## 4 Conclusions  
In this study, we report that by using an appropriate lens and a higher resolution of the IR microbolometer, high-resolution thermograms of a pharmaceutical formulation undergoing a freeze-drying process were obtained. It was also confirmed that presence of probes in the material alters the freezing behaviour and the primary drying process (as already observed). However, by using the current setup, it was possible to quantify the thermal effect of the probes present in the material at different stages of the freeze-drying process. The temperature was around 3.5 K higher during primary drying in comparison with the vials without probes. All other (cuvettes) vials thus lagged in drying speed in comparison with the ones containing probes. Thus, the presence of probes generally overestimates the temperature prevailing during primary drying. The main sensors used for the monitoring of the freeze-drying processes are Pt100 probes and LyoRX probes. These probes are always in direct contact with the materials undergoing drying. In this study, 8.5 mL of pharmaceutical formulation was freeze-dried. This is a rather large volume in comparison with large-scale operations in the pharmaceutical industry, which normally uses smaller vials filled with 1-2 mL of liquid. It is very likely that the thermal effect due to the presence of the probes would increase even further as the volumetric between probe and liquid increases. It would be worthwhile to repeat experiments with a lower fill-volume to confirm this assumption. IR thermography provides superior spatial and thermal resolution that is also contact-free. To date, such studies have relied on special designs of freeze-dryers and sometimes even special vials equipped with Ge-windows (cuvettes) for full exploitation. IR cameras combined with freeze-dryers have therefore been limited to research applications. In large-scale freeze-drying, it would be impossible to use vials/cuvettes equipped with germanium windows. It would, be possible to quantify the temperature (contactless) and especially the time of freezing at the surface of the material in every single standard vial standing on each shelf. This could be realized if a small enough camera (per shelf) could be integrated with an adequate lens. Miniature versions of IR cameras could then be incorporated into new equipment relatively easily for monitoring surface temperatures even for routine applications. Such small IR cameras are commercially available and could possibly be installed on the underside of each shelf [19]. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app14073120/s1](https://www.mdpi.com/article/10.3390/app14073120/s1)]([https://www.mdpi.com/article/10.3390/app14073120/s1](https://www.mdpi.com/article/10.3390/app14073120/s1)), Figure S1: Nucleation temperatures can be seen at the dip of each measurement area on the y-axis with respective time of nucleation on the x-axis. Measurements of average temperature at the top and bottom of each cuvette R6 to R15 and R16 were used to generate the plot. Figure S2: Entire freeze-drying process; top and bottom view of cuvettes with and without probes using average temperature readouts from R6 to R15 and R16. Figure S3: Primary drying process, top and bottom view of cuvettes 1 to 5 with and without probes using average temperature readouts from R6 to R15 and R16. Figure S4: Selection showing primary drying process. Surface, top and bottom view of cuvettes 1 and 2 with and without a probe using average temperature readouts from R1, R2, R6, R7, R11, R12 and R16. Figure S5: Thermogram of cuvettes 1 to 5 with profiles L1 to L5 at the surface and L6 along the depth profile after 2700 min, 45 h. Figure S6: Temperature readout of lines 1-6 as a function of cuvette at the surface and depth (for line 6) after 2700 min (45 h).