Comparison of FTIR Spectra and Related Derivatized Spectra of Tablets Containing Levothyroxine Obtained ATR and With KBr Pellets

Thyroid hormones are biological molecules that play a critical role in regulating metabolic rate and maintaining many physiological functions of the organism. Lack of iodine leads to various endocrine disorders, especially hypothyroidism. Synthetic levothyroxine (LT4) is generally preferred in the medication of hypothyroidism. LT4 is a molecule with low water solubility and high thermosensitivity. Absorption of the drug varies depending on gastric pH, integrity of the gastrointestinal mucosa and concomitant medications. Levotiron tablet samples of 100 mg and 25 mg were used in this study. The powdered tablets were first analyzed directly in FTIR-ATR and then in FTIR using KBr. Spectra were obtained in the mid-infrared region (4000-550 cm^-1 and 4000-400 cm^-1) with 64 scans and a resolution of 4 cm^-1.  The obtained spectra were peak analyzed with Origin Pro software. Savitzky-Golay smoothing and filtering method was applied during 2nd order differentiation to remove noise and background effects in the spectra. When the spectra of 25 mg samples prepared directly and with KBr pellet were examined, different intensities were found at the same peak positions. However, some peaks such as C-I appeared better in samples prepared with pellets. It is thought that derivatized spectra will support chemometric analysis in quantitative analysis studies.