Can SPMDs be used for both integrative and equilibrium partition sampling? What are the pros and cons of the two approaches?
The answer to the first question depends on the magnitude of the Kows of the target analytes, the SPMD design and environmental conditions. Investigators have shown that SPMDs (standard configuration as described in the tutorial) integratively sample compounds with log SPMD-water partition coefficients (KSPMDs) 5.0 during exposures of less than 1 month at 18 oC, and a flow velocity <1 cm/sec. Note that in some cases small amounts of dispersed carbon adsorbent in SPMD triolein increased SPMD capacity, and permitted integrative sampling of even low Kow compounds (e.g., naphthalene log Kow = 3.4 and for low Kows, KSPMD Kow) as well. Also, it has been shown for compounds with log Kows < 4.0, 90% of equilibrium concentrations may be achieved in < 40 days using the standard SPMD design. The time to equilibrium can be decreased by increasing the flow-rate of water and air (the likely switch to membrane control limits the effects of flow for compounds with log Kows < 4.5) and the temperature.
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