Product: Semipermeable Membrane Device (SPMD) and
its Deployment
Semipermeable Membrane Devices (SPMDs) are used as bioaccumulators of lipophilic environmental contaminants in aqueous, sediment, and atmospheric media in a large number of research and monitoring studies throughout the world. These devices mimic biological systems to provide a measure of bioavailable pollutants in both fresh and salt water. Its passive transport mechanism is similar to that of chemical transport throug fish gills and human lungs. The SPMD, however, unlike the typical biota used in pollution testing, does not metabolize the sequestered compounds, is site-specific, is much easier to extract, and is not affected by poor water quality conditions which may not be suitable for bio-monitoring organisms to survive.
The SPMD tubing on its carrier
The Semipermeable Membrane Device (SPMD) is composed of lay flat, low density polyethylene tubing containing a thin film of a pure, high-molecular weight lipid (triolein). The polymer, often thought to be non-permeable, actually consists of transport corridors of less than 10 Å in diameter. These pores allow for the selective diffusion of hydrophobic organic chemicals, which are then sequestered in the lipid phase. These chemicals can be assessed or analyzed by a variety of techniques. Screening can be accomplished using biomarker tests such as MICROTOX, MUTATOX, EROD and VITELLGENIN.
The SPMD as a sampler in conjunction with sensitive analytical techniques, allows the analyst to achieve accurate, reproducible data in the parts per quadrillion level. Mathematical modeling of SPMD uptake has been accomplished with concentrations of most contaminants can be accurately assessed.
Through the use of SPMDs, it is feasible to estimate the time-integrated dose of waterborne bioavailable pollutants to aquatic organisms. Analytical data can be acquired by using HPLC, GC (FID/PID/ECD) or GC/MS (low and high resolution). As with any environmental sampler, appropriate cleanup and fractionation should be performed in order to achieve the highest quality results.
Entire carrier assembly with the SPMD
Field deployment of the SPMDs is best accomplished using the stainless steel SPMD carrier in a stainless steel canister. This setup can be rapidly deployed to minimize exposure to atmospheric contaminants. Because the SPMD is a very potent air sampler a field blank is always recommended for simultaneous exposure during deployment and retrieval. The analytical results from the field blank can be used to adjust the site results to reflect just the amount of contamination in the water.
Typical deployment periods are two weeks to two months (28 days is the most common), but this time can be adjusted to allow for logistics problems, or if there is historical data indicating high levels of the target analytes.
The cost, ease of usage, sensitivity, reproducibility and application to water concentrations make SPMD's the best available passive sampler for lipophilic organic contaminants. The extensive collection of published and current on-going research enhance the knowledge base and reliability of the SPMD.
Specifications of Standard Semipermeable Membrane Device (SPMD):
- Length: (between the welds) 91.4cm
- Width: 2.5cm
- Wall thickness: 70-95µm
- Tubing: lay flat low density polyethylene, additive free
- Triolein: Ultra High Purity (UHP) (l.0mL used for standard 91.4cm length)
-
Membrane: surface area to total SPMD volume
(SA-V) ratio
≈90cm2/mL or ≈460cm2/mL of triolein - Lipid-to-membrane: mass ratio ≈0.2
- Weight of standard SPMD: 4.4 to 4.6 grams
SPMDs can be made at custom lengths upon request.
Deployment Options
The deployment device is a 304 stainless steel canister, available in four sizes (small, large, well and disposable), and depending on your needs and style of canister, it can hold from one to five carriers. The deployment device allows for a fixed sampling location eliminating the migration and mortality problems connected with aquatic organisms.
Small
Description: Holds one to two SPMD carriers with standard length (91.4 cm) SPMDs.
Dimensions: 15 cm high x 16 cm wide. Two "D" rings on the body of the canister and one "D" ring on the lid. The distance between the "D" ring on the lid and the one on the body is 6.5 cm. The "D" rings are 25 mm wide and 19 mm deep.
Large
Description: Holds one to five SPMD carriers which use standard length (91.4 cm) SPMDs.
Dimension: 30 cm high x 16 cm wide. Two "D" rings on the body of the canister and one "D" ring on the lid. The distance between the "D" ring on the lid and the one on the body is 6.5 cm. The "D" rings are 25 mm wide and 19 mm deep.
Well
Description: Holds one to two standard lengths (91.4 cm) SPMDs.
Dimensions: 73 cm length x 4.5 cm wide.
Disposable
Description: Holds one or two six-inch SPMDs.
Dimensions: 9.5 cm length x 4.5 cm wide.
Additional Considerations
The Semipermeable Membrane Device (SPMD) can be combined with the Polar Organic Chemical Integrative Samplers (POCIS). Please view our POCIS page for information on sampling water soluble contaminants.