Absorbance detector for high-performance liquid chromatography based on light-emitting diodes for the deep-ultraviolet range

A HPLC-detector has been designed which employs light-emitting diodes in the deep-UV-range below 300 nm as wavelength specific radiation sources and special UV-photodiodes for measuring the signal. A monochromator is therefore not needed. The design features a beam splitter and a reference photodiode, precision mechanics for adjustment of the light beams and electronics for stabilization of the LED-current. The processing of the photodiode currents is carried out with a high performance log-ratio amplifier which allows direct absorbance measurements. The optical and electronic performance of the detector was characterised and high precision over several absorbance units was obtained. Testing of analytical separation methods in isocratic as well as gradient modes employing UV-detection at 255 and 280 nm showed a very similar performance to a commercial photodiode-array detector used in the fixed wavelength mode in terms of linearity, precision and detection limits. The chief advantages of the new device are small size, low power consumption, and low cost. (C) 2011 Elsevier B.V. All rights reserved

Absorbance detector based on a deep UV light emitting diode for narrow-column HPLC

A detector for miniaturized HPLC based on deep UV emitting diodes and UV photodiodes was constructed. The measurement is accomplished by the transverse passage of the radiation from the light-emitting diode (LED) through fused-silica tubing with an internal diameter of 250 m. The optical cell allows flexible alignment of the LED, tubing, and photodiode for optimization of the light throughput and has an aperture to block stray light. A beam splitter was employed to direct part of the emitted light to a reference photodiode and the Lambert-Beer law was emulated with a log-ratio amplifier circuitry. The detector was tested with two LEDs with emission bands at 280 and 255 nm and showed noise levels as low as 0.25 and 0.22 mAU, respectively. The photometric device was employed successfully in separations using a column of 1 mm inner diameter in isocratic as well as gradient elution. Good linearities over three orders of magnitude in concentration were achieved, and the precision of the measurements was better than 1% in all cases. Detection down to the low micromolar range was possible

Automated capillary electrophoresis with on-line preconcentration by solid phase extraction using a sequential injection manifold and contactless conductivity detection

An extension of a capillary electrophoresis instrument coupled to a sequential injection analysis manifold was developed for automated measurements with on-line solid-phase extraction preconcentration. An in-house built capacitively coupled contactless conductivity detector was employed for sensitive detection with narrow capillaries of 25 mu m internal diameter. The system was assembled into standardized 19 in. frames and racks for easy transport and mobile deployment. The system can be left running unattendedly without manual intervention with good operation stability. To demonstrate the application of the system, a method for the determination of four drugs, namely ibuprofen, diclofenac, naproxen and bezafibrate, was developed with enrichment factors of up to several hundreds. Detection of the drug residues down to the nM-scale was found possible and the method was found suitable for the detection of ibuprofen in the waste water of a hospital in Hanoi. (C) 2012 Elsevier B.V. All rights reserved