Preconcentration of 3-nitrotyrosine in urine by transient isotachophoresis in MEKC

The buffer in MEKC system plays an important role in stacking of an anion in urine. HEPES serves as a terminating electrolyte, and self stacking of nitrotyrosine in urine occurs when voltage is applied. Meanwhile, SDS is concentrated to fulfill the KRF rule. Nitrotyrosine and other component in urine would be enriched in the micelle stack. [Display omitted] ► Rapid and direct analysis of 3-nitrotyrosine in urine by MEKC was involved. ► We discussed concentration of an anion in high-salt stacking. ► We provided a new insight into high-salt stacking. Transient isotachophoresis (tITP), usually performed in CZE, is a useful on-line sample preconcentration technique for high saline samples. However, only a few papers have applied tITP in MEKC especially SDS system. This study compared tITP in MEKC with that in CZE for 3-nitro-tyrosine (NT) analysis in urine. No sample clean-up was required. Self-stacking occurred simultaneously as chloride in urine acted as a leading ion. HEPES–Tris buffer at pH 8.2 was used as a terminating electrolyte and separation buffer. UV detection wavelength was set at 426nm. Experiments showed that tITP in MEKC exhibited much higher peak efficiency (up to 1000000), and improved 4-fold sensitivity, compared with those by tITP in CZE. The limit of detection was 0.07μM for 3-nitrotyrosine in urine.