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Pharmaceutical Technology BIOLOGICS AND STERILE DRUG MANUFACTURING 2018 33 Adequate control of the test pa- rameters is essential. Control of the temperature should be within a reasonable variation for repro- ducibility of the conditions and consistency of the results. If a re- duced pressure is part of the test conditions, then the proper mea- surement is also important. To assure the test conditions are re- produced, it would be beneficial if these test parameters were re- corded on an instrument as well. The oven instruments should be calibrated on a regular basis for confidence in the results. Points to consider for loss on drying. LOD is an effective method, particularly when there are potential chem- ical reactions involving the product and solvents or reagents. This method presents challenges when the dry weight of the finished product and water content are low. Special handling considerations, container weighing and drying steps, and packaging compo- nent measures are described online (4). Thermogravimetric analysis (TGA) method. TGA is an instrumental method that records the mass of a sample as a function of temperature or time. During testing, the mass of the sample is continu- ously monitored by a microbalance. The changes in weight are recorded by the instrument. During the analysis, the sample is protected from atmo- spheric moisture as nitrogen, or another inert dry gas, is continually purged through the instrument sample chamber. Figure 1 is an example of a TGA instrument. The sample is weighed into a sample pan. De- pending on the instrument, there may be more than one type and size of sample pan available. The sample pan, for example, may be made of plat- inum metal or ceramic, which can be reused, or made of aluminum and be disposable. The sample pan is then hung from the hang down wire, which is connected to a microbalance to record the mass of the sample as the sample is heated. A thermo- couple is positioned close to the sample to record the temperature during testing. When the testing is initiated, the furnace moves up into position sur- rounding the sample pan. In Figure 1, the furnace is in the down position. The change in weight can be correlated to tem- perature. The thermogram in Figure 2 ref lects a material having three distinct weight loss events, noted by three distinct downward slopes in the percent weight loss line (green), as well as the three sharp peaks in the derivative line (blue) (5). When analyzing thermograms, the start of the weight loss event is when the derivative begins to stray from the baseline; the end of the event is when the derivative then returns to the baseline. The temperature at which the weight loss is complete Figure 1: Example of thermogravimetric analysis (TGA) instrument. FIGURES COURTESY OF THE AUTHORS