**7. Limitations of FTIR and 2DIR**

FTIR and 2DIR technique used in analysis has their limitations that could reduce the degree of efficiency. Fractions in solution form are not eligible for 2DIR analysis except using liquid sample cell, since special sample cell is needed to create high temperature changes and the rate of evaporation of the natural product solution is unknown. However, liquid sample cell is expensive. Besides, there is no appropriate FTIR equipment to capture the changes of spectrum within a few seconds, such as oxidation from the natural product. The thermal perturbation is commonly utilised for analysis of different substances and difficult to interpret compound with more than one isomers structure. However, no standardise method exist to determine the degree of peak differences. Some researchers agree that the range 2–3 cm−1 is for detecting the pure compound and the fraction, while the range 5–8 cm−1 is for the raw material and other materials. However, the acceptance of these ranges is still debatable. Lastly, there will be confusion on spectra for comparison when the quality of extraction is not the same especially the fractions.
