Industrial problem solving using infrared photoacoustic spectroscopy

Abstract

Until recently photoacoustic detectors coupled to infrared spectrophotometers were low signal-to-noise devices. Often long acquisition times and low resolution were used in order to obtain any spectrum at all.

However, newer designs of photoacoustic detectors which are optimized for use in the infrared have become available. Nearly theoretical signal-to-noise values of 2000/l for a single 8 cm⁻¹ scan have been observed using the MTEC photoacoustic detector on the Perkin-Elmer Model 1800 FT-IR. Using this combination of photoacoustic detector and the Model 1800, it is feasible to conduct quantitative measurements and so it becomes very important to understand the parameters of the measurements which determine the precision.

This paper will discuss the various types of analysis that can be performed on industrial samples by using a photoacoustic detector. Aspects of sample handling and the effect of mirror velocity in the interferometer on quantitative analysis will be discussed. Not only will quantitative results be reported, but also the results of spectral difference calculations, which require the same precision as quantitative measurements, will be presented. Depth profiling and sample identification will also be discussed.