The Use Of Impedance Analysis For The Study Of Critical Events In The Frozen State, For Formulation And Lyo-Cycle Development

By Kevin Ward, Biopharma Technology Limited; and Kiran Malik and Paul Matejtschuk, National Institute for Biological Standards & Control (NIBSC)

There are a number of well-established techniques for the characterisation of a formulation prior to lyophilisation, in order to determine therate and extent of cooling required for complete solidification, the ‘maximum allowable product temperature'for safe yet efficient lyophilisation, and indeed whether a material would benefit from further development (reformulation) prior to freeze-drying.

Chemicals were obtained from Sigma (Poole, UK), Fisons(Loughborough, UK) or VWR (Northampton, UK) and biological standards from NIBSC (Potters Bar, UK) and were analytical grade or higher. Impedance (Zsinf) analysis and DTA was carried out simultaneously on samples (3ml) of each solution using a Lyotherm2 analyser (Biopharma Technology Ltd., Winchester, UK). Freshly prepared aqueous samples in stainless steel sample cells were cooled to below -100ºC and warmed at approximately 2-4ºC perminute to above 0ºC. During cooling and warming, the level of Zsinfwas monitored at 1000 Hz. For DTA, the value for ?T (temperature difference) upon warming was obtained by subtracting sample temperature from reference temperature, where the reference was analytical grade water or water for injection (3ml) in an identical cell. Data from Lyotherm2 were compared with data obtained using a range of other analytical methods, including FDM (Lyostat2, Biopharma Technology Ltd., Winchester, UK) and modulated temperature differential scanning calorimetry (TA Instruments, Crawley, UK), in order to determine whether correlation existed between these methods.