**8.1 Fourier-transform infrared spectroscopy (FTIR)**

FTIR has proven to be a valuable tool for the characterization and identification of compounds or functional groups (chemical bonds) present in an unknown mixture of plant extracts. It helps for identification and structure determination of the molecule. In addition, FTIR spectra of bioactive compounds are usually so unique that they are called as a molecular "fingerprint." Once the isolation of bioactive compound is possible, then drying of extract and isolates using rotary evaporator is done. Dried powdered plant extract spectrum can be obtained from FTIR. FTIR software contains library of known compounds, and thus, the spectrum of an unknown compound can be identified by its comparison. Preparation of samples for FTIR analysis can be done in different ways. In earlier years, solid herbal plant extract powder was milled with potassium bromide (KBr) with good trituration techniques and then compressed into a thin pellet, which can be analyzed. Now due to new advancements, only solid or liquid sample is available and you only have to place one drop or one pinch of sample between two plates and the drop or sample forms a thin film between the plates. It is the easiest way for performing FTIR, and graphs and wave number are recorded by using computer-based software. The region in IR spectrum above 1200 cm<sup>−</sup><sup>1</sup> shows spectral bands or peaks due to the vibrations of individual bonds or functional groups under examination. The region below 1200 cm<sup>−</sup><sup>1</sup> is known as the 'fingerprint region.' It indicates bands due to the vibrations of the complete bioactive molecule. Complexity of compounds is seen in fingerprint region. Intensities of the various bands in FTIR are recorded specifically on a simple scale as strong (S), medium (M), or weak (W). And as per new techniques developed, the advanced instruments of company bruker, jasco has made easier by application of one drop or pinch of sample on the instruments and this software will give the results. Lastly, the advantage is that samples can be reused.
