SASS® 2300 Frequently Asked Questions
Perhaps most importantly, the device incorporates a patented method of maintaining the same physical amount sampling water in the device, independent of collection duration, air temperature, or relative humidity. This means that the device can be used in situations where it is desirable to sample for a period of several hours. In addition to permitting wet sampling over long periods, any aerosol target in surrounding air will be continually concentrated over time. For example, collecting for 1 hour will produce a concentration of the target species that is 12 times higher than if only a 5 minute sample was taken. Other samplers resort to dry collection and later re-hydration to accomplish long-term collection. This may kill many delicate organisms.
The SASS 2300 only requires a liquid sample volume of 4 to 6 ml. This is considerably smaller than some competing devices and results in higher target organism concentrations in the sample fluid.
The SASS 2300's sample fluid is pure water. No additives are required. This can be an advantage for PCR and other analysis methods that may be degraded in performance because of the presence of salts and surfactants in the sample solution.
The SASS 2300 can operate continuously for 24 hours. It is the longest-operating high volume portable collector on the market.
The wetted-wall cyclone technology used in the SASS 2300 captures micro-organisms gently, minimizing damage to them and increasing viability of captured dehydration-sensitive organisms.
The SASS 2300 is reprogrammable. A software package is provided with each unit that allows user customizing of air sampling rate, start time and collection time, and the setup of periodic sampling protocols. It is the most programmable sampler on the market.
The SASS 2300 may be controlled remotely through a Bluetooth wireless link from over 1000 feet away.
The fan is operated at a constant RPM, so the airflow is constant, independent of battery or mains voltage. Of course, if you took it onto a high mountain where the air density was much different, there might be a small change in the actual flow rate.
It is calibrated with an orifice-style flowmeter at the factory before shipment. If you compare it with some other type of flowmeter, you have to be careful that the flowmeters airflow resistance does not affect the reading, that is, slow the flow of air down. Our calibration flowmeters have a pressure drop of only about 0.25 cm of water at 300 liters/minute. The overall pressure difference driving air through the SASS 2300 is only about 5 to 6 cm of water. That is why it can operate on a battery for such a long time. It has been designed to very efficiently use the air capability of the fan.
You cannot replace the make-up water in the make-up reservoir with PBS, since it will result in increasing sample salinity with long operating time. We maintain a constant level of sample water in the collector by periodically adding small increments of distilled water to it. However, you could inject PBS into the sampler's inlet throat initially, which would provide the saline environment you want, and then the distilled water automatically provided by our unit would maintain the sample level. If you do this, you might want us to initially set the system up for a 'dry' start-up. Normally, the unit injects a full charge of distilled water immediately upon turn-on to minimize start-up time. With the proposed scenario, you would be providing that start-up fluid charge manually. By the way, the PBS cannot have surfactant in it, since an excessive amount of foam would be created during operation. At least one other customer is doing something like this, but they have not confided details of their procedures to us. You might also want to wash the interior of the SASS from time-to-time so that salts did not build up near the fan entrance, or inside the fan.
It is likely that the salts would also disappear at roughly the same rate - perhaps faster. You might visualize the situation as being due to sub-micron droplets carrying salts (produced during the spraying process) that are not captured and are instead discharged out the exhaust. The SASS 2300 has a secondary rotor structure that prevents larger droplets from exiting and being a source of pathogen spreading, but it will not be effective on the sub-micron droplets. Prolonged operation may lead to a buildup of salts in the secondary rotor structure that may get into the bearing and either physically stop it from rotating or corrode it. Occasional disassembly and washing with DI water should reduce the risk of that happening.
I want to add a buffer to the cyclone at sampling start to achieve better viability of the microorganism of interest. Will it be possible to use a salt concentration in the makeup reservoir that will maintain the same salt concentration as the starting point?
Some other customers have injected various agents into the collection water, but we do not have access to their results data. There are two different scenarios here. If you just inject buffer into the sampler throat and have DI water in the reservoir, then the buffer concentration will gradually fall with time. If you put it into the reservoir, then the concentration will increase fairly rapidly. The water at 50% RH and 25C evaporates at a rate of about 0.8 cc/minute, which should dominate over any loss mechanism. Since you have a fixed volume Vsass of (let's say) 4.5 cc, there will be a linear increase in buffer concentration as
[S(t)] = [s]( 1 + Vdot x t/Vsass)
Where [S(t)] is the salt concentration as a function of time in minutes in the 2300, [s] is the concentration of salt in the reservoir, Vdot is the make-up water introduction rate (around 0.8 cc/minute), Vsass is the constant fluid volume in the SASS, and "t" is the operating time in minutes.
The concentrator can be used with or without the software. You do not need to be connected to a computer. The software is only necessary if you want to change any operating characteristics (such as fluid sample size) from the default levels set at the factory. The software is also useful where the sampler is used as part of an automated, computer-controlled system. Otherwise, the SASS 2300 is completely self-contained and may be operated with the switches on the instrument.
With the standard BA5590/U 15 Ampere-Hr primary battery, the unit will run continuously for about 20+ hours. If you use the AC electrical adapter supplied with the unit, there is no limit to operating time, insofar as electric power is concerned.
The unit automatically adds distilled makeup water from an onboard reservoir that holds about 1200cc, minimum, to offset evaporation. The evaporation rate of course varies with relative humidity and temperature, but as a first approximation, assume that you will evaporate 0.8 cc of water per minute. This means that you can operate continuously for about 24+ hours before the reservoir is exhausted of water. If you want to operate continuously for a longer period, you will need to supplement the internal water reservoir, or add water periodically. For one customer the sampler was fixed in location and we provided a supplemental reservoir that allowed 7 days continuous operation.
It is made of shock-resistant plastic and is not autoclavable. Sterilization is commonly done using bleach or an oxidizing solution such as hydrogen peroxide. Since it is made in part of plastic components, we do not recommend you use organic solvents without first asking us if they will harm the unit.
You can recover a sample at any time. The only downside to collecting a sample while the SASS is operating is that the sample may be a combination of water and air, and the amount of liquid may vary somewhat from sample to sample.
The maintenance of a constant fluid sample size is by sensor feedback. We use a proprietary sensor and algorithm in the SASS's electronics to monitor the fluid level, and add water as needed.
Is the carry case necessary for flight transport? Will the box that the instrument came in be sufficient if the need arises to send the instrument back for repair?
The instrument is shipped to you in its carrying case, inside a cardboard box. It is reasonably tough, and could just be shipped back in a cardboard box with packing foam. Or you could ship it back as received, if you prefer.
What is the function of the BioLink RF Data Radio? Is it necessary for the operation of the instrument?
The BioLink is convenient if you want to control, operate or monitor the SASS from a remote location, and don't want to have an RS-232 cable between the SASS and the control computer. It is an accessory, and is not needed for basic operation.