Method of measuring liquid junction potentials in small (nanolitre) droplets of biological fluids

1. A method is described which allows the determination of liquid junction potentials between biological fluid samples of less than 1 nL with a reproducibility of 10%. This was achieved by use of a micro-method and the use of 3% agarose added to the electrolyte in the measuring electrodes. 2. Validation was performed with a modified flowing boundary method and the system was also tested using a solution containing divalent ions. Liquid junction potential between surface fluid from rat kidneys and harvested renal proximal tubular fluids was -0.62 +/- 0.11 mV (mean +/- s.d., n = 66).