Microcapillary liquid chromatography in open tubular columns with diameters of 10–50 μm (original) (raw)
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High-sensitivity micro ultraviolet absorption detector for high-performance liquid chromatography
Journal of Chromatography A, 1989
A UV absorption detector with a 0.6-4 flow cell for high-performance liquid chromatography (HPLC) was developed. In order to improve the signal-to-noise ratio when the cell volume is reduced, the flow cell has a reflective layer on the internal wall of the optical path. The cell transmittance is hardly affected by changes in solvent conditions, based on a pulse flow from a pump. The flow cell can enhance sensitivity in the low-volume UV detector by making it possible to reduce the baseline shift and noise which are caused by variations of solvent conditions. Extra-column dispersion in the detector flow cell is reduced at high flow-rates of over 0.5 ml/min. The detector is especially effective for fast and micro-scale HPLC.
Comparison of universal detectors for high-temperature micro liquid chromatography
Journal of Chromatography A, 2007
This study compares, through micro high-temperature liquid chromatography (HTLC), three commercial universal detectors that allow a direct detection of lipids. The detectors are: the charged aerosol detector (CAD), the evaporative light-scattering detector (ELSD) and the ion trap mass spectrometer with atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) sources (APCI-MS and ESI-MS). This study shows the feasibility to use the high temperature with these detectors and hybrid behavior between concentration and mass flow rate detector in HTLC. The detectors were compared in terms of response intensity, linearity and limit of detection for different high temperatures. The charged aerosol detector shows a linear response from 5 to 500 g/mL and the correlation coefficients (r 2) obtained for squalene, cholesterol and ceramide IIIB exceed 0.99.
Journal of Chromatography A, 2012
The kinetic performance of 0.5 mm × 50 mm columns packed with 2.7 m Halo-C 18 core-shell particles and 3 m EP-120-C 18 fully porous particles fitted on an Eksigent LC-Express Ultra HPLC system were measured. The instrument contribution to band broadening was obtained by directly connecting the injection valve and the detector cell with a short, narrow PEEKSIL tube. The connections between the column and the connecting tubes, the column endfittings and its frits contribute to band spreading and are responsible for a significant rear peak tailing, even for retained compounds, resulting in a significant loss of efficiency. Our results show that the HPLC system could outperform the current VHPLC systems using 2.1 mm I.D. columns packed with 1.7 m particles if it were using 0.5 mm I.D. columns packed with 1 m particles, if it could operate at a few kbar pressure drop, and if the sum of the contributions of the instrument, column endfittings and the column frits to band dispersion were three times smaller than it is at present.
Evolution in miniaturized column liquid chromatography instrumentation and applications: An overview
The purpose of this article is to underline the miniaturized LC instrumental system and describe the evolution of commercially available systems by discussing their advantages and drawbacks. Nowadays, there are already many miniaturized LC systems available with a great variety of pump design, interface and detectors as well as efficient columns technologies and reduced connections devices. The solvent delivery systems are able to drive the mobile phase without flow splitters and promote gradient elution using either dual piston reciprocating or syringe-type pumps. The mass spectrometry as detection system is the most widely used detection system; among many alternative ionization sources direct-EI LC-MS is a promising alternative to APCI. In addition, capillary columns are now available showing many possibilities of stationary phases, inner diameters and hardware materials. This review provides a discussion about miniaturized LC demonstrating fundamentals and instrumentals' aspects of the commercially available miniaturized LC instrumental system mainly nano and micro LC formats. This review also covers the recent developments and trends in instrumentation, capillary and nano columns, and several applications of this very important and promising field.
Talanta, 2008
A versatile, simple, liquid core waveguide (LCW)-based fluorescence detector design is described for capillary systems. A Teflon AF coated fused silica capillary serves as the LCW. The LCW is transversely excited. The light source can be a conventional or high power (HP) light emitting diode (LED) or a laser diode (LD). The source can be coupled to the LCW directly or via an optical fiber. Fiber coupling is convenient if a high power (necessarily heat sink mounted) emitter is used. The LCW is concentrically placed within a slightly larger opaque jacket tube and the LCW terminates just short of the jacket terminus, which is sealed with an optical window. The influent liquid thus exits the LCW tip, flows back around the LCW through the jacket annulus to exit via an aperture on the jacket tube. The problem of coupling the emitted light efficiently to the photodetector is thus solved by placing the tip of the annular tubular assembly directly on the detector. For excitation wavelengths of 365 nm (LED/HPLED) and 405 nm (LD), the tris(8-hydroxyquinoline-5sulfonic acid (sulfoxine)) chelate of aluminum (em,max ∼ 500 nm) and Coumarin 30 were respectively used as the model analyte. For source-detector combinations comprising (a) a UV LED (∼1.5 mW @ 15 mA) and a photodiode, (b) a LD (∼5 mW, abstracted from a "Blu-Ray" recorder) and a miniature photomultiplier tube (mPMT), and (c) a high power (210 mW @ 500 mA) surface-mount HPLED-mPMT, the S/N = 3 LODs were, respectively, 1.7 pmol Al, 3-100 fmol Coumarin 30 (depending on laser intensity and integration time), and 4 fmol Al. In the last case, the relative standard derivation (R.S.D.) at the 20 fmol level was 1.5% (n = 10).
Journal of Chromatography A, 1995
Simultaneous measurements of absorbance and fluorescence are possible with axial-illuminated flow cells, fashioned with a unique bend geometry. The optical properties of these flow cells have been studied. Effects of variations in lumen refractive index, capillary wall thickness and physical pathlength have been examined. A theoretical understanding of the various light propagation modes and of light intensity distributions in these modes, based upon lumen refractive index, has been attained. Of more practical significance, optical pathlengths from < 1 cm to 6 cm are simply attained by positioning the inlet optical fiber along the capillary axis with respect to the bend. The flow cell volumes obtained with different combinations of capillary I.D. and optical pathlength make the flow cell and resulting detector compatible with conventional HPLC and microscale separations. Also, studies have been performed to determine the effects of increased optical pathlength on overall analytical separation efficiency and detectability in the analysis of polynuclear aromatic hydrocarbons using laser-induced fluorescence micro-LC.
Simultaneous absorbance, fluorescence and refractive index (SAFRIN) detection for Micro LC
Analytica Chimica Acta, 1999
Absorbance, fluorescence and refractive index detection are simultaneously accomplished in a Micro LC system. A unique double eccentric-bend fused silica capillary is employed with axial illumination to achieve a long path length, multisensing flow cell. Two different optical sources, one that excites fluorescence through absorption and one that is not absorbed by eluting analytes, are imaged into the bends with optical fibers, placed within the capillary lumen in separate legs of the device. Axially-propagating light exits at each bend where photodetectors simultaneously collect attenuated light, one signal based on absorption and the other signal based on refractive index. A nearby cylindrical lens, optical filter and photomultiplier tube collect fluorescence in the 'absorption' leg of the capillary. Thus, trifunctional detection is achieved in microscale liquid chromatography.