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LED-based UV absorption detector with low detection limits for capillary liquid chromatography Sonika Sharma, H. Dennis Tolley, Paul B Farnsworth, and Milton L. Lee Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/ac504275m • Publication Date (Web): 12 Dec 2014 Downloaded from http://pubs.acs.org on December 23, 2014
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Analytical Chemistry
LED-based UV absorption detector with low detection limits for capillary liquid chromatography Sonika Sharma¥, H. Dennis Tolley€, Paul B. Farnsworth¥* and Milton L. Lee¥*
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ABSTRACT: A 260 nm deep UV LED-based absorption detector with low detection limits was
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developed and integrated with a small nano-flow pumping system. The detector is small in size
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(5.2 × 3.0 cm) and weighs only 85 g (without electronics). This detector was specifically
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designed and optimized for on-column detection to minimize extra-column band broadening. No
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optical reference was included due to the low drift in the signal. Two ball lenses, one of which
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was integrated with the LED, were used to increase light throughput through the capillary
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column. Stray light was minimized by the use of a band-pass filter and an adjustable slit. Signals
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down to the ppb level (nM) were easily detected with a short-term noise level of 4.4 µAU,
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confirming a low limit of detection and low noise. The detection limit for adenosine-5’-
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monophosphate was 230 times lower than any previously reported values. Good linearities (three
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orders of magnitude) were obtaind using sodium anthraquinone-2-sulfonate, adenosine-5’-
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monophosphate, DL-tryptophan and phenol. The LC system was demonstrated by performing
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isocratic separation of phenolic compounds using a monolithic capillary column (16.5 cm × 150
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µm i.d.) synthesized from poly(ethylene glycol) diacrylate.
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INTRODUCTION
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€
Department of Chemistry & Biochemistry, Brigham Young University, Provo, UT 84602, USA Department of Statistics, Brigham Young University, Provo, UT 84602, USA. Corresponding Authors:
[email protected];
[email protected] Standard ultraviolet (UV) light sources, such as the mercury lamp, suffer from short
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lifespan, long warm-up time 1, 2 and unstable light output. New light sources have been proposed
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that are more stable and produce less noise compared to standard UV light sources. Among
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these, light-emitting diodes (LEDs) have gained interest due to their long life, high stability,
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bright output and low power requirement.3 Additionally, they are small in size and more compact
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compared to standard light sources.4 Considering the nearly monochromatic behavior of LEDs, a
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monochromator is not required.5 A LED-based detector can be fabricated without using
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expensive optical lenses. All of these factors make LED-based UV-absorption detectors
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attractive for small, inexpensive instrumentation.
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Since LEDs were introduced, several papers have been reported on the use of LED-based
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detectors for different applications.6 These have been comprehensively reviewed.7-11
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Commercially available deep UV LEDs (
