High-throughput characterization for organic pollutants in environmental waters using a capillary electrophoresis chip

Nano-capillary electrophoresis for environmental analysis

Many analytical techniques have been used to monitor environmental pollutants. But most techniques are not capable to detect pollutants at nanogram levels. Hence, under such conditions, absence of pollutants is often assumed, whereas pollutants are in fact present at low but undetectable concentrations. Detection at low levels may be done by nano-capillary electrophoresis, also named microchip electrophoresis. Here, we review the analysis of pollutants by nano-capillary electrophoresis. We present instrumentations, applications, optimizations and separation mechanisms. We discuss the analysis of metal ions, pesticides, polycyclic aromatic hydrocarbons, explosives, viruses, bacteria and other contaminants. Detectors include ultraviolet-visible, fluorescent, conductivity, atomic absorption spectroscopy, refractive index, atomic fluorescence spectrometry, atomic emission spectroscopy, inductively coupled plasma, inductively coupled plasma-mass spectrometry, mass spectrometry, time-of-flight mass spectrometry and nuclear magnetic resonance. Detection limits ranged from nanogram to picogram levels.

Characterization of dissolved organic carbon at low levels in environmental waters by microfluidic-chip-based capillary gel electrophoresis with a laser-induced fluorescence detector

A microfluidic analytical system for characterization of dissolved organic carbon (DOC) in environmental waters, based on a capillary gel electrophoresis (CGE) device with a laser-induced fluorescence (LEF) detector, was developed. The applied voltage and the running buffer were investigated to control the simple floating injection and CGE separation for convenient cross-type microchips made from polymethyl-methacylate. We obtained reproducible peaks for standard organic solutions and the determination time is less than 70 s. The values of the relative standard deviation (RSD) were 0.17-2.01% for repetitive injection (n = 12). We demonstrated high-throughput characterization of DOC in environmental water from the Biwa Lake and the Hino River using microfluidic chip and determined that the content of DOC in the Biwa Lake changed with the seasons.

Band-broadening suppressed effect in long turned geometry channel and high-sensitive analysis of DNA sample by using floating electrokinetic supercharging on a microchip

A featured microchip owning three big reservoirs and long turned geometry channel was designed to improve the detection limit of DNA fragments by using floating electrokinetic supercharging (FEKS) method. The novel design matches the FEKS preconcentration needs of a large sample volume introduction with electrokinetic injection (EKI), as well as long duration of isotachophoresis (ITP) process to enrich low concentration sample. In the curved channel [ approximately 45.6 mm long between port 1 (P1) and the intersection point of two channels], EKI and ITP were performed while the side port 3 (P3) was electrically floated. The turn-induced band broadening with or without ITP process was investigated by a computer simulation (using CFD-ACE+ software) when the analytes traveling through the U-shaped geometry. It was found that the channel curvature determined the extent of band broadening, however, which could be effectively eliminated by the way of ITP. After the ITP-stacked zones passed the intersection point from P1, they were rapidly destacked for separation and detection from ITP to zone electrophoresis by using leading ions from P3. The FEKS carried on the novel chip successfully contributed to higher sensitivities of DNA fragments in comparison with our previous results realized on either a single channel or a cross microchip. The analysis of low concentration 50 bp DNA step ladders (0.23 mugml after 1500-fold diluted) was achieved with normal UV detection at 260 nm. The obtained limit of detections (LODs) were on average 100 times better than using conventional pinched injection, down to several ngml for individual DNA fragment.

Development of an analytical method using microchip capillary electrophoresis for the measurement of fluorescein-labeled salivary components in response to exercise stress

We have developed an analytical method using microchip capillary electrophoresis (microchip CE) for the high-speed separation of fluorescein-labeled salivary components in response to exercise stress. Optimal separation was obtained using a borate buffer at pH 9.5 containing 10 mM beta-cyclodextrin and 1.0% (w/v) methylcellulose. To minimize individual differences in human saliva, such as viscosity, conductivity, and contaminants, the concentration of methylcellulose in the analytical conditions played a key factor. The optimized separation conditions produced identical electropherograms successfully despite of the use of different microchips made from quartz glass or poly-methylmethacrylate (PMMA). In addition, a practical application of bicycle ergometer stress was performed. Some components in human saliva showed a marked decrease after exercise stress.

On-chip micellar electrokinetic chromatographic separation of phenolic chemicals in waters

This paper describes on-chip micellar electrokinetic chromatography (MEKC) separation of bisphenol A and 3 kinds of alkylphenols, which have been recently recognized as endocrine disrupting chemicals for fish by the Japanese government, using microchip capillary electrophoresis with UV detection. We successfully obtained high-speed separation of the phenolic chemicals within 15 s as optimizing in microfluidic controls and MEKC separation conditions. We obtained fairly good linearity with correlation coefficient of over 0.98 from 0 to 50 mg/l phenolic chemicals except for 4-nonylphenol, which sample is the mixture of many geometrical isomers (r = 0.86). The values of the relative standard deviation for peak height in 50 mg/l phenolic chemicals were less than 8% except for bisphenol A (11.0%). The limits of detection obtained at a signal-to-noise ratio of 3 were from 5.6 to 20.0 mg/l. To realize on-site monitoring, we described strategy for on-chip MEKC analysis of the phenolic chemicals in waters using a portable analyzer based on microfluidic devices.

High-throughput nitric oxide assay in biological fluids using microchip capillary electrophoresis

In order to develop a high-throughput screening method for the nitrogen monoxide metabolites, nitrite and nitrate, in biological fluids, we have investigated the simultaneous determination of these metabolites using microchip capillary electrophoresis (MCE). In this study, the control of applied voltage to obtain higher sensitivity by increasing the sample injection volume was investigated. Also, the improvement of reproducibility by correcting the injection volume using the internal standard was investigated. By increasing the sample volume, the limits of detection achieved for nitrite and nitrate were 24 and 12 microM, respectively. Because we used a 10-fold diluted sample when detecting nitrite and nitrate in human serum, it was necessary to increase the sensitivity by a factor of 10-50. The run-to-run and day-to-day relative standard deviations achieved were improved to less than 10% by using an internal standard to correct the injection volume. Moreover, we obtained successful separation of nitrite and nitrate in spiked human serum within 6.5 s under optimum analytical conditions. As a result, although it is necessary to obtain greater sensitivity, it was concluded that determination of the amount of NO metabolites in biological fluids using MCE is possible.

Estimation of logPow values for neutral and basic compounds by microchip microemulsion electrokinetic chromatography with indirect fluorimetric detection (μMEEKC-IFD)

Microchip microemulsion electrokinetic chromatography with indirect fluorimetric detection (muMEEKC-IFD) was used to obtain logP octanol/water (logP(ow)) values for neutral and basic compounds. Six compounds, with logP(ow) values between 0.38 and 5.03, were used to create a calibration curve relating the log of retention factors (logk) obtained from muMEEKC-IFD with the known logP(ow) values. The logP(ow) values for six additional compounds were determined using the logk values obtained by muMEEKC-IFD and the linear relationship between logP(ow) and logk established for the standard compounds. The muMEEKC-IFD buffer was composed of 50 mM 3-[cyclohexylamino]-1-propane-sulfonic acid (CAPS) buffer (pH 10.4) containing 1.2% n-heptane (v/v), 2% sodium dodecylsulfate (w/v), 8% 1-butanol (v/v) and 4 microM 5-carboxytetramethyl-rhodamine (TAMRA) as the fluorophore probe for indirect detection. The muMEEKC-IFD provided an accurate method for estimating logP(ow) values and also a means for analyzing compounds that are non-fluorescent.

Determination of inorganic ions using microfluidic devices

The separation and detection of inorganic ions on microfluidic devices has received little attention since the 'lab-on-a-chip' concept has revolutionised the field of electrokinetically driven analysis. This review presents a summary and discussion of the published literature on inorganic analysis using microfluidic devices and includes sections on electromigration separation methods, namely isotachophoresis (ITP), capillary electrophoresis (CE), and hyphenated ITP-CE, together with a brief account of flow injection analysis. The review concludes with the authors' perspective on future directions for inorganic analysis on microfluidic devices.

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.