Characterizing sorbent affinity for a target compound
(described
by sorbent–water distribution coefficient, K
sw) is a necessary step in the sorbent selection and performance-testing
process in the process of capturing aquatic contaminants. However,
no standardized procedure exists to measure K
sw, and studies display significant variations in setup and
performance. For per- and polyfluoroalkyl substances (PFAS), most K
sw determinations employ batch experiments with
small-scale water–sorbent mixtures, methanol-based spike of
target compound(s), and analysis after assumed equilibrium, but methodological
details of the above procedure differ and might cause artifacts in
the determination of K
sw. We conducted
several batch experiments systematically varying a general procedure
to characterize the effects of suboptimal experimental design. Using
a selection of PFAS (6-carbon fluorinated chain length with differing
functional groups) and two sorbents, we tested variations of a solution/sorbent
ratio, methanol content, and PFAS initial concentration and compared
derived K
sw values. Each methodological
component affected log(K
sw) usually by
suppressing the value (by 0–48%) when compared with a “best
design” procedure. Thus, we suggest (1) a reference procedure
for PFAS and sorbents used here and (2) general guidelines for batch
experiment design with different compounds and sorbents. Additionally,
we report well-constrained K
sw values
for 23 PFAS and two sorbents.