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@article{1408053,
author = {Vetráková, Ľubica and Vykoukal, Vít and Heger, Dominik},
article_location = {AMSTERDAM},
article_number = {1-2},
doi = {http://dx.doi.org/10.1016/j.ijpharm.2017.08.005},
keywords = {Protein cryopreservation; Freezing; Lyophilization; pH shift; Freezing stress; pH memory; Formulation buffers},
language = {eng},
issn = {0378-5173},
journal = {International Journal of Pharmaceutics},
title = {Comparing the acidities of aqueous, frozen, and freeze-dried phosphate buffers: Is there a "pH memory" effect?},
url = {https://www.sciencedirect.com/science/article/pii/S0378517317307135?via%3Dihub},
volume = {530},
year = {2017}
}
TY - JOUR
ID - 1408053
AU - Vetráková, Ľubica - Vykoukal, Vít - Heger, Dominik
PY - 2017
TI - Comparing the acidities of aqueous, frozen, and freeze-dried phosphate buffers: Is there a "pH memory" effect?
JF - International Journal of Pharmaceutics
VL - 530
IS - 1-2
SP - 316-325
EP - 316-325
PB - ELSEVIER SCIENCE BV
SN - 03785173
KW - Protein cryopreservation
KW - Freezing
KW - Lyophilization
KW - pH shift
KW - Freezing stress
KW - pH memory
KW - Formulation buffers
UR - https://www.sciencedirect.com/science/article/pii/S0378517317307135?via%3Dihub
L2 - https://www.sciencedirect.com/science/article/pii/S0378517317307135?via%3Dihub
N2 - The concept of "pH memory" has been established in the literature for the correlation between the pH of a pre-lyophilization solution and the ionization state of freeze-dried powder (lyophile). In this paper, the concept of "pH memory" is explored for the system of an aqueous solution, a frozen solution, and a lyophile. Sodium and potassium phosphate buffers in the pH range of 5-9 were frozen and lyophilized with sulfonephthalein indicators as acidity probes, and their Hammett acidity functions were compared to the initial pH of the aqueous solution. The results show that the acidities of the lyophiles are somewhat changed compared to the initial pHs, but the acidities in the frozen state differ more substantially. The Hammett acidity functions of the frozen buffers were found to be markedly dissimilar from the initial pH, especially in the sodium phosphate frozen at 233 K, where an increase in the initial pH led to a decrease in the Hammett acidity function of the frozen state at a certain pH range. The large acidification observed after freezing the sodium phosphate buffer was not detected in the lyophiles after the sample had been dried; the phenomenon is explained considering the formed crystals analyzed by X-ray powder diffraction. The results suggest that monitoring the final acidity of a lyophile is not sufficient to predict all the acidity changes throughout the whole lyophilization process. The importance of well-controlled freezing and lyophilization conditions follows from the results of the research.
ER -
VETRÁKOVÁ, Ľubica, Vít VYKOUKAL and Dominik HEGER. Comparing the acidities of aqueous, frozen, and freeze-dried phosphate buffers: Is there a ''pH memory'' effect? \textit{International Journal of Pharmaceutics}. AMSTERDAM: ELSEVIER SCIENCE BV, 2017, vol.~530, 1-2, p.~316-325. ISSN~0378-5173. Available from: https://dx.doi.org/10.1016/j.ijpharm.2017.08.005.
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