Capillary electrophoresis coupled with chloroform‐acetonitrile extraction for rapid and highly selective determination of cysteine and homocysteine levels in human blood plasma and urine

Abstract

A rapid and selective method has been developed for highly sensitive determination of total cysteine and homocysteine levels in human blood plasma and urine by capillary electrophoresis (CE) coupled with liquid-liquid extraction. Analytes were first derivatized with 1,1'-thiocarbonyldiimidazole and then samples were purified by chloroform-ACN extraction. Electrophoretic separation was performed using 0.1M phosphate with 30mM triethanolamine, pH 2, containing 25μM CTAB, 2.5μM SDS, and 2.5% polyethylene glycol 600. Samples were injected into the capillary (with total length 32cm and 50μm id) at 2250mbar*s and subsequent injection was performed for 30s with 0.5M KОН. The total analysis time was less than 9min, accuracy was 98%, and precision was <2.6%. The LOD was 0.2μM for homocysteine and 0.5μM for cysteine. The use of liquid-liquid extraction allowed the precision and sensitivity of the CE method to be significantly increased. The validated method was applied to determine total cysteine and homocysteine content in human blood plasma and urine samples obtained from healthy volunteers and patients with kidney disorders.