Dr. Yamamoto et.al published a paper about sample preparation methods with Formic acid to improve sensitivity on LC-UV.
https://www.sciencedirect.com/science/article/pii/S2949771X23000208
Sample preparation for NA analysis in pharmaceutical drugs
Approximately 140 mg of atorvastatin(ATS) or 600 mg of itraconazole (ITC) was weighed into a 1.0 mL volumetric flask. Formic acid(FA) was then added to dissolve the sample and bulk up the volume to 1.0 mL. A 250 μL aliquot of this solution was transferred to a 1.5 mL PP tube, to which 500 μL of 0.5 mol/L ammonium acetate (AmAc) was added to precipitate/crystallize the API, and stored in a refrigerator overnight (>12 h). The samples were then centrifuged at 10,000 rpm for 10 min at 4 °C. The supernatant was then transferred to an HPLC vial and used as the sample solution for analysis.
