# Calculating the concentration of product in a solution based on the peak area of HPLC [closed]

A sample solution, $$\pu{0.24mg/mL}$$ Compound A, is exposed to heat to form Compound B. From HPLC data report I have peak area for Compound A and Compound B. The STD concentration is 0.3 Compound A. The concentration of Compound A in sample solution is $$\pu{0.20mg/mL}$$ Compound A calculated using STD Compound A information. Which is the correct way to calculate concentration of Compound B?

My advisor in the project I'm participating insist I must calculate the concentration of Compound B since is a degradation of Compound A in term of the amount lost of Compound A is the amount gained by Compound B (she call it a indirect method for calculating the concentration). I'm at lost! Originally I performed the calculation using a STD Compound A at the LOQ level of the impurity: $$\text{[Compound B]} = \frac{\text{Area Compound B} \times \text{[STD Compound A]}}{\text{Area STD Compound A}}$$

The new approach is calculate the [compound A] using a STD at the level of the sample and then indirectly calculate the [Compound B].

• There is no way! You need to construct calibration curve for compound B or have a single standard injection for compound B. – M. Farooq Aug 30 at 20:55
• @M. Farooq: I agree with you about calibration curves. Also, may need a calibration curve for compound B, if two compounds are structurally different (based on detecting method, usually an UV detector). – Mathew Mahindaratne Aug 30 at 23:32
• I think my advisor bold approach is based in Coumpond B is the enantiomer of Compound A (Doxycycline and 4-EPI-Doxycycline). – Ada J. Guzman Sep 1 at 10:52
• Okay, then his assumption is valid. The UV spectrum of enantiomers is identical. – M. Farooq Sep 1 at 21:29