-neon laser is launched down the fiber, producing a steady intensity distribution within the fiber, but a low background of scattered light. When sample vapor is introduced to the sensor, and an analyte-rich volume interacts with the polymer cladding, Chromatographic retention is observed simultaneously with a change in the local refractive index of the cladding. An increase in cladding refractive index (RI) causes light to be coupled out of the fiber, with detection at a right-angle to the annular column length to provide optimum S/N ratio. This detection mechanism is called mode-filtered light detection. We report a gas Chromatographic separation on a 3.1 m annular column (320 microm i.d. silica tube, 228 microm o.d. fiber with a 12 microm fluorinated silicone clad) of methane, benzene, butanone and chlorobenzene in 6 min. The annular column length was reduced to 22 cm to function as a sensor, with selected organic vapors exhibiting unique retention times and detection selectivity. The detection selectivity is determined by the analyte RI and the partition coefficient into the cladding. The calculated limit of detection (LOD) for benzene vapor is 0.03% by volume in nitrogen, and several chlorinated species had LOD values less than 1%. For binary mixtures of organic vapors, the detected response appears to be the linear combination of the two organic standards, suggesting that the annular column may be useful as a general approach for designing chemical sensors that incorporate separation and optical detection principles simultaneously.     

A simple and compact fluorescence detection system for capillary electrophoresis and its application to food analysis

A novel fluorescence detection system for CE was described and evaluated. Two miniature laser pointers were used as the excitation source. A Y‐style optical fiber was used to transmit the excitation light and a four‐branch optical fiber was used to collect the fluorescence. The optical fiber and optical filter were imported into a photomultiplier tube without any extra fixing device. A simplified PDMS detection cell was designed with guide channels through which the optical fibers were easily aligned to the detection window of separation capillary. According to different requirements, laser pointers and different filters were selected by simple switching and replacement. The fluorescence from four different directions was collected at the same detecting point. Thus, the sensitivity was enhanced without peak broadening. The fluorescence detection system was simple, compact, low‐cost, and highly sensitive, with its functionality demonstrated by the separation and determination of red dyes and fluorescent whitening agents. The detection limit of rhodamine 6G was 7.7 nM (S/N = 3). The system was further applied to determine illegal food dyes. The CE system is potentially eligible for food safety analysis.     

Determination of ultra trace levels of 1,2-dichloroethane in air by sample enrichment micromachined gas chromatography-differential mobility detection

A novel analytical procedure has been developed for the analysis of ultra trace levels of 1,2-dichloroethane (EDC) in air using sample enrichment in combination with micromachined gas chromatography (GC) and differential mobility detection (DMD). When compared to other contemporary GC techniques, such as GC-flame ionization detection, GC-electron capture detection, or GC-electrolytic conductivity detection, the employment of a DMD in combination with a preconcentrator provided better sensitivity and markedly improved selectivity. The increase in sensitivity reduces false-negative results, while the improvement in selectivity decreases the potential for false-positive results. Using the technique described, a complete analysis can be conducted in less than 10 min, with a detection limit of 0.7 ppb (v/v) of EDC and a short term precision of less than 6%. A correlation coefficient of 0.9988 was obtained over an EDC concentration range from 0.7 ppb to 36.4 ppb (v/v). The analytical system also has an on-board microTCD in series with the DMD, allowing both detector outputs to be monitored simultaneously. With the pre-concentration technique, the microTCD can detect EDC as low as 15 ppb (v/v) with a substantially enhanced linear dynamic range in addition to providing a confirmation means for the presence of EDC at the level cited.     

Thiamine analysis in biological media by capillary zone electrophoresis with a high-sensitivity cell

A capillary zone electrophoresis method with high-sensitivity cell (Z-cell) has been developed for the determination of thiamine in biological media (plasma, urine, saliva). The urine samples were diluted (1:1, v/v) in water and were directly injected into the apparatus. For the quantitative assay of thiamine in plasma it is necessary to precipitate the protein component. Good results were achieved by treating the sample with acetonitrile (1:3, v/v). Using a capillary with high sensitivity cell led to an approximately nine-fold improvement of the detection limit compared to standard capillaries and four-fold improvement compared to capillary with bubble cell. The samples in the biological media were analysed using a calibration curve for thiamine concentrations between 0.1 and 200 microg ml(-1). The detection limit, the effective mobility and the relative standard deviation of the migration times and of the peak areas were determined.