PROTON NUCLEAR MAGNETIC RESONANCE SOLVENT SHIFTS IN AQUEOUS ELECTROLYTE SOLUTIONS .I. BEHAVIOR OF INTERNAL REFERENCES

Water line shifts in solutions of nine salts were measured relative to four internal references as a function of salt molality, ms, and the results were fitted to the equation δ= ams + bms2. The a and b values for a given salt are systematically dependent upon the reference, a result of simultaneous salt effects upon the water and reference proton resonances. The values of a and b in solutions of the alkali halides and their mixtures can be predicted by empirical equations of the form a = ra + RaS where r and R are parameters characteristic of the reference and S is characteristic of the salt. The salt shifts of 18 more internal references of widely varied structure were determined in a single salt solution. The manner in which these reference line shifts due to 1:1 inorganic electrolytes depend upon the structure of the reference compound is not easily accounted for on the basis of direct ion-molecule interactions alone; indirect effects of ions on the water structure are believed to be important. Direct interactions do occur in solutions containing C6H5SO3-, C3F7CO2-, Li+, and Ca2+. The implications of these results for internal referencing of aqueous salt solutions are discussed.