Rotation Impaction Aeroallergen Samplers
Aerobiology Research Laboratories offers two sampler models: the GRIPS-99M and the GRIPST-2009. The GRIPS series sampler was designed strictly for conducting qualitative analyses of the particles in the air, but can be adapted to collect for short periods of time. The GRIPST series samplers can be used for both qualitative and quantitative sampling applications by providing settings to allow collections at varying duty cycles.
The GRIPS-99M, as with its predecessor GRIPS-99, is targeted primarily for agricultural uses and other qualitative sampling applications. Featured components include a rugged, waterproof PVC plastic casing suitable for all types of extreme weather, a rain shield roof to protect samples from wash off, a super-heavy-duty maintenance-free Maxon motor for extended life, and voltage regulator that provides constant rotation speed for any >12VDC power source and allowing for adjustment and calibration. This sampler is equipped with a one and one-half inch sampling head mounting post, designed to reduce air turbulence and thus optimize pollen and fungal spore collection. The post has been C&C machined for balance to reduce motor wear.
|Input Power:||DC 12V to 30V, 300mA|
|Power Plug:||Banana jacks, screw-clamp|
The GRIPST-2009 is our flagship sampler. This model is designed for long-term aeroallergen monitoring projects. The compact sampler casing is constructed from galvanized steel, with a tightly-closing hatch for easy access to the sampler internals. All exterior components are rated NEMA-4 or better. This model includes a super-heavy-duty maintenance-free Maxon motor for extended life, and a voltage regulator that provides stable rotation speed for any >12VDC power source and the ability to adjust and calibrate rotation speed to suit the needs of the monitoring project. This sampler incorporates a solid-state relay timer that allows the sampler to be set to any desired duty cycle, and is equipped with a 1.5" long sampling head mounting post, C&C machined, to reduce air turbulence.
|Dimensions:||16cm x 18cm x 16cm (including post)|
|Input Power:||DC 12V to 30V, 300mA|
|Power Plug:||Banana jacks, screw clamp|
Each sampler comes with an auto-retracting sampling head for "Type-I" sampling rods, a 12-foot long extension cord with a choice of banana plugs or automotive battery "gator clips", and a package of 100 "Type-I" rods. Samplers are shipped calibrated to 2400RPM, and set to a 10% duty cycle (one minute on, nine minutes off) when applicable.
Rotation Impaction Technology
Rotation impaction samplers have become one of the most widely used mechanical devices for collecting air-borne particles in North America. Developed originally in the 1940's, this technology has been shown to be equally effective at collecting particles with sizes ranging from over 100 microns to as small as 2 microns, and is therefore suitable for collecting pollen grains and fungal spores.
A basic rotation impaction sampler consists of two rods attached to a bar known as a "sampling head", which in turn is attached to a motor. The rods are very thin (less than 2mm wide), and are coated with an embedding material such as silicone grease. As the motor spins, particles in the air impact against the leading surface of the rods and become embedded in the grease. As the rods spin in a circle, sampling occurs independently of wind direction. Wind speed is also independent, as rods travelling with the wind will come into contact with proportionally less air while rods travelling against the wind come into contact with proportionally more air. Standard practice in aerobiology is to sample at speeds of 2400RPM, providing the rods with a travel speed of over 80Km/h and further negating the effect of wind.
To determine the number of particles in the air over the sampling duration, a formula is used to convert the area of the collection surface to a unit of volume over time. In order to support this conversion formula, the number of rotations of the sampling head and the duration of sampling must be known. It is therefore very important that the speed at which the motor spins the sampling head is known and remains consistent. Analysis of samples is performed under a microscope, where particles of interest in a measured sample area are identified and counted. As the conversion formula provides a direct relation between the number of particles on the sample and the number of particles per unit volume of air, the methodology for sample analysis is straight-forward in both theory and practice.
In most instances it is necessary to collect samples over long periods of time. This poses a problem of rod overload: if too many particles are collected on the rods, the sample will be difficult, if not impossible, to accurately analyze. When long collection periods are required, it is recommended that the collection be made intermittently over the sampling period, using a reduced duty cycle. Standard practice in aerobiology is to sample a 24-hour period using a 10% duty cycle (one minute of sampling, nine minutes of rest), thus providing an even sampling of particles over the course of a day without overloading the rods' surface. The GRIPST series samplers from Aerobiology Research Laboratories have integrated timers that provide the capability of sampling with reduced duty cycles.
Aerobiology Research Laboratories supplies sampling heads that are auto-retracting. The rods are contained inside of the sampling head while at rest, and during sampling are extended downwards at 90° to the sampling head by centrifugal force. Retracting the rods while the sampler is at rest protects them from unmetered particle impaction as well as from the elements.
Rotation impaction samplers are non-selective, meaning that they will collect all airborne particles including debris. This should be an important consideration when determining the period and duration of sampling, as well as the duty cycle. These samplers are also capable of sampling for only one duration at a time, at which point the rods must be switched before a second sample can be obtained. Arrays of multiple samplers are often used in combination with a switching power supply when more than one sample is required for a given duration.
Other sampling methods and equipment are being used in this industry, but these 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 suction samplers have the ability to shift their collection surface, so that the sample can be sub-sectioned into hourly or daily increments -- an advantage over rotation impaction samplers. However, the equipment is highly susceptible to human error in configuration of the sampler, in changing of the samples, and when analysis and interpreting results. Aerobiology Research Laboratories has researched sampling and analysis methodologies with the objectives of reproducibility and accuracy, and has found that there is no method of analyzing the samples from these suction type machines (Seven day spore traps) that provides as consistent a result as rotation impaction.
Research has been performed over the years comparing different types of samplers and their respective results. As of yet, however, very little research has been published on how representative each of these different types of samplers are in what they collect compared to what is actually in the air. The collections of different samplers with a constant, known amount of particles, of varying sizes. Our research has found, for instance, that the calibration of suction samplers significantly affect the rate at which particular sizes of particles are collected: calibration for larger particles (pollen) results in an oversampling of smaller particles (spores). When sampling in the field, it is often difficult to know how each piece of equipment is maintained and used, and therefore it is very difficult to tell from day to day if the sampler is even functioning as expected. The complexity and reliability of the equipment used, the amount of training provided to the operator, and the methodology and abilities of personnel involved in analysis all affect the validity of the data.