Plant hormones, also known as phytohormones, are naturally occurring signalling molecules that influence physiological processes, such as plant growth, differentiation and development [1,2,3]. They include a wide variety of organic compounds, which regulate physiological processes at extremely low concentrations [4,3].
The first class of plant hormones to be identified were auxins already in the late 1920s . Later investigations resulted in the discovery of other classes of hormones, ethylene, gibberellins, cytokinins, and abscisic acid. More recently further groups of compounds were identified as plant hormones, such as brassinosteroids, jasmonates and salicylic acid , and most recently strigolactones were discovered.
Plant hormones can cause a lot of change in plants and each hormone has its distinct job. Auxins positively influence cell enlargement, bud formation, and root initiation ; gibberellins are responsible for stem elongation , ethylene stimulates the ripening of fruit, the opening of flowers, and the shedding of leaves ; cytokinins regulate a number of important developmental processes ; abscisic acid is an important plant growth inhibitor ; jasminates have an important role in plant defence , by deterring insect feeding; and salicylic acid plays an essential role in the defence against pathogens . In most of the cases various plant hormones effect not only one, but a wide range of physiological processes in plants.
Phytohormones interact with each other and act together either in unison or in opposition to each other. The responses given by the plant to various environmental changes is the result of the effect of the hormonal balance. [3,11]
Although the term ‘hormone’ used in medicine has begun to carry the meaning, ‘a chemical transported message’, long distance transport has not been demonstrated for all plant hormones. By way of example the production of the gas ethylene can act at very short distances triggering changes within the same tissue, or even within the same cell, where it has been synthesized. 
The accurate identification and quantification of plant hormones is essential for determining their biological activity, as it depends on the concentration of these compounds in the plant . The development of sensitive analytical methods is critical for gaining a better understanding of the biosynthesis of hormones in the plants, of how chemical signals are transmitted through a cell, and about the effects of various compounds .
However, the extremely low concentration of these compounds makes their effective extraction and analysis difficult  calling for the application of highly sensitive techniques. For the identification and quantification of plant hormones the plant tissue must be first homogenized and extracted and then purified, during which a pure sample is prepared for the analysis through removing interfering substances from the crude extract .
The advancement of the technology has made analysis much easier. A couple of decades ago it was not uncommon that hundreds of grams of plant tissues were needed for purification. In contrast, nowadays only a few milligrams of tissue are sufficient for the determination of hormone levels in certain organs of the plant . Furthermore, major progress in mass spectrometry has made the analytical methodology highly sensitive and accurate .