See methods in this paper: Article Food for Pollinators: Quantifying the Nectar and Pollen Reso...

if you wany to do something novel, see also this one:

Article Ecological stoichiometry of the honeybee: Pollen diversity a...

Kind regards

Michał

The best tool, depends on what you want to look for. If it is merely sugar concentration, a reflectormeter is fine. If you want to look for pesticides, there are a range of protocols. If you want to look for phytochemical, I think you need to develop a lot yourself.

Is it possible to take the stigma only without the stamens and to other parts?

Nectar is a sugar-rich component with varying proportions of sucrose, glucose, and fructose. In addition, it also has carbohydrates, amino acids, several volatile, and a diverse group of phytochemicals. You can study the composition of nectar through the HPLC technique. The diversity of flower visitors depended on several factors and nectar concentration and composition also played an important role as attractants. Mainly Hymenopteran members preferred high sugar-rich nectar-based flowers for their foraging but a number of phytochemicals present in the nectar also act as an attractant. The attached paper might be helpful.

Respected Sir,

You may follow this paper 10.1111/2041-210X.12928RESEARCH

Thank you.