Preparative Supercritical/Subcritical Fluid (SFC) Chromatography Method Development Solvent effects Particle size 37
Preparative Supercritical (Subcritical) Fluid Chromatography: Benefits CO 2 is miscible with more solvents than alkanes CO 2 is cheaper than alkane bulk solvents CO 2 is much less flammable than alkane bulk solvents Removal of CO 2 is simple Low pressure drop higher flow higher productivity No need for additives for acids (esterification) 38
Criteria for Preparative SFC Method Development Selectivity Always the most important factor in preparative separations. Solubility Important as injection volume may be limiting. Sample is dissolved in a strong solvent. Too large an injection can distort the peaks. Inherent difficulty of measure solubility in the supercritical phase. 39
Mobile Phase Selection for Preparative SFC Method Development Analytical screening protocols using immobilized polysaccharide based CSPs reported at the SFC Conference, Pittsburgh, Sept 2007. MTBE, MeOH, IPA, THF, DCM, MeCN, EtOAc, CHCl3 39 different solutes Best separations MTBE > MeOH > IPA > THF > DCM > MeCN > EtOAc > CHCl3 Most useful initial screen: THF, MTBE*, MeOH, IPA. * Containing 20% methanol to adjust solvent strength 40
Preparative SFC Method Development: Loading Studies Carried out as for preparative HPLC loading studies, but samples dissolved in polar modifier; peak distortion due to modifier and mixing effects. 0.847 0.604 0.852 0.606 0.615 0.842 60 mg/ml X 20 microl 40 mg/ml X 30 microl 20mg/mL X 60microL Use highest concentration possible volume overload very common. Note the short time window! use maximum scaleable flow rate. Column 25 x 0.46 cm. 41
Fast Semi Preparative SFC Sample : Cycle Time : Mobile Phase : Flow Rate : Production : 40 mg/injection 1.7 min 5% methanol 80 g/min 1.4 g/hr (en) 120.00 122.00 124.00 126.00 128.00 130.00 [min] 42
Fast Semi Preparative SFC µv 1.2E+06 1.0E+06 8.0E+05 6.0E+05 4.0E+05 2.0E+05 0.0E+00 50.00 100.00 150.00 200.00 [min] SFC enantiomer separation of 10.0 g of a racemic drug within 3.6 h using a 25 X 2.1 cm i.d. column packed with CHIRALCEL OJ H CSP. 43
Preparative SFC A Question of Pressure Preparative SFC Is Often Preferred over HPLC Low viscosity allows high flow rates, and therefore high production rates within system pressure limits. Samples are dissolved in the polar modifier and not the mobile phase (can be a disadvantage too!). Organic solvent use is 10 to 40% of that in HPLC. As with all chromatographic processes, the production rate of a system is limited by pressure. 44
SFC vs. HPLC: Flow Rates Required to Produce Equivalent Column Pressure Drops Column i.d. (cm) 0.46 1.0 2.0 3.0 5.0 Flow Rate (ml/min) HPLC SFC 1.0 4.0 4.73 18.9 18.9 75.6 42.5 170 118 472 45
SFC Pressure Drops in Presence of Methanol Flow Rate (ml/min) 200 300 400 500 600 10% 30 45 65 87 110 CHIRALPAK AD H (5 micron) (250 x 50 mm i.d.) Back Pressure: 100 bar Composition (% Methanol in CO 2 ) 20% 30% 40% 34 50 85 110 Pressure 120 100 80 60 40 20 41 66 102 0 50 67 10 % MeOH 20% MeOH 30 % MeOH 40 % MeOH 0 100 200 300 400 500 600 700 Flow 46
SFC Pressure Drops in Presence of 2 Propanol: Flow Rate & Particle Size 160 % IPA: 10, 20 & 30 in CO 2 1000 800 5 micron particles Pressure drop (bar) 140 120 100 80 60 40 20 30% 30% 20% 10% 0 0 100 200 300 400 500 600 700 800 Flow rate (ml/min) CHIRALPAK AD H (5 micron) & CHIRALPAK AD (20 micron) 250 x 50 mm i.d., Back Pressure: 100 bar 5 20 600 400 200 250 200 150 100 0 0 50 0 0 1 1 2 2 3 3 4 20 micron particles 4 5 5 6 6 7 7 47 8 8 9 9
Preparative SFC & Pressure Limitations: Summary High flow rates can be attained at high modifier concentrations with preparative 5 micron SFC columns. Higher flow rates can be attained with 20 micron CSP where selectivity allows. The available pressure is limited between the back pressure and the maximum equipment pressure allowing for pressure spikes on injection etc 48
Causes of High Pressure Drops in SFC & HPLC High Concentration of Viscous Modifier Sample Contaminants Salts Metal Catalysts Sample Insolubility in the Supercritical Phase 49
Causes of High Pressure Drops in SFC & HPLC: Frit Blockage by Contaminants Blocked Frits as seen in 5 cm i.d. SFC columns When the inlet frit is blocked, there is a high pressure differential across it; it may deform 50
Consequences of Frit Blockage in SFC & HPLC The Seal between the Frit and Its housing Is Broken; Loss of CSP and Performance 51
How to Avoid Frit Blockage in SFC & HPLC Always filter samples (use 0.5 micron filter membranes)!! Use metal scavenger (metals coat out on the frit). Beware of sample precipitation as it mixes with the supercritical fluid Look for pressure spike on injection. Look for steady increase in pressure on each injection. Decrease the sample concentration if required or (if possible) change modifier to enhance solubility. 52
Questions, Comments and Complaints Contact: Norbert M Maier, Ph.D. Chiral Technologies, Inc. West Chester, PA 19380, USA nmaier@chiraltech.com Clint Amoss, Ph.D. Senior Applications Expert questions@chiraltech.com 53