Trace gas detection of benzene, toluene, p-, m- and o-xylene with a compact measurement system using cantilever enhanced photoacoustic spectroscopy and optical parametric oscillator

A compact measurement system based on a novel combination of cantilever enhanced photoacoustic spectroscopy (CEPAS) and optical parametric oscillator (OPO) was applied to the gas phase measurement of benzene, toluene, and o-, m- and p-xylene (BTX) traces. The OPO had a band width (FWHM) of 1.3nm, was tuned from 3237 to 3296nm in steps of 0.1nm and so spectra of BTX at different concentrations were recorded. The power emitted by the OPO increased from 88mW at 3237nm to 103mW at 3296nm. The univariate detection limits (3σ, 0.951s) for benzene, toluene, p-, m- and o-xylene at 3288nm were 12.0, 9.8, 13.2, 10.1 and 16.0ppb, respectively. Multivariate data analysis using science-based calibration was used to resolve the interference of the analytes. The multivariate detection limits (3σ, 3237–3296nm, 591 spectral points each 0.951s) for benzene, toluene, p-, m- and o-xylene in the multi-compound sample, where all other analytes and water interfere were 4.3, 7.4, 11.0, 12.5 and 6.2ppb, respectively. Without interferents, the multivariate detection limits varied between 0.5 and 0.6ppb. The sum of the cross-selectivities (3237–3296nm, 591 spectral points, each 0.951s) per analyte were below 0.05ppb/ppb, with an average of 0.038ppb/ppb. The cross-selectivity of water to the analytes was on average 1.22×10−4ppb/ppb. The OPO is small in size (L×W×H 125×70×45mm), commercially available, and easy to operate and integrate to setups. The combination with sensitive CEPAS enables compact measurement systems for industrial as well as environmental trace gas monitoring.