Pressure-assisted electrokinetic injection for the stacking of biogenic amines gives enhancement factor up to 1000 in CE with UV detection

Pressure-assisted electrokinetic injection (PAEKI) was applied for stacking of positively charged biogenic amines (BAs) to improve the sensitivity of capillary electrophoresis (CE). It is well known that the essential step for PAEKI is finding a stationary state of the running buffer such that the movement of the running buffer due to electroosmotic flow (EOF) is counterbalanced by external pressure in the opposite direction of the EOF under a given electric field. In order to find the balance point systematically and integrally, we studied the velocity of the whole BGE in the capillary by the impetus of opposite direction pressure (-0.1 to -0.6 psi), and the velocity of EOF with different voltages. According to the two sets of linear data, the EOF of CE coupled with PAEKI could be counterbalanced at the opposite direction pressure (-0.1 psi) and voltage (7.8 kV). In this study, the injection time was extended up to 0.35 min for all BAs and 0.70 min for the direct ultraviolet (UV) detection of BAs. Compared with hydrodynamic injection (HDI), the enrichment factors for sample injection times of 0.35 min and 0.70 min were 480-fold and 970-fold, respectively. The limits of detection (LODs) (S/N = 3) of indirect and direct UV detection were respectively 8.7-24.3 nmol L^-1 and 0.4-4.5 nmol L^-1, which reaches the sensitivity of high-performance liquid chromatography-mass spectrophotometry (HPLC-MS). With appropriate sample dilution, PAEKI can be used in the analysis of BAs in chicken.

CE-MS with electrokinetic supercharging and application to determination of neurotransmitters

Electrokinetic supercharging (EKS) is known as one of the most effective online electrophoretic preconcentration techniques, though pairing with it with mass spectrometry has presented challenges. Here, EKS is successfully paired with ESI-MS/MS to provide a sensitive and robust method for analysis of biogenic amines in biological samples. Injection parameters including electric field strength and the buffer compositions used for the separation and focusing were investigated to achieve suitable resolution, high sensitivity, and compatibility with ESI-MS. Using EKS, the sensitivity of the method was improved 5000-fold compared to a conventional hydrodynamic injection with CZE. The separation allowed for baseline resolution of several neurotransmitters within 16 min with LODs down to 10 pM. This method was applied to targeted analysis of seven biogenic amines from rat brain stem and whole Drosophila tissue. This is the first method to use EKS with CE-ESI-MS/MS to analyze biological samples.

Analysis of Seven Biogenic Amines and Two Amino Acids in Wines Using Micellar Electrokinetic Chromatography

A low-cost, simple, and fast method utilizing micellar electrokinetic chromatography for the simultaneous determination of seven biogenic amines and two amino acids was developed. A background electrolyte containing 5 mM phosphate buffer (pH 3.7) and 20 mM sodium dodecyl sulfate was used. The optimal separation of nine investigated analytes was achieved in 11 min, with limits of detection (S/N = 3) ranging from 0.11 to 0.61 µM. The linear ranges for all analytes were observed between 0.55 and 10.0 μM (R2 > 0.990). The developed approach was extended to the analysis of analytes in commercial wine and beer samples. The recoveries of the proposed method ranged from 98.8% to 115.6%.