The development of gas-flow modulation for high-frequency MTDSC measurements

The purpose of this study was to investigate the feasibility of modulating the temperature programme of a conventional DSC by use of an alternating ga s-flow system. Modulated temperature differential scanning calorimetry (MTD SC) is an important thermal analysis technique but suffers from a limited a pplicable frequency range due to the mass of the sample and DSC cell leadin g to the impingement of thermal conductivity effects. We suggest that the f requency limit can be increased by replacing the cell as the source of temp erature modulation with an external gaseous source, directed towards the sa mple and reference pans. In this evaluation, an alternating gas-flow was pa ssed through a line to a forced gas-flow accessory (FGFA). The FGFA consist ed of two matched cylinders containing chambers that allowed pre-temperatur e-equilibration of the stream of gas before it was passed over the sample a nd reference pans. The development of this device revealed the essential pr actical requirements of gas-flow modulation for high-frequency temperature modulation. These include the following: an appropriately sealed tunable ga s supply to both sample and reference pans, an effective method for high-fr equency cycling of the gas-flow rate, a small aperture to deliver the flowi ng gas directly over the pan and a temperature equilibration chamber. The r esults from samples of quenched PET and amorphous Saquinavir indicate that gas-flow modulation is indeed feasible, with the FGFA able to raise the att ainable temperature modulation frequency by an order of magnitude compared to conventional MTDSC.