Quenched Phosphorescence Detection in Cyclodextrin-Based Electrokinetic Chromatography

Abstract

Quenched phosphorescence detection is a sensitive detection method recently introduced in capillary zone electrophoresis. It is based on the dynamic quenching interaction of the analytes (quenchers) with a phosphorophore, 1-bromo-4-naphthalenesulfonate (BrNS), present in the separation buffer. In this study, it is shown that this detection method can also be used in cyclodextrin-based electrokinetic chromatography (CD-EKC) despite the presence in the buffer solution of cyclodextrins, which are known to reduce the luminescence quenching rate constants. Experiments indicate that BrNS mainly resides in the aqueous phase, while the analytes are distributed between both phases. In principle, the observed quenching might arise from the interaction of BrNS with uncomplexed as well as complexed analytes. However, from the dependence of the fractional quenching on the capacity factor (the normalized fractional quenching was found to be equal to the fraction of analyte in the aqueous phase), it was concluded that only aqueous-phase quenching contributes significantly to the observed quenching. Nevertheless, separation and detection can be regarded as fully compatible, because the capacity factors encountered in CD-EKC are generally low (in this study they ranged from about 0.1 to 2.5). Indeed, with nitroaromatic compounds as the target analytes, limits of detection in the 10(-8) M range were achieved.

Sensitive chiral analysis by capillary electrophoresis

“…The basic instrumentation is the same as for LIF detection [114] but a UV-Vis lamp has usually been employed [115][116][117][118]. There are two additional settings in phosphorescence not used in fluorescence: the delay time (time of waiting after the lamp pulse to remove all fluorescence from the signal) and the gating time (time of measurement of the phosphorescence signal), which have to be considered.…”

Laser‐induced quenched phosphorescence detection in capillary electrophoresis

“…A device was designed to allow injection of samples while maintaining the deoxygenated buffer conditions required for obtaining phosphorescence. This device as well as the CE program used to perform the separations has been discussed in detail before [6]. Samples were injected using 5066 mbar?s.…”

“…Hence, for compounds that show no photodecomposition and for which W ISC is equal to zero, the population of the ground state will be constant for every pulse. However, when triplets are involved and the solution is deoxygenated, the situation is completely different: for BrNS, W ISC is close to unity and the triplet excited states thus generated are far from completely deactivated when the next pulse arrives (t 0 , 300 ms) [6,11].…”

Sensitized phosphorescence as detection method for the enantioseparation of bupropion by capillary electrophoresis

“…Cooling with nitrogen gas around the capillary was applied to keep the temperature constant, and the samples were injected by pressure (50 mbar for 0.16 min). A modified vial was used to purge the buffer solution continuously with nitrogen since deoxygenation of the buffer is required to observe RTP [13]. The nitrogen flow rate was kept constant with a flow regulator.…”

“…In this article, we investigate whether room temperature phosphorescence (RTP) is an appropriate alternative detection technique, focusing on the chiral drug bupropion. RTP in liquid deoxygenated solutions has shown to be an attractive luminescence spectroscopic method for detection in CE [12][13][14][15][16][17][18][19]. Contrary to fluorescence, its lifetime is in the 0.01-10 ms range so that scattering problems and impurity fluorescence can be readily avoided by means of time resolution.…”