Question

discuss the use of HPLC vs UV for dissolution testing

also include: pros and cons.

Thank you very much

Answer 1

HPLC chromatography is used for the separation of compounds according to the polarity of the same and the interaction with the stationary phase in the separation column, highly sensitive and adequate to each compound according to the stationary phase. The technique is based on passing a liquid through a column at high pressure, said column comprises a compound to which passive fluid compounds adhere that retard or accelerate the passage of the liquid through it, the time it takes for each fluid to exit This column is called the retention time and is characteristic of each compound that is separating, which is why it is considered an identification technique. On the other hand the UV-vis technique involves the absorption of ultraviolet radiation - visible by a molecule, causing the promotion of an electron from a basal state to an excited state, releasing excess energy in the form of heat. The visible or UV light is absorbed by the valence electrons, these are promoted to excited states (of higher energy). By absorbing electromagnetic radiation of a correct frequency, a transition occurs from one of these orbitals to an empty orbital. The differences between energies vary between the different orbitals. Some links, such as doubles, cause coloration in the molecules since they absorb energy in the visible as well as in the UV. This technique, in addition to being identifying, we can also quantify with it through the Lambert-beer Law, which relates the absorvance of the analyte with its concentration in the dissolution.
Both techniques use different physico-chemical principles, in the case of HPLC to quantify we would have to make calibration curves of the analyte to quantify it while by UV-vis directly using Lambert-Beer Law we can obtain the concentration of our analyte depending on others more technical factors. Both techniques are very useful in the identification of organic compounds by various chemical characteristics such as their polarity and / or conjugation of links that provides chromophore groups easily identified by UV. The difference of principles in the operation of the technique makes the disadvantages, for example a compound that does not absorb in UV-vis is impossible to identify by this technique while by HPLC placing a suitable stationary phase in which we can by polarity difference identify the retention times of the different analytes, could be easily identifiable. Now, if we want to quantify in addition and the compound absorbs in the UV-vis region, it is advisable to perform this technique instead of HPLC