Bio-Concentrators

Originally designed for the detection of airborne biological agents, the Bioconcentrators Models 4220 and 4240 are high-performance particle concentrating aerosol samplers which can be used in any application where particle concentration presents a problem.

In many cases of particle sampling from ambient air, the concentration of airborne particles is so low that it becomes necessary to sample for prolonged periods of time in order to obtain sufficient mass for chemical or biological characteristion.

One such case is the identification of biological aerosols by mass spectrometry. In this application, the aerosol sampler delivers a representative sample of the airborne particles to a pyrolysis tube which, periodically, converts the sample thermally and chemically to components that are then analysed by mass spectrometry.

The mass rate of delivery of material to the pyrolysis tube must be sufficient to allow the detection of biological aerosols with a concentration of about 1 particle per litre of air.

At the same time, in certain situations, any delay in analysis is to be avoided. Indeed, a response time in the order of minutes is desired. As a result, a need arises for a device capable of concentrating particles from several hundred litres per minute of air into a low flow rate compatible with the spectrometric technique outlined above.

The Bioconcentrator draws air at 300 L/min from the surrounding environment and then splits the air into a particle-rich stream and a particle-depleted reject stream.

The resulting particle-rich stream contains only 0.3% of the inlet air i.e., 1 L/min, but up to 90% of the ambient particles in the size range 2.5-10 microns in the case of Model 4220 thus increasing the sensitivity of the analysis by up to 300 times (1-10 microns in the case of Model 4240).

The Biocentrator is effectively a three-stage virtual impactor. In a conventional impactor, particles with sufficient inertia (size) strike a collection plate where they remain for later analysis. In a virtual impactor, particles are drawn through a series of nozzles and upon exiting these nozzles encounter a receiving tube.

The design is such that those particles with sufficient inertia (above the desired cut-point) continue forward with a small portion of the flow into the receiving tube whilst the rest of the flow carrying only small particles below the cutpoint is diverted around the receiving tube.

Ambient air is sampled at 330 L/min through an initial impactor (inlet scalper) which removes particles larger than 10 microns and discards them together with 30 L/min of the air flow.

The remaining 300 L/min sampled air flow then passes through a two-stage concentrating virtual impactor (CVI) which concentrates particles in the 2 to 10 micron (or 1 to 10) diameter ranges into a single 1 L/min stream for output to an external collector or detector (not provided).

Two lightweight, high performance vacuum pumps draw the inlet air flow through the system. The air flow streams are precisely balanced and no valves are used to control the flow.

The Concentrator measures 356 x 394 x 254 mm and weighs 16 kg.