Quartz capillaries, mounting crystals

In low temperature studies, it is preferable to mount the crystal in a flow cell [215]. This permits the gradual change of cryoprotectant concentration as the temperature is lowered and substrate is introduced into the crystal. A quartz capillary is attached to a brass support by epoxy cement and a tight-fitting polyethylene tube sealed to the bottom of the capillary. The capillary is filled with protein mother liquor solution. The crystal is introduced to the top and allowed to settle either on to a bed of pipe cleaner fibres placed on top of the polyethylene tube as support or on to a support made by previously introducing a constriction into the quartz capillary. The crystal may be secured further by additional fibres. The inlet polyethylene tube is sealed to the top of the capillary. The inlet and outlet tubes are then connected to the reservoir and sink, respectively (Fig. 13). 

Figure 5.8 A Debye-Scherrer powder camera for X-ray diffraction. The camera (a) consists of a long strip of photographic film fitted inside a disk. The sample (usually contained within a quartz capillary tube) is mounted vertically at the center of the camera and rotated slowly around its vertical axis. X-rays enter from the left, are scattered by the sample, and the undeflected part of the beam exits at the right. After about 24 hours the film is removed (b), and, following development, shows the diffraction pattern as a series of pairs of dark lines, symmetric about the exit slit. The diffraction angle (20) is measured from the film, and used to calculate the d spacings of the crystal from Bragg s law.

Crystals that are unaffected by air, moisture, or light are usually mounted directly on a quartz or glass fiber, which is inserted into a goniometer head (Figure 14.3). If the crystal is sensitive to moisture or air, a sealed capillary tube may be used. Suitable apparatus can be used when nonambient temperatures and pressures are needed. The diamond anvil has been developed for high pressure. 

Since the compound is highly moisture sensitive, the crystals were manipulated in the dry atmosphere of a Vacuum Atmospheres Corp. Dri-Lab, with the aid of a long focal length microscope mounted externally. Crystals were wedged in 0.3-mm quartz X-ray capillaries. The mouth of each loaded capillary was plugg with Kel-F grease prior to removal from the Dri-Lab. Outside the Dri-Lab, the capillaries were immediately sealed by drawing down in a small flame. Crystal Data... 

If not working with an ATR FT-IR, the standard techniques of sample preparation employed to obtain infrared spectra of microscale laboratory products are the use of capillary films with liquids on NaCl (or AgCl) plates and the use of KBr disks and melts in solids. This, of course, assumes that for a spectrum to be obtained in the infrared region, the sample must be mounted in a cell that is transparent to the radiation. V 4th an ATR FT-IR spectrometer, liquids and solids are placed in direct contact with the ATR crystal. Since glass and quartz absorb in this spectral region, cells constructed of these materials cannot be... 

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