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Tablets & Capsules September 2020 35 This moisture content value of 0.016 percent can be used to look up the corresponding water activity value in the sorption isotherm of the blend. Assuming the change of moisture content will be linear over the range of 0.1 to 0.2 A w , the final water status at which the sample equilibrates will be approximately 11 percent RH or 0.11 A w . Note that the free moisture content is generally not linearly correlated with the water activity, however. You can obtain more accurate results by increasing the num- ber of measurement points of the isotherms. To evaluate the impact of excipient hygroscopicity on a blend's final moisture content, a second example two-component blend contains the same API but a more hygroscopic microcrystalline cellulose (MCC) excipient (Pharmacel 101). The MCC is blended with the API in an 80:20 ratio (% w/w). The initial water activity of the API is 0.1, and the initial water activity of the MCC is 0.3. The sorption isotherm of the MCC is measured using a ProUmid SPS-1ยต advanced system with the same parameters used for the lactose, and, again, the API iso- therm is imaginary. The component isotherms are com- bined using Equation (2) into the sorption isotherm of the proposed 80:20 blend, as shown in Figure 7. From the sorption isotherms, one can see that the API contains 0.060 percent moisture at 0.1 water activity, and the MCC contains 2.855 percent moisture at 0.3 water activity. The total moisture content of the blend will therefore be: (80% 2.855%) + (20% 0.060%) = 2.296% This moisture content value of 2.296 percent can be used to look up the corresponding water activity value in the sorption isotherm of the blend. Assuming the change of moisture content will be linear over the range of 0.20 Figure 7 Sorption isotherms of MCC, API, and an 80:20 (% w/w) blend of the two (Data points relevant for the example calculation are indicated in the graph.) Pharmacel 101 API Blend (20% API) m (%) 12 10 8 6 4 2 0 Relative humidity (%) 0 20 40 60 80 100 2.855 2.312 1.670 0.060 EXPERIENCE THE DIFFERENCE THE ELIZABETH DIFFERENCE. Compression Tooling | Tablet Presses | Turrets | Replacement Parts| Field Services & Training Blister Packaging Tooling & Feeders | Tablet Press & Turret Repairs We understand that your products are trusted by consumers each and every day. Consistent quality of your solid dose products is expected and non-negotiable. Your products depend upon the integrity of your equipment and tooling. For over 65 years, Elizabeth Companies have put a personal guarantee on customer satisfaction and takes pride in delivering innovative solutions. We promise our customers an unequaled level of customer service, trust, product performance, and prompt & courteous communication. ELIZ.COM | 412-751-3000 @ELIZCOMPANIES