Equipment
Rotation Impaction Sampling Technology
Rotation impaction samplers have become one of the most widely used mechanical devices for collecting air-borne particles. They have proven to be effective for collecting particles as small as 2 to 3 microns and are therefore suitable for collecting pollen grains and fungal spores.
The sampling head was re-designed by Aerobiology Research Laboratories with corrosion-resistant materials to support the collecing rods. These rods are 32mm long, which provides a minimum exposed sampling surface of 1.59mm x 23mm when mounted in the sampling head. When the sampler is at rest the rods are retracted inside the sampling head. Using approximately 12 Volts (DC), the motor spins the sampling head at a nominal rate of 2400 RPM.* The rods extend downwards at a 90° angle at which point particles may be impacted against the leading surfaces. The amount of particles collected is a function of the volume of air sampled. This, in turn, depends on the size of the rods, the speed of the rotation and the length of exposure time. In order to retain these particles the rods must be coated with a substance that is both tacky and allows for in situ examination under visible light. We recommend a specific silicone grease to coat the rods. Hexane should be used as a carrier when dipping since this is the only way to have an even layer of grease. It is not recommended to coat the rods with silicone grease using fingers since this is not a safe practice and will not make for an even coating on the rods.
In some instances it is necessary to collect samples over long periods of time. This poses the problem of rod overload. If too many particles are collected the rods will become difficult, if not impossible, to accurately analyze. When long collection periods are required, it is recommended that the collection be made in timed cycles. The Model GRIPST 2000 and GRIPST 2003 can be set at timed sampling rates with the timer activating the retracting head to spin intermittently. When it is at rest the rods are retracted inside the head to prevent particle impaction. Professionals who study aeroallergens often use these models to collect samples over 24 hour periods, with a 10% (one minute on, nine minutes off) duty cycle. With these models they are able to produce counts which are both accurate and representative of the time period that they are interested in.
Since the GRIPST 2000 and 2003 are non-selective samplers they will collect all air-borne particles including debris. This should be an important consideration when setting the timer.
When sampling is complete the removable rods may be mounted in a special grooved stage adapter for examination under the microscope.
Other sampling methods and equipment are being used in this industry but are more labour intensive and are costly to buy. These are based on suction sampling and are highly affected by wind speed and direction (Manual for Sampling Airborne Pollen, E.C. Ogden, et al.) Some of these samplers have the advantage of providing multiple hourly or daily sections to their sample, but the equipment is highly susceptible to human error both in daily or weekly changing and interpretation of the samples. We have found that there is no consistent method of analazing the samples with the use of these suction type machines (Seven day spore traps). Aerobiology Research Labs has researched our methodology for reproducibility and accuracy, therefore, we have developed a standardized method of analyzing samples which is used by all of our trained staff.
Research has been done over the years comparing different types of samplers and their respecive counts. We, as of yet, have to do some research on how representative each of these different types of samplers are and what they collect compared to what is actually in the air. Research has to be done in comparing the collections of different samplers with a constant, known amount of different sizes of particles. In the field it is difficult to know how each piece of equipment is maintained and used, and it is impossible to tell from day to day if the sampler is functioning properly. The complexity of the equipment used and the amount of training provided to the operator and the person analyzing the samples all affect the validity of the data.
* PLEASE NOTE: Power adapters are not supplied with the samplers due to variability in voltage output which affects the RPM and timing. We have found that a fully charged 12 volt battery is the most reliable device for voltage output, however a 12 volt, 300 milliamp adapter will usually produce 2400 RPM. Our GRIPST-2003 model has an integrated voltage regulator which will provide a sustained RPM with any >12V DC power source.
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