Have you seen these  pH electrodes from Camlab?  They feature a liquid junction design similar to the Ross Sureflow® but at a fraction of the price.  It’s special design allows you to create a fresh junction by simply pressing the top cap of the electrode. This opens the lower portion a fraction allowing fresh electrolyte to flow through the gap. Releasing the cap traps a film of filling solution creating a brand new junction every time. Anyone trying to measure pH on samples with high protein content, sulphides or pectin will be all too familiar with the gradual poisoning of the junction and subsequent loss of performance and drift. EpoxyTough Double junction pH designs go some way to eliminating this but even these will die in time. Using the Camlab Rapid pH electrodes with liquid junctions will eliminate this and give you faster and better results for longer.