pH, conductivity and long-term stability in the Crystal Screen solutions

Accurate knowledge of pH and ionic strength are very important when crystallization conditions are refined. The pH and conductivity of each of the 50 solutions in the Crystal Screen kit [Jancarik & Kim (1991). J. Appl. Cryst. 24, 409-411] were measured before and after incubation in a sealed chamber for six weeks. Two such kits were tested in this way. The results indicate that the measured pH of the solutions in the Crystal Screen is reproducible between different kits but that the measured value is not always related to the buffer system. Furthermore, it was observed that the protein crystal dye Izit (Hampton Research, Laguna Niguel, California, USA) forms crystals when added to several of the conditions in the crystal screen.