Question

How is infrared spectroscopy used in an industry to find the purity of an ester?

Answer 1

There are various ways which are used to purify the ester but recently the way which is used in industries to find the purity of an ester is called differential infrared spectroscopy. In this method, the sample ester spectrum is compared to the pure ester.

Complete answer:
There are various ways which are used by the industry to find the purity of samples of an ester. In the old times the way used was quite simple. In the old way, periodically the infrared spectrum of the given sample was recorded and then that spectrum was compared with the infrared spectrum of the pure ester.
If the peaks which were caused by the presence of impurities, were then matched with those of known impurities then they can be used in the intensities to calculate the purity of an ester.
There is also a new way, which is recently used in the industry to find the purity of an ester is a method which is called differential infrared spectroscopy. In this method, the ester flows through a machine in a continuous flow process. A spectrum will be obtained periodically and then a stored spectrum of the pure spectrum will be subtracted from that of the sample digitally. Then the spectrum of the impurities can be compared to the stored database of impurities.
After that the computer identifies the impurity and automatically determines a report on the composition of the ester. And then the purity of an ester can be determined.

Note:
In the differential infrared spectroscopy, The carbonyl stretch $C = O$ of aliphatic esters appears from $1750 - 1735c{m^{ - 1}}$ ; that of α, β-unsaturated esters appears from $1730 - 1715c{m^{ - 1}}$ .