Optimizing Evaporation Conditions of Reversed-Phase Prep HPLC Fractions
The V-10 Rapid Solvent Evaporator quickly evaporates reversed-phase prep HPLC fractions using a pre-set method. However, when evaporating Acetonitrile-containing fractions, the Acetonitrile (MeCN) will sometimes evaporate too quickly causing an issue with product yield.
The V-10 Rapid Solvent Evaporator quickly evaporates reversed-phase prep HPLC fractions using a pre-set method. However, when evaporating Acetonitrile-containing fractions, the Acetonitrile (MeCN) will sometimes evaporate too quickly causing an issue with product yield. A study was conducted to find optimal conditions for evaporating MeCN/water solutions, looking for the conditions which evaporate the most liquid and allow the least to pull through the vacuum pump.
Experimental Conditions:
Variables:
Vacuum settings: 14 to 22 mbar
Evaporation time at different pressure and pump settings:
Pump 1 Hi, Low
Pump 2 Med, Low
Test Conditions:
Solvent: MeCN/H20 (3:1)
Vial: 20-mL scintillation
Volume/vial: 4 mL
Method: HPLC frac
Vial rotation: 6000 rpm
Temperature: 36° C
Results and Discussion:
Table 1. Vacuum settings
| # of vials tested | Vacuum (mbar) | Volume in pot (mL) | Volume in vial (mL) |
| 7 | 14 | 1.50 | 0.21 |
| 7 | 16 | 0.67 | 0.10 |
| 7 | 18 | 0.40 | 0.06 |
| 7 | 20 | 0.20 | 0.03 |
| 7 | 22 | 0.10 | 0.01 |
Table 2. Evaporation time test
| # of vials tested | Vacuum (mbar) | Pump speed 1 | Pump speed 2 | Evaporation time (min.) |
| 1 | 22 | Hi | Med | 6.53 |
| 1 | 20 | Hi | Med | 6.25 |
| 1 | 14 | Hi | Med | 6.36 |
| 1 | 14 | Low | Low | 8.50 |
The data in Table 1. indicate that by reducing the vacuum (increased mbar) the MeCN/H2Omix becomes more efficiently evaporated as evidenced by both lower vial and pot volumes. At higher vacuum,MeCN can “flash” off and bypass the condenser.
The data in Table 2. shows the impact of altering the pump 1 and pump 2 speeds (pump 1 is the speed of the vacuum pump in mbar/sec when the pressure is >150 mbar and pump 2 is vacuum pump speed when the pressure is
Conclusion:
From this data, the recommended conditions for evaporating Acetonitrile/ H2O fractions are:
Temperature: 36° C
Pressure: 20 or 22 mbar
Maximum evaporation power: 100%
Final dry time: 3.0 min.
Rotation speed: 6000 rpm
Pump speed 1: Hi (mbar/sec)
Pump speed 2: Med (mbar/sec)
End evaporation: Auto
Min. evaporation time: 0.8 min.
Max. evaporation time: 20 min.
External vacuum: No