On-line sample concentration via micelle to solvent stacking of cations prepared with aqueous organic solvents in capillary electrophoresis

Innovative analysis of diazepam, zolpidem and their main metabolites in human urine by micelle-to-solvent stacking in capillary electrophoresis

Diazepam and zolpidem are the most widely used medications for managing insomnia. However, significant concerns regarding the potential risks of misuse and abuse problems arose in many literatures. While urine analysis is a valuable diagnostic tool, a challenge arises from the fact that some parent drugs may remain undetectable in urine. This necessitates concurrent monitoring of their metabolites. Here, we described an innovative on-line sample preconcentration technique known as micelle to solvent stacking (MSS) for the analysis of diazepam, zolpidem, and their main metabolites in urine. Several key parameters warrant further discussion to optimize the MSS model, enhancing its performance in terms of sensitivity and resolution. After optimizing the conditions, we conducted a validation test, achieving high correlation coefficients (greater than 0.9977) for intra-day and inter-day regression lines. Additionally, both the relative standard deviation (RSD) and relative error (RE) remained below 6.10% and 12.55%, respectively. The limits of detection (LODs, S/N = 3) for all five analytes ranged from 2.0 to 56 ng/mL. Compared to the conventional capillary zone electrophoresis method, this new approach exhibited remarkable sensitivity enhancements, ranging from 123 to 235-fold. Upon applying this method to actual urine samples from patients, we successfully detected nordiazepam, zolpidem, and its metabolites. This simple and sensitive approach has promising applications in supporting patient medication safety and bolstering forensic investigations.

A dual preconcentration method by combining micro matrix solid-phase dispersion extraction with field-enhanced sample injection and micelle to cyclodextrin stacking for sensitive analysis of neutral coumarins

A rapid, sensitive, environmental friendly dual preconcentration method by combining micro matrix solid-phase dispersion extraction with field-enhanced sample injection and micelle to cyclodextrin stacking has been developed for the determination of furocoumarins. Molecular sieve, KIT-6, was used as an adsorbent in micro matrix solid-phase dispersion process. The important parameters affecting off-line and online CE preconcentration efficiency were optimized. Under the optimal experimental conditions, all analytes showed good linearity (R² > 0.999). The LODs of notopterol, isoimperatorin, and imperatorin were 0.1 μg/mL, 1.2 mg/kg, and 1.0 mg/kg, respectively. Compared with the normal CE method, the enrichment times were up to 300. Moreover, Angelicae Dahuricae Radix was used as the mode of complex solid sample matrix to demonstrate the prospect of application of this methodology. The results showed the proposed strategy is promising for determining trace furocoumarins in complex matrix samples, which might be applied as a powerful and economic tool in monitoring illegal cosmetic adding.

Simultaneous determination of five metal ions by on-line complexion combined with micelle to solvent stacking in capillary electrophoresis

A direct on-line complexion combined with micelle to solvent stacking method was proposed for simultaneous determination of metal ions by capillary electrophoresis coupled diode array detector. During the experiment, a plug of complexing agent was first injected to the inlet of capillary, followed by introducing the micelle-bound metal ions. Then the metal ions produced a micelle-to-solvent stacking effect and interacted with the complexing agent under a positive voltage. Continued application of voltage, the analytes were effectively focused and separated in the capillary zone electrophoresis. Repeatability was ranged from 1.89% to 1.94% for the migration time. The detection limits were 2.66-27.9 ng mL^-1 for Ni²⁺, Co²⁺, Cu²⁺, Hg²⁺ and Cd²⁺. Furthermore, the developed method showed a great potential for the determination of metal ions in the crayfish, beebread and Dendrobium officinale samples.

On-line two-step stacking in capillary zone electrophoresis for the preconcentration of strychnine and brucine

An on-line sample preconcentration method by two-step stacking i.e., sweeping and micelle to solvent stacking, in capillary zone electrophoresis (CZE) has been developed for the determination of strychnine and brucine in traditional Chinese herbal medicines. After experimental optimizations, the best separation was achieved by using 75 mM phosphate buffer (pH 2.5) with 30% methanol (v/v). Compared with normal CZE injection, 51- and 38-fold improvement in concentration sensitivity was achieved for strychnine and brucine, respectively. The calibration curve was linear in the range of 0.1-5.0 μg mL(-1) for both strychnine and brucine, with the correlation coefficients of 0.9998 and 0.9997, respectively. The limits of detection (S/N=3) for both alkaloids were 0.01 μg mL(-1). The inter-day (n=8) and intra-day (n=5) reproducibilities expressed as the relative standard deviations for corrected peak area were less than 9.5%. The method was applied to determine strychnine and brucine in two Chinese herbal medicines, with recoveries ranging from 94.2% to 105.4%. The results indicated that the method is simple, rapid, reliable, and can be applied to determine strychnos alkaloids in traditional Chinese herbal medicines.