Feasibility of measuring free and total bilirubin electrochemically in serum

Bilirubin undergoes irreversible reduction at the hanging-mercury-drop electrode in tris(hydroxymethyl)methylamine buffer (0.1 mol/L, pH 8.5). Peak current is linearly related to concentration in the range 0-1 mg/L. The half-wave potential of -1.32 V vs the saturated calomel electrode is little affected by pH, whereas peak current increases with pH to pH 9.5, then decreases rapidly. Exposing the test solution to light causes the peak current to decline at a rate proportional to concentration. Albumin-bound bilirubin is electrochemically inactive, so free bilirubin can be measured in the presence of bilirubin-saturated albumin. Serum total bilirubin can be measured after much of the protein is precipitated by adding methanol. Results for serum bilirubin as measured electrochemically (y) in 20 methanolic filtrates of serum compared well with the Jendrassik-Grof Method (x) in preliminary studies: y = 0.981x -0.311; r = 0.9716. We discuss the possible mechanism of the reduction process and potential clinical applications. Polarographic measurement of bilirubin and bilirubin-binding capacity is feasible and may be advantageous as compared with existing techniques.