A fast and simple method based on LC with fluorescence detection has been developed for the determination of insulin in innovative formulations consisting of microparticles and inserts for oral and nasal drug administration, respectively.
A reverse-phase C8 column and a mobile phase composed of pH 3.7, 40 mM sodium sulphate solution and acetonitrile (24%, v/v) were employed. Using isocratic elution at 1.0 mL/min flow, analysis is completed within 7 min.
Three different kinds of spray-dried microparticles were analysed, consisting of an insulin loaded core composed of chitosan salts (chitosan succinate, chitosan adipate or chitosan suberate) coated with stearic acid. Nasal inserts consisted of chitosan/hyaluronate polyelectrolyte complexes which were loaded with insulin and freeze-dried.
Insulin was extracted from both the oral and nasal formulations using pH 7.4 phosphate buffer. The employment of fluorescence detection (λexc = 276 nm, λem = 306 nm) granted high selectivity, with no interference from the matrix.
Full method validation was performed with good results in terms of linearity (insulin concentration range 0.10–30.0 μg/mL), LOD (0.03 μg/mL) and LOQ (0.10 μg/mL), precision (R.S.D.% < 3.6) and accuracy (recovery percentage > 90.0%).
Insulin content in innovative formulations, expressed as percentage w/w, resulted to be between 0.90 and 0.97 for oral innovative formulations, while an average value of 342 μg of insulin was found in a single nasal insert, in good agreement with preparative protocols.