Dear Sir. Regarding your issue about how to measure total phenolic acids, rosmarinic acid and caffeic acid with spectophotometery method. Phenolic acids were determined  according to European Pharmacopoeia. For the purpose of phenolic acids determination 0.2 g of sample powder was refluxed with 190 mL of 50% ethanol on the water bath. Total phenolic acids were determined by measuring the absorbance at 505 nm of the complex formed between phenolic acids and sodium molybdate—sodium nitrite as an equivalent of rosmarinic acid. For more details you can see the following below links which may help you in your analysis:

http://www.hindawi.com/journals/jamc/2013/658596/

http://www.herbapolonica.pl/magazines-files/2876731-05.pdf

http://www.inia.es/gcontrec/Pub/106-112-(7804)-Seasonal_1161760628640.pdf

https://bib.irb.hr/datoteka/145388.29.pdf

Thanks

Dear Ghasem Esmaeili,

Please find the method for the determination of total phenols, and phenolic acid in my publication ( Food Measurement and Characterization).

Best regards

Aly R Abdel-moemin

Article Analysis of phenolic acids and anthocyanins of pasta-like pr...

Thank you so much! 

https://www.intechopen.com/.../flavonoids-and-phenolic-acids-as-pot...