A model for a correct evaluation of the sensitivity, detection limit and selectivity constants of ion selective electrodes

A modification of the Nernst-Like equation had been proposed containing an "apparent activity" term as an addend to the logarithm argument. Taking int o account this term, which is an adjustable term for each electrode, slopes nearer the Nernstian ones can be obtained and the selectivity constants re sult much less dependent on the concentration of the interferent ions. In a ddition the value of the "apparent activity", as it is the activity corresp onding to the signal of the blank, is a good basis for the computation of t he Detection Limit. The consistency of results of the whole treatment 'afte r the introduction of such a parameter, allows us to believe in the hypothe sis that the "activity" is not merely "apparent", even though its true natu re is a matter of further investigation.