Capillary electrophoresis analysis of nitrite and nitrate in sub-microliter quantities of airway surface liquid

We developed a simple capillary electrophoresis (CE) method to measure nitr ite and nitrate concentrations in sub-microliter samples of rat airway surf ace liquid (ASL), a thin (10-30 mum) layer of liquid covering the epithelia l cells lining the airways of the lung. The composition of ASL has been poo rly defined, in large part because of the small sample volume (similar to1- 3 mu1 per cm(3) of epithelium) and difficulty of harvesting ASL. We have us ed capillary tubes for ASL sample collection, with microanalysis by CE usin g a 50 mM phosphate buffer (pH 3), with 0.5 mM spermine as a dynamic flow m odifier, and direct UV detection at 214 mn. The limit of detections (LODs), under conditions used, for ASL analysis were 10 muM for nitrate and 30 muM for nitrite (S/N=3). Nitrate and nitrite were also measured in rat plasma. The concentration of nitrate was 102 +/- 12 muM in rat ASL and 70 +/-1.0 m uM in rat plasma, whereas nitrite was 83 +/- 28 muM in rat ASL and below th e LOD in rat plasma. After instilling lipopolysaccharide intratracheally to induce increased NO production, the nitrate concentration in ASL increased to 387 +/- 16 muM, and to 377 +/- 88 muM in plasma. The concentration of n itrite increased to 103 +/-7.0 muM for ASL and 138 +/- 17 muM for plasma. ( C) 2001 Elsevier Science B.V. All rights reserved.