In practice, one of the most widely used polymers is PDMS because it is a material that has good partitioning properties such as low mass transfer resistance for hydrophobic and nonpolar compounds (Mayer et al. 6148) and recently there has been many studies investigating PDMS absorptive properties, however, only a few have focused on the ability of PDMS to release absorbed chemicals into water. In general, experiments have proven that PDMS can be used to calculate the equilibrium concentrations of many different compounds dissolved in water once the concentrations of these analytes absorbed in the pellets are determined. Since PDMS is not affected by the nature of the matrices or by exposure to hydrophilic chemicals, it can be used for…show more content… Assuming that the process exhibit a labguimir equilibrium distribution, the thermodynamic behavior of the partitioning process can be modeled by using a first order one compartment equation (Vrana et al. 845).
C_PDMS (t)=C_w (k_1/k_(2 ) )(1-e^(-tk_2 ))
C_w represents the concentration of analyte in water, C_s(t) the concentration of analyte at a given time on the PDMS, and k1/k2 are the uptake and release rates constants in the kinetic process. The exchange of solute into and out of a passive sampling system usually follows a predictable languimuir isotherm as shown in figure 1 (Seethapathy, Górecki, and Li 234).Labumier isotherms occurs when… Figure 1. Passive sampling devices operate in two main regimes (kinetic and equilibrium).
Therefore, a mathematical equation that relates the concentration of analyte absorbed in the PDMS pellets as a function of uptake or release rate constants k, equilibrium concentration of the compounds in the polymer and the t95% can be used (Smith, Oostingh, and Mayer 55). T95% is the time to reach 95% of the maximum measure concentration or steady state (Smith, Oostingh, and Mayer 55), so at t95% the concentration of analyte at time t is 0.95 of the equilibrium concentration (Ct = 0.95Ceq) (Brown and A. 4097).
C_(PDMS(t))=C_PDMS(eq) (1-e^(-tk_upload )) t_(95%)=3/k Where C_(PDMS(t)) represents the concentration of analyte that is absorbed on