DIFFERENTIAL ELUTION FROM A SEPHADEX G-15 COLUMN OF SODIUM AND PHOSPHATE IONS OF SODIUM-PHOSPHATE WITH SODIUM OR POTASSIUM PHOSPHATE BUFFER

When a sample solution containing sodium-22-labelled sodium chloride and carrier-free phosphorus-32-labelled phosphoric acid was eluted from a Sephadex G-15 column with either 0.025 M sodium or potassium phosphate buffer (pH 7.0), the labelled phosphate ion was eluted earlier than the sodium-22. The presence of cold 0.72 M sodium chloride with the sodium-22-labelled sodium chloride in the sample did not affect the elution sequence. When 1 M monosodium phosphate was eluted with distilled water from fresh and phosphate-treated Sephadex columns, the sodium and phosphate ions were eluted together in approximately the same fractions in both instances. From these observations, it is concluded that sodium ion repeatedly exchanges its partner phosphate ion with that in the eluent during its elution from Sephadex.