Injection Technique for Generating Accurate Adsorption Isotherm Data Using the Elution by Characteristic Points Method

With the use of the elution by characteristic points (ECP) method, the adsorption isotherms are rapidly determined from the diffusive part of an overloaded elution profile. However, very large injection volumes are required, which lead to extremely tailed rears of the injection profiles. The ECP method is based on a theory assuming rectangular injection profiles and can therefore not account for such profiles. Consequently, the use of the ECP method in the traditional way, with classical full-loop injections, results in serious errors on the determined adsorption isotherm parameters which has not been demonstrated until this study. Therefore, we developed and validated a new experimental injection method, here denoted the "cut-injection" technique where instead nearly rectangular injection profiles are generated. The result convincingly shows that adsorption isotherms acquired by using the new cut-injection technique nearly totally coincide with adsorption isotherms determined using the accurate reference methods.