Open-path FT-IR spectrometry: is completely unattended operation feasible

Most protocols used for open-path Fourier transform infrared spectrometry ( OP/FT-IR) require that spectra be measured at a resolution of 1 cm(-1) and that the concentrations of the analytes be calculated by classical least sq uares regression (CLS). These specifications were largely developed for mon itoring light molecules with easily resolvable rotational fine structure. F or most volatile organic compounds in air, the rotational fine structure is not resolvable and better accuracy can be obtained when the spectrum is me asured at lower resolution (typically 8 cm-l), provided that the algorithm used for quantification is partial least squares regression (PLS). By measu ring the spectrum at low resolution, the need for a liquid-nitrogen-cooled mercury cadmium telluride detector is reduced and a pyroelectric detector o perating at ambient temperature can be used instead. By using PLS rather th an CLS, spectral features due to water vapor do not have to be compensated and a short-path background spectrum can be used, greatly simplifying field measurements. (C) 2000 Elsevier Science B.V. All rights reserved.