I cannot disclose too much but for example how can I figure out if the iron in a plant extract is really from the plant extract or is the material spiked with maybe synthetic ferrous sulphate. 

Thank you for the reply, so can it be distinguished using FTIR ? or maybe MS-HPLC?

Thank you so much! This helps a lot. It definitely solves my problem. Thanks.

Check this related thread:

https://www.researchgate.net/post/Can_anyone_explain_to_me_how_to_determine_the_mineral_constituents_of_crude_extract_of_plant2?_tpcectx=profile_answers

The assessment of the ash content offers an estimation of the total minerals/ microelements content, while AAS (Atomic Absorption Spectrometry) method can be used in order to identify one specific element (e.g., Fe) by directly reporting to a standard calibration curve (n dilution series); unfortunately, AAS method do not make differences between mineral and adulterant iron.

You can also estimate by X Ray Fluorescence Spectometer (XRF) 

XRF can be used to determine the elemental composition of the plant but XRD will be more use full in ur case to determine which form of mineral as XRD differentiates the different compounds containing same elemental composition. 

ICP is another method to determine quantitatively mineral constituants of an extract, but you can also use this method from your starting material to determine the source of your constituents.

Respected Sir, In my opinion Quantitative analysis of minerals (macro and microelements) can be estimated with the help of Flame photometry (macroelements) and Atomic absorp[tion spectoscopy (AAS) for microelements and XRD/XRF could also be a good tool. For qualitative analysis of minerals Ash values can be utilized. 

I agree with JThomas Pierson, ICP is a good method for quantitative analysis of minerals in a plant extract.

see the following paper it may help you its agood research to estimate minerals in fenugreek  plant extract