Micellar electrokinetic capillary chromatography for fast separation and sensitive determination of melatonin and related indoleamines using end‐column amperometric detection

Abstract

MEKC was used in conjunction with end-column amperometric detection (AD) at a carbon disc electrode (0.3 mm diameter) for the selective and sensitive determination of melatonin and its five related indoleamines including its precursors and metabolites in the pineal gland. The introduction of a sample stacking technique in injection and the buffer additive SDS in the buffer solution system provided the rapid and sensitive analysis. Optimal buffer conditions (10 mmol/L phosphate containing 20 mmol/L SDS, pH 7.2), detection potential (+1.0 V vs. Ag/AgCl), and electrokinetic injection 10 s with the separation voltage of 24 kV were employed to achieve the baseline separation of six pineal hormones within 15 min. The peak currents and the analyte concentrations have a good linear relationship over the range of 6.0 x 10(-8) 6.0 x 10(-5 )mol/L. The detection limits for six pineal hormones by AD are 9.7 to 41.8 nmol/L (equal to 2.0 to 9.7 ng/mL) (S/N = 3), respectively. It is proved to provide about 30- to 250-fold improvement over UV, and be comparable with the sensitive fluorescence detection, which needs pre-column derivatization. The proposed method has been applied for analysis of melatonin and related indoleamines in rat pineal glands. A very simple sample pretreatment procedure, merely involving the homogenization step in perchloric acid, was enough to achieve recoveries in the range of 71 to 127% for all the analytes in the pineal gland.

Measurement of melatonin in body fluids: Standards, protocols and procedures

“…Detection of analyte was performed with a UV and fluorescence [124–126, 129] or electrochemical detector [127, 128]. The detection limit of melatonin with CE is comparable with the data obtained by HPLC methods reported previously.…”

“…Some laboratories have taken and developed capillary electrophoresis (CE) for the separation and determination of melatonin in blood plasma [124–126] and in pineal gland [127, 128]. Detection of analyte was performed with a UV and fluorescence [124–126, 129] or electrochemical detector [127, 128].…”

“…The detection limit of melatonin with CE is comparable with the data obtained by HPLC methods reported previously. Recently, for the separation of melatonin from related compounds, CE with micellar electrokinetic chromatography was applied [125, 126, 128, 129]. This technique permitted the effective separation of melatonin and its precursors or metabolites.…”

Highly sensitive analysis of nucleic acids using capillary gel electrophoresis with ultraviolet detection based on the combination of matrix field-amplified and head-column field-amplified stacking injection

“…Under field-amplified stacking injection (FASI), two modes termed head-column field-amplified stacking injection (HC-FASI) and matrix field-amplified stacking injection (M-FASI) are frequently applied. HC-FASI injects a short low-conductivity medium (such as a water-plug) before electrokinetic injection [21][22][23][24][25][26], and M-FASI utilizes a low-conductivity medium (such as deionized water) to reduce the ion strength of the sample solution before electrokinetic injection [27][28][29][30][31]. However, they offer limited effects in enhancing sensitivity.…”

Enhanced sensitivity and resolution for the analysis of paralytic shellfish poisoning toxins in water using capillary electrophoresis with amperometric detection and field‐amplified sample injection

“…Due to its versatility and compatibility, CE with electrochemical detection represents a sensitive and widely used method in real application . Especially, amperometric detection (AD) has attracted much attention in portable designs, owing to its ease of miniaturization at a low cost relative to other detectors, as well as the enhanced selectivity as a result of the limited number of electroactive substances.…”