Even I experienced the same in case of phytochemical screening of flavanoids.

what tests did you use? Folin method can mistakenly identify amino acids as phenolics

its necessary to perform HPLC analysis and mass-spectrometry for a fine-tune analysis.

I think also it is necessary to use HPLC analysis for a fine-tune analysis.

HPLC analysis will give more accurate results. FC colorimetric analysis may sometimes puzzles as amino acids also give colour with FC reagent.

it happens sometimes but its rather impossible that a plant doesn't possess phenolic compounds. Moreover, the solvent in which the extracts is prepared is also important. Many a times reagents used or method used is not appropriate coz there are several interfering components. So, other chromatographic and spectral techniques is very important viz., TLC, HPLC, LC-MS, GC-MS and others.

thank you.

hptlc fingerprint showed , presence of plumbagin and quercetiin........

Is any chance to get as because of secondary phenolic metabolite?

Well the question is not very clear?

It may due to the interference of some other compounds reacting also with the reagent used to measure the phenolic content.

what method would you use? It's not clear

If you mean the FeCl3 test,- the preliminary color test, it will answer only if you have ortho phenolic groups. Mostly trihydroxy phenols etc.The Phenolic method with FC reagent will take cre of all pphenolic groups.

yes, FeCl3 test given negative result.

thank you for your answer.

I meant phenolic OH groups in adjacent positions,in Flavonoid type compounds. ..eg. 3,4 dihydroxy or 3' ,4' OH groups.

Please, check the sensitivity of the method used for phytochemical screening or used another procedure. Most often it is advised to use more than one procedure for phytochemical screening of secondary metabolites to testify their presence or absence.