5
2
M
ETHOD OF
O
PERATION
The AirPrep Cub Sampler uses an electret filter to capture particles. To recover
the trapped particles, a novel Wet Foam Elution™ process is employed to break
the electrostatic charge and flush the particles off the filter into a small liquid
volume in seconds.
2.1
S
AMPLE
C
OLLECTION ON AN
E
LECTRET
F
ILTER
The dry 52 mm electret filters are made with a combination of positively charged
and negatively charged fibers. This substantially increases the collection
efficiency of the filter and allows for the use of lower pressure drop filters, which,
in turn, allows for higher sampling rates for extended periods using battery
power.
2.2
I
NSTANT
W
ET
F
OAM
E
LUTION
™
The patented wet foam elution process uses a very specific high-quality foam
to elute the filter. The elution fluid is composed of water, a low concentration
surfactant (0.15% Tween 20), and a pH buffer (Tris or PBS). This solution is
carbonated, which dissolves significant amount of CO
2
into the fluid. During the
elution process, the valve opens as the elution canister is pushed into the
elutor cap that is fitted onto the filter, forcing the elution fluid through the
pressure orifice, through the filter and into the sample cup. As the fluid passes
from the high-pressure environment on one side of the orifice, to the low-
pressure environment on the other side, the dissolved CO
2
expands, comes out
of the solution to form micro-bubbles. These micro-bubbles increase the
volume of the fluid six-fold or more as it passes through the filter. The foam
immediately collapses back into a liquid and is ready for sample processing and
analysis. InnovaPrep’s patented Wet Foam Elution process
https://www.innovaprep.com/patents)
is much more efficient than liquid
rinsing for the following reasons:
•
Volume Expansion
- When rinsing a filter with liquid, most of the liquid
volume is used to fill the dead space inside the filter housing; only a small
portion of the fluid covers the filter surface. This can be avoided to an extent
by reducing the cross-sectional area of the fluid path across the filter, but a
large portion of the liquid is still underutilized. Because our elution foam is
80-90% gas, this fills the empty space without contributing to the final
sample volume.
•
Increased Viscosity -
Liquid has a tendency toward “channeling” when
flowing through a filter, creating an area of high flow in the center of the
fluid path, while the portion of flow in contact with the filter surface is much
slower. The higher viscosity of our elution foam prevents channeling and
allows for a more uniform flow through the interstitial spaces of the filter.
