Calculating Pathlength of Liquid Cells
FTIR analysis of liquid samples is often done using either a sealed liquid cell or demountable liquid cell using a spacer of optimal thickness. When making comparisons of results from different cells, it is important to know the actual cell pathlength. The transparent windows have parallel sides and smooth surfaces and measurement of the FTIR spectrum from an empty cell will produce a well known “fringing effect”1, 2, which originates from constructive and destructive interference of the IR beam from the parallel surfaces of the cell. This effect is clearly seen in the FTIR spectrum (Figure 1) of an empty Demountable Liquid cell with 0.05 mm spacer installed.
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