| Environmental concerns regarding the leaching of cadmium (and other metals) from ash pits, and the concomitant legislation which has recently been enacted in Europe and elsewhere, has driven a search for rapid, simple analyses of plastics and incinerator ash fro the presence of metals.
Most infrared analysis is done in the mid-IR range (around 4000 to 400 cm-1). However, because the frequency of a vibration is inversely proportional to the square-root of the reduced mass, the frequency drops as the molecular weight rises. Thus, for high molecular-weight species such as metallic complexes or some halides, this relationship shifts the vibrations into the far-IR, roughly defined as below 400 cm-1.
Most far-IR samples are analyzed by transmission, after processing the sample. However, moisture affects far-IR spectra badly, so the purge system must clear moisture from the spectrometer after each sample loading.
AN50827 provides an automated method for quickly changing the detector and spectral ranges, and purging the system with dry air.
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