Patent ID: 7555337

Claim:
A method for non-invasively determining the relative levels of two substances present in a biological system, said method comprising contacting an anodal chamber and a cathodal chamber of an iontophoresis device comprising reversible electrodes with a biological system; extracting by reverse iontophoresis charged and uncharged substances from said biological system, and collecting said charged and uncharged substances each independently into the anodal chamber or the cathodal chamber; determining a first substance and a second substance from said extracted charged and uncharged substances a) such that the first substance is different from the second substance and b) such that i) a transport and/or a transference number of the first substance is independent of ii) a transport and/or a transference number of the second substance; analysing the collected amount of the first substance and the second substance; subsequently, determining the extraction ratio of the first substance to the second substance to determine their relative levels in the biological system; determining at least one of a physiological and pathological condition based on the determined extraction ratio and without requiring blood sampling for calibration.