Zhao-Lun Fang

Combination of flow injection with capillary electrophoresis. Part I. The basic system

Abstract A combined flow injection (FI)-capillary electrophoresis (CE) system was developed using conventional FI and CE equipment. A flow-through reservoir equipped with a conical inlet was used as an interface to connect the FI system to the capillary inlet. A grounded electrode was inserted in the reservoir. Split-sampling was achieved in the electrokinetic mode when an injected sample zone in the microliter range was transported into the conical inlet by a carrier solution which also served as the separation buffer. Using benzoic acid as a model the combined system demonstrated significantly improved precision in peak height, peak area, and migration time as compared to conventional manual electrokinetic sample introduction while achieving similar sensitivity and column efficiency. Using a test sample containing magnolol and benzoic acid, a series of samples was injected continuously without current interruption, achieving sample throughputs at least three times higher than conventional CE sample introduction.

Chemiluminescence detection in capillary electrophoresis

An overview on developments of chemiluminescence (CL) detection in capillary electrophoresis (CE) systems is presented covering the related publications till early 2000. Contributions are reviewed both in relation to developments in instrumental design, CL chemistry and application field. Future prospects for development are discussed.

Capillary electrophoresis system with flow injection sample introduction and chemiluminescence detection on a chip platform

A capillary electrophoresis (CE) system with chemiluminescence (CL) detection was combined with flow injection (FI) sample introduction on a chip platform. A falling-drop interface was applied to perform FI split-flow sample introduction while achieving electrical isolation from the CE high voltage. A tubular reservoir at the capillary outlet served as both the CL reaction and detection cell for the luminol-peroxide-metallic ion chemiluminescent reaction, with the luminol included in the separation buffer and CL reagent H2O2 continuously introduced into the outlet reservoir. An optical fiber was positioned within the outlet reservoir directly opposite, and 300 microns away from, the capillary outlet for collecting and transferring the generated CL to the PMT. The peak height signals and the separation efficiency were almost independent of the reagent flow-rate, making the system a robust one. The performance of the system was illustrated by the separation of Co(II) and Cu(II), achieving baseline separation in 60 s. Detection limits (3 sigma) were 1.25 x 10(-8) and 2.3 x 10(-6) mol dm-3 for Co(II) and Cu(II), respectively. Peak height precision was 1.9% RSD (n = 9) at the 10(-7) mol dm-3 Co level.

The use of a micropump based on capillary and evaporation effects in a microfluidic flow injection chemiluminescence system

The performance of a micropump operating on evaporation and capillary effects, developed for microfluidic (lab-on-a-chip) systems, was studied employing it as the fluid drive in a microfluidic flow injection (FI) system, with chemiluminescence (CL) detection. The micropump featured simple structure, small dimensions, low fabrication cost and stable and adjustable flow-rates during long working periods. Using a micropump with 6.6cm(2) evaporation area, with the ambient temperature and relative humidity fluctuating within 2h in the ranges 20-21 degrees C and 30-32%, respectively, an average flow-rate of 3.02muL/min was obtained, with a precision better than 1.2% R.S.D. (n=61). When applied to the microchip FI-CL system using the luminol/hexacyanoferrate/H(2)O(2) reaction, a precision of 1.4% R.S.D. (n=11) was obtained for luminol at a sampling frequency of 30h(-1).

Simultaneous monitoring of aspirin, phenacetin and caffeine in compound aspirin tablets using a sequential injection drug-dissolution testing system with partial least squares calibration

An automatic system for drug-dissolution studies based on the sequential-injection (SI) technique is described and used for simultaneous monitoring of dissolution profiles of aspirin, phenacetin and caffeine in compound aspirin tablets. The partial least squares calibration technique was used for simultaneous determination of the three components. 300 μl test solution in dissolution vessel was aspirated into a PTFE holding coil via on-line filters by a syringe pump. After delivering an aliquot (10 μl) of each aspirated solution into the transferring line connected to the detector, the residual dissolution solution in the holding coil was fed back to the dissolution vessel to clear the filter and decrease sample consumption. The sampled aliquot was carried and stopped in the spectrophotometric detector and scanned within 220 and 310 nm. Fifteen samples run in triple-replicates were processed per hour with a total of 45 measurements.

Trends of flow injection sample pretreatment approaching the new millennium

Abstract The important role of flow injection (FI) techniques for the automation, acceleration and miniaturization of solution handling in sample pretreatment as well as some recent trends in the development of the field are discussed, illustrated mainly by recent achievements in the author’s laboratory, including: (a) sample pretreatment for vapor generation and electrothermal AAS based on sequential injection (SI) techniques, with low reagent consumption and enhanced ruggedness; (b) combination of FI and SI sample pretreatment (filtration, dialysis, gas diffusion, column sorption) with capillary electrophoresis (CE) giving enhanced reproducibility and efficiency; (c) application of on-line microdialysis in in vivo monitoring of blood glucose in test animals and (d) application of on-line microdialysis and solvent extraction in continuous monitoring of drug dissolution processes with high resolution of process events. Future perspectives of FI sample pretreatment are discussed, emphasizing the improvement in ruggedness of the equipment and methods, the combination and synchronization of different means for liquid propulsion, and the development of miniaturized systems.

Developments and trends in flow injection atomic absorption spectrometry

An overview is given on the development of flow injection atomic absorption spectrometry (FI-AAS) within the last decade, highlighting the main achievements and trends in the field within the period. The review is appended by a full bibliography covering the period from 1972 to early 1995, indexed according to the sub-disciplines of AAS, techniques, application fields and analyte species.

DNA mutation detection with chip-based temperature gradient capillary electrophoresis using a slantwise radiative heating system

A simple and robust chip-based temperature gradient capillary electrophoresis (TGCE) system was developed for DNA mutation/single-nucleotide polymorphism (SNP) analysis using a radiative heating system. Reproducible, stable and uniform temperature gradients were established along a 3 cm length of the electrophoretic separation channel using a single thermostated aluminium heater plate. The heater was slightly slanted relative to the plane of the glass chip at 0.2-1.3 degrees by inserting thin spacers between the plate and chip at one end to produce differences in radiative heating that created the temperature gradient. On-chip TGCE analyses of 4 mutant DNA model samples amplified from plasmid templates, each containing a single base substitution, with a wide range of melting temperatures, showed that mutations were successfully detected under a wide temperature gradient of 10 degrees C and within a short gradient region of about 3 cm (3.3 degrees C cm(-1) gradient). The radiative heating system was able to establish stable spatial temperature gradients along short microfluidic separation channels using simple peripheral equipment and manipulation while ensuring good resolution for detecting a wide range of mutations. Effectiveness of the system was demonstrated by the successful detection of K-ras gene mutations in 6 colon cancer cell lines.

Combination of flow injection with capillary electrophoresis. Part 2. Chiral separation of intermediate enantiomers in chloramphenicol synthesis

Abstract The combined flow injection (FI)-capillary electrophoresis (FI-CE) system described in Part I of this series was developed for achieving chiral separation of intermediate racemates in the synthesis of chloramphenicol. Hydroxypropyl-β-cyclodextrin, β-cyclodextrin and heptakis-(2,2-di-o-methyl)-β-cyclodextrin were employed as chiral selectors in the separation buffers. Baseline resolution of enantiomers of the rac-threo bases 2-amino-1-(p-nitrophenyl-1,3-propanediol) was achieved using the combined system demonstrating significantly improved precision and sample throughput compared to conventional CE with manual electrokinetic sample introduction, while achieving similar resolution and column efficiencies. A series of samples (the rac-threo bases) was injected continuously without current interruption, achieving sample throughputs at least a factor of five higher than conventional CE sample introduction.

Enhancement of signal-to-noise level by synchronized dual wavelength modulation for light emitting diode fluorimetry in a liquid-core-waveguide microfluidic capillary electrophoresis system

The signal-to-noise level of light emitting diode (LED) fluorimetry using a liquid-core-waveguide (LCW)-based microfluidic capillary electrophoresis system was significantly enhanced using a synchronized dual wavelength modulation (SDWM) approach. A blue LED was used as excitation source and a red LED as reference source for background-noise compensation in a microfluidic capillary electrophoresis (CE) system. A Teflon AF-coated silica capillary served as both the separation channel and LCW for light transfer, and blue and red LEDs were used as excitation and reference sources, respectively, both radially illuminating the detection point of the separation channel. The two LEDs were synchronously modulated at the same frequency, but with 180 degrees -phase shift, alternatingly driven by a same constant current source. The LCW transferred the fluorescence emission, as well as the excitation and reference lights that strayed through the optical system to a photomultiplier tube; a lock-in amplifier demodulated the combined signal, significantly reducing its noise level. To test the system, fluorescein isothiocyanate (FITC)-labeled amino acids were separated by capillary electrophoresis and detected by SDWM and single wavelength modulation, respectively. Five-fold improvement in S/N ratio was achieved by dual wavelength modulation, compared with single wavelength modulation; and over 100-fold improvement in S/N ratio was achieved compared with a similar LCW-CE system reported previously using non-modulated LED excitation. A detection limit (S/N=3) of 10nM FITC-labeled arginine was obtained in this work. The effects of modulation frequency on S/N level and on the rejection of noise caused by LED-driver current and detector were also studied.