IV. SAMPLE HANDLING

A. General Considerations

The only sample preparation necessary with FTIR-PAS measurements is to have a sample size smaller than 10 mm in diameter in order to fit into the sample holder. The thickness should not exceed 6 mm. Any sample geometry can be directly analyzed including disks, slabs, chips, chunks, pellets, powders, fibers, and sheets. Semi-solid and liquids can also be analyzed. Larger samples are cut or abraded to suitable dimensions, typically using razor a blade, scissors, hacksaw, corker borer (#6), or a file or abrasive. Figure 4 shows a typical sample ready for analysis.

Fig. 4 Sample holder with a polymer chunk sample ready to be inserted into the photoacoustic detector.

B. Sample loading

A MTEC sample holder is shown in Fig. 5 with large and small stainless steel sample cups and brass spacers. The latter are used to minimize the gas volume and thereby increase the photoacoustic signal. A small cup is shown in Fig. 6 placed in the sample holder. A funnel for loading powdered samples and other components for handling samples are shown in the figure also. The sample should be approximately one millimeter below the rim of the sample holder in order to allow a layer of gas between the sample and the detector window for photoacoustic signal generation in the gas. If very high or low modulation frequencies are used, an approximate distance that the sample should be below the cup rim can be calculated from the formula where D = 1.51 cm²/s for helium and D= 0.187 cm² for air. The value used for f, when a rapid scan FTIR spectrometer is used, should be calculated from wereis the lowest wave number value in the spectrum.