EST Lab – EST-Lab.com

Frequently Asked Questions

Here are some FAQs that we are asked routinely. Click on a question and you will taken to the question and answer below.

  1. What are the current applications of Semipermeable Membrane Device (SPMD) technology?
  2. What chemicals do SPMDs sample?
  3. What chemicals do Polar Organic Chemical Integrative Sampler (POCIS) sample?
  4. What types of environmental media can be sampled by SPMDs and POCIS?
  5. What advantages do SPMDs and POCIS offer over grab sampling?
  6. Do SPMDs sample only dissolved or vapor phase chemicals?
  7. What factors determine how much of a bioavailable chemical will be sequestered by an SPMD?
  8. How can SPMDs have a constant sampling rate independent of environmental concentration when the amount of chemical sequestered is proportional to the ambient chemical concentration?
  9. What is the size of the loops on the deployment devices?
  10. What is an economical way to keep the SPMD cold during the return shipment?
  11. What are the deployment canisters made of?
  12. What is the capacity of the deployment canisters?
  13. Can the deployment devices be deployed vertically?
  14. What is a Field Blank for?
  15. What is a Trip Blank for?
  16. How are SPMDs used?
  17. How are POCIS used?
  18. How are SPMDs and POCIS shipped?
  19. How are finished samples shipped?

Questions and Answers

  1. What are the current applications of Semipermeable Membrane Device (SPMD) technology?

    Current applications of SPMDs include:

    • determination of pollutant sources and relative levels at different locations
    • estimation of ambient dissolved or vapor phase chemical concentrations (integrative or equilibrium)
    • in situ biomimetic concentration of ambient bioavailable chemicals for bioassay and immunoassay
    • estimation of organism exposure or bioconcentration potential
    • analytical enrichment of contaminant residues
    • toxicity identification evaluation (TIE) procedures

  2. What chemicals do SPMDs sample?

    SPMDs sample nonionic organic compounds with Kow's > 3 and some neutral organo-metal complexes. The following classes of compounds have been shown to concentrate in SPMDs:

    • Polycyclic Aromatic Hydrocarbons
    • Polychlorinated biphenyls
    • Polychlorinated dioxins and furans
    • Organochlorine pesticides
    • Pyrethroid insecticides
    • Nonyl phenols
    • Several herbicides and many industrial chemicals
    • Alkylated selenides
    • Others

  3. What chemicals do Polar Organic Chemical Integrative Sampler (POCIS) sample?

    Most polar pesticides, prescription and OTC drugs, steroids, hormones, antibiotics, personal care products, etc.

  4. What types of environmental media can be sampled by SPMDs and POCIS?

    SPMDs can be used to sample air (vapor phase), water (surface groundwater) and sediment-soil (pore water and vapors). They have been used in a wide range of environments, i.e from the tropic to the Arctic and Antarctic, and in highly turbulent systems to stagnant backwater areas. POCIS are normally used to sample water.

  5. What advantages do SPMDs and POCIS offer over grab sampling?

    In the case of water and air, grab samples provide data only on single point in time, and because small volumes are typically sampled (<5 L), the approach is often inadequate for the detection of trace bioconcentratable residues. Over a typical one month deployment, a SPMD or POCIS might sample the equivalent of tens to hundreds of liters of water. For compounds with relatively large Kows, SPMDs integratively sample residues (i.e., losses of accumulated chemicals are insignificant) during an exposure period. Integrative sampling mimics the bioconcentration process and permits the concentration of trace chemicals to detectable levels. Also, episodic events can be detected without an intensive sampling program.

  6. Do SPMDs sample only dissolved or vapor phase chemicals?

    Nonporous polymeric films such as low density polyethylene (membrane of choice for SPMDs) contain transient cavities having maximum diameters of about 10 Å. These cavities are far too small to accommodate colloids or macromolecular dissolved organic carbon such as humic acids. Also, comparisons of chemical concentrations determined by traditional analytical methods in ultra filtered river water (colloids and DOC > 50 Å diameter were removed) to those estimated from SPMDs exposed to unfiltered water, appear to confirm that SPMDs sample only dissolved residues, which are readily bioavailable. Finally, note that water quality criteria and threshold limit values (airborne chemicals) are based on dissolved and vapor phase concentrations, respectively, and that toxicity data bases are as well.

  7. What factors determine how much of a bioavailable chemical will be sequestered by an SPMD?

    The amount of a chemical sampled by an SPMD is largely dependent on its sampling rate (liters of water or air extracted per day by an SPMD), Kow or analyte capacity, the water concentration, and exposure duration. Factors affecting sampling rate are complex, but nonpolar lipophilic organic compounds whose molecules have some conformational freedom (ability to rotate and flex) and are moderately sized (< 10 Å cross sectional diameter) are sampled at the highest rates. Assuming biofouling is minimal, a 1- g triolein SPMD will daily extract individual PAHs, PCBs, and organochlorine pesticides (OCs) from about 0.5 to 10 L of water. As the lipophilicity or Kow of a series of organic compounds rises, so does the capacity of the SPMD triolein to sequester them. For compounds with relatively large Kow's (i.e., > 100,000) longer exposure periods will typically result in greater analyte masses sequestered.

  8. How can SPMDs have a constant sampling rate independent of environmental concentration when the amount of chemical sequestered is proportional to the ambient chemical concentration?

    Sampling rate can be defined several different ways. Often sampling rate is expressed as mass of chemical extracted (taken up) per unit time. This is a zero-order expression of uptake rate and is clearly dependent on chemical concentration. However in the case of SPMDs, sampling rate is generally expressed as a first-order uptake rate constant, which has units of the volume of water cleared of chemical per gram of sampler times time (L*g-1d-1).

  9. What is the size of the loops on the deployment devices?

    Both small and large canisters have two "D" rings on the body of the canister and one "D" ring on the lid. They are 25mm wide and 19mm deep.

  10. What is an economical way to keep the SPMD cold during the return shipment?

    Exposed SPMDs returned to EST for dialysis must be kept frozen. This can be accomplished by placing the carriers holding the SPMDs in their original cans and packing them in ice. Plastic or styrofoam coolers or plastic lined boxes can be used for transport. The most economical source for ice is one-liter plastic soda bottles of frozen water. These will adequately cool the samples and can be discarded after use.

  11. What is are the deployment canisters made of?

    The canisters are made of 304 stainless steel mesh body with perforated 304 SS lid and bottom.

  12. What is the capacity of the deployment canisters?

    A small canister will hold one to two standard SPMDs or one to three POCIS on their holder. A large canister will hold one to five standard SPMDs; one to three standard SPMDs AND one to three POCIS on their holder; or a maximum of six POCIS on two of their holders.

  13. Can the deployment devices be deployed vertically?

    All deployment devices can be deployed either vertically or horizontally.

  14. What is a Field Blank for?

    Elimination of possible contaminates in the air during deployment and retrieval of the passive sampler is achieved by using a field blank. A field blank is simply an SPMD or POCIS in a solvent-rinsed metal can that is exposed to the ambient air surrounding the test site. It is then frozen and returned to EST along with the samples for dialysis.

  15. What is a Trip Blank used for?

    A trip blank is an SPMD or POCIS from the same lot as the project SPMDs that is packed in its own solvent-rinsed quarter-pint tin and shipped with the samples. Once it arrives it is immediately removed and frozen unopened until the samples are retrieved; then the tin is sent on with the site samples for processing and analysis. The data obtained from the Trip Blank will show if there had been any loss of PRCs during the time the SPMDs were being shipped.

  16. How are SPMD used?

    Deploy the canister loaded with the carriers holding the SPMD's for 28 days, retrieve it, return it to us, and we do the rest. Following dialysis and GPC cleanup (if you request it), your samples will be ready for analyses of trace contaminants in the parts per quadrillion levels. The GPC cleanup is a service offered by our lab personnel. Carry-over biofouling, triolein by-products, and sulfur contamination are removed during GPC cleanup to prevent contamination and interferences during GC analysis.

  17. How are POCIS used?

    Deploy the canister loaded with the POCIS holder(s) for 28 days, then retrieve. The POCIS can be returned to EST for extraction, or you can request copies of our methods for processing for use in house or at the analytical lab of your choice.

  18. How are SPMDs and POCIS shipped?

    UNEXPOSED: SPMDs on the EST carriers (for use with EST deployment canisters) are shipped in hexane-rinsed, gallon-sized tin cans, similar to paint cans, under argon gas. The gallon sized can will hold up to 3 carriers, and can be stored in cool temperatures for upto a week. For longer storage time the cans should be frozen at - 20.0°C; at this temperature they will keep indefinitely. Field blanks will be shipped in hexane rinsed tin cans under argon gas. Can size will vary with the number of SPMDs in the field blank. POCIS on holders (for use with EST deployment canisters) are shipped in methanol rinsed gallon-sized tin cans with a spacer to keep the holder stable during shipping. The lids of the can are secured with metal clips that will require a screw driver (or similar tool) to remove. Loose POCIS are shipped threaded onto two carriage bolts and secured with self locking nuts to keep the POCIS stable. These are placed in methanol rinsed gallon-sized tin cans and the lids secured with metal clips that will require a small screwdriver (or similar tool) to remove. Storage for the POCIS is the same as for SPMDs.

    EXPOSED: Exposed SPMDs/POCIS should be shipped to EST Lab frozen and on ice. Make sure the can lids are on securely when packing. Please do not use dry ice as it could damage the membrane. The easiest and least expensive method is to freeze water in twelve ounce, or one liter, plastic soda bottles and put 6-8 of them per cooler. Coolers and "blue ice" will be returned if you provide a Fed Ex or UPS shipping label. If you choose not to use "blue ice" or other form of contained ice, please make sure the labels on your cans are waterproof.

  19. How are finished samples shipped?

    Samples that have undergone dialysis/GPC (SPMDs) or extraction (POCIS)will be shipped to the lab of the client's choice in amber ampoules that have been flamed sealed with an acetylene/oxygen torch. Volume size of the ampoules can be lmL, 2mL or 5mL. The actual sample volume is approximate. Do not take an aliquot from the ampoule...it must be concentrated or diluted to a known volume before analyses. Samples are typically in hexane, but can be in iso-octane, DMSO or appropriate solvent of client's choice. If the samples have undergone GPC cleanup there may be traces of methylene chloride present. POCIS are typically left in their extraction solvent of Methanol, 80:20 Methylene Chloride:MTBE. Once the samples have been ampulated they can be stored at room temperature for short periods of time, for long periods of time storing n a freezer at -4.0°C or below might be recommended.

Got Handling Questions?

We have covered additional handling and deployment topics in our Support page.

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