High-sensitivity micro ultraviolet absorption detector for high-performance liquid chromatography (original) (raw)
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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.
LED-Based UV Absorption Detector with Low Detection Limits for Capillary Liquid Chromatography
Analytical chemistry, 2015
A 260 nm deep UV LED-based absorption detector with low detection limits was developed and integrated with a small nanoflow pumping system. The detector is small in size (5.2 × 3.0 cm) and weighs only 85 g (without electronics). This detector was specifically designed and optimized for on-column detection to minimize extra-column band broadening. No optical reference was included due to the low drift in the signal. Two ball lenses, one of which was integrated with the LED, were used to increase light throughput through the capillary column. Stray light was minimized by the use of a band-pass filter and an adjustable slit. Signals down to the parts per billion level (nanomolar) were easily detected with a short-term noise level of 4.4 μAU, confirming a low limit of detection and low noise. The detection limit for adenosine-5'-monophosphate was 230 times lower than any previously reported values. Good linearities (3 orders of magnitude) were obtained using sodium anthraquinone-2-s...
On-line dynamic flowing reference compensation for high-performance liquid chromatographic detectors
Journal of Chromatography A, 1984
In many types of high-performance liquid chromatography (HPLC), compensation for background response and instrument variation by a detector reference channel becomes advisable and at times essential. With commercial detectors which have incorporated only limited offsetting capability in the electronics, high background response of a mobile phase containing detectable components can become a formidable obstacle in attaining baseline stability and background response suppression. For refractive index (RI) detectors, compensation using the reference side of the detector is usually performed with a, static solution of the mobile phase. With ultraviolet (W) absorption detectors an air reference is usually used. In cases where the mobile phase exhibits a high detector response, this reference compensation is especially critical.
Analytical Chemistry, 1972
A new pumping system is presented for high speed liquid chromatography, a continuous gas displacement pump (CDP), operating on a new principle. The system pressure is maintained constant with a gas regulator, and a pulsating piston pump supplies the flow. This flow is split between the main flowstream and a controlled leak section which recycles the excess solvent to a reservoir. The CDP controls pressure to +0.5% which is equivalent to the performance of a gas displacement pump and a pulsating piston pump with pressurized gas ballast. High frequency noise (in a UV detector) for the CDP and the above other two pumping systems is equivalent to that of a trapped solvent in the sample cell. Short term noise is also comparable for the three systems but a factor of ten times higher than the trapped solvent case. Both high frequency and short term noise are significantly less than those obtained with undampened pulsating piston pumps. The influence of flow and pressure on high frequency and short term noise for both the CDP and a pulsating piston pump is also examined. Suggestions are presented for several of the origins of high frequency and short term noise in high speed liquid chromatography using an ultraviolet and refractive index detector. Finally, the use of a liquid ballast to minimize high frequency noise is presented. IN RECENT YEARS there has been increased interest in high speed, high efficiency, column liquid chromatography (LC) involving high inlet pressures to achieve the required flows. The pumps necessary for these high pressures may operate at either constant flow or constant pressure (I). Constant flow is desired for qualitative analysis, as well as quantitative analysis when using concentration sensitive detectors (2). In many types of chromatographic systems, the column permeability and viscosity of the eluent are maintained constant so that inexpensive and simple constant pressure devices can be successfully used. Of the constant flow devices, pulseless, motor driven displacement pumps are expensive, and reciprocating piston pumps introduce pulsations which, if not removed, can seriously affect the limits of detectability of a solute. One way in which the pulsations can be removed is by using a pressurized gas ballast; however, start up is complicated, ballast capacity changes with time, and dissolved gas may bubble out in the detector (detector outgasing). Of the constant pressure devices, gas displacement pumps are frequently used at pressures up to 5000 psi to produce constant flow if the permeability of the column and connecting lines is maintained constant (3, 4). However, these simple pumps require a bulky reservoir, have limited operating time, and have detector outgasing problems. Despite these disadvantages, the low detector noise, simplicity, and low cost of (1) R. A. Henry, "Modern Practice of Liquid Chromatography,''
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).
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.
Spectroelectrochemical detector for flow-injection systems and liquid chromatography
Analytica Chimica Acta, 1985
Flow-through spectroelectrochemical detectors for flow-injection systems and liquid chromatography are described. The detectors have a rectangular flow channel with a reticulated vitreous carbon working electrode followed by an open optical window.The dead volumes of the cells are 27 ul (liquid chromatography) and 80 ul (flow injection). In situ spectral monitoring of reaction products and intermediates for compounds that are both weakly and highly absorbing is demonstrated by using o-tolidine and N,N,N',N'-tetramethyl-p-phenylenediamine. As a detector for flow-injection systems, components in two-component mixtures can be quantified. As a detector for liquid chromatography, simultaneous absorbance and electrochemical chromatograms allow more eluting compounds to be identified and quantified. Mixtures of nitro-and chloro-phenols are used to illustrate the simultaneous profiling of spectral and redox properties.
Photoelectrochemical detector for high-performance liquid chromatography and flow injection analysis
Analytical Chemistry, 1985
Photoelectrochemical detection (PED) combines photochemistry with amperometry. The union allows one to take advantage of the new and/or altered electrochemical properties of photogenerated excited states, lntermedlates or products. A flow-through, thin-layer amperometric cell modifled to Irradiate the warklng electrode surface with optical energy is mated to a high-performance liquid chromatography (HPLC-PED) or flow injection analysis (FIA-PED) system. The PED is responsive to alkyl and aryl ketones and aldehydes. The response is linear over 3 to 4 orders of magnitude, replicate injection reproduciblllty is better than 2 % standard deviation, and minimum detection limits for conjugated carbonyl derivatlves are in the 10-2 ng range with a signal to noise ratio
Journal of Chromatography A, 2001
In this work we present some applications of near-UV laser-induced fluorescence (LIF) with micro-HPLC (mHPLC) and HPLC. To test the sensitivity of the detection, we used pyrene and aflatoxins, because both of these molecules exhibit native fluorescence. Then we studied catecholamines derivatized with 1,2-diphenylethylenediamine. The results show that we were able to reach better sensitivity levels than previously described in LIF studies. For catecholamines, a 50-fold increase in sensitivity compared to conventional fluorescence was obtained. These results indicate that LIF detection associated with HPLC or mHPLC can be used to detect very low concentrations of substances that can be excited in the near-UV range after labeling at nanomolar concentrations.