Improving the Detectability of Sequential Injection Chromatography (SIC): Determination of Triazines by Exploiting Liquid Core Waveguide (LCW) Detection

Coupling a liquid core waveguide cell to a sequential injection chromatograph improved the detection limits for determination of triazine herbicides without compromising peak resolution. Separation of simazine, atrazine, and propazine was achieved in water samples by a 25 mm long C₁₈ monolithic column. Detection was made at 238 nm using a type II LCW (silica capillary coated with Teflon® AF2400) cell with 100 cm of optical path length. Detection limits for simazine, atrazine, and propazine were 2.3, 1.9, and 4.5 µg L^?1, respectively. Reduced analysis time and low solvent consumption are other remarkable features of the proposed method.     

基于液芯波导原理的微流控芯片长光程光度检测系统

提出了一种基于液芯波导(Liquidcorewaveguide,LCW)原理的微流控芯片吸收光度检测系统.通过芯片与外界接口技术实现液芯波导管与芯片的耦合,建立了芯片上长光程(毫米至厘米级)吸收光度检测池.采用邻菲啉-铁(Ⅱ)显色体系验证系统分析性能,以5.5cm外覆TeflonAF液芯波导管作为检测池(检测池体积240nL)时,芯片系统的检测线性范围为0.03～50μmol/L,对邻菲啉-铁(Ⅱ)配合物的检出限为8nmol/L,检测池有效光程达1.7cm,分析精度RSD(n=5)为0.8%.     

Liquid core waveguide-based optical spectrometry for field estimation of dissolved BTEX compounds in groundwater: A feasibility study

The utility of a liquid core waveguide (LCW) system for acting as a sentry monitor for compounds such as benzene, toluene, ethylbenzene, xylene (BTEX) in water was examined. A vapor-permeable LCW suitable for long path length absorbance spectroscopy based on a Teflon AF 2400 tube was fabricated. Multiwavelength spectroscopy in the near-UV was carried out using a fiber optic-based flashlamp-photodiode array (PDA) combination with hexane as the solvent in the waveguide core. Using multicomponent calibration, quantitation of benzene and toluene accurate to 6±5% could be conducted at sub-mg l⁻¹ levels in mixtures after a sampling period of 10 min.     

Reverse flow injection analysis of nanomolar soluble reactive phosphorus in seawater with a long path length liquid waveguide capillary cell and spectrophotometric detection

A novel reverse flow injection analysis method coupled with a liquid waveguide capillary cell (LWCC) and spectrophotometric detection for the determination of nanomolar soluble reactive phosphorus in seawater was established. Reagent was injected into the sample stream and detected in a 2-m path length LWCC with detection wavelength set at 710 nm. Experimental parameters, including the reagent concentration, the injection volume, the flow rate and the length of the mixing coil, were optimized based on univariate experimental design. The interference of silicate and arsenate were also investigated. Under optimized conditions, the linearity and the detection limit of the proposed method were found to be 0-165.0 nM and 0.5 nM, which was estimated to be three times the standard deviation of the measurement blanks (n = 9). The relative standard deviations for the determination of 24.7 and 82.5 nM samples were 1.54% and 1.86% (n = 9), respectively. Three seawater samples were analyzed with recoveries ranging from 87.8% to 101.8%. Using the Student's t-test at the 95% confidence level, the results of the proposed method and a segmented flow analyzer reference method for determination of the two samples showed no significant difference. The proposed method had the advantages of being less reagent consuming, more sensitive and with higher throughput (15 h⁻¹).     

Microfluidic device capable of sensing ultrafast chemiluminescence

Based on the principle of liquid core waveguide, a novel microfluidic device with micro-scale detection window capable of sensing flashlight emitted from rapid 1,1′-oxalyldi-4-methylimidazole (OD4MI) chemiluminescence (CL) reaction was fabricated. Light emitted from OD4MI CL reaction occurring in the micro-dimensional pentagonal detection window (length of each line segment: 900.0 μm, depth: 50.0 μm) of the microfluidic device with two inlets and one outlet was so bright that it was possible to take an image every 1/30 s at the optimal focusing distance (60 cm) using a commercial digital camera. Peaks obtained using a flow injection analysis (FIA) system with the micro-scale detection window and OD4MI CL detection show excellent resolution and reproducibility without any band-broadening observed in analytical devices having additional reaction channel(s) to measure light generated from slow CL reaction. Maximum height (H_max) and area (A) of peak, reproducibility and sensitivity observed in the FIA system with the microfluidic device and OD4MI CL detection depends on (1) the mole ratio between bis(2,4,6-trichlorophenyl) oxalate and 4-methyl imidazole yielding OD4MI, (2) the flow rate to mix OD4MI, H₂O₂ and 1-AP in the detection window of the microfluidic device, and (3) H₂O₂ concentration. We obtained linear calibration curves with wide dynamic ranges using H_max and A. The detection limit of 1-AP determined with H_max and A was as low as 0.05 fmole/injection (signal/background = 3.0).     

A novel long path length absorbance spectroscopy for the determination of ultra trace organophosphorus pesticides in vegetables and fruits

A simple, rapid, sensitive and reproducible spectrophotometry for determination of ultra trace organophosphorus pesticides (OPs) with liquid core waveguide light intensity technique is presented. OPs were degraded into phosphate with UV light, potassium peroxydisulphate as oxidant and nanosized titanium dioxide as catalyst. Under the optimum selected conditions, linear light intensity response was obtained in the range of 2.0 x 10(-11) to 8.0 x 10(-10)g mL(-1) phosphate, and the limit of detection (LOD) 6.7 x 10(-12)g mL(-1) was achieved. Both the low limit of linear range and the LOD of the proposed method were lower over 1000-fold than that of classical spectrophotometry. The proposed method was applied to the determination of ultra trace OPs in vegetables and fruits samples.     

Ferrozine colorimetry and reverse flow injection analysis (rFIA) based method for the determination of total iron in aqueous solutions at nanomolar concentrations

Iron is one of the most microbiologically and chemically important metals in natural waters. The biogeochemical cycling of iron is significantly influenced by the redox cycling of Fe(II) and Fe(III). Because of the unique chemistry of iron, it is often needed to analyze iron at nano-molar concentrations. This article describes a reverse flow injection analysis (rFIA) based method with ferrozine spectrophotometric detection to quantify total iron concentration in stream water at nanomolar concentrations. The rFIA system has a 0.65 nM detection limit and a linear dynamic range up to 1.40 μM for the total iron analysis. The detection limit was achieved using a 1.0 m long liquid waveguide capillary flow cell, 1.50 m long knotted reaction coil, 87.50 μL injection loop and a miniature fiber optics spectrophotometer. The optimized colorimetric reagent has 1.0 mM ferrozine, 0.1 M ascorbic acid, 1.0 mM citric acid and 0.10 M acetate buffer adjusted to pH 4.0. The best sample flow rate is 2.1 mL min^?1 providing a sample throughput of more than 15 samples h^?1. The linear dynamic range of the method can be adjusted by changing the volume of the injection loop. The rFIA manifold was assembled exclusively from commercially available components.     

A disposable blood cyanide sensor

Deaths due to smoke inhalation in fires are often due to poisoning by HCN. Rapid administration of antidotes can result in complete resuscitation of the patient but judicious dosing requires the knowledge of the level of cyanide exposure. Rapid sensitive means for blood cyanide quantitation are needed. Hydroxocyanocobinamide (OH(CN)Cbi) reacts with cyanide rapidly; this is accompanied by a large spectral change. The disposable device consists of a pair of nested petri dish bottoms and a single top that fits the outer bottom dish. The top cover has a diametrically strung porous polypropylene membrane tube filled with aqueous OH(CN)Cbi. One end of the tube terminates in an amber (583 nm) light emitting diode; the other end in a photodiode via an acrylic optical fiber. An aliquot of the blood sample is put in the inner dish, the assembly covered and acid is added through a port in the cover. Evolved HCN diffuses into the OH(CN)Cbi solution and the absorbance in the long path porous membrane tube cell is measured within 160 s. The LOD was 0.047, 1.0, 0.15, 5.0 and 2.2 μM, respectively, for water (1 mL), bovine blood (100 μL, 1 mL), and rabbit blood (20 μL, 50 μL). RSDs were < 10% in all cases and the linear range extended from 0.5 to 200 μM. The method was validated against a microdiffusion approach and applied to the measurement of cyanide in rabbit and human blood. The disposable device permits field measurement of blood cyanide in <4 min.     

Absorbance characteristics of a liquid-phase gas sensor based on gas-permeable liquid core waveguides

The absorbance characteristics and influential factors on these characteristics for a liquid-phase gas sensor, which is based on gas–permeable liquid core waveguides (LCWs), are studied from theoretical and experimental viewpoints in this paper. According to theory, it is predicted that absorbance is proportional to the analyte concentration, sampling time, analyte diffusion coefficient, and geometric factor of this device when the depletion layer of the analyte is ignored. The experimental results are in agreement with the theoretical hypothesis. According to the experimental results, absorbance is time-dependent and increasing linearly over time after the requisite response time with a linear correlation coefficient r² > 0.999. In the linear region, the rate of absorbance change (RAC) indicates improved linearity with sample concentration and a relative higher sensitivity than instantaneous absorbance does. By using a core liquid that is more affinitive to the analyte, reducing wall thickness and the inner diameter of the tubing, or increasing sample flow rate limitedly, the response time can be decreased and the sensitivity can be increased. However, increasing the LCW length can only enhance sensitivity and has no effect on response time. For liquid phase detection, there is a maximum flow rate, and the absorbance will decrease beyond the stated limit. Under experimental conditions, hexane as the LCW core solvent, a tubing wall thickness of 0.1 mm, a length of 10 cm, and a flow rate of 12 mL min⁻¹, the detection results for the aqueous benzene sample demonstrate a response time of 4 min. Additionally, the standard curve for the RAC versus concentration is RAC = 0.0267 c + 0.0351 (AU min⁻¹), with r² = 0.9922 within concentrations of 0.5–3.0 mg L⁻¹. The relative error for 0.5 mg L⁻¹ benzene (n = 6) is 7.4 ± 3.7%, and the LOD is 0.04 mg L⁻¹. This research can provide theoretical and practical guides for liquid–phase gas sensor design and development based on a gas-permeable Teflon AF 2400 LCW.     

Performance of an in-plane detection cell with integrated waveguides for UV/Vis absorbance measurements on microfluidic separation devices

A microfluidic device with integrated waveguides and a long path length detection cell for UV/Vis absorbance detection is presented. The 750 microm U-cell detection geometry was evaluated in terms of its optical performance as well as its influence on efficiency for electrophoretic separations in the microdevice. Stray light was found to have a strong effect on both, the sensitivity of the detection and the available linear range. The long path length U-cell showed a 9 times higher sensitivity when compared to a conventional capillary electrophoresis (CE) system with a 75 microm inner diameter (ID) capillary, and a 22 times higher sensitivity than with a 50 microm ID capillary. The linear range was comparable to that achieved in a 75 microm ID capillary and more than twice as large as in a 50 microm ID capillary. The use of the 750 microm U-cell did not contribute significantly to band broadening; however, a clear quantification was made difficult by the convolution of several other band broadening sources.     

微流控液液萃取-液液波导集成化分析系统

利用溴化1-丁基-3-甲基咪唑离子液体/碳酸钠溶液双水相体系,实现了多相层流液液萃取.以具有较高折射率的离子液体为液芯,较低折射率的盐溶液为包层,实现了液液波导吸光度检测.据此建立了一种液液萃取与液液波导检测集成化的微流控分析系统.该系统对甲酚红试样的萃取率在93%以上,对甲酚红试样检测的线性范围为0.01~0.40 mg/m L,相对标准偏差为3.4%(n=11),检出限为3.8μg/m L(3σ).该系统将萃取分离与液液波导长光程吸光度检测集成在一起,为拓展吸光度检测在微流控系统中的应用提供了新思路.     

Sensitive detection of beryllium using a fiber optic liquid waveguide cell

The metallochromic chelating agent, Chromazurol S, has been utilized in conjunction with a fiber optic liquid waveguide capillary cell to enable the sensitive detection of beryllium in solution (30 ng l⁻¹ detection limit) and following extraction from a contaminated plexiglas surface (0.5 ng cm⁻² detection limit). The addition of a cationic surfactant, cetylpyridinium chloride, to Chromazurol S at pH 10 in Tris-HCl buffer results in the formation of two bathochromic peaks in the visible spectrum following metal chelation by beryllium. The first absorbance band, at 515 nm, is intermediate in nature, permitting maximal sensitivity for low beryllium concentrations, but diminishing in intensity at concentrations above 100 μg l⁻¹. The second absorbance band, centered at 610 nm, dominates for beryllium concentrations of 100 μg l⁻¹ and above. Experimental conditions including pH, buffer type, additive surfactants, masking agents, and dye concentration were investigated in order to optimize detection sensitivity and selectivity. A fiber optic spectrometer is used with both a liquid waveguide capillary cell and 1 cm cuvette cell, to give a sensitive and broad dynamic range for beryllium detection that capitalizes on both beryllium metal chelate absorbance bands formed under these conditions.     

Capillary scale light emitting diode based multi-reflection absorbance detector

We describe a light emitting diode (LED) based multi-reflection capillary scale absorbance detector based on both square and round capillaries and compare their performance with a conventional single-pass on-tube detector. The optical path length is extended by silver coating, the external surface of the capillary. The reflective geometry has been reported to be less prone to artifacts induced by refractive index changes; we do find this to be true. Although the detection volume/illuminated volume is increased some, a multi-reflection cell based on a 180 μm bore capillary with a ∼2-cm long illuminated volume shows over a 50-fold gain in signal-to-noise (S/N) compared to a single-pass on-tube configuration with the same capillary. The limit of detection (LOD) is 4.4 fmol (2.6 pg, 1 μL of 22.0 nM injected dye) BTB under pulseless (pneumatic) flow conditions. The cells behave as multipath devices where the effective path lengths are greater at low absorbance values. In our experiments, where non-coherent light is launched through optical fibers that are large compared to capillary bore dimensions, increase in the effective path length of the cell do not occur in a predictable fashion with the angle of incidence of the light beam. Although the effective path length almost linearly increases with increasing distance between the light entry and exit windows, the absolute values of the effective path lengths are always lower than this physical distance, suggesting that after some passage through the solution, light largely travels through or along the glass wall. Square capillaries have better light transmission and offer some performance advantages. Multi-reflection cells can indeed be of value for sensitive detection in microflow systems.     

液芯光纤长光路系统吸收测定卡马西平

液芯光纤长光路系统主要由聚光系统和液芯光纤长光路吸收管组成。采用不同长度的光纤管,用该系统吸收测定药物卡马西平(Carbamazepine),实验表明,吸光度要比郎伯-比尔定律预期值大。随着液芯光纤长度的增加,线性区域向更低浓度方向移动,因此,液芯光纤长光路系统更宜于作痕量元素分析。     

毛细管区带电泳法分离白花丹参中主要的水溶性活性成分

为建立一种快速分离白花丹参水溶性有效成分的毛细管区带电泳体系,分别考察了缓冲液浓度、缓冲液pH、运行电压、检测波长对样品的分离度、迁移时间等因素的影响。最终优化的分离条件为:5 mmol/L硼砂缓冲液（pH 7.5）;毛细管柱75 μm×60.2 cm,有效长度50 cm,压力进样(3.45 kPa×4 s),27.5 kV恒压分离,210 nm波长下检测,柱温25 ℃。在优化的条件下,8 min内使白花丹参样品中的原儿茶醛、丹参素、原儿茶酸组分达到完全基线分离。     

Application of advanced nuclear analytical techniques for the electrocatalyst's characterization: Paving the path for mechanistic investigations

As the application of electrocatalyst continues to expand, envisaging the hidden mechanisms occurring at various length scale affecting the catalytic efficiency became important. To enhance the stability of electrocatalyst and reduce the cost, it is of paramount importance to reveal the active site's dynamics (using in situ techniques for getting the real-time information) which directly affect the reactions such as oxygen evolution reaction, hydrogen evolution reaction, and so on. Since such reactions are crucial for many engineering and scientific applications, in situ characterization techniques are required, which could capture such reactions happening at a different length and time scale. This article analyzes the recent progress made in the field of electrocatalyst's characterization using in situ neutron techniques. The article also paves the future path and has delineated the future challenges involved in multiscale correlative techniques (e.g., neutron techniques in the combination of synchrotron or microscopic techniques) used for getting the multiscale (atomic to micrometer range) mechanistic information about the electrocatalyst's working and degradation.     

Spectrophotometric determination of zinc and copper in a multi-syringe flow injection analysis system using a liquid waveguide capillary cell: application to natural waters

This work exploits a multi-syringe injection analysis (MSFIA) system coupled with a long liquid waveguide capillary cell for the spectrophotometric determination of zinc and copper in waters. A liquid waveguide capillary cell (1.0 m pathlength, 550 μm i.d. and 250 μL internal volume) was used to enhance the sensitivity of the detection. The determination for both ions is based on a colorimetric reaction with zincon at different pH values. The developed methodology compares favourably with other previously described procedures, as it allows to reach low detection limits for both cations (LODs of 0.1 and 2 μg L⁻¹, for copper and zinc, respectively), without the need for any pre-concentration step. The system also provided a linear response up to 100 μg L⁻¹ with a high throughput (43 h⁻¹) and low reagent consumption and effluent production. The developed work was applied to natural waters and three certified reference water samples.     

A versatile total internal reflection photometric detection cell for flow analysis

A total internal reflection (TIR) flow-through cell that is highly tolerant of schlieren effects, has limited hydrodynamic dispersion and does not trap gas bubbles, and which is suitable for sensitive photometric measurements in flow analysis, is described. Light from an optical fibre is introduced into a short length of quartz capillary through the sidewall at an incident angle of ca. 53°. Under this condition, incident light undergoes total internal reflection from the external air-quartz interface and is propagated by successive reflections from the external walls through the aqueous liquid core of the cell. Detection of the transmitted beam is enabled by intentionally introducing an optical coupling medium at a predetermined distance along the capillary wall, which allows the internally reflected light to be captured by a second optical fibre connected to a charge-couple device detector.This configuration embodies a number of the desirable features of a liquid core waveguide cell (i.e. total internal reflection), a multi-reflection (MR) flow cell (i.e. minimum susceptibility to schlieren effects, low hydrodynamic dispersion and little tendency to trap bubbles), and a conventional Z-cell (wide dynamic range). When employed with a flow injection system, a limit of detection of 2.0 μg PL⁻¹ was achieved for the determination of reactive phosphate using the TIR cell, compared with LOD values of 3.8 μg PL⁻¹ and 4.9 μg PL⁻¹ obtained using the MR and Z-cells with same manifold.The combined advantages of schlieren-tolerance and lack of bubble entrapment of the MR cell with the higher S/N ratio and wider dynamic range of a conventional Z-cell, make the TIR cell eminently useful for photometric measurements of samples with widely differing refractive indices.     

多材料3D打印技术制作用于毛细管电泳的非接触电导/激光诱导荧光二合一检测池

利用多材料3D打印技术研制了用于毛细管电泳(CE)的二合一检测池,实现了电容耦合非接触电导(C⁴D)与共聚焦激光诱导荧光(LIF)两种检测方法在毛细管柱上同一位置同时检测。3D打印的检测池采用了导电的复合聚乳酸(PLA)材料制作C⁴D的屏蔽层,采用普通的绝缘PLA材料支撑C⁴D金属管电极并隔离屏蔽层。两根金属管电极通过“打印-暂停-打印”的方式嵌入到检测池中,两电极被2 mm厚的导电屏蔽层隔开,在屏蔽层中有一直径为1 mm的圆形通孔用于LIF检测。该检测池与带流通式进样接口的自组装CE系统联用,用于同时检测无机离子和异硫氰酸荧光素(FITC)标记的氨基酸。研究优化了C⁴D激励信号频率与电泳缓冲液浓度,选用的电泳缓冲溶液为10 mmol/L 3-吗啉丙烷-1-磺酸(MOPS)与10 mmol/L二(2-羟乙基)亚氨基三(羟甲基)甲烷(Bis-Tris)的混合溶液,选用C⁴D激励频率为77 kHz。二合一检测池应用于内径为25 μm的毛细管时,C ⁴D对Na⁺、K⁺和Li⁺的检出限分别为2.2、2.0和2.6 μmol/L; LIF对荧光素和FITC的检出限分别为7.6和1.7 nmol/L。两种检测方法的相对标准偏差在0.3%至4.5%之间(n=3),工作曲线的相关系数r ²≥0.9904。采用3D打印技术可以在实验室内实现复杂结构的制作,降低了制作的成本,且便于方法的推广和改进。     

Polycyclic aromatic hydrocarbons in food and beverages. Analytical methods and trends

Polycyclic aromatic hydrocarbons (PAHs) are compounds widespread in the environment, many of them showing carcinogenic effects. These compounds can reach the food chain by different ways and, therefore, the analysis of PAHs in food is a matter of concern. This article reviews the extraction methodologies together with the separation and detection techniques which are currently applied in the determination of PAHs in food and beverages. Specific extraction conditions, performance characteristics, chromatographic and detection parameters are discussed. A review of the occurrence of these compounds in the matrixes under study is also provided.