The Electrolyte Is Not Inert

In several studies, non-inert electrolytes were purposely added to the studied system. Ca(C104)2 was used as a supporting electrolyte in [2288]. CaCl2 was used as a supporting electrolyte or as one of its components in [2918-2921]. The PZC reported in [2922] was determined in the presence of sulfate. Buffers were used 

the solid particles may contain water-soluble substances, which undergo leaching and specific adsorption. Reference [1865] reports the IEP of phosphate-containing goethite. One sample studied in [32] contained sulfate and phosphate, and its IEP and PZC differed significantly. The silica studied in [2929] was prepared in the presence of a nonionic surfactant. No attempt was made to remove that surfactant from the final product. Phosphate-doped titania was studied in [2930] and polymer-stabilized latex was studied in [2931], A few results presented above have been cited by others as pristine PZCs/IEPs. 

Surface charging of complex and/or ill-defined natural materials was studied in [2939] (anthracites), [2940,2941] (coal), [531,662,2942-2948] (soils), [2949] (china clay), [2950,2951] (complex clays), [2952] (chromite mine overburden), [2953] (sawdust and sawdust-derived ion exchanger), [2954] (natural red earth). 

Multicomponent films were studied in [2963], and multilayer membranes in [279,2964-2967]. The polymeric membranes studied in [2968] were modified by post-treatment. Also, a-alumina identical to the material in Membralox membrane from SCT, studied in [1851], probably underwent surface treatment. 

The lEPs obtained in [2969] probably represent metal oxide-dextrin precipitates rather than pure metal oxides. Activated carbons studied in [2970] had very high ash content. Water treatment residual was studied in [2971]. The material studied in [2972] was impure. Other examples of surface charging studies carried out in complex, ill-defined materials can be found in [2722,2834,2973-2978]. 

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