Rapid determination of catecholamines in urine samples by nonaqueous microchip electrophoresis with LIF detection

Separation and determination of 3-hydroxyaspartate by online concentration capillary electrophoresis/laser-induced fluorescence with microwave-assisted derivatization

A chiral analytical method was proposed based on capillary electrophoresis with laser-induced fluorescence detection coupled with microwave-assisted derivatization for the simultaneous baseline separation and sensitive detection of four stereoisomers of 3-hydroxyaspartate. The derivatization reaction of 3-hydroxyaspartate with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole was greatly accelerated by microwave irradiation. Under the optimized conditions, the derivatization yield was increased by 20% and the derivatization time was shortened by 20 min when compared with those from conventional water bath heating. In addition, the sensitivity was improved by online sample concentration methods. The detection limit of l-threo-3-hydroxyaspartate obtained by large-volume sample stacking with polarity switching was 5.3 nmol/L, which was around 1000-fold lower than that of the capillary electrophoresis/laser-induced fluorescence without stacking. The excellent analytical performance in terms of linearity and precision was also achieved. Furthermore, the developed method was successfully applied to the determination of 3-hydroxyaspartate in the spiked urine, and satisfactory recoveries were obtained ranging from 90.5 to 107.0%.

Non-aqueous electrophoresis integrated with electrospray ionization mass spectrometry on a thiol-ene polymer-based microchip device

Non-aqueous capillary electrophoresis (NACE) on microfluidic chips is still a comparatively little explored area, despite the inherent advantages of this technique and its application potential for, in particular, lipophilic compounds. A main reason is probably the fact that implementation of NACE on microchips largely precluded the use of polymeric substrate materials. Here, we report non-aqueous electrophoresis on a thiol-ene-based microfluidic chip coupled to mass spectrometry via an on-chip ESI interface. Microchips with an integrated ESI emitter were fabricated using a double-molding approach. The durability of thiol-ene, when exposed to different organic solvents, was investigated with respect to swelling and decomposition of the polymer. Thiol-ene exhibited good stability against organic solvents such as methanol, ethanol, N-methylformamide, and formamide, which allows for a wide range of background electrolyte compositions. The integrated ESI emitter provided a stable spray with RSD% of the ESI signal ≤8%. Separation efficiency of the developed microchip electrophoresis system in different non-aqueous buffer solutions was tested with a mixture of several drugs of abuse. Ethanol- and methanol-based buffers provided comparable high theoretical plate numbers (≈ 6.6 × 10⁴-1.6 × 10⁵ m^-1) with ethanol exhibiting the best separation efficiency. Direct coupling of non-aqueous electrophoresis to mass spectrometry allowed for fast analysis of hydrophobic compounds in the range of 0.1-5 μg mL^-1 and 0.2-10 μg mL^-1 and very good sensitivities (LOD ≈ 0.06-0.28 μg mL^-1; LOQ ≈ 0.20-0.90 μg mL^-1). The novel combination of non-aqueous CE on a microfluidic thiol-ene device and ESI-MS provides a mass-producible and highly versatile system for the analysis of, in particular, lipophilic compounds in a wide range of organic solvents. This offers promising potential for future applications in forensic, clinical, and environmental analysis. Graphical abstract.

Microfluidic chip-capillary electrophoresis device for the determination of urinary metabolites and proteins

Microfluidic chip-CE (MC-CE) devices have caught recent attention for diagnostic applications in urine. This is due to the successes reported in handling real urine samples by integrating microfluidic chips (MC) with analyte enrichment and sample cleanup to CE with high separation efficiency and sensitive analyte detection. Here, we review the determination of urinary metabolites and proteins by MC-CE devices within the past 7 years. The application scope for MC-CE integrated devices was found to exceed the use of either technique alone, showing comparable performance to laser-induced fluorescence detection using less sensitive UV detectors, offering the flexibility to handle difficult urine samples with on-chip dilution and online standard addition and delivering enhanced performance as compared with commercial microfluidic chip electrophoresis chips.