Gas phase microdialysis and chemiluminescence detection: A small, fast, selective, and sensitive method to monitor aqueous nitric oxide.

A method using a gas-phase microdialysis probe interfaced with a modified commercially available nitric oxide (NO) detector is shown to selectively measure aqueous NO at low µM levels with high selectivity. The detector measures chemiluminescence resulting from the gas-phase reaction of NO with ozone. The microdialysis probe is small enough (3 mm × 200 µm) to be used in vivo. Because the processes of extraction across the microdialysis membrane and transport from the probe to the detector are both very fast, the response time is shorter than 5 s. The method was verified using two different quantifiable sources of NO: nitrite and methylamine hexamethylene methylamine (MAHMA) NONOates. To demonstrate ruggedness and to show the impact of matrix on NO generation, the method was used to measure NO in a cell culture matrix. The continuous extraction, fast response time, and rugged nature make the method useful for monitoring NO in biological applications. Our results also show that predicting NO concentration for in vitro experiments based on NONOate concentration may be a poor assumption due to the pH dependence of NO formation and the rapid decline in NO concentration.

Analysis and monitoring of volatile analytes from aqueous solutions by extractions into the gas phase using microdialysis membranes and coupling to fast GC.

Microdialysis membranes (3 mm lengthx200 microm i.d.) have been used to extract volatile analytes from aqueous samples into the gas phase and interfaced with fast gas chromatography. Gas-phase extracts generated from aqueous samples reach steady-state concentrations and are transported to the detector in 5 s. The recovery of the system ranges from 1.28% for toluene to less than 0.1% for ethanol. The lowest detectable concentration without preconcentration was 5 mM for most compounds using a flame ionization detector, and as low as 0.01 mM for more volatile hydrophobic analytes. When interfaced with a fast GC system, changes in aqueous phase concentrations were monitored with a temporal resolution of 10 s.