A derivative UV spectrophotometric method for the determination of levothyroxine sodium in tablets

A derivative UV (D-UV) spectrophotometric method was developed for the determination of Levothyroxine Sodium (L-T₄) in tablets of different doses. Quantification was performed using the second derivative of the absorption spectrum at 253 nm (²D₂₅₃) in methanol: water (50: 50; v/v) (pH 11.2). The method was validated and compared with an HPLC procedure carried out using a RP-18 column (125 × 4 mm, 5 μm) and methanol: phosphoric acid (0.1%) (70: 30, v/v) (pH 3) as mobile phase. Flow rate was set at 1.5 mL/min, and detection was performed at 225 nm. The proposed D-UV method was linear in the range 3.0–40.0 μg/mL with an appropriate precision and accuracy, and it was selective for the drug under study. On the other hand, results obtained by ²D₂₅₃ analysis were similar to those obtained by HPLC, with no statistically significant differences between them. Therefore, it was concluded that the developed method is suitable for the determination of L-T₄ in tablets at the tested doses.