The XcelVap® Evaporation/
Concentration System Pressure
Profiling
Zoe Grosser and William Jones, Horizon Technology, Salem, NH USA
Key Words
XcelVap, Pressure Profiling, Evaporation, Concentration
Programmable pressure profiling in an evaporation system allows the gas pressure to be
gradually increased as the evaporation cycle progresses. The low flow rate early in the
process promotes gradual evaporation under the vortex gas flow (Figure 1). As the
solution evaporates and more space is available in the vessel, the gas flow is increased
to further speed evaporation. Evaporation proceeds optimally, avoiding splashing and
eliminating the possibility of cross contamination and poor recoveries.
The pressure profile is a linear ramp, so the initial gas pressure and the final gas
pressure (24 psi max) are spread over the time set for the process to take place. Once
this ramp has been developed the sample can be run unattended and the audible alarm
will signal when the ramp is complete and the evaporation cycle is done. Figure 2
shows the software for setting the pressure profile ramp. Simply set the initial and final
pressure and the software will automatically calculate a ramp to gradually increase the
gas flow over the time set for the evaporation.
Figure 1. Gas vortex flow
The initial pressure should be determined by testing a sample in the glassware chosen
for the run by gradually increasing the pressure until a gentle vortex circular motion is
seen on the surface, depicted in Figure 3. This pressure will be used as the initial
pressure and the final pressure should also be determined for the final extract volume
with the maximum allowable being 24 psi.
Figure 4 compares the time needed for evaporation of ethyl acetate, using a constant
pressure vs. a ramped pressure profile for 7-mL extract evaporated to dryness. The
sample evaporated over 30% faster using the ramped pressure profile. The entire
process was handled without operator intervention.
Figure 5 shows an example of an evaporation process for a 200-mL dichloromethane
sample evaporated in a bath at 40oC and with three different gas ramp profiles. The
isobaric pressure profile is shown for comparison, but is generally only used on older
equipment not offering a ramping option. The ramp set using the criteria described for
the small volume sample was used for this larger-volume sample and the time for the
Figure 2. Pressure Profile Software
Screen
Figure 3. Gas vortex looking
into the sample from the top
Page 2
desired evaporation is significantly shorter. Another
alternative to further customize the pressure profile
and speed evaporation is to use a two-step process.
To start, the ramp is used until the amount of solvent
being evaporated is at a safe level where an increase
in the gas flow will not cause splattering. Then, the
gas flow is increased to the maximum pressure and
maintained for the remained of the run. This
involves an additional interaction by the operator to
reset the profile to continued maximum pressure
when the alarm sounds, indicating the ramp part of
the program is finished. This program should be
developed experimentally to determine if a ramp or
step gives the best performance for the solvent,
sample size and glassware. This may not be practical
on a routine basis, but when time is of the essence
for a series of samples, this is another alternative to
consider, especially for a larger volume of solvent.
Although operator intervention is necessary to
change the profile when the audible alarm sounds
after the first 10 minutes of the evaporation process,
the step profile does reduce the evaporation time.
The XcelVap system offers several options for
automatic gas increase during the evaporation
process. The laboratory can choose the profile
appropriate for their needs, based on time, solvent,
and demand.
Figure 4. Comparison of evaporation using ramped pressure and
isobaric pressure profiles for a 7-mL sample evaporated to dryness
Figure 5. Comparison of isobaric pressure run with pressure profile
ramp and manual stepped ramp for a 200-mL sample
TN0021405-01
16 Northwestern Drive, Salem, NH 03079 USA ▪ Tel: (603) 893-3663 ▪ Email: [email protected]