The effects of a wide variety of electrolytes (each at 0.4M) on bubble production in agarose gels has been studied. The relative effectiveness of the different ions tested in decreasing the degree of bubble formation in the aqueous gels was as follows: As sodium salts, citrate 3->SO 42-, tartrate2->F-≫ acetate->SCN->Br-, NO3 -, I->Cl-; as potassium salts, citrate 3->SO42->F-, tartrate 2->acetate-, SCN->Br ->I-, NO3->Cl-; as chloride salts, Cd2+>Mg2+>Li+, Na +, Ca2+≥NH4+, K +>Ba2+≫Ni2+>Sr2+>Co 2+; as nitrate salts, Mg2+, Sr2+>Na +, K+, Li+>Ag+, NH 4+, Ca2+>Cd2+>Zn 2+≫Ni2+. In view of many similarities with published data in the physicochemical literature for salting out of identified nonionic surfactants, the above anion and cation sequences probably reflect a decreasing tendency of the ions toward salting out of predominantly nonionic surfactant(s) stabilizing the gas cavitation nuclei present in agarose gels. Moreover, the precise pattern of electrolyte effects on bubble formation carries certain implications as to the structural characteristics of these nonionic surfactants. Specifically, the pronounced and very similar anion sequences, combined with earlier data, suggest that the polar portions of these nonionic surfactants represent either weak bases and/or amide groups. This view is in accordance with the relative position of Mg2+ in the two cation sequences, indicating strong salting out in both cases, and hence rendering it quite unlikely that ether linkages contribute to the hydrophilicity of the nonionic surfactants stabilizing gas nuclei. Finally, the relative position of SCN - within each anion sequence, corresponding to appreciable salting out rather than salting in, indicates that large portions of these nonionic surfactant molecules are composed of hydrocarbon moieties, specifically methyl and methylene groups. © 1979 American Institute of Physics.
