Development of a novel method based on liquid chromatography–evaporative light scattering detection for the direct determination of streptomycin and dihydrostreptomycin in raw materials, pharmaceutical formulations, culture media and plasma

A novel method for the non-derivatization liquid chromatographic determination of streptomycin (STR) and dihydrostreptomycin (DHSTR) was developed and validated based on evaporative light scattering detection (ELSD). Utilizing a ThermoHypersil BetaBasic C18 analytical column, evaporation temperature of 50 °C and pressure of nebulizing gas (nitrogen) of 3.5 bar, the optimized mobile phase was 1.25 mL L−1 TFA aqueous solution, in an isocratic mode at a rate of 1.0 mL min−1. STR was eluted at 5.6 min and DHSTR at 7.8 min with a resolution of 4.4. Linear calibration curves were obtained from 2 to 120 μg mL−1 (r > 0.9990) for STR and 2–75 μg mL−1 (r > 0.9994) for DHSTR, with a LOD equal to 0.7 and 0.5 μg mL−1, respectively. The developed method was applied for the assay of STR and DHSTR (sulfate) in pharmaceutical raw materials and formulations, while the simultaneous direct determination of sulfate was feasible (tR = 2.5 min, LOD = 1.4 μg mL−1, double logarithmic calibration curve in the range of 4–50 μg mL−1, r > 0.9998). Modified isocratic mobile phase (H2O–ACN, 90:10, v/v, containing 1.25 mL L−1 TFA), was used for the determination of streptomycin B impurity in STR sulfate raw material and a gradient mobile phase (H2O–ACN containing TFA) was used for the determination of DHSTR in the presence of penicillinG procaine. The developed method was also applied for the assay of commercial formulations (STR powder and DHSTR injection solution and suspension) (%recovery 98–102, %RSD < 1.3, n = 3 × 3), for the determination of STR in bacteria culture medium (%recovery 99.6, %RSD = 0.8, n = 3 × 3), and for the determination of DHSTR in human plasma (2.0–23.0 μg mL−1) after solid phase extraction using carboxylate cartridges (%recovery 98.4–101.8, %RSD = 3.2, n = 3 × 3).