Impurity detection using FTIR

Analytically, IR (FTIR) spectroscopy is unquestionably one of the most versatile techniques available for the measurement of molecular species in the laboratory today, and also for applications beyond the laboratory. A major benefit of the technique is that it may be used to study materials in almost any form, and usually without any modification all three physical states are addressed solids, liquids and gases. Also, it is a fundamental molecular property, and as such the information content can be considered to be absolute in terms of information content, and as such can be very diagnostic in terms of material purity and composition. Traces of impurities can be both uniquely detected and in most cases characterized. This is a very important attribute in a process analytical enviromnent. 

The shallow hydrogenlc donors, on the other hand, have small binding energies and also have small central-cell corrections. This makes the resolution of different donors resulting from different chemical impurities difficult to achieve. The early experiments from which different chemical donors were identified employed hlgh-resolutlon Fourier-transform infrared magnetospectroscopy (FTIR) which used the modulated photoconductivity detection technique to monitor the 1S-2P transition In a fixed magnetic field. 

Infrared spectroscopy is an effective way to identify the presence of certain frmctional groups in a molecule. Also, one can use the unique collection of absorption bands to confirm the identity of a pure compound or to detect the presence of specific impurities [19, 20]. The FTIR spectra of wheat straw and pretreated wheat straws (Fig. 4) initially appeared rather similar. However, in a closer examination, spectra of pretreated wheat straw with water (lines 2 and 3) were similar to those of untreated wheat straw (line 1), and spectra of NaOH pretreated wheat straw (lines 4-7) can be clearly distinguished from those of untreated wheat straw (line 1) by the disappearance of ester linkage absorption (1,733 cm band). 

---