Application of Chemometrics in determination of the effects of ionic and non-ionic surfactants on acid dissociation constant (pKa) of Meloxicam using spectrophotometric method

The purpose of this study was to determine the acid dissociation constants (pKa) of meloxicam in the presence of various surfactants including sodium lauryl sulfate (SLS) as an anionic surfactant, cetyltrimethylammonium bromide (CTAB) as a cationic surfactant and Triton® TX-100 (TX-100) as a non-ionic surfactant in different pre-determined concentrations. The related pKa was determined spectrophotometrically at a constant ionic strength of 0.1 M at 250°C. In order to investigate the effect of solvent on pKa of meloxicam, the pKa was also determined in different concentrations of ethanol, separately. The acid dissociation constant of all appropriate species were calculated using chemometric methods. In this study, DATAN® software was applied for analysis and interpretation of data. The acid dissociation constants (i.e. pKa) for meloxicam as poorly soluble drug were reported as 1.22±0.56 and 4.00±0.12 for pKa1 and pKa2, respectively. The obtained data showed that by increasing the concentration of SLS up to 0.05% (w/v), both the pKa1 and pKa2 of meloxicam were increased and to 2.67±0.054 and 5.73±0.029, respectively, while by increasing the concentration of CTAB, significant decrease was observed in pKa2 of meloxicam to 2.53 ± 0.16. Different concentrations of TX-100 posed non-significant changes in pKa1 and pKa2. It was also reported that by increasing the concentration of ethanol as a co-solvent, both pKa1 and pKa2 of meloxicam were increased to 2.42±0.083and 5.81±0.23, respectively.