Sensitive capillary electrophoresis microchip determination of trinitroaromatic explosives in nonaqueous electrolyte following solid phase extraction

Non-aqueous electrophoresis integrated with electrospray ionization mass spectrometry on a thiol-ene polymer-based microchip device

Non-aqueous capillary electrophoresis (NACE) on microfluidic chips is still a comparatively little explored area, despite the inherent advantages of this technique and its application potential for, in particular, lipophilic compounds. A main reason is probably the fact that implementation of NACE on microchips largely precluded the use of polymeric substrate materials. Here, we report non-aqueous electrophoresis on a thiol-ene-based microfluidic chip coupled to mass spectrometry via an on-chip ESI interface. Microchips with an integrated ESI emitter were fabricated using a double-molding approach. The durability of thiol-ene, when exposed to different organic solvents, was investigated with respect to swelling and decomposition of the polymer. Thiol-ene exhibited good stability against organic solvents such as methanol, ethanol, N-methylformamide, and formamide, which allows for a wide range of background electrolyte compositions. The integrated ESI emitter provided a stable spray with RSD% of the ESI signal ≤8%. Separation efficiency of the developed microchip electrophoresis system in different non-aqueous buffer solutions was tested with a mixture of several drugs of abuse. Ethanol- and methanol-based buffers provided comparable high theoretical plate numbers (≈ 6.6 × 10⁴-1.6 × 10⁵ m^-1) with ethanol exhibiting the best separation efficiency. Direct coupling of non-aqueous electrophoresis to mass spectrometry allowed for fast analysis of hydrophobic compounds in the range of 0.1-5 μg mL^-1 and 0.2-10 μg mL^-1 and very good sensitivities (LOD ≈ 0.06-0.28 μg mL^-1; LOQ ≈ 0.20-0.90 μg mL^-1). The novel combination of non-aqueous CE on a microfluidic thiol-ene device and ESI-MS provides a mass-producible and highly versatile system for the analysis of, in particular, lipophilic compounds in a wide range of organic solvents. This offers promising potential for future applications in forensic, clinical, and environmental analysis. Graphical abstract.

A Low-Cost Palmtop High-Speed Capillary Electrophoresis Bioanalyzer with Laser Induced Fluorescence Detection

In this work, we developed a miniaturized palmtop high-speed capillary electrophoresis (CE) system integrating whole modules, including picoliter-scale sample injection, short capillary-based fast CE, high-voltage power supply, orthogonal laser induced fluorescence (LIF) detection, battery, system control, on-line data acquisition, processing, storage, and display modules. A strategy of minimalist miniaturization combining minimal system design and low-cost system construction was adopted to achieve the instrument miniaturization with extremely low cost, which is differing from the current microfabrication strategy used in most reported miniaturized CE systems. With such a strategy, the total size of the bioanalyzer was minimized to 90 × 75 × 77 mm (length × width × height) and the instrument cost was reduced to ca. $500, which demonstrated the smallest and lowest-cost CE instrument with LIF detection in so far reported systems. The present bioanalyzer also exhibited comparable analytical performances to previously-reported high-speed CE systems. A limit of detection of 1.02 nM sodium fluorescein was obtained. Fast separations were achieved for multiple types of samples as amino acids, amino acid enantiomers, DNA fragments, and proteins with high efficiency. We applied this instrument in colorectal cancer diagnosis for detecting KRAS mutation status by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method.

High performance separation of quaternary amines using microchip non-aqueous electrophoresis coupled with contactless conductivity detection

This study describes the development of an analytical methodology for the separation of quaternary amines using non-aqueous microchip electrophoresis (NAME) coupled with capacitively coupled contactless conductivity detection (C⁴D). All experiments were performed using a commercial microchip electrophoresis system consisting of a C⁴D detector, a high-voltage sequencer and a microfluidic platform to assemble a glass microchip with integrated sensing electrodes. The detection parameters were optimized and the best response was reached applying a 700-kHz sinusoidal wave with 14V_pp excitation voltage. The running electrolyte composition was optimized aiming to achieve the best analytical performance. The mixture containing methanol and acetonitrile at the proportion of 90:10 (v:v) as well as sodium deoxycholate provided separations of ten quaternary amines with high efficiency and baseline resolution. The separation efficiencies ranged from 8.7×10⁴ to 3.0×10⁵ plates/m. The proposed methodology provided linear response in the concentration range between 50 and 1000μmol/L and limits of detection between 2 and 27μmol/L. The analytical feasibility of the proposed methodology was tested in the determination of quaternary amines in corrosion inhibitor samples often used for coating oil pipelines. Five quaternary amines (dodecyltrimethylammonium chloride, tetradecyltrimetylammonium bromide, cetyltrimethylammonium bromide, tetraoctylammonium bromide and tetradodecylammonium bromide) were successfully detected at concentration levels from 0.07 to 6.45mol/L. The accuracy of the developed methodology was investigated and the achieved recovery values varied from 85 to 122%. Based on the reported data, NAME-C⁴D devices exhibited great potential to provide high performance separations of hydrophobic compounds. The developed methodology can be useful for the analysis of species that usually present strong adsorption on the channel inner walls.

Capillary Electrophoretic Analysis of Classical Organic Pollutants

The synthesis and usage of a wide range of organic compounds have shown a considerable increase in the past few decades. Many of these compounds are potential pollutants for the environment. They differ from each other in their chemical structure and properties. Correspondingly different separation strategies are required for their separation. There is need to assess the human exposure to these chemicals and to identify and develop analytical methods for their identification. In this chapter we have presented some methods for the separation and the analysis of the organic pollutants like dyes, phenolic pollutants, phthalates, endocrine disrupting chemicals, polycyclic aromatic hydrocarbon, explosives, agricultural pesticides, and toxins.

Rapid determination of catecholamines in urine samples by nonaqueous microchip electrophoresis with LIF detection

Nonaqueous microchip electrophoresis (NAMCE), which makes use of an organic medium instead of a conventional aqueous buffer solution, is a promising separation method for analytical chemistry due to the enhanced solubility of hydrophobic analytes and tailored selectivity of separation. Here, we describe an NAMCE with LIF detection combined with a pump-free negative pressure sampling device for rapid determination of catecholamines (CAs) in urine samples, and the whole analysis time (including sampling time and separation time) was less than 1 min.

Coupling paper-based microfluidics and lab on a chip technologies for confirmatory analysis of trinitro aromatic explosives

A new microfluidic paper-based analytical device (μPAD) in conjunction with confirmation by a lab on chip analysis was developed for detection of three trinitro aromatic explosives. Potassium hydroxide was deposited on the μPADs (0.5 μL, 1.5 M), creating a color change reaction when explosives are present, with detection limits of approximately 7.5 ± 1.0 ng for TNB, 12.5 ± 2.0 ng for TNT and 15.0 ± 2.0 ng for tetryl. For confirmatory analysis, positive μPADs were sampled using a 5 mm hole-punch, followed by extraction of explosives from the punched chad in 30 s using 20 μL borate/SDS buffer. The extractions had efficiencies of 96.5 ± 1.7%. The extracted explosives were then analyzed with the Agilent 2100 Bioanalyzer lab on a chip device with minimum detectable amounts of 3.8 ± 0.1 ng for TNB, 7.0 ± 0.9 ng for TNT, and 4.7 ± 0.2 ng for tetryl. A simulated in-field scenario demonstrated the feasibility of coupling the μPAD technique with the lab on a chip device to detect and identify 1 μg of explosives distributed on a surface of 100 cm(2).

Optical chemosensors and reagents to detect explosives

This critical review is focused on examples reported from 1947 to 2010 related to the design of chromo-fluorogenic chemosensors and reagents for explosives (141 references).

Solid-phase extraction using hierarchical organosilicates for enhanced detection of nitroenergetic targets

A novel porous organosilicate material was evaluated for application as a solid phase extraction sorbent for preconcentration of nitroenergetic targets from aqueous solution prior to HPLC analysis. The performance of the sorbent in spiked deionized water, groundwater, and surface water was evaluated. Targets considered included 2,4,6-trinitrotoluene, 2,4-dinitrotoluene, RDX, HMX, and nitroglycerin. The sorbent was shown to provide improved performance over Sep-Pak RDX. The impact of complex matrices on target preconcentration by the sorbent was also found to be less dramatic than that observed for LiChrolut EN. The impact of changes in pH on target preconcentration was considered. Aqueous soil extracts generated from samples collected at sites of ordnance testing were also used to evaluate the materials. The results presented here demonstrate the potential of this novel sorbent for application as a solid phase extraction material for the preconcentration of nitroenergetic targets from aqueous solutions.

Fluorescence-based sensing of 2,4,6-trinitrotoluene (TNT) using a multi-channeled poly(methyl methacrylate) (PMMA) microimmunosensor

Fluorescence immunoassays employing monoclonal antibodies directed against the explosive 2,4,6-trinitrotoluene (TNT) were conducted in a multi-channel microimmunosensor. The multi-channel microimmunosensor was prepared in poly (methyl methacrylate) (PMMA) via hot embossing from a brass molding tool. The multi-channeled microfluidic device was sol-gel coated to generate a siloxane surface that provided a scaffold for antibody immobilization. AlexaFluor-cadaverine-trinitrobenzene (AlexaFluor-Cad-TNB) was used as the reporter molecule in a displacement immunoassay. The limit of detection was 1–10 ng/mL (ppb) with a linear dynamic range that covered three orders of magnitude. In addition, antibody crossreactivity was investigated using hexahydro-1,3,5-triazine (RDX), HMX, 2,4-dinitrotoluene (DNT), 4-nitrotoluene (4-NT) and 2-amino-4,6-DNT.

Absorbance Based Light Emitting Diode Optical Sensors and Sensing Devices

The ever increasing demand for in situ monitoring of health, environment and security has created a need for reliable, miniaturised sensing devices. To achieve this, appropriate analytical devices are required that possess operating characteristics of reliability, low power consumption, low cost, autonomous operation capability and compatibility with wireless communications systems. The use of light emitting diodes (LEDs) as light sources is one strategy, which has been successfully applied in chemical sensing. This paper summarises the development and advancement of LED based chemical sensors and sensing devices in terms of their configuration and application, with the focus on transmittance and reflectance absorptiometric measurements.

Capillary electrophoretic analysis of organic pollutants

Environmental pollutants comprise a variety of compounds from inorganic anions, cations, ionizable organic compounds and moderately hydrophobic organic compounds to highly hydrophobic organic compounds. Correspondingly different separation strategies are required for their separation. In this chapter, we have presented some methods for the separation and the analysis of the organic pollutants such as polycyclic aromatic hydrocarbons, phenoxy acids, dithiocarbamates, paraquat and diquat, endocrine disruptors, toxins and explosives.

An evaluation of the experimental approaches to detection of small ions in CE

This review points out some important trends in the development of the detection techniques for small ions in CE. On the basis of selected literature references it briefly discusses some general requirements on detection techniques in CE. Various optical measurements, mass spectrometric approaches and electrochemical detection techniques are dealt with. Some specific features of microchip CE separation and detection are pointed out and possibilities of dual detection are mentioned. The principal parameters of the above detection techniques are then briefly compared.

Sensors--an effective approach for the detection of explosives

The detection of explosives and explosive related illicit materials is an important area for preventing terrorist activities and for putting a check on their deleterious effects on health. A number of different methods, based on different principles, have been developed in the past for the detection of explosives. Sensors are one of those methods of detection which have capability to mimic the canine system and which are known to be the most reliable method of detection. The objective of this review is to provide comprehensive knowledge and information on the sensors operating on different transduction principles, ranging from electrochemical to immunosensors, being used for the detection of explosives as they pose a threat for both health and security of the nation. The review focuses mainly on the sensors developed in the recent 5 years and is prepared through summary of literature available on the subject.

CE detector based on light-emitting diodes

CE detectors based on light-emitting diodes (LEDs) as light sources are receiving considerable attention due to their exceptionally high stability, high intensity, low cost, and a variety of wavelengths in the UV and visible spectrum. This article is a comprehensive review on CE methods using LED-based detectors with absorbance and fluorescence detection, and several applications on the determination of riboflavin, bacteria, drug, and amino acids in biological samples are described.

Analysis of explosives via microchip electrophoresis and conventional capillary electrophoresis: a review

The upsurge in terrorist activity has generated tremendous demand for innovative tools capable of detecting major industrial, military, and home-made (improvised) explosives. Fast, sensitive, and reliable detection of explosives in the field is a very important issue in nowadays. CE, especially in its miniaturized format (lab-on-a-chip), offers great possibilities to create portable, field deployable, rapidly responding, and potentially disposable devices, allowing security forces to make the important decisions regarding the safety of civilians. This article overviews the microchip and conventional capillary electrophoretic techniques for analysis of a wide variety of explosive compounds and mixtures.

Micellar electrokinetic chromatography and capillary electrochromatography of nitroaromatic explosives in seawater

The ability to separate nitroaromatic and nitramine explosives in seawater sample matrices is demonstrated using both MEKC and CEC. While several capillary-based separations exist for explosives, none address direct sampling from seawater, a sample matrix of particular interest in the detection of undersea mines. Direct comparisons are made between MEKC and CEC in terms of sensitivity and separation efficiency for the analysis of 14 explosives and explosive degradation products in seawater and diluted seawater. The use of high-salt stacking with MEKC results, on average, in a three-fold increase in the number of theoretical plates, and nearly double resolution for samples prepared in 25% seawater. By taking advantage of long injection times in conjunction with stacking, detection limits down to sub mg/L levels are attainable; however, resolution is sacrificed. CEC of explosive mixtures using sol-gels prepared from methyltrimethoxysilane does not perform as well as MEKC in terms of resolving power, but does permit extended injection times for concentrating analyte onto the head of the separation column with little or no subsequent loss in resolution. Electrokinetic injections of 8 min at high voltage allow for detection limits of explosives below 100 microg/L.

Nonaqueous capillary electrophoretic assays ofp-phenylene-bis-4,4'-(1-aryl-2,6-diphenylpyridinium) molecular wires

A nonaqueous CE system for separation and detection of novel electron-dopable molecular wires based on p-phenylene-bis-4,4'-(1-aryl-2,6-diphenylpyridinium) oligomers is described. The method is based on the coupling of CE separation in pure organic solvent, DMF with 50 mM acetic acid, and UV detection at 338 nm. The system offers a rapid measurement in less than 20 min for two priority nanowires and their impurities. Calibration data confirmed linear response for all compounds of interest in the concentration range 0.1-1.0 mg/mL. A highly stable response was observed for repetitive injections (RSD < or = 2.8%, n = 10).

Fabrication of an integrated PDMS microchip incorporating an LED-induced fluorescence device

A microfluidic device with an integrated fluorescence detection system has been developed in order to miniaturize the entire analytical system. A blue or green light-emitting diode (LED) and an optical fiber were mounted in a polydimethylsiloxane-based microchip. The performance of this device was evaluated by microchip electrophoresis. When a green LED was used as the light source, the calibration curve of Sulforhodamine-101 was linear over the range 1-100 microM. The detection limit was found to be 600 nM (240 amol) for a S/N ratio of 3. When using a blue LED, the calibration curve of Fluorescein was linear over the range 0.2-100 microM. The detection limit was estimated to be 120 nM (50 amol) (S/N=3). The detection sensitivity per unit power was comparable to that of LIF. The RSD values for the migration time, peak height and peak area were 0.74, 7.18 and 9.45%, respectively. The integrated microfluidic device was successfully used to determine amino acid derivatives.

Rapid voltammetric determination of nitroaromatic explosives at electrochemically activated carbon-fibre electrodes

The electrochemical behaviour of some nitroaromatic explosives (2,4,6-trinitrotoluene, TNT; 2,6-dinitrotoluene, 2,6-DNT; 2-nitrotoluene, 2-NT; 2-amino-4,6-dinitrotoluene, 2-A-4,6-DNT; 3,5-dinitroaniline, 3,5-DNA; and nitrobenzene, NB) at electrochemically activated carbon-fibre microelectrodes is reported. Electrochemical activation of such electrode material by repeated square-wave (SW) voltammetric scans between 0.0 and +2.6 V versus Ag/AgCl, produced a dramatic increase in the cathodic response from these compounds. This is attributed to the increase of the carbon-fibre surface area, because of its fracture, and the appearance of deep fissures along the main fibre axis into which the nitroaromatic compounds penetrate. Based on the important contribution of adsorption and/or thin layer electrolysis to the total voltammetric response, a SW voltammetric method for rapid detection of nitroaromatic explosives was developed. No interference was found from compounds such as hydrazine, phenolic compounds, carbamates, triazines or surfactants. The limits of detection obtained are approximately 0.03 microg mL(-1) for all the nitroaromatic compounds tested. The method was applied for the determination of TNT in water and soil spiked samples; recoveries were higher than 95% in all cases.

Analysis of inorganic and small organic ions with the capillary electrophoresis microchip

Capillary electrophoresis microchip devices are receiving considerable attention due to their versatility, portability, and sample handling capabilities. This article is a comprehensive review of the analysis of inorganic and small, charged organic species on microchip platforms. The application of conductivity, amperometry, laser-induced fluorescence, absorbance, and chemiluminescence detection methods are discussed. The potential utilization of these devices for miniaturized analytical systems is described.

Microscale solid-phase extraction system for explosives

A simple, semi-automated, microcolumn solid-phase extraction (SPE) system is optimized for the extraction, preconcentration and HPLC analysis of seven different explosives and explosive derivatives contaminating seawater, river water and well water samples. The microcolumns were constructed from 1/16 in. O.D. PTFE tubing (1 in.=2.54 cm) packed with 0.5-1.5 mg of SPE material. LiChrolut EN or Porapak R. The extraction system consisted of two syringe pumps and several solenoid valves. Optimal detection limits were realized when the sample water flow-rate was maximally increased within the limits of the pump, 5-10 ml/min (despite exceeding the breakthrough threshold of the SPE microcolumn), and when the eluate volume collected from the column was minimized, <5 microl (despite very low recovery percentages).

Nonaqueous based microchip separation of toxic metal ions using 2-(5-bromo-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino)phenol

The colorimetric metal chelating agent, 2-(5-bromo-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino)phenol (5-Br-PAPS), was demonstrated on a capillary electrophoresis microchip in the separation and detection of six metal ions of environmental concern, Cd2+, Pb2+, Cu2+, Co2+, Ni2+, and Hg2+. The inclusion of methanol in the buffer was found to improve both the separation efficiency and sensitivity, in addition to making the technique directly amenable to the application of solid-phase extraction. The combination of metal chelation with solid-phase extraction on a C18 silica gel microcolumn gave several hundred fold improvements in detection limits for the CE microchip measurements of toxic metal ions in water and extracted from a solid Plexiglas surface.