AAPS PharmSciTech

, Volume 19, Issue 3, pp 1477–1482 | Cite as

Process Analytical Technology in Freeze-Drying: Detection of the Secondary Solute + Water Crystallization with Heat Flux Sensors

  • Qiming Wang
  • Evgenyi Shalaev
Brief/Technical Note


In situ and non-invasive detection of solute crystallization during freeze-drying would facilitate cycle optimization and scale-up from the laboratory to commercial manufacturing scale. The objective of the study is to evaluate heat flux sensor (HFS) as a tool for monitoring solute crystallization and other first-order phase transitions (e.g., onset of freezing). HFS is a thin-film differential thermopile, which acts as a transducer to generate an electrical signal proportional to the total heat applied to its surface. In this study, HFS is used to detect both primary (ice formation) and secondary (also known as eutectic) solute + water crystallization during cooling and heating of solutions in a freeze-dryer. Binary water-solute mixtures with typical excipients concentrations (e.g., 0.9% of NaCl and 5% mannitol) and fill volumes (1 to 3 ml/vial) are studied. Secondary crystallization is detected by the HFS during cooling in all experiments with NaCl solutions, whereas timing of mannitol crystallization depends on the cooling conditions. In particular, mannitol crystallization takes place during cooling, if the cooling rate is lower than the critical value. On the other hand, if the cooling rate exceeds the critical cooling rate, mannitol crystallization during cooling is prevented, and crystallization occurs during subsequent warming or annealing. It is also observed that, while controlled ice nucleation allows initiation of the primary freezing event in different vials simultaneously, there is a noticeable vial-to-vial difference in the timing of secondary crystallization. The HFS could be a valuable process monitoring tool for non-invasive detection of various crystallization events during freeze-drying manufacturing.


lyophilization solute crystallization mannitol process analytical technology annealing NaCl 



We thank Brian Ivin, Adrian Marley, and Kieran Joyce for an expert assistance in preliminary experiments with HFS, and TN Thompson for supporting the study and reviewing the manuscript.


  1. 1.
    Kim AI, Akers MJ, Nail SL. The physical state of mannitol after freeze-drying: effects of mannitol concentration, freezing rate, and a noncrystallizing cosolute. J Pharm Sci. 1998;87(8):931–5.CrossRefPubMedGoogle Scholar
  2. 2.
    Chatterjee K, Shalaev EY, Suryanarayanan R. Raffinose crystallization during freeze-drying and its impact on recovery of protein activity. Pharm Res. 2005;22:303–9.CrossRefPubMedGoogle Scholar
  3. 3.
    Shalaev EY, Malakhov DV, Kanev AN, Kosyakov VI, Tuzikov FV, Varaksin NA, et al. Study of the phase diagram water fraction of the system water-glycine-sucrose by DTA and X-ray diffraction methods. Thermochim Acta. 1992;196:213–20.CrossRefGoogle Scholar
  4. 4.
    Cavatur RK, Suryanarayanan R. Characterization of frozen aqueous solutions by low temperature X-ray powder diffractometry. Pharm Res. 1998;15(2):194–9.CrossRefPubMedGoogle Scholar
  5. 5.
    Bhatnagar BS, Martin SM, Hodge TS, Das TK, Joseph L, Teagarden DL, et al. Investigation of PEG crystallization in frozen and freeze-dried PEGylated recombinant human growth hormone-sucrose systems—implications on storage stability. J Pharm Sci. 2011;100(8):3062–75.CrossRefPubMedGoogle Scholar
  6. 6.
    Jiang G, Akers M, Jain M, Guo J, Distler A, Swift R, et al. Mechanistic studies of glass vial breakage for frozen formulations. I. Vial breakage caused by crystallizable excipient mannitol. PDA J Pharm Sci Technol. 2007;61(6):441–51.PubMedGoogle Scholar
  7. 7.
    Milton N, Gopalrathnam G, Craig GD, Mishra DS, Roy ML, Yu L. Vial breakage during freeze-drying: crystallization of sodium chloride in sodium chloride-sucrose frozen aqueous solutions. J Pharm Sci. 2007;96(7):1848–53.CrossRefPubMedGoogle Scholar
  8. 8.
    Williams NA, Dean T. Vial breakage by frozen mannitol solutions: correlation with thermal characteristics and effect of stereoisomerism, additives, and vial configuration. J Parenter Sci Technol. 1991;45(2):94–100.PubMedGoogle Scholar
  9. 9.
    Shalaev E, Franks F. Solid-liquid state diagrams in pharmaceutical lyophilisation: crystallisation of solutes. In: Levine H, editor. Progress in amorphous food and pharmaceutical systems. Cambridge: The Royal Society of Chemistry; 2002. pp. 200–215.Google Scholar
  10. 10.
    Suzuki T, Franks F. Solid-liquid phase transitions and amorphous states in ternary sucrose-glycine-water systems. J Chem Soc Faraday Trans. 1993;89(17):3283–8.CrossRefGoogle Scholar
  11. 11.
    Chatterjee K, Shalaev EY, Suryanarayanan R. Partially crystalline systems in lyophilization: I. Use of ternary state diagrams to determine extent of crystallization of bulking agent. J Pharm Sci. 2005;94:798–808.CrossRefPubMedGoogle Scholar
  12. 12.
    Gomez G, Pikal MJ, Rodriguez-Hornedo N. Effect of initial buffer composition on pH changes during far-from equilibrium freezing of sodium phosphate buffer solutions. Pharm Res. 2001;18:90–7.CrossRefPubMedGoogle Scholar
  13. 13.
    Romero-Torres S, Wikström H, Grant ER, Taylor LS. Monitoring of mannitol phase behavior during freeze-drying using non-invasive Raman spectroscopy. PDA J Pharm Sci Technol. 2007;61:131–45.PubMedGoogle Scholar
  14. 14.
    Nail S, Tchessalov S, Shalaev E, Ganguly A, Renzi E, Dimarco F, et al. Recommended best practices for process monitoring instrumentation in pharmaceutical freeze drying—2017. AAPS PharmSciTech. 2017;
  15. 15.
    Thompson TN, Wang Q, Reiter C. Developing transferrable freeze-drying protocols using accuflux and a MicroFD®. San Diego: PepTalk; 2017.Google Scholar
  16. 16.
    Chen R, Slater NKH, Gatlin LA, Kramer T, Shalaev EY. Comparative rates of freeze-drying for lactose and sucrose solutions as measured by photographic recording, product temperature, and heat flux transducer. Pharm Dev Technol. 2008;13(5):366–74.CrossRefGoogle Scholar
  17. 17.
    Archer DG. Thermodynamic properties of the NaCI + H20 system II. Thermodynamic properties of NaCI (aq), NaCI·2H20 (cr), and phase equilibria. J Phys Chem Ref Data. 1992;21(4):793–829.CrossRefGoogle Scholar
  18. 18.
    Billaux MS, Flourie B, Jacquemin C, Messing B. Sugar alcohols. In: Marie S, Piggott JR, editors. Handbook of sweeteners. New York: Springer Science+Business Media; 1991. p. 72–103.CrossRefGoogle Scholar
  19. 19.
    Kauppinen A, Toiviainen M, Aaltonen J, Korhonen O, Järvinen K, Juuti M, et al. Microscale freeze-drying with Raman spectroscopy as a tool for process development. Anal Chem. 2013;85:2109–16.CrossRefPubMedGoogle Scholar
  20. 20.
    Cavatur RK, Suryanarayanan R. Characterization of phase transitions during freeze-drying by in situ X-ray powder diffractometry. Pharm Dev Techn. 1998;3(4):579–86.CrossRefGoogle Scholar

Copyright information

© American Association of Pharmaceutical Scientists 2017

Authors and Affiliations

  1. 1.Millrock Technology, IncKingstonUSA
  2. 2.Pharmaceutical Development, Allergan plcIrvineUSA

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