Proposal for Determining Sulfate Counter Ion in Amikacin Sulfate Formulations by Fourier-Transform Infrared Derivative Spectroscopy

Amikacin (AMK) is a semi-synthetic aminoglycoside antibiotic used under the sulfate salt form and manufactured under parenteral formulations. The determination of the sulfate concentration is important to confirm the completeness of salt formation. Continuing the approach followed by some authors in FTIR spectroscopy, the principle of using analyses of aqueous samples in the mid-IR region, by transmission, was adopted as a tool for the development of the proposed approach. Spectroscopic discrimination between the sulfate counter ion and the carbohydrate moiety was achieved by using derivative spectroscopy. The selected measurement criterion was the amplitude from the minimum of the negative wavenumber band (1054 cm-1) of the 1st order derivative spectrum to a cross-over point coincident with the maximum negative slope of the conventional absorbance spectrum. Linear response (r > 0.999) was observed for sulfate concentrations in the range 2.5 to 25 (mg mL-1), with a detection limit of 0.4 mg mL-1. The sampling frequency was estimated as 13 measurements per hour in a continuous flow mode sample-to-sample with a coefficient of variation < 0.5 % (n = 10). The found equivalent sulfate content in AMK sulfate formulations showed in most cases a good agreement with the values declared on the label of each analyzed pharmaceutical product. The proposed analytical strategy allows the analysis of the sample either directly or just requiring only an aqueous dilution which can be understood as a green analytical approach alternative to methods employing either titrimetric approaches or chromatographic and electrophoretic separation methods.