Colorful Drying

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Drying is one of the standard unit operations in the pharmaceutical industry and it is important to become aware of the circumstances that dominate during the process. The purpose of this study was to test microcapsulated thermochromic pigments as heat indicators in a fluid bed drying process. The indicator powders were manually granulated with α-lactose monohydrate resulting in three particle-size groups. Also, pellets were coated with the indicator powders. The granules and pellets were fluidized in fluid bed dryer to observe the progress of the heat flow in the material and to study the heat indicator properties of the indicator materials. A tristimulus colorimeter was used to measure CIELAB color values. Color indicator for heat detection can be utilized to test if the heat-sensitive API would go through physical changes during the pharmaceutical drying process. Both the prepared granules and pellets can be used as heat indicator in fluid bed drying process. The colored heat indicators give an opportunity to learn new aspects of the process at real time and could be exploded, for example, for scaling-up studies.

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  1. 1.

    Florence AT, Attwood D. Drug stability. In: Florence AT, Attwood D, editors. Physicochemical principles of pharmacy. 4th ed. Great Britain: Pharmaceutical; 2006. p. 94–138.

  2. 2.

    Miroshnyk I, Khriachtchev L, Mirza S, Rantanen J, Heinämäki J, Yliruusi J. Insight into thermally induced phase transformations of erythromycin A dihydrate. Cryst Growth Des. 2006;6(2):369–74.

  3. 3.

    Rankell AS, Lieberman HA, Schiffmann RF. Drying. In: Lachman L, Lieberman HA, Kanig JL, editors. The theory and practice of industrial pharmacy. 3rd ed. Philadelphia: Lea and Febiger; 1986. p. 47–65.

  4. 4.

    ChromaZone® free flowing powder. (Accessed 05/26/09).

  5. 5.

    Burgath A, Burtscher P, Salz U, Rheinberger V. Thermochromic dental material. Patent EP1230906 (2002).

  6. 6.

    Schroeer J, Jablonka D, Raidt HP, Ruediger L. Building material. Patent WO2007042127 (2007).

  7. 7.

    Ohno Y. CIE Fundamentals for color measurements. IS&T NIP 16 Conference, Vancouver; 2000. pp. 16–20.

  8. 8.

    Siddiqui A, Nazzal S. Measurement of surface color as an expedient QC method for the detection of deviations in tablet hardness. Int J Pharm. 2007;341:173–80.

  9. 9.

    Chan LW, Chan WY, Heng PWS. Characterization of surface coverage of coarse particles coated with stearic acid. Int J Pharm. 2001;213:63–74.

  10. 10.

    Bogdansky FM. Measurement of surface color and color difference of tablet colorants by tristimulus colorimetry. J Pharm Sci. 1975;64(2):323–8.

  11. 11.

    Oram PD, Strine J. Color measurement of a solid active pharmaceutical ingredient as an aid to identifying key process parameters. J Pharm Biomed Anal. 2006;40:1021–4.

  12. 12.

    Berberich J, Dee K-H, Hayauchi Y, Pörtner C. A new method to determine discoloration kinetics of uncoated white tablets occurring during stability testing—an application of instrumental color measurement in the development pharmaceutics. Int J Pharm. 2002;234:55–66.

  13. 13.

    Gren T, Nyström C. Characterization of surface coverage of coarse particles coated with stearic acid. Int J Pharm. 1991;74:49–58.

  14. 14.

    Bechard SR, Down GRB. Infrared imaging of pharmaceutical materials undergoing compaction. Pahrm Res. 1992;9(4):521–8.

  15. 15.

    Ketolainen J, Ilkka J, Paronen P. Temperature changes during tableting measured using infrared thermoviewer. Int J Pharm. 1993;92(1–3):157–66.

  16. 16.

    Johansson J, Pettersson S, Taylor LS. Infrared imaging of laser-induced heating during Raman spectroscopy of pharmaceutical solids. J Pharm Biomed Anal. 2002;30:1223–31.

  17. 17.

    Kelen Á, Ress S, Nagy T, Pallai E, Pintye-Hódi K. Mapping of temperature distribution in pharmaceutical microwave vacuum drying. Powder Tech. 2006;162:133–7.

  18. 18.

    Yamada J, Kurosaki Y, Nagai T. Radiation heat transfer between fluidizing particles and a heat transfer surface in a fluidized bed. J Heat Transf. 2001;123:458–65.

  19. 19.

    Ochoa AD, Baughn JW, Byerley AR. A new technique for dynamic heat transfer measurements and flow visualization using liquid crystal thermography. Int J Heat Fluid Flow. 2005;26:264–75.

  20. 20.

    Šubert J, Čižmárik J. Application of instrumental colour measurement in development and quality control of drugs and pharmaceutical excipients. Pharmazie. 2008;63(5):331–6.

  21. 21.

    Hayauchi Y. A precise colour determination method for tablets—an application of instrumental color measurement in the pharmaceutical development. Pharmeur Sci Notes. 2005;2005–1:21–262005.

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Niina Kivikero is acknowledged for advising with fluid bed dryer. Outi Pajunen is thanked for her assistance with the coating equipment. The authors also thank Henri Salokangas for language consulting.

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Correspondence to Satu Lakio.

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Lakio, S., Heinämäki, J. & Yliruusi, J. Colorful Drying. AAPS PharmSciTech 11, 46–53 (2010).

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Key words

  • colored heat indicator
  • fluid bed drying
  • thermochromatism
  • tristimulus colorimetry