Trace detection of NO and NO 2 by photoionization and laser induced fluorescence techniques

Abstract

The analytical capabilities of photoionization spectroscopy (PIS) and laser induced fluorescence (LIF) techniques have been evaluated to determine the relative merits of each technique for measurements of NO and NO 2 at the ppb and sub-ppb level. For both techniques, excitation is accomplished via the A–X (1,0) band of NO near 215 nm. For the ionization measurements, a (1 + 1) PIS scheme is utilized where NO molecules are photoionized by a second laser operating at 355 nm. Nitrogen dioxide (NO 2) is determined by a photofragmentation approach where NO is photofragmented from the parent molecule and then detected by PIS. Limits of detection by the PIS approaches are 0.05 ppb for NO in air and 6 ppb for NO 2 in air. For LIF, fluorescence emission is measured via the A–X (0,1) band at 237 nm. Limits of detection by LIF are 0.2 ppb and 30 ppb for NO in N 2 and air, respectively.