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3152 Duy Anh Bui1,2 Benjamin Bomastyk1 Peter C Hauser1 Department of Chemistry, University of Basel, Basel, Switzerland Centre for Environmental Technology and Sustainable Development (CETASD), Hanoi University of Science, Hanoi, Vietnam Received June 5, 2013 Revised July 12, 2013 Accepted July 12, 2013 J Sep Sci 2013, 36, 3152–3157 Research Article 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 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 Keywords: Light-emitting diode / Narrow-bore chromatography / UV detection DOI 10.1002/jssc.201300598 Introduction Light-emitting diodes (LEDs) are compact, have high efficiency, and stability as well as long lifetimes They also show relatively narrow emission bands When employed in analytical instrumentation, monochromators or optical filters are therefore generally not necessary, and it is possible to construct simple and inexpensive yet powerful devices by substituting incandescent or discharge lamps and monochromators or filters with LEDs Their emission bands of typically 30 nm width are well matched to the absorption bands of molecules Flaschka et al., in 1973, were the first to suggest the use of LEDs as emitters in photometry [1] Since then, LED-based devices have been developed for many different analytical applications These include detection in flow injection analysis (see e.g Ref [2, 3]), membrane-based optical sensors (see e.g Ref [4–6]), detection in CE (see e.g Ref [7–10]), and the initiation of polymerization in the fabrication of monolithic columns for chromatography [11] Different aspects have been reviewed repeatedly [2, 12–15] The use of LEDs for detectors employed in column chromatography has also been reported Schmidt and Scott, in 1984, developed a simple 550 nm green LED-based detector coupled to an ion chromatographic setup to determine trace Correspondence: Dr Peter C Hauser, Department of Chemistry, University of Basel, Spitalstrasse 51, Basel 4056, Switzerland E-mail: Peter.Hauser@unibas.ch Fax: +41-61-267-1013 Abbreviations: AU, absorbance unit; LEDs, light-emitting diodes C 2013 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim metals complexed with 4-(2-pyridylazo)resorcinol [16] A photometric detector for the indirect determination of alcohols in RPLC based on measuring the absorption of methylene blue with a 565 nm LED and a photodiode was described by Berthod et al in 1990 [17] In 2006, Diamond and co-workers also reported devices employing green LEDs for the determination of metals complexed by 4-(2-pyridylazo)resorcinol [18] and o-cresolphthalein complexone in column chromatography [19] For HPLC, however, the deep UV range
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