Laser Photolytic Fragmentation-Fluorescence Spectrometry of Ammonia and Aliphatic Amines

Abstract

Ammonia and eight aliphatic amines (ranging in alkyl chain length from C1 to C16) are photolyzed at 193 nm, producing fluorescent molecular fragments (NH from ammonia; CN, CH, and NH from the amines). Fluorescence from NH is used to quantify ammonia; CN fluorescence is used to quantify the amines. Limits of detection in the 10–50 pmol regime, precision of ∼6% RSD, and linear dynamic ranges of 1–3 decades in quantity of parent compound are observed. A small but discernible “large molecule effect” exists; as the size of the alkyl chain in RNH2 increases, the limit of detection increases, and the dependence of the fragment fluorescence signal on photolysis laser fluence also increases. Attempts to enhance fragment fluorescence intensities via “probe-laser” excitation of ground-state fragments were unsuccessful; it is inferred that, at the photolysis fluences employed (∼2 × 1018 photons/cm2), few ground-state fragments are formed.