How do you read IR spectrum graphs?

Hint : IR spectrum that is infrared spectroscopy is the measurement or analysis of infrared radiation or light with matter or molecule by means of emission, reflection and absorption. It is basically used to determine chemical substances or functional groups in solid, liquid or gas.

Complete Step By Step Answer:
In any given IR spectrum the first thing to do is divide it into two parts. Draw a vertical line at $ 1500 $ . The region before $ 1500 $ that is a functional group region and region beyond $ 1500 $ fingerprint region. Just like a fingerprint is unique for every person, fingerprint region is also unique to every chemical so if we match any peak from fingerprint region to some known chemical peak value we will find out the exact component. On the other side we have a functional region or diagnostic region, now here also we need to analyse every peak to know which functional groups are present in the substance. IR correlation table has a functional group with its wavenumber that is peak value which will help us to identify the functional group present in any substance. Presence of impurity causes a peak in the graph and if the peak value matches any known impurity then we could use this to calculate purity.

Note :
IR spectrum is a simple method which is widely used in research and various industries. It is used for quality control and dynamic measurements. It is a very useful method to use in forensic analysis to analyse structural, compositional and functional change in cells and tissues.