See pharmacopia or Food Chemical Codex or AOAC

- spectrophotometrically when you need total content

- chromatography when you need fractionation

best wishes

Thanks for your precious suggestion @Eshak Mourad El-Hadidy

The effective and economical methods to find a clue about the various phytochemicals in a plant part is Thin Layer Chromatography.

We can take small amount of powdered sample and can extract in 2-5 ml solvent.

TLC plate response either a spot/no spot could help to detect something in a particular solvent extract.

Good luck

You can look a book from Shishir, where details of some of these methods have been mentioned.

preliminary screening chemical tests is helpful for determining the kind (class) of chemical constituents of the plant 

Preliminary phytochemical screening will be basic good and cost effective, If you planned for HPLC and GC-MS make sure that they library are updated with recent discoveries also....

you could see the PhD thesis of mine where you could find detail of total as well as specific components determination methods/protocols.

Md. Rahat Ahmad Redoy

As Mr.Eshak Mourad El-Hadidy said, you can determine total content expectrophotometrically using folin ciocalteu to determine total phenolic content.

non-volatile compounds can be measured by Hplc method to determine organic acids, vitamines and ...

Volatile compounds can be measured by GC/MS method.

I can help you to estimate - total phenolic compounds, flavonoids and carotene content.

You can use preliminary determination of phytochemicals in plant extracts. Then, determine total phenolic content and total flavonoid content using Folin Ciocalteu reagent and aluminium chloride, respectively.