Portable analytical system integrating purge and trap and microplasma optical emission spectrometry for online discriminative detection of NOx

Pollution caused by nitrogen oxides (NO x , mainly NO and NO 2 ) has attracted considerable attention due to its negative implications on the environment and human health. Herein, a novel, portable, and battery-operated system integrating a purge and trap (P&T) system with a miniaturized point discharge optical emission spectrometer ( μ PD-OES) was developed for monitoring atmospheric NO x . Among NO x , NO 2 can be selectively and directly absorbed by sodium hydroxide (NaOH) solution and converted to nitrite (NO 2 − ). In contrast to NO 2 , NO cannot be absorbed by NaOH and must be oxidized to NO 2 by KMnO 4 prior to its absorption. When NO 2 and NO x samplers were exposed simultaneously, NO can be calculated as the difference. The concentration of NO x in the air was determined by analyzing the NO 2 − . The obtained NO 2 − solution was purged with an argon carrier gas at a rate of 400 mL min −1 for 5 min to remove all the volatile organic compounds contained in the solution before reacting with cyclamate to generate volatile cyclohexene, which was efficiently isolated and preconcentrated by P&T. Subsequently, the cyclohexene was desorbed from the P&T unit and swept into the μ PD-OES for its detection under optimized conditions. The system demonstrated a detection limit of 0.02 ppbv (0.04 μg/m 3 ) for NO 2 , surpassing conventional methods. Precision expressed as the relative standard deviation (RSD, n = 11) was better than 3.5 %. The system was validated by analyzing two NO 2 standard gases and fourteen ambient air samples, and the obtained analytical results demonstrated its promising potential for rapid, sensitive, and precise NO x evaluation and monitoring.