A study of the effect of proteins and endogenous cations on a lipophilic beta-cyclodextrin-based potentiometric...

2,6 Didodecyl beta cyclodextrin (2,6ddbetaCD) modified ion-selective electrodes (ISEs) were used in discrete solutions and in a flow injection analysis manifold for monitoring the local anaesthetic lidocaine hydrochloride (lignocaine) in the presence of endogenous cations and proteins. Membrane matrices comprised of either high molecular weight poly (vinyl chloride) (PVC) or polyurethane (Tecoflex SG 80) were compared. The behaviour of these electrodes in the presence of bovine serum albumin (BSA), alpha(1) acid glycoprotein (AAG) and human serum (HS) indicate that the Tecoflex-based membrane matrices are preferable to PVC as the drift induced by proteins on baseline lines and peak height reproducibility was considerably reduced in the former. Interference from 'serum' levels of sodium, potassium and calcium (145 mmol dm(-3) Na(+), 1.26 mmol dm(-3) Ca(2+), 4.30 mmol dm(-3) K(+)) was negligible (-Log K(ij)(POT) (overall) >/=4.0). The major organic interferents were molecules of similar size and structure, which caused reduced slope and drift in baseline potentials, at equimolar concentration levels. A reduction in interferent concentration by a factor of 10 negated these effects.