EDS, XPS, and RBS were used to characterize the foulant layers of NF membranes.

Use of a single technique may lead to incorrect conclusions.

EDS, XPS, and RBS detected major foulants; XPS and RBS also detected trace foulants.

SEM-EDS was well suited for studying areal heterogeneity and surface features.

RBS was able to depth profile elemental composition of depth heterogeneous samples.