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.     

Application of a xenon arc lamp as a light source for evaporative light scattering detection

The standard tungsten-halogen light source used in a commercial evaporative light scattering detector (ELSD) was replaced with a 180 W xenon arc lamp. The xenon arc lamp possesses a broader spectrum in the UV region than the halogen source. The influence of the UV transmittance of five selected solvents was studied with a size-exclusion chromatography column. This solvent parameter was not observed to influence the ELSD response between the two light source settings. With the solvents studied, better sensitivity was obtained with the xenon arc lamp than the halogen lamp. This high-energy source was applied to ceramide III analysis with an octadecyl-grafted silica column and methanol:tetrahydrofuran 97:3 as the mobile phase, and the sensitivity of the quantification of ceramide III increased 16-fold for injected amounts of 14∼140 ng. The molecular species in a sample of naturally occurring ceramides was analyzed using two C18 columns at 40 °C and gradient elution from 100% acetonitrile to 100% isopropanol in 30 min. The increased ELSD sensitivity achieved when using the xenon arc lamp allowed both the minor and major ceramide species to be observed, in contrast to the results achieved when the halogen lamp was used, where the increased photomultiplier voltage needed to observed the signals from the minor species caused the signals from the major ceramide species to occur above the detector response window.     

Determination of radiation power of the solar-simulated light source

Calorimetric method for the determination of radiation power of the solar-simulated light sources has been proposed. The application of the differential scanning calorimetry guarantees very high sensitivity (1 mW) of the measuring property, independent of the wavelength (within 300-1200 nm). The applied method yields reliable calibration curves of the radiation power vs. wavelength with good accuracy. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

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.     

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.     

模式滤光光纤pH传感器的研究

采用溶胶-凝胶法将邻苯二酚紫涂覆在光纤上,然后将涂好的光纤插入毛细管中,构建新型的模式滤光光纤pH传感器.该传感器的模式滤光信号随pH的增加而降低,且在pH=6.0～9.0范围内有良好的线性关系(R=0.999),响应时间(t95％)为168 s,相对标准偏差为1.95％(n=6);而涂层中未加邻苯二酚紫的光纤传感器对...     

Anomalies in evaporative light scattering detection

A two-dimensional (2-D) “heart-cutting” HPLC system was used to fractionate oligostyrenes into the respective diastereoisomers. For samples of known composition, the response of an ultraviolet (UV) absorbance detector followed the anticipated pattern. The response of an evaporative light-scattering (ELSD) detector on the other hand indicated quite different concentrations for the two diastereoisomers, relative to what was anticipated and what was indicated by the UV detector. Whereas approximately the same concentration was indicated by UV, ELSD in some cases indicated no detection of the later eluting isomer. The magnitude of the errors depended on both the molecular weight and the tacticity of the diastereomers. These anomalies appear to be an artifact of power transform functions imbedded within the firmware processor of the ELSD, invisible to the user.     

Fibre coupled micro-light emitting diode array light source with integrated band-pass filter for fluorescence detection in miniaturised analytical systems

In this work, a new type of miniaturized fibre-coupled solid-state light source is demonstrated as an excitation source for fluorescence detection in capillary electrophoresis. It is based on a parabolically shaped micro-light emitting diode (μ-LED) array with a custom band-pass optical interference filter (IF) deposited at the back of the LED substrate. The GaN μ-LED array consisted of 270 individual μ-LED elements with a peak emission at 470 nm, each about 14 μm in diameter and operated as a single unit. Light was extracted through the transparent substrate material, and coupled to an optical fibre (OF, 400 μm in diameter, numerical aperture NA = 0.37), to form an integrated μ-LED-IF-OF light source component. This packaged μ-LED-IF-OF light source emitted approximately 225 μW of optical power at a bias current of 20 mA. The bandpass IF filter was designed to reduce undesirable LED light emissions in the wavelength range above 490 nm. Devices with and without IF were compared in terms of the optical power output, spectral characteristics as well as LOD values. While the IF consisted of only 7.5 pairs (15 layers) of SiO₂/HfO₂ layers, it resulted in an improvement of the baseline noise as well as the detection limit measured using fluorescein as test analyte, both by approximately one order of magnitude, with a LOD of 1 × 10⁻⁸ mol L⁻¹ obtained under optimised conditions. The μ-LED-IF-OF light source was then demonstrated for use in capillary electrophoresis with fluorimetric detection. The limits of detection obtained by this device were compared to those obtained with a commercial fibre coupled LED device.     

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.     

Comparison between evaporative light scattering detection and charged aerosol detection for the analysis of saikosaponins

Saikosaponins are triterpene saponins derived from the roots of Bupleurum falcatum L. (Umbelliferae), which has been traditionally used to treat fever, inflammation, liver diseases, and nephritis. It is difficult to analyze saikosaponins using HPLC-UV due to the lack of chromophores. Therefore, evaporative light scattering detection (ELSD) is used as a valuable alternative to UV detection. More recently, a charged aerosol detection (CAD) method has been developed to improve the sensitivity and reproducibility of ELSD. In this study, we compared CAD and ELSD methods in the simultaneous analysis of 10 saikosaponins, including saikosaponins-A, -B₁, -B₂, -B₃, -B₄, -C, -D, -G, -H and -I. A mixture of the 10 saikosaponins was injected into the Ascentis^® Express C18 column (100 mm × 4.6 mm, 2.7 μm) with gradient elution and detection with CAD and ELSD by splitting. We examined various factors that could affect the sensitivity of the detectors including various concentrations of additives, pH and flow rate of the mobile phase, purity of nitrogen gas and the CAD range. The sensitivity was determined based on the signal-to-noise ratio. The best sensitivity for CAD was achieved with 0.1 mM ammonium acetate at pH 4.0 in the mobile phase with a flow rate of 1.0 mL/min, and the CAD range at 100 pA, whereas that for ELSD was achieved with 0.01% acetic acid in the mobile phase with a flow rate at 0.8 mL/min. The purity of the nitrogen gas had only minor effects on the sensitivities of both detectors. Finally, the sensitivity for CAD was two to six times better than that of ELSD. Taken together, these results suggest that CAD provides a more sensitive analysis of the 10 saikosaponins than does ELSD.     

大科学装置同步辐射光源在生命分析化学中的应用

大科学装置的建设和水平是一个国家科技发展程度的标志. 同步辐射装置是一种先进的多学科交叉的高端大科学研究设施, 作为独特的宽光谱高亮度光源, 同步辐射光源提供了其他光源所无法比拟的优势. 我国迄今已建成的最大的大科学装置—— 上海光源的建立和应用是新中国成立60年来的重大成就之一, 标志着我国在建设国际先进水平的大型科学实验装置方面具备了高水平的技术和集成与创新的能力, 已进入国际先进行列. 本文侧重介绍同步辐射光源在生命分析化学领域中的巨大作用, 并以上海光源为例介绍同步辐射光源装置的发展和应用状况, 旨在唤起和推动我国分析化学家的高度重视, 并充分利用我国这一先进的大型科学装置, 将生命分析化学的研究推进到一个崭新的、更高的层次.     

A simple and compact blue diode laser powered excitation source for fluorescence detection in capillary electrochromatographic microchip separation

A simple and compact fluorescence excitation source was prepared using a 405 nm blue laser diode module and characterized in capillary electrochromatographic or capillary electrophoretic microchip separation. An inexpensive blue laser diode module with a tiny focusing lens was simply mounted at the center of an aluminum block on a miniature linear motion guide for heat dissipation and position control. A slit unit has a series of fifteen laser-machined slits with 1 mm space along the direction of the separation channel of the microchip above this unit. The laser beam was focused through a slit with 50 μm width to the separation channel at the position of a desired length. Although the excitation source unit was connected to a simple current controlled power supply, it was stable with 0.1% drift per hour and 1.3% (1σ) fluctuation in intensity. This simple excitation source can be prepared easily with inexpensive minimum optical components and mounted with a microchip on the stage of an ordinary fluorescence microscope for daily separation studies using a CE or CEC microchip. The applicability of the excitation source was evaluated with FITC-amino acid derivative mixtures using a polymer based CEC microchip packed fully with submicron silica beads in its microchannel.     

Progress in the development of techniques based on light scattering for single nanoparticle detection

Nanoparticles have recently attracted extensive attention in view of their great potential in biomedicine and bioanalytical ap- plications. Single particle detection via light scattering offers a simple and efficient approach for the size, size distribution, and concentration analysis of nanoparticles. In particular, intrinsic heterogeneity or rare events masked by ensemble averaging can be revealed. However, the sixth power dependence of Rayleigh scattering on particle size makes it very challenging to det...     

Pulsed multi-wavelength excitation using fiber-in-capillary light emitting diode induced fluorescence detection in capillary electrophoresis

A novel instrument was developed using a multi-wavelength pulsed LED array with in-column optic-fiber induced fluorescence detection by capillary electrophoresis. The light from 2 different wavelength LEDs (450 nm and 480 nm) was pulsed for short intervals at high intensity. The beam from each LED was collimated and reshaped with the gradient index (GRIN) lens group to achieve a highly effective coupling between LED light source and an optical fiber. The optical fiber was placed inside the capillary for in-capillary LED-induced fluorescence detection. The advantages of this system were validated by the simultaneous determination of vitamin B2 and fluorescein. Detection limits for vitamin B2 and fluorescein were estimated to be 5 nM and 0.29 nM (S/N = 3), respectively. The relative standard deviations (RSDs, n = 6) of the both compounds for migration time and peak area were better than 0.83%, 2.20% and 1.21%, 2.75%, respectively. The method was applied to the determination of vitamin B2 in commercial tablets and fluorescein in fluorescein sodium injection and the recoveries obtained were in the range of 96.6-102.0% and 99.9-102.8%, respectively. It was also applied to human serum, where the recoveries were found to be in the range of 94.4-97.0% and 92.6-96.4%, respectively. The system has been successfully applied in separation and determination of the both biological samples with acceptable analytical performance.     

Dual ambient plasma source ionization mass spectrometry for the rapid detection of trace sterols in urban water

A direct analytical method based on dual ambient plasma ion source tandem mass spectrometry was used for the simultaneous determination of four sterols in the environment. This technology has very high sensitivity and the method detects the four sterols in methanol–water (1:3) solutions with limits of detection (LOD) and limits of quantification (LOQ) ranging from 1.2 ng/L to 6.9 ng/L and 7.6 ng/L to 10.0 ng/L, respectively. The method was also used to test water quality at three locations within the city and successfully detected all four sterols at very low concentrations. The dual plasma source tandem mass spectrometry technique is extremely simple, rapid, sensitive and highly efficient compared to other traditional methods, providing a useful screening tool for sterols in water.     

Evaporative light scattering detection: trends in its analytical uses

Evaporative light scattering detection (ELSD) is widely recognized as a universal tool for liquid and supercritical chromatographies. In addition, this detection technique is fully compatible with continuous-flow systems. In fact, the combination of continuous non-chromatographic techniques and ELSD affords the design of simple, reliable systems for extracting qualitative information. This paper reviews instrumental innovations regarding the miniaturization of evaporative light scattering detectors and their uses in micro and capillary liquid chromatography; also, it discusses their increasingly important role in the development of vanguard configurations for sample screening and the determination of total indices without the need for chromatographic separation. Moreover, it compares them with other types of chromatographic detectors in terms of performance. Finally, the potential of ELSD for solving real-life analytical problems arising from the need to meet (bio)chemical information needs is illustrated with various selected applications. Figure New trends in evaporative light scattering detection: recent chromatographic uses and its role in vanguard/rearguard strategies     

Separation of monosaccharides by hydrophilic interaction chromatography with evaporative light scattering detection

Hydrophilic interaction liquid chromatography (HILIC) was used to separate monosaccharides that are common in N-linked oligosaccharides in glycoproteins and other compounds. A TSKgel Amide-80 column was eluted with 82% acetonitrile, in 5 mM ammonium formate (pH 5.5). Column temperature was 60 degrees C and evaporative light scattering was used for detection (ELSD). With this method, L-fucose, D-galactose, D-mannose, N-acetyl-D-glucosamine, N-acetylneuraminic acid, and D-glucuronic acid were separated, with detection limits of 0.3-0.5 microg for each monosaccharide, and intermediate precisions were 3-6% RSD (n=6).