Dual-opposite multi-walled carbon nanotube modified carbon fiber microelectrode for microfluidic chip-capillary electrophoresis determination of methyl parathion metabolites in human urine.

Methyl parathion (MP) is a highly toxic organophosphate and its exposure may lead to substantial adverse effects to human health. The existence of 4-nitrophenol (4-NP) in the form of free phenol, glucuronide (4-NP-G) or as a sulfate ester (4-NP-S) can be used as biomarkers to assess the duration and extent of MP exposure. In this work, a MC-CE device incorporating post-CE amperometric detection using multi-walled carbon nanotubes (MWNTs) modified carbon fiber microelectrode (CFME) was fabricated and assessed for simultaneous determination of 4-NP, 4-NP-G, and 4-NP-S in human urine.

Determination of taurine in human tear fluid by capillary electrophoresis with indirect amperometric detection based on electrogenerated bromine.

A new method for the determination of taurine was developed based on indirect amperometric detection after capillary electrophoresis. A serial dual-electrode detector comprising an on column Pt film electrode (upstream electrode) and an end column Pt microdisk electrode (downstream electrode) was utilized to conduct the indirect amperometric detection. Bromide is oxidized to bromine at upstream electrode and reduced back to bromide at downstream electrode.

Multidimensional microchip-capillary electrophoresis device for determination of functional proteins in infant milk formula.

Functional proteins have been found in infant milk formula as supplements, added by an increasing number of manufacturers. Their supplementations are expected to be controlled and monitored. Here, we describe a microchip-integrated CE method for the determination of these low levels of functional proteins in a protein-rich sample matrix.

A serial dual-electrode detector based on electrogenerated bromine for capillary electrophoresis.

A new serial dual-electrode detector for CE has been designed and fabricated for postcolumn reaction detection based on electrogenerated bromine. A coaxial postcolumn reactor was employed to introduce bromide reagent and facilitate the fabrication of upstream generation electrode by simply sputtering Pt film onto the outer surface of the separation capillary. Bromide introduced could be efficiently converted to bromine at this Pt film electrode and subsequently detected by the downstream Pt microdisk detection electrode.

Simultaneous determination of gaseous and particulate carbonyls in air by coupling micellar electrokinetic capillary chromatography with molecular imprinting solid-phase extraction.

A novel method coupling molecular imprinting solid-phase extraction (MISPE) and micellar electrokinetic capillary chromatography (MEKC) was developed to enable the hourly determination of low level of ambient carbonyls, and study their partition between gaseous phase and particulate phase. With 2,4-dinitroaniline (DNAN) as dummy imprinting template, the unreacted 2,4-Dinitrophenylhydrazine (DNPH) in sampling solution could be removed effectively using MISPE, and an average recovery of 97±5.3% (n=5) for the carbonyl-DNPH derivatives was achieved.

Assessment of adulteration of soybean proteins in dairy products by 2D microchip-CE device.

To determine the adulteration of soybean proteins in dairy product, a microchip-CE device was developed to isolate selected fraction of soybean and milk proteins in pI range from 5.5 ∼ 7.0 by 1D IEF, followed by ITP/CZE in the embedded capillary for preconcentration, separation and UV detection at 280 nm.

Microfluidic chip capillary electrophoresis coupled with electrochemiluminescence for enantioseparation of racemic drugs using central composite design optimization.

Optimization based on central composite design (CCD) for enantioseparation of anisodamine (AN), atenolol (AT), and metoprolol (ME) in human urine was developed using a microfluidic chip-CE device. Coupling the flexible and wide working range of microfluidic chip-CE device to CCD for chiral separation of AN, AT, and ME in human urine, a total of 15 experiments is needed for the optimization procedure as compared to 75 experiments using the normal one variable at a time optimization. The optimum conditions obtained are found to be more robust as shown by the curvature effects of the interaction factors.

Multi-dimension microchip-capillary electrophoresis device for determination of functional proteins in infant milk formula.

To improve resolution of important minor proteins and eliminate time-consuming precipitation of major protein with associated analyte co-precipitation risk, a multi-dimension strategy is adopted in the 2D microchip-CE device to isolate major proteins on-chip, enrich minor proteins in capillary before their separation in CE for UV quantitation. A standard fluorescent protein mixture containing FITC-BSA, myoglobin and cytochrome as specific pI markers has prepared to demonstrate capability of the device to fractionate minor proteins by IEF. The results using a standard protein mixture with profile resembling infant milk formula show a complete isolation of high abundance proteins by a 2-min 1D IEF run.

Microfluidic chip-capillary electrophoresis with dynamic multi-segment standard addition for rapidly identifying nephrolithiasis markers in urine.

A microchip-CE device was fabricated for bed-side monitoring of nephrolithiasis biomarkers in urine by incorporating on-chip continuous passive mixing and standard addition to reduce sample matrix interference, increase sample throughput and eliminate accessories for active mixing. Under optimized conditions with buffer containing 20 mM borate and 0.5 mM CTAB at pH 10.

2-D t-ITP/CZE determination of clinical urinary proteins using a microfluidic-chip capillary electrophoresis device.

To replace the time-consuming sample pretreatment procedure, a microfluidic chip-CE device incorporating on-chip sample desalting/preconcentration with transient isotachophoresis (ITP)/capillary zone electrophoresis (CZE) was fabricated to perform sequential on-chip sample pretreatment and CE determination of four urinary proteins in clinical samples. On-chip sample desalting, clean-up and analyte preconcentration enable removing interfering sample matrix prior to transferring analytes to separation capillary for transient ITP/CZE determination. Four important urinary proteins transferrin, β2-microglobulin, human serum albumin (HSA) and immunoglobulin G (IgG), investigated were shown to achieve quantitation limits sufficiently high to meet medical requirements, sensitivity enhancement up to 40-fold and detection limits down to 0.

Microfluidic chip-capillary electrophoresis for two orders extension of adjustable upper working range for profiling of inorganic and organic anions in urine.

To meet the need for onsite monitoring of urine anions, a microfluidic chip-capillary electrophoresis device was designed, fabricated and tested to extend the upper CE working range for an enhancement up to 500 fold (100 fold for sample dilution and 5 folds for CE injection) in order to analyze highly variable anionic metabolites in urine samples. Capillaries were embedded between two PMMA plates with laser-fabricated microchannel patterns to produce the microfluidic chip-capillary electrophoresis to perform standard/sample dilution and CE injection with adjustable dilution ratios. A circular ferrofluid valve was incorporated on-chip to perform cleanup and conditioning, mixing and dilution, injection and CE separation.

Determination of free bilirubin and its binding capacity by HSA using a microfluidic chip-capillary electrophoresis device with a multi-segment circular-ferrofluid-driven micromixing injection.

A PMMA microfluidic chip-CE device with a multi-segment circular-ferrofluid-driven micromixing injector has been developed for the determination of free bilirubin and its binding capacity by HSA at equilibrium. The design of the device and its fabrication by a low cost CO(2) laser are discussed for intended applications. Under optimized conditions, the total binding capacity of HSA for bilirubin was determined as 16.

Development of CE-dual opposite carbon-fiber micro-disk electrode detection for peak purity assessment of polyphenols in red wine.

A new dual opposite carbon-fiber micro-disk electrode detector was fabricated and tested for hyphenation with CE in the polyphenol determination. Under optimized conditions, CE-dual opposite carbon-fiber micro-disk electrode was found able to baseline separate and determine five important polyphenols (trans-resveratrol, (+)-catechin, (-)-epicatechin, quercetin and gallic acid) in red wine within 16 min with low detection limit (0.031-0.

Determination of gaseous and particulate carbonyls in air by gradient-elution micellar electrokinetic capillary chromatography.

A new continuous-flow gradient-elution micellar electrokinetic capillary chromatography method is developed for the determination of airborne carbonyls after derivatization with 2,4-dinitrophenylhydrazine. A total of 16 carbonyls can be determined with detection limits ranging from 0.94 to 8.

Microchip capillary electrophoresis for frontal analysis of free bilirubin and study of its interaction with human serum albumin.

To meet the need for bedside monitoring of free bilirubin for neonates under critical conditions, a microfluidic chip was fabricated and tested for its coupling with CE/frontal analysis (FA) to determine free bilirubin and study of its binding interaction with HSA, which regulated its concentration in plasma. The poly(methyl methacrylate) (PMMA) multichannel chip was fabricated by CO2 laser ablation and bonded with a fused-silica separation capillary for CE/FA separation with UV detection. The chip was designed to allow a complete assay of four electrophoretic runs using preconditioned channels to speed up the determination of free bilirubin and to deliver quick results for bedside monitoring.

Separation and determination of metal cations in milk and dairy products by CE.

To prevent casein adsorption and improve between-run repeatability, a CE procedure is developed for cation analysis in milk using a modified imidazole/alpha-hydroxyisobutyric acid (HIBA) BGE system to operate at pH 6 to match the pH of milk and elevate imidazole concentration to enhance its buffer action. The procedure is shown to produce a fast, economic and efficient method for cation separation in milk with only simple dilution. Upon direct hydrodynamic injection of diluted milk sample at 8 cm for 30 s in an uncoated column with a BGE consisting of 10 mM imidazole, 10 mM HIBA and 10% methanol at pH 6.

Variable selection for discriminating herbal medicines with chromatographic fingerprints.

When discriminating herbal medicines with pattern recognition based on chromatographic fingerprints, typically, the majority of variables/data points contain no discrimination information. In this paper, chemometric approaches concerning forward selection and key set factor analysis using principal component analysis (PCA), unweighted and weighted methods based on the inner- and outer-variances, Fisher coefficient from the between- and within-class variations were investigated to extract representative variables. The number of variables retained was determined based on the cumulative variance percent of principal components, the ratio of observations to variables and the factor indicative function (IND).

Determination of volatile components in ginger using gas chromatography-mass spectrometry with resolution improved by data processing techniques.

Ginger is widely used as either a food product or an herbal medicine in the world. In this paper, a method was developed for determining volatile components in essential oils from both dried and fresh ginger by use of gas chromatography-mass spectrometry (GC-MS) and chemometric approaches. With the resolution improvement by chemometric methods upon two-dimensional data from GC-MS, the drifting baseline can be corrected.

Correction of retention time shifts for chromatographic fingerprints of herbal medicines.

In this study, the combination of chemometric resolution and cubic spline data interpolation was investigated as a method to correct the retention time shifts for chromatographic fingerprints of herbal medicines obtained by high-performance liquid chromatography-diode array detection (HPLC-DAD). With the help of the resolution approaches in chemometrics, it was easy to identify the purity of chromatographic peak clusters and then resolve the two-dimensional response matrix into chromatograms and spectra of pure chemical components so as to select multiple mark compounds involved in chromatographic fingerprints. With these mark components determined, the retention time shifts of chromatographic fingerprints might be then corrected effectively.

Analysis of volatile components from Cortex cinnamomi with hyphenated chromatography and chemometric resolution.

In this paper, the combination of hyphenated chromatography and chemometric resolution was investigated as a method to qualitatively and quantitatively determine volatile components in Cortex cinnamomi from four main producing areas. With the help of chemometric resolution approaches, whether the chromatographic elution of chemical components is featured by "first-in-first-out" or embedded peaks could be determined. Upon this useful information obtained, the matrix data generated by hyphenated chromatography could be uniquely resolved into pure chromatogram and spectrum of each chemical component involved followed by qualitative and quantitative analysis.

Analysis of organic acids and inorganic anions in beverage drinks by capillary electrophoresis.

To meet the need for a new and validated analytical method for simultaneous determination of inorganic and organic acid anions in beverage drinks, a capillary zone electrophoresis (CZE) procedure had been developed based on a new background electrolyte (BGE) system containing 3 mmol/L 1,3,5-benzenetricarboxylic acid (BTA), 15 mmol/L tris(hydroxymethyl)aminomethane and 1.5 mmol/L tetraethylenepentamine (TEPA) at pH 8.4.