A simplified ion exchange bead-based KOH electrodialytic generator for capillary ion chromatography

A simple potassium hydroxide electrodialytic generator (EDG) with singe membrane configuration is described. In this setup, one cation exchange resin (CER) bead is used to fabricate the EDG in place of the common membrane sheet. The device is implemented simply in a commercial stainless steel (SS) Tee which serves as both the EDG cartridge and the cathodic electrode. The present EDG has much lower internal volume (∼0.16 (L), which is well suited with capillary ion chromatography system. The device has been tested up pressures to 3200 psi and could be directly deployed on the high-pressure side of the pump. The electrolysis gas can be effectively removed by a segment of PTFE tubing. In the tested range of 0-100 mM, the KOH concentration is generated linearly with the applied current being near-Faradaic efficiency. The device permits both isocratic and gradient operation with good reproducibility, as demonstrated by the analysis of anions.     

Electrochemically generated multifunctional suppressor for ion chromatography

Summary A multifunctional suppressor for both anion and cation chromatography has been designed. The suppressor comprises five thin chambers—an anion eluent suppressive chamber, a cation eluent suppressive chamber, a cathode chamber, an anode chamber, and a common electrode chamber, all of which are clipped together. An electrochemical process—electrolysis of deionized water or detector effluent—is used to regenerate the suppressor for continuous operation. Two power sources are used to supply current. The device can work as an anion suppressor, a cation suppressor, or as both anion and cation suppressors, with high suppression capacity (60 mmol L⁻¹) and good reproducibility (RSD=0.80–0.91%) and linearity (r=0.9992).     

Physico-chemical transformations in swift heavy ion modified poly(ethyleneterephthalate)

Thin films of poly(ethyleneterephthalate) (PET) were exposed to different radiation dose brought about by 80 MeV carbon and 98 MeV silicon ion beam. The UV-vis absorption studies reveal that there is decrease in optical band gap energy to the extent of ∼29.3 and 42.1%. The X-ray diffraction analyses have shown that crystallite size decreased by ∼18.6 and 52.6%, indicating amorphization of PET. The colour of PET films change from colourless to light yellowish followed by light brown as radiation dose is increased. The colour formation has been ascribed to an increase in conjugation in the carbon chain. In the case of PET irradiated with carbon ion, the electrical conductivity increased with frequency beyond a threshold value of 1 kHz. The increase in conductivity of PET films on irradiation is due to formation of defects and carbon clusters as a result of polymer chain scission. The thermal study further confirmed the increase in amorphous nature with increase in radiation dose. The results indicate that radiation dose brings about significant physicochemical transformations in PET.     

Integrated chemical sensor array platform based on a light emitting diode, xerogel-derived sensor elements, and high-speed pin printing

We report a new, solid-state, integrated optical array sensor platform. By using pin printing technology in concert with sol-gel-processing methods, we form discrete xerogel-based microsensor elements that are on the order of 100 μm in diameter and 1 μm thick directly on the face of a light emitting diode (LED). The LED serves as the light source to excite chemically responsive luminophores sequestered within the doped xerogel microsensors and the analyte-dependent emission from within the doped xerogel is detected with a charge coupled device (CCD). We overcome the problem of background illumination from the LED reaching the CCD and the associated biasing that results by coating the LED first with a thin layer of blue paint. The thin paint layer serves as an optical filter, knocking out the LEDs red-edge spectral tail. The problem of the spatially-dependent fluence across the LED face is solved entirely by performing ratiometric measurements. We illustrate the performance of the new sensor scheme by forming an array of 100 discrete O₂-responsive sensing elements on the face of a single LED. The combination of pin printing with an integrated sensor and light source platform results in a rapid method of forming (∼1 s per sensor element) reusable sensor arrays. The entire sensor array can be calibrated using just one sensor element. Array-to-array reproducibly is <8%. Arrays can be formed using single or multiple pins with indistinguishable analytical performance.     

A cation exchange resin bead-based microscale electrolytic suppressor for capillary ion chromatography

A cation exchange resin (CER) bead-based microscale electrolytic suppressor for capillary ion chromatography (CIC) has been fabricated and evaluated. Relative to common ion exchange membrane, the use of CER beads presents a simple way to fabricate a microscale suppressor due to its small surface area and spherical shape. The internal volume of the device is ∼600 nL, which matches the requirements by CIC. Continuous online regeneration is readily achieved using pure water or diluted sulfuric acid as the regenerant. The use of a cation exchange functionalized monolithic segment inserted between two CER beads greatly reduces the electrical resistance and improves the suppression efficiency. The device works well only in the electrolytic mode, chemical regeneration alone is ineffective. The suppressed background is ∼3 μS/cm for 10 mM KOH eluent generated online by a microscale KOH electrolytic generator operated at the flow rate of 3 μL/min. The preliminary application for capillary ion chromatography has been demonstrated.     

Ion chromatographic system with a novel switching suppression device

Ion chromatography (IC) has been a powerful tool for measuring ionic species in environmental samples such as tap, river and drain waters. Suppressor modules (membrane and disposable column types) have been used for reducing the background of a baseline. A new type of suppressor device, which has a suppressor resin and switching valve was developed. Fresh ionic resin is introduced into a groove for each analysis to perform the suppression of the working eluent. The eluent composition for obtaining higher sensitivity and better resolutions among ionic species and carbonate ion was also investigated. Although carbonate buffers are used for ion separation in general, the separation of carbonate ion from other ions was not achieved. A borate eluent resulted in good resolutions and higher sensitivity. A new column was also developed for obtaining higher column efficiency and resolution. The optimization of anion separation using a new IC system (IC-2001) that consists of a new suppressor device, an anion-exchange column (TSKgel SuperIC-Anion, 150x4.6 mm), an autosampler, a conductivity cell and a pump in a compact module is described.     

Graphene-based field effect transistor in two-dimensional paper networks

We demonstrate the fabrication of a graphene-based field effect transistor (GFET) incorporated in a two-dimensional paper network format (2DPNs). Paper serves as both a gate dielectric and an easy-to-fabricate vessel for holding the solution with the target molecules in question. The choice of paper enables a simpler alternative approach to the construction of a GFET device. The fabricated device is shown to behave similarly to a solution-gated GFET device with electron and hole mobilities of ∼1256 cm² V⁻¹ s⁻¹ and ∼2298 cm² V⁻¹ s⁻¹ respectively and a Dirac point around ∼1 V. When using solutions of ssDNA and glucose it was found that the added molecules induce negative electrolytic gating effects shifting the conductance minimum to the right, concurrent with increasing carrier concentrations which results to an observed increase in current response correlated to the concentration of the solution used.     

A disposable laser print-cut-laminate polyester microchip for multiplexed PCR via infra-red-mediated thermal control

Infrared (IR)-mediated thermal cycling system, a method proven to be a effective for sub-μL scale polymerase chain reaction (PCR) on microchips, has been integrated with DNA extraction and separation on a glass microchip in a fully integrated micro Total Analysis System by Easley et al., in 2006. IR-PCR has been demonstrated on both glass and PMMA microdevices where the fabrication (bonding) is not trivial. Polyester-toner (PeT) microfluidic devices have significant potential as cost-effective, disposable microdevices as a result of the ease of fabrication (∼$0.25 USD and <10 min per device) and availability of commercial substrates. For the first time, we demonstrate here the thermal cycling in PeT microchips on the IR-PCR system. Undesirable IR absorption by the black-toner bonding layer was eliminated with a spatial filter in the form of an aluminum foil mask. The solution heating rate for a black PeT microchip using a tungsten lamp was 10.1 ± 0.7 °C s⁻¹ with a cooling rate of roughly −12 ± 0.9 °C s⁻¹ assisted by forced air cooling. Dynamic surface passivation strategies allowed the successful amplification of a 520 bp fragment of the λ-phage genome (in 11 min) and a 1500 bp region of Azospirillum brasilense. Using a centrosymmetric chamber configuration in a multichamber PeT microchip, homogenous temperature distribution over all chambers was achieved with inter-chamber temperature differences at annealing, extension and denaturing steps of less than ±2 °C. The effectiveness of the multichamber system was demonstrated with the simultaneous amplification of a 390 bp amplicon of human β-globin gene in five PeT PCR microchambers. The relative PCR amplification efficiency with a human β-globin DNA fragment ranged from 70% to 90%, in comparison to conventional thermal cyclers, with an inter-chamber standard deviation of ∼10%. Development of PeT microchips for IR-PCR has the potential to provide rapid, low-volume amplification while also integrating PCR with extraction upstream and separation/detection downstream.     

Automated on-line liquid–liquid extraction system for temporal mass spectrometric analysis of dynamic samples

Most real samples cannot directly be infused to mass spectrometers because they could contaminate delicate parts of ion source and guides, or cause ion suppression. Conventional sample preparation procedures limit temporal resolution of analysis. We have developed an automated liquid–liquid extraction system that enables unsupervised repetitive treatment of dynamic samples and instantaneous analysis by mass spectrometry (MS). It incorporates inexpensive open-source microcontroller boards (Arduino and Netduino) to guide the extraction and analysis process. Duration of every extraction cycle is 17 min. The system enables monitoring of dynamic processes over many hours. The extracts are automatically transferred to the ion source incorporating a Venturi pump. Operation of the device has been characterized (repeatability, RSD = 15%, n = 20; concentration range for ibuprofen, 0.053–2.000 mM; LOD for ibuprofen, ∼0.005 mM; including extraction and detection). To exemplify its usefulness in real-world applications, we implemented this device in chemical profiling of pharmaceutical formulation dissolution process. Temporal dissolution profiles of commercial ibuprofen and acetaminophen tablets were recorded during 10 h. The extraction-MS datasets were fitted with exponential functions to characterize the rates of release of the main and auxiliary ingredients (e.g. ibuprofen, k = 0.43 ± 0.01 h⁻¹). The electronic control unit of this system interacts with the operator via touch screen, internet, voice, and short text messages sent to the mobile phone, which is helpful when launching long-term (e.g. overnight) measurements. Due to these interactive features, the platform brings the concept of the Internet-of-Things (IoT) to the chemistry laboratory environment.     

Dielectrophoresis assisted immuno-capture and detection of foodborne pathogenic bacteria in biochips

This study integrated dielectrophoresis (DEP) with non-flow through biochips to enhance the immuno-capture and detection of foodborne pathogenic bacteria. It demonstrated two major functions provided by DEP to improve the chip performance: (i) concentrating bacterial cells from the suspension to different locations on the chip surface by positive and negative DEP; (ii) making the cells in close contact with the immobilized antibodies on the chip surface so that immuno-capture efficiency can be dramatically enhanced.The microchip achieved the immuno-capture efficiencies of ∼56.0% and ∼64.0% to Salmonella cells with 15 and 30 min DEP, respectively, which were considerably higher than those of ∼10.4% and ∼17.6% for 15 and 30 min immuno-capture without DEP. The immuno-captured bacterial cells were detected by the sandwich format ELISA on the chips. The final absorbance signals were enhanced by DEP assisted immuno-capture by 64.7-105.2% for the samples containing 10³-10⁶ cells/20 μl. The integration of DEP with the biochips has the potential to advance the chip-based immunoassay methods for microbial detection.     

Gas-phase separation using a trapped ion mobility spectrometer

In the present work we describe the principles of operation, versatility and applicability of a trapped ion mobility spectrometer (TIMS) analyzer for fast, gas-phase separation of molecular ions based on their size-to-charge ratio. Mobility-based separation using a TIMS device is shown for a series for isobar pairs. In a TIMS device, mobility resolution depends on the bath gas velocity and analysis scan speed, with the particularity that the mobility separation can be easily tuned from low to high resolution (R?>?50) in accordance with the analytical challenge . In contrast to traditional drift tube IMS analyzer, a TIMS device can be easily integrated in a mass spectrometer without a noticeable loss in ion transmission or sensitivity, thus providing a powerful separation platform prior to mass analysis.     

离子色谱的抑制系统及相关技术的发展

抑制系统是抑制型(双柱型)离子色谱系统极为重要的一个组成部分,也是离子色谱有别于其它类型的液相色谱的最重要特点之一。抑制器的发展经历了多个发展时期,而目前商品化的离子色谱仪亦分别采用不同形式的抑制手段。近年来,还发展了一些特殊的辅助抑制器,如接在抑制器后面CO2除去装置,用于提高被测离子的信号或进一步降低背景电导值。     

Humidity independent mass spectrometry for gas phase chemical analysis via ambient proton transfer reaction

In this work, a humidity independent mass spectrometric method was developed for rapid analysis of gas phase chemicals. This method is based upon ambient proton transfer reaction between gas phase chemicals and charged water droplets, in a reaction chamber with nearly saturate humidity under atmospheric pressure. The humidity independent nature enables direct and rapid analysis of raw gas phase samples, avoiding time- and sample-consuming sample pretreatments in conventional mass spectrometry methods to control sample humidity. Acetone, benzene, toluene, ethylbenzene and meta-xylene were used to evaluate the analytical performance of present method. The limits of detection for benzene, toluene, ethylbenzene and meta-xylene are in the range of ∼0.1 to ∼0.3 ppbV; that of benzene is well below the present European Union permissible exposure limit for benzene vapor (5 μg m⁻³, ∼1.44 ppbV), with linear ranges of approximately two orders of magnitude. The majority of the homemade device contains a stainless steel tube as reaction chamber and an ultrasonic humidifier as the source of charged water droplets, which makes this cheap device easy to assemble and facile to operate. In addition, potential application of this method was illustrated by the real time identification of raw gas phase chemicals released from plants at different physiological stages.     

A novel surface ionization source for ion mobility spectrometer

A surface ionization (SI) source is designed and prepared for ion mobility spectrometer (IMS). The source acts not only as an emitter but also an ion injector which can inject ions periodically into the drift region of drift tube. Using the dual-role source, the dimension of the drift tube can be decreased and the circuit for high voltage can be simplified efficiently. The IMS with the SI source has a response range of ∼4 orders of magnitude and a good reproducibility to tri-ethylamine. Compared with radioactive ionization (RI), the ultra-short time for ion injection and the zero level base line of ion mobility spectrum are characteristics of the surface ionization.     

Environmental remediation by an integrated microwave/UV illumination technique: VI. A simple modified domestic microwave oven integrating an electrodeless UV-Vis lamp to photodegrade environmental pollutants in aqueous media

A simple device is described based on a modified domestic microwave oven that incorporates an UV-Vis lamp encased in Teflon to photodegrade environmental pollutants in aqueous media. The performance of this device was examined using the photodegradation of the agrochemical pollutant 2,4-dichlorophenoxyacetic acid (2,4-D) as the test process driven by a coupled photocatalytic/microwave method in an aqueous TiO₂ dispersion. The aqueous dispersion was contained in a high-pressure Teflon batch (TB) reactor that also integrated a double glass cylindrical plasma lamp (DGCPL) as the source of the UV-Vis radiation. This DGCPL lamp contained mercury gas with a minute amount of neon gas and was powered solely by microwave radiation. The coupled microwave-UV-Vis irradiation of the TB-DGCPL reactor led to an enhancement of the decomposition of the 2,4-D target substrate in the modified microwave oven relative to the photocatalytic method alone. Specifically, the rates of degradation were 2×10⁻³ mM min⁻¹ (photocatalytic/microwave method (PD/MW)) and 1.1×10⁻³ mM min⁻¹ (photocatalytic method (PD)) even though the light irradiance was some six-fold greater in the latter method. That is, the coupled PD/MW method was about 10 times more efficient than the PD method alone.     

Superhydrophobic polyethylcyanoacrylate coatings. Contact area with water measured by Raman spectral images, contact angle and Cassie-Baxter model

Apolar fibers wired into a mesh-like microstructure forming a coating with a contact angle larger than 160° and fabricated by polycyanoacrylate polymerization are described. Interconnected fibers with diameters measuring approximately 5 μm are formed by texturized linear or folded nanowires. The structure forming the deposited film occupies ∼1.5% of the coating’s top geometric area. This value agrees with the water/coating contact area given by the Cassie-Baxter contact-angle model (∼1.5%). The spatial distribution of the surface in contact with water was determined by Raman spectral imaging (∼1.5%) using the polycyanoacrylate lines and by scanning electron microscopy (∼2.0%).     

An improved pyrolysis route to synthesize carbon-coated CdS quantum dots with fluorescence enhancement effect

Well-dispersed carbon-coated CdS (CdS@C) quantum dots were successfully prepared via the improved pyrolysis of bis(1-dodecanethiol)-cadmium(II) under nitrogen atmosphere. This simple method effectively solved the sintered problem resulted from conventional pyrolysis process. The experimental results indicated that most of the as-prepared nanoparticles displayed well-defined core-shell structures. The CdS cores with diameter of ∼5 nm exhibited hexagonal crystal phase, the carbon shells with thickness of ∼2 nm acted as a good dispersion medium to prevent CdS particles from aggregation, and together with CdS effectively formed a monodisperse CdS@Carbon nanocomposite. This composite presented a remarkable fluorescence enhancement effect, which indicated that the prepared nanoparticles might be a promising photoresponsive material or biosensor. This improved pyrolysis method might also offer a facile way to prepare other carbon-coated semiconductor nanostructures.     

Flow-injection analysis with a small cylindrical wire type electrode

An amperometric detector with a small thin mercury film electrode is described. The device demonstrates advantageous operational characteristics such as small dispersion (D<2) and “memory effect” (me<0.6%), extensive maximum sample frequency (msf −200 samples/h), and high sensitivity. It has been proven useful in flow-injection analysis at a constant potential under hydrodynamic conditions.     

Evaluation of sorption of uranium onto metakaolin using X-ray photoelectron and Raman spectroscopies

Metakaolin prepared from a natural clay mineral ore of aluminium kaolinite is a promising low cost and high activity aluminosilicate material that has been investigated for studying the sorption behavior of uranium. Here, metakaolin was characterized using X-ray photoelectron spectroscopy (XPS) and the effects of pH, contact time and initial metal ion concentration on its sorption behavior were studied. The sorption process was found to initially be rapid (∼60% at time 0 min) but became slower with time; equilibrium was established within 24 h (∼80% sorption). The data were applied to study the kinetics of the sorption process. The Langmuir and Dubinin-Radushkevich (D-R) sorption isotherms were used to describe partitioning behavior for the system at room temperature. The binding of metal ions was found to be pH dependent, with optimal sorption occurring at pH 5. The retained metal ions were eluted with 5 mL of 0.1 M HNO₃. Raman spectroscopy and XPS were used to evaluate the sorption mechanism of U(VI).     

Integrated internal standards: A sample prep‐free method for better precision in microchip CE

Point‐of‐care systems based on microchip capillary electrophoresis require single‐use, disposable microchips prefilled with all necessary solutions so an untrained operator only needs to apply the sample and perform the analysis. While microchip fabrication can be (and has been) standardized, some manufacturing differences between microchips are unavoidable. To improve analyte precision without increasing device costs or introducing additional error sources, we recently proposed the use of integrated internal standards (ISTDs): ions added to the BGE in small concentrations which form system peaks in the electropherogram that can be used as a measurement reference. Here, we further expand this initial proof‐of‐principle test to study a clinically‐relevant application of K ion concentrations in human blood; however, using a mock blood solution instead of real samples to avoid interference from other obstacles (e.g. cell lysis). Cs as an integrated ISTD improves repeatability of K ion migration times from 6.97% to 0.89% and the linear calibration correlation coefficient (R²) for K quantification from 0.851 to 0.967. Peak area repeatability improves from 11.6–13.3% to 4.75–5.04% at each K concentration above the LOQ. These results further validate the feasibility of using integrated ISTDs to improve imprecision in disposable microchip CE devices by demonstrating their application for physiological samples.