Gradient elution in ion chromatography

Abstract

Both theoretical and practical considerations for the use of gradient elution in ion chromatography are discussed. The theory for the dependence of an analyte's retention on eluent concentration for both isocratic and gradient elution is presented and shown to agree with experimental results. Practical solutions to problems not encountered in isocratic ion chromatography are presented. Background conductivity changes caused by increasing eluent concentration are greatly minimized by the use of eluents containing salts of weak acids with p K a values greater than 7, which are converted to low-conductivity free acids in the suppressor. Sodium hydroxide based eluents produce a minimal baseline shift. Small baseline shifts produced by other eluents can be compensated by chemical means. Using a gradient, as many as 36 ions can be separated and eluted in one run.