Chemical stability of the lipid matrices of solid lipid nanoparticles (SLN)-development of an analytical method and determination of long-term stability

Solid lipid nanoparticles (SLN) were produced with different lipids (cetylpalmitate, Dynasan 118, Softisan 154) by the hot homogenisation technique. A gas chromatography (GC) analysis in combination with a method for lipid extraction from aqueous SLN dispersions was established to investigate the chemical stability of the lipid excipient forming the particle matrix. A new procedure for transmethylation of liquid lipids was adopted to solid lipids. Storage of the aqueous SLN dispersions was performed at room temperature for 2 years. The particles sizes were determined by photon correlation spectroscopy and laser diffractometry. GC analysis was shown to be suitable for qualitative and quantitative determination of the chemical stability of the lipids used as excipients in the SLN matrix. Cetylpalmitate and Dynasan 118 showed the highest chemical stability (loss <2% within 2 years). Sufficient stability of the lipid excipients (content >90%) - a prerequisite for a drug formulation - could be shown for these two Lipids for 2 years.