Operating Instructions
Tel: 724-941-9701 Fax: 724-941-1369 e-mail: skctech@skcinc.com
863 Valley View Road, Eighty Four, PA 15330 USA
Gelatin Filters
Cat. Nos. 225-9551 and 225-9552
SKC Gelatin Filters are designed for the detection and analysis of airborne
microbes. Gelatin fi lters not only retain bacteria and molds but are also eff ective for
the collection of viruses. Used to quantitatively collect airborne microorganisms,
gelatin fi lters have an inherent high moisture content that helps to maintain
viability of stress-sensitive microorganisms for sampling periods up to 30 minutes.
The gelatin material can be dissolved easily in a buff er or agar medium for easy
detection of bacteria and viruses.
Performance Profi le
Material .......................Water-soluble gelatin
Pore Size .....................While having a nominal pore size of 3.0 μm, a higher capture
effi ciency of sub-micron particles can be expected due to the
separations that occur on the surface and within the fi lter. It
is through inertial impaction and diff usional interception that
these fi lters can remove particles much smaller than 3.0 μm.
Diameter .....................25 or 37 mm
Thickness ....................Approximately 250 μm
Thermal
Resistance ...................Maximum 140 F (60 C)
Residual
Dampness Content ....46 to 49%
Max. Temperature
and Humidity ............Maximum room temperature is 86 F (30 C);
maximum relative humidity is 85%
Sterilization ................Presterilized by gamma radiation
Max. Sampling
Time ............................30 minutes (see Sampling Parameters on page 2)
Storage ........................Refrigerator storage is recommended (39.2 to 46.4 F [4 to 8 C])
for gelatin fi lters.
Caution: Do not store gelatin fi lters below 39.2 F (4 C).
Condensation during thawing will dissolve fi lter. Avoid
exposing fi lters to moisture, chemical vapors, and extreme
temperatures.
Shelf-life ......................3 years from date of manufacture
Analysis ......................Direct method or indirect method (see pages 3 and 4)
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Sampling Parameters
Max. sampling time: 30 minutes
Max. recommended air face velocity (through fi lter): 0.4 meters/second (m/sec)
Prolonged sampling time and high air velocity may destroy gelatin pores leading
to a decrease in collection effi ciency of gelatin fi lters.
Note: Air velocities nearer 0.4 m/sec require shorter sampling times. Conversely, lower
air velocities allow longer sampling times.
Face velocity for specifi c samplers/fi lter diameters:
• IOM Sampler with 25-mm fi lter at 2 L/min fl ow rate = air face velocity of
0.08 m/sec
• Bu on Sampler with 25-mm fi lter at 4 L/min fl ow rate = air face velocity
of 0.16 m/sec
• 37-mm fi lter at:
2 L/min fl ow rate = air face velocity of 0.035 m/sec
4 L/min fl ow rate = air face velocity of 0.07 m/sec
10 L/min fl ow rate = air face velocity of 0.17 m/sec
Operation
Filter Handling Guidelines
• Gelatin fi lters are bri le; handle fi lters carefully.
• Do not touch fi lters with fi ngers or foreign objects.
• Use forceps to handle fi lters.
• Do not grip fi lters too tightly with forceps; this will cause breakage.
• Avoid bending fi lters.
• Keep pocket on fi lter until ready to load into a casse e. See Loading a Gelatin
Filter into a Casse e.
Loading a Gelatin Filter into a Casse e
Note: Load the fi lter only under sterile conditions. Follow Filter Handling Guidelines.
1. Disassemble the casse e and carefully let the gelatin fi lter slide out of its
pocket into the casse e.
2. Use forceps to aid in positioning the fi lter.
3. Reassemble the casse e.
4. Use fl exible tubing to connect the outlet of the casse e to the inlet of an
air sample pump capable of the desired fl ow rate.
5. Sample for the appropriate sampling period up to 30 minutes (see Sampling
Parameters). Sampling periods should be brief to help reduce microorganism
stress.
Handling and Shipping the Filter A er Sampling
Determine the method of analysis to be used, direct or indirect, before preparing
the sample for shipment. There are two methods for shipment preparation.
Method 1 can be used for shipping to a laboratory at a diff erent location.
Method 2 should only be used if there is an on-site laboratory that can perform
microbial analysis.
Method 1
Note: This method prepares the sample for the indirect analysis method.
1. Turn off the pump.
2. Disassemble the casse e and use forceps to gently remove the fi lter. Place it
in 10 ml of sterile water. (
10 ml is recommended. Add more water, if needed.)
3. Once the fi lter dissolves, pour the solution in a water-tight container or tube.
4. Seal the container and ship to a laboratory for analysis. See Analysis &
Additional Application Notes.
Caution: Avoid extreme temperatures during storage and shipping.
Method 2
Note: Use this method only if there is an on-site laboratory. Determine the
appropriate agar before collecting the sample. These steps prepare the sample for the direct
analysis method.
1. Turn off the pump.
2. Open the casse e.
3. Place a prepared agar-fi lled petri dish base over the fi lter in the casse e until
they are touching. The gelatin fi lter will adhere to the agar surface.
4. Carefully li the agar plate base with the gelatin fi lter.
5. Immediately cover the petri dish base with its lid.
6. The gelatin fi lter will dissolve due to the moisture in the agar culture
medium allowing the microbes to come into direct contact with the nutrient
medium. The plates are incubated and the colonies counted. See Analysis &
Additional Application Notes.
Analysis & Additional Application Notes
Direct Method
Note: This method is not recommended for virus aerosols.
1. A er transferring the fi lter to the culture medium,
incubate it in an incubator with the lid of the petri
dish facing up.
Note: To prevent liquid from collecting on the agar surface,
always use predried agar that is not freshly prepared.
2. Choose the time, temperature, and type of culture
medium suitable for the target microbes. Follow
these guidelines:
• Standard, Caso, or Plate Count Agar are suitable
for determining colony count (total CFU count).
• Sabouraud, Malt Extract, or Wort Agar can be
used for detecting yeasts and molds.
• Blood Agar is suitable for detecting pathogenic
microbes causing hemolysis.
3. Count the colonies that form.
Direct Method
Sample
Gelatin fi lter to agar
Dissolve gelatin on agar
Incubate
Count
Indirect Method
Dissolving Gelatin Filters A er Sampling Airborne Microbes
This method is used to prevent osmotic shock to
the sampled organisms, to provide sub-samples for
removal of inhibitors such as disinfectants, for dilution
of the sample where high counts are expected, or to
allow plating onto diff erent nutrient media where
species identifi cation is required.
1. Dissolve the gelatin fi lter in sterile liquid warmed
to 35 to 40 C, such as physiological saline or 0.1%
peptone water.
2. Stir the solution using a sterile magnetic stirrer to
accelerate fi lter dissolution.
3. Process the solution according to Koch’s pour plate
method or the membrane fi ltration technique.
4. Incubate samples.
Indirect Method
Sample
Dissolve gelatin in sterile
solution
Filter solution through
membrane fi lter
Filter to agar
Incubate
Count
5. Evaluate colonies that form.
Note: During the dissolving and stirring process (indirect method), the colony-forming
units are separated into individual microbes so you will obtain a higher CFU count than
with directly placing the exposed fi lter on a culture medium (direct method).
Calculation of Colony-forming Units per m
3
To determine the quantity of colony-forming units per cubic meter of air (CFU/
m3), compare the number of colonies in relation to the volume of air originally
sampled.
Removing Disinfectants
Note: It is strongly recommended that you use the indirect method when analyzing
samples from an area sprayed with disinfectants or where antibiotic airborne particles are
present. Using this method allows the removal of the disinfectants that inhibit the growth
of microbes on the culture medium. Follow this procedure:
1. Dissolve the gelatin fi lter as instructed above.
2. Before Step 3, fi lter the resulting liquid through a 0.45-μm pore size
membrane fi lter.
3. Add sterile water to rinse the fi lter.
SKC Limited Warranty and Return Policy
SKC products are subject to the SKC Limited Warranty and Return Policy, which
provides SKC’s sole liability and the buyer’s exclusive remedy. To view the complete SKC Limited Warranty and Return Policy, go to h p://www.skcinc.com/
warranty.asp.
Form 40060 Rev 1201
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