Section 5.1.2.2.2. Capillaries

The capillaries used for crystal mounting are made of thin-walled glass. These capillaries range from 0.1 to 2.0 mm in diameter and have a stated wall thickness of 0.01 mm. In practice, however, the larger the diameter of the capillary, the thinner the glass wall. Therefore, handling of the larger-diameter capillaries is generally very difficult because they are so fragile. Capillaries made of fused quartz are also available, but are not recommended for general use because they produce a higher background with X-rays. Quartz capillaries are not as fragile as the thin-walled glass capillaries, however, and may be useful in experiments where the tensile strength of the capillary is important, for example, when a diffraction flow-cell experiment is planned (Petsko, 1985). In addition, small-diameter capillaries (produced in the laboratory by drawing out glass tubing or Pasteur pipettes) will be needed to aid in the removal of excess liquid around the crystal after the transfer from the crystallization dish to a capillary has been completed.