Solute crystallization in frozen systems-use of synchrotron radiation to improve sensitivity.
OBJECTIVE
To demonstrate the sensitivity of low temperature synchrotron X-ray diffractometry (SXRD) for detecting solute crystallization in frozen sodium phosphate buffer solutions. To determine the effect of annealing on solute crystallization in frozen solutions.


METHODS
Sodium phosphate buffer solutions, at initial buffer concentrations ranging from 1 to 100 mM (pH 7.4) were cooled to -50 degrees C. The crystallization of disodium hydrogen phosphate dodecahydrate (Na(2)HPO(4) *12H(2)O) was monitored using a laboratory as well as a synchrotron source. At selected concentrations, the effect of annealing (at -20 degrees C) was investigated.


RESULTS
With the laboratory source, solute crystallization, based on the appearance of one diagnostic peak with a d-spacing of 5.4 A, was evident only when the initial buffer concentration was at least 50 mM. In contrast, using SXRD, crystallization was detected at initial buffer concentrations down to 1 mM. In addition, the use of a high-resolution 2D detector enabled the visualization of numerous diffraction rings of the crystalline solute. At both 10 and 100 mM buffer concentration, there was no increase in solute crystallization due to annealing.


CONCLUSIONS
By using synchrotron radiation, solute crystallization was detected with substantially increased sensitivity, making the technique useful for freeze-drying cycles of practical and commercial importance. Since numerous peaks of the crystalline solute appeared, the technique has potential utility in complex, multi-component systems.
Varshney
Dushyant B
DB
Department of Pharmaceutics, College of Pharmacy, University of Minnesota, Minneapolis, Minnesota 55455, USA.
Kumar
Satyendra
S
Shalaev
Evgenyi Y
EY
Kang
Shin-Woong
SW
Gatlin
Larry A
LA
Suryanarayanan
Raj
R
D002021:Buffers; D003080:Cold Temperature; D003460:Crystallization / Q000379:methods*; D005615:Freezing; D007202:Indicators and Reagents; D010710:Phosphates / Q000737:chemistry; D017356:Synchrotrons; D014961:X-Ray Diffraction / Q000379:methods*
D002021:Buffers; D007202:Indicators and Reagents; D010710:Phosphates; C018279:sodium phosphate