Fig. 19 Micromanipulator attached to a laboratory microscope. The manipulator allows precise control of the tungsten needle which is used to pick up particles for analysis.

The best FTIR-PAS spectra of microparticles are obtained with low mirror velocities, a helium gas atmosphere, and adequate time for the desiccant to work. It is possible to measure spectra of single particles as small as 25 micrometers in diameter with the standard 2X reduction mirror of MTEC photoacoustic detectors at an OPD FTIR mirror velocity of 0.05 cm/s. FTIR-PAS analysis of smaller particles should be possible with higher concentration of the beam intensity on the sample and lower mirror velocity.
Spectra of three single coal particles are plotted in Fig. 20 with a macrosample spectrum of the same coal at the top of the figure. The coal particle size is between 125 and 150 micrometers. The particle spectra show that there are a number of compositional differences in coal particles in this size range related to mineral, hydroxyl, and aromatic/aliphatic concentrations.