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SASS® 3010 Manual Particle Extractor

The SASS 3010 is used to extract and transfer to a small fluid volume, aerosols captured by Research International’s electret filters. Captured particulates can be difficult to remove: Induced dipole fields create a strong holding force and must be neutralized. Once particulates have been released, they must then be removed from within the fibrous filter matrix and collected in a small amount of sample fluid. These processes are efficiently performed in a matter of 1 to 2 minutes using the SASS 3010 manual extractor.

Extraction efficiencies are typically in the range of 60 to 80%. To test extraction efficiency, a SASS 3000 and several electret filters were used to collect airborne fluorescent polystyrene beads of 1.8 microns diameter. Each filter was operated for a period of 10 minutes. After the collection phase was completed, the filters were mounted in a SASS 3010 and captured beads transferred to 5 ml of extraction buffer using the protocol outlined below. Extraction efficiencies were then determined using fluorimetric assay methods.

It was found that an average recovery of 77% was achieved. A second extraction with an additional 5 ml of extraction fluid resulted in recovery of another 17% of the embedded beads, while two more 5 ml extractions resulted in small 4.5% and 1.5% additions to the total number of beads recovered, respectively.

In a second test series designed to study the effect of particle size on extraction efficiency, fluorescent polystyrene beads of 0.9 to15.0 microns diameter were spotted uniformly over either the filter’s inlet (air-side) or outlet (fan-side) face from water-based particle suspensions: Each fluid spot had a volume of 10 ul. For inlet-side spotting, a dilute surfactant solution was used: dilute surfactant assists in wicking injected fluid and suspended particles deep into the hydrophobic filter matrix. For fan-side spotting, particle suspensions in distilled water were used: Distilled water results in poor penetration of the particles and provides a worst-case scenario of particle position within the filter. That is, during extraction the particles must travel through the filter’s entire vertical cross-section.

After the filters had been allowed to air dry, each was extracted with 6 ml of Research International’s extraction solution (Part number 1760-0006-17). Recovery percentages are shown in Figure 1 for the air-side and fan-side spotting tests, and for the previously described aerosol loading test. From this Figure it can be seen that extraction efficiency for particles lodged on the air side of the filter shows no apparent dependence on particle size. For particles deposited on the fan side of the filter, there is a noticeable improvement in extraction efficiency as particle size increases, until the difference in extraction efficiency becomes insignificant between inlet- and outlet-side deposition, for particles larger than about 10 microns. Note that the aerosol extraction test results with 1.8 micron diameter particles are very similar to results when the particles were spotted onto the filter’s air-side from a surfactant solution.

Figure 1: Extraction efficiency versus particle size and initial vertical locations in electret filter.

Taken together, this data implies that the 3010 extractor can be expected to recover about 60% to 80% of the aerosol particles captured by the electret filters used in the SASS3000 and SASS4000 dry samplers.

In a third test series, extraction efficiency was determined as a function of extraction fluid volume. For this purpose, 1.8 micron fluorescent polystyrene beads were embedded in the filters by spotting dilute surfactant solutions containing the particles onto the filter’s air-side face, as described previously. Results are shown in Figure 2. These tests indicate that overall collection efficiency is maximized if 4 ml or more of extraction fluid is used.

The comparatively high transfer efficiencies found with a single extraction are the result of several design elements:

• An effective extraction fluid;
• The use of sonic vibration to dislodge particles from the fiber matrix; and
• Regulation of flow so that the extraction fluid enters the rear of the filter and exits the air inlet face, where particle concentrations are highest.

Figure 2: Extraction efficiency versus extraction fluid volume.

Operation is straightforward. Please refer to the Figures below.

As a first step, the Extractor’s upper housing is removed by rotating the cap so that the latch pins are free, that is, at the center position between the “DECON” and “EXTRACT” positions (See Figure 3). The user then inserts the filter assembly into the exposed lower housing with the rear of the filter facing upward (Figure 4). The cap is then reattached and the latch pins rotated to the “EXTRACT” position. This causes an O-ring seal to press against the plastic filter ring, and to seal the filter in place within the extractor.

Figure 4: Extractor internal components.

Next, a Leur cap on the upper housing is detached and the dropper bottle’s 6 ml of fluid (needed to recover 5 ml of sample) is slowly injected into the interior of the extractor. The empty dropper bottle is slid into a holder on the side of the extractor.

The dropper bottle has two purposes- Initially, as a purging fluid reservoir and after extraction, as a sample fluid container. The bottle’s dropper attachment can be used to provide sample fluid drops of about 25 uL each, for use with lateral flow assay strips and the like. The bottle holder on the SASS 3010 provides a friction fit, and the bottle should be slid upward in the holder to a built-in stop that prevents fluid from splashing out during the final extraction

At this point the Leur cap is reattached to seal the instrument (Figure 5) and the agitation button (Figure 6) is pressed and held for about a 15 second period, causing particulates to be loosened from the fibers through sonic action. The fluid sample is now ready to be removed.

Figure 5: Extractor showing Luer cap and sample bottle.

Figure 6: Extractor agitation button.

To discharge sample fluid into the dropper bottle, slowly press down on the extraction pump plunger (2 to 3 second stroke) until it bottoms in travel (Figure 7). Release and allow the return spring to extend the handle. Repeat the purging sequence 5 times, observing that the fluid is being properly and completely deposited into the dropper bottle. This stroking process initially creates a pressurized condition over the filter surface, causing sample water to flow out a discharge line to the dropper bottle. At the end of each stroke, a plate at the lower end of the plunger compresses the filter media and pushes any residual sample water out of it and into the sample vial.

Figure 7: Using the extraction pump plunger.

To remove the extracted filter assembly, remove the upper housing as before. Then remove the filter by inserting a finger into the cutout in the side of the lower housing and lift the tab on the filter to release it.

No external power is used- two “D” batteries power the sonication step. The batteries can be replaced with no tools by removing 4 finger-nuts on the device’s bottom surface. Due to the short sonication time, a long battery life can be expected. Specifications are provided in Table 1.

• Download SASS 3010 Data Sheet (83 KB)