Viscosity Measurement of CO-Solvent Mixtures for the Study of the Morphology and Size of Crystalline Particles Obtained Using Supercritical Antisolvent Precipitation.

The viscosity values of CO-dimethylphormamide, chloroform, methanol, isopropanol, ethyl acetate, acetone, and dimethyl sulfoxide mixtures were measured at a pressure of 150 bar and a temperature of 313 K. The correlation of the mean size of levofloxacin hydrochloride and malonic acid particles precipitated using the SAS method with the viscosity of the used CO-solvent mixtures is shown. The high viscosity of the mixtures leads to slower mixing of the solution and the antisolvent.

Solute Diffusion into Polymer Swollen by Supercritical CO by High-Pressure Electron Paramagnetic Resonance Spectroscopy and Chromatography.

High-pressure electron paramagnetic resonance (EPR) was used to measure translational diffusion coefficients (D) of a TEMPONE spin probe in poly(D,L-lactide) (PDLLA) and swollen in supercritical CO. D was measured on two scales: macroscopic scale (>1 μm), by measuring spin probe uptake by the sample; and microscopic scale (<10 nm), by using concentration-dependent spectrum broadening. Both methods yield similar translational diffusion coefficients (in the range 5-10 × 10 m/s at 40-60 °C and 8-10 MPa).

Unusual effect of flow rate on retention in analytical supercritical fluid chromatography exemplified by polyethylene glycol separation.

We report a case of a peculiar effect of flow rate on retention in a separation of polyethylene glycol oligomers via supercritical fluid chromatography. During method development, we tested flow rate gradients and notices that for some PEG oligomers retention times at flow rate gradient were lower than at constant flow with the largest flow rate value used in a gradient. For instance, at BEH stationary phase and CO-MeOH gradient from 10 to 35% at 20 min a PEG oligomer having mass of 1225 Da has a retention time 14 min at 1 mL/min flow rate, 10.

Unexpected separate elution of cation and anion of an ammonium salt in supercritical fluid chromatography.

Amines are frequently used as additives in supercritical fluid chromatography (SFC). They allow eluting basic analytes with reasonable retention times and less distorted peak shapes. Since amines are chemically active compounds, their introduction into SFC mobile phase always raises a question on whether they can react with analytes or mobile phase constituents and, if so, can it affect chromatography separation.