If DAD is Amperometric Detection, it is more sensitive than fluorescence detection, but the baselines in chromatograms have more noise .

Pedro, DAD = Diode Array Detection.

Mafalda, it is all depending on what concentrations levels you expect and need to analyse. If we talk about HPLC analysis: both ECD (electrochemical detection) and Fluorescence detection are both very sensitive techniques, but in case of high concentration levels of Melatonin in your samples I would choose UV detection due to its simplicity. Also HPLC-MS is used in literature, although a powerful and sensitive technique it is less cost effective (more expensive equipment).

Here a link of an article about analysis of Melatoninin plants:

http://cms.galenos.com.tr/Uploads/Article_15535/TJPS-14-75-En.pdf

Although this is a completely different sample/matrix (plant) , it nicely summarised a lot of literature of data obtained with different HPLC detection techniques (ECD, FD, UV, MS and combinations HPLC-FD-MS) but also using ELISA and RIA. It might be worthwhile to have a look at some references.

Here another example of analysis in milk using ELISA:

Melatonin concentration in cow’s milk and sources of its variation"

https://www.tandfonline.com/doi/full/10.1080/09712119.2019.1583570?scroll=top&needAccess=true

Hope it helps, greetings, Hendrik

Hendrik-Jan Brouwer thank you for your answer. It was very helpful.