Linearity evaluation in absorbance detection: The use of light‐emitting diodes for on‐capillary detection in capillary electrophoresis

Abstract

A model which takes into account both stray light and polychromatic light was used to predict and evaluate linearity in on-capillary detection in capillary electrophoresis (CE). According to the model the stray light is the major factor which determines linearity under typical CE operating conditions. By calculating theoretical absorbance versus concentration plots, the influence of different levels of stray light and polychromatic light on linearity is demonstrated. Experimentally, six light-emitting diodes (LEDs) in the range from 563 to 654 nm were examined as light sources for on-capillary detection in CE. Fitting theoretical curves to measured linearity plots enabled determination of the values of both effective path length and stray light for a particular detection system. The detector linearity for the four LEDs was compared to mercury and tungsten lamps used with interference filters. For potassium permanganate as the test compound, the linear range for a 563 nm LED was two times greater than that for a mercury lamp operated at 546 nm. The relatively poor linearity of the mercury lamp detector is explained by its high level of stray light. The noise of the LED563-based detector was the same as for the mercury lamp, whereas the other LEDs of higher light intensity gave approximately half the noise of the mercury lamp. The lowest noise level of 3 x 10(-5) AU was obtained for the LED at 554 nm (determined at a detector time constant of 0.1 s).

Fibre coupled micro-light emitting diode array light source with integrated band-pass filter for fluorescence detection in miniaturised analytical systems

“…In the area of on-capillary detection including CE, LEDs have been used in miniaturised low-cost detection systems, both photometric [29][30][31][32][33][34][35][36][37][38][39][40] and LED induced fluorimetric (LED-IF) [41][42][43][44][45], with advantages especially for portable CE instruments [46]. A number of LED-IF detection designs for microfluidic chip-based CE [47][48][49][50] systems have been reported as well.…”

Design and performance of a light‐emitting diode detector compatible with a commercial capillary electrophoresis instrument

“…Macka et al [15] studied the use of LEDs with emission wavelengths between 563 and 654 nm as light sources. A Waters Quanta 4000 instrument was modified to allow a mercury lamp holder to be adapted to hold a LED light source.…”

“…One approach at optimizing the potential benefits of using highly absorbing probes is to use a light source with better characteristics in the visible region. Light-emitting diodes (LEDs) have found some use for this purpose [13,[15][16][17][18] because they emit strongly in the visible region (and for some recent examples, also in the high-UV region [17]), have near monochromatic output, are highly stable, have long lifetimes, and are very affordable. Unfortunately, there are currently no commercially available LED-based detectors for CE.…”

Indirect photomeric detection of anions in capillary electrophoresis using dyes as probes and electrolytes buffered with an isoelectric ampholyte

“…Detection using the deuterium lamp at the absorption maximum of the dye did not bring about better signal-tonoise ratios because of considerably higher noise levels. It is well documented that LEDs are low noise-light sources and this can be used to advantage for photometric detection in CE [16]. An improvement in limits of detection by a factor of approximately two could be expected if an LED having an appropriate wavelength of maximum emission was to be used.…”