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S Tablets & Capsules March 2017 41 analytical techniques Benefits of a laser-based system to measure the solid fraction of compacted ribbons and tablets Terry Chriss Solid Fraction Measurement Systems Using a laser-based method to measure the solid fraction (SF) of compacted ribbons and tablets is faster than traditional meth- ods and more reproducible because it's operator independent. It also simplifies the transfer of products to new equipment. cientists who formulate tablets generally agree that the SF (or porosity) of a roller-compacted ribbon has an important influence on the flowability of the powder pro- duced from granulating the ribbon. Knowing the SF is also key to achieving acceptable "re-compactability" once the granulation reaches the tablet press. A review paper by Hancock et al. [1] discusses the benefits of monitoring the SF of roller-compacted ribbons and tablets when designing, optimizing, and scaling up a process to manu- facture solid dosage forms. Traditional methods of measuring the SF/porosity of rib- bons and tablets include direct measurement, fluid displace- ment, and fluid intrusion. These techniques have been described by Hancock and Allesø et al. [2]. Most traditional techniques of measuring the SF of roller-compacted ribbons are fairly slow, requiring 30 minutes or more, which limits the utility of the measurements. With a laser-based system, it is possible to take reliable, unattended measurements in approximately 2 minutes. As a result, formulators and others can make more routine use of SF data to address production and formulation challenges. Terminology Because some scientists prefer to think in terms of porosity rather than SF, it's important to define each and how the two parameters relate to one another and to envelope density. SF is the percentage of a ribbon or tablet that is solid material (as opposed to pore space). Porosity, the inverse of SF, is the percentage of the rib- bon or tablet that is pore space. The relationship between SF and porosity is expressed in Equation 1: (1) Equation 2 provides a means to calculate the envelope density, which refers to ratio of the mass of the ribbon or tablet to its volume: The basics of laser-based SF measurement If you know the pore-free density (sometimes called the true density) of a powder before you compact it into a ribbon or tablet, determining the SF only requires measur- ing the envelope density (or bulk density) of the ribbon or tablet. A laser-based SF system measures the envelope density by incorporating laser distance sensors to determine the SF = 1 - ( ) Porosity 100 (Total mass) (Total volume of ribbon or tablet) Envelope density = (2) A laser-based SF measurement system

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