Determination of nitrite and nitrate in cerebrospinal fluid by microchip electrophoresis with microsolid phase extraction pre-treatment
Abstract
A new method for the determination of nitrite and nitrate, indicators of various neurological diseases(meningitis, multiple sclerosis, Parkinson’s disease) in cerebrospinal fluid (CSF) on an electrophoresis chipwas developed. An on-line combination of isotachophoresis (ITP) with capillary electrophoresis (CE) ona poly(methylmethacrylate) chip assembled with coupled separation channels (CC) and contact conduc-tivity detectors was employed.
ITP separations performed at low pH (3.6) in the first separation channelenabled a highly selective transfer of the analytes to the second CE stage working under micellar con-ditions implemented by zwitterionic surfactant, 3-(N,N-dimethyldodecylammonio)-propanesulfonate.The proposed method achieved low limits of detection varied from 0.2 to 0.4 g L−1when the samplevolume injected onto the chip (9.9 l) was almost the same as the volume of both separation chan-nels. Preferable working conditions on the CC chip (suppressed hydrodynamic and electroosmotic flow)contributed for reproducible migration velocities (intra-day reproducibility up to 2.1% RSD) and determi-nations of trace concentrations of nitrite and nitrate (intra-day precision up to 3.0% RSD).
Huge amount ofchloride present in CSF (approx. 4.5 g L−1) was removed from analyzed CSF samples by microsolid phaseextraction performed on silver-form resin prior to the ITP-CE analysis. Developed method provided fast(approx. 20 min total analysis time) and reliable determinations of trace nitrite and nitrate and could befully integrated into the analysis of CSF samples.