Secondary drying, change

A change of the chamber during secondary drying to less than 0.26 mbar, e. g. to 0.065 mbar, does not change the drying speed. ... 

Pikal [1.60] described two possibilities to define the change from main to secondary drying ... 

For a product a reproducible desorption isotherm exists, and the product does not change at the end temperature during secondary drying. 

The main drying has been terminated, when Tice had decreased for the first time from max. Tice by 1.5 °C followed by a secondary drying as described. The desired dW was not reached measurably early than by the change of 2 °C in two successive measurements. 

Raman spectroscopy was used by Sane et al. [1.165] to quantitate structural changes in proteins freeze- or spray-dried. Monoclonal antibodies(e.g. RhuMAbVEGF) underwent secondary structural changes in the absence of a lyoprotectant. Increasing molar ratios of cryoprotectant could lead to complete structural preservation. The long-term stability of the dried proteins correlates with structural changes observed by Raman spectroscopy. 

If these conditions are met, the curves as shown in Figure 1.78.1 are measured. Figure 1.78.3 shows one measurement and one repetition of this measurement and a third measurement with another product and other process data. Towards the end of main drying, the data on Tice will systematically decrease this effect can be used for an automatic change from main to secondary drying (see Section 2.6.2.2). 

The change from main drying to secondary drying is difficult to determine by the product temperature, as shown in Figure 1.79. This can also be seen in Figures 1.80.1... 

---