The type of HPLC does not matter (sometimes), but you can adapt this method.

https://www.researchgate.net/publication/236192690_Validated_HPLC-PDA_Method_For_Rosmarinic_Acid_Quantification_in_Rosemary

Article Validated HPLC-PDA Method For Rosmarinic Acid Quantification...

 Dear Prof. Bruce Neagle,

Thank you very for your help.

Best regards 

M. Ouhsaine Morocco 

Hi Dr. Ouhsine,

thanks for your question.

I am the author of the manuscript mentioned by Dr. Neagle. (By the way, I appreciate Dr. Neagle).

If you need any additional help, just let me know.

Have all a nice and safe weekend.

Best regards.

Renê Couto

Dear Rene O Couto

Pl refer the below publication

A validated RP-HPLC-UV/DAD method for simultaneous quantitative

determination of rosmarinic acid and eugenol in Ocimum sanctum L.

Vishruta Domlur Thyagaraj a, *, Rojison Koshy b

, Monica Kachroo a

, Anand S. Mayachari b

,

Laxman P. Sawant b

, Murali Balasubramanium b, **

a Department of Pharmaceutical Chemistry, Al-Ameen College of Pharmacy, Bangalore 560027, India

b R&D Centre, Natural Remedies Pvt. Ltd., Bangalore 560100, India