Sample Tube Placement

The reagent, diluent, and carrier/wash solutions should be accommodated in specific flasks made from materials compatible with the solutions to be pumped, into which the sampling tubes are permanently immersed. Alternatively, the sampling tube can be attached near the flask bottom, in order to permit the placement of the reagent containers above the height of the manifold. This is recommended for minimising the eventual formation of air bubbles under reduced hydrodynamic pressure. 

When a resistively heated filament pyrolyzer (e.g., the Pyroprobe from CDS Analytical, Inc., Oxford, PA) is used, the sample may be placed directly on a platinum filament or in a quartz tube or boat inside a platinum coil. In either case, the placement of sample with respect to the sampling tube or the ribbon should be the same for all samples. For liquid sample suspensions placed on a ribbon or in a coil, the solvent is evaporated prior to pyrolysis. Solid microbial samples can be sandwiched between quartz wool plugs inside the quartz sampling tube so as to reduce extraneous nonvolatile material from leaving the sampling tube during pyrolysis. With quartz, the sample never comes into direct contact with the pyrolyzer filament, as it does when sample is coated directly on a thin ribbon filament. Ribbon filaments sometimes exhibit a memory effect (particularly with polar components), are harder to clean, and typically have a shorter lifetime. Quartz tubes may be reused after cleaning. 

The intensity of the X-ray beam is measured by ionization chambers or pin-diodes13. Pin-diodes can only be operated in the beam stop. The variation of the beam intensity during the experiment should be measured both before and after the sample. If the beam intensity monitors are set up properly, the absorption of the primary beam by the sample can be computed for each scattering pattern. The placement of the first ionization chamber in or after the X-ray guide tube to the sample is uncritical. 

Mix components in a 0.5-mL Eppendorf tube and heat in a boiling water bath for 3 minutes to denature the proteins. Cool to room temperature and apply 10 pL of a sample to a well on the gel. Use gel-loading tips on an automatic pipettor to deliver these small samples. One or two wells should contain molecular weight standards. Be sure to record placement of each protein and standards in a sample well in your notebook. Follow the instructions provided with your electrophoresis apparatus and by the supplier of precast gels. 

The simplest collimation can be achieved by placing a slit between the x-ray source and the sample, as shown in Figure 2.9, top left. The angular divergence of thus collimated beam is established by the dimensions of the source, the size, and the placement of the slit. This slit is usually called the divergence slit and in the majority of powder diffractometers, the placement of the divergence slit is fixed at a certain distance from the x-ray tube focus. 

Fig. 9.6 Different mechanisms for placement of the final analytical solution in the measuring instrument. Indirectly, via the instrument autosampler, which can receive either a vial (A) or a sample aliquot to be held in cups (B). Directly, by means of a sensor (C) or by aspiration (D) at a fixed point where the tube is taken or with the aid of a moving aspiration tube, which is inserted by the robot arm (RA) in each tube in the rack in turn.

Coil configuration. The relative orientation of the highband and broadband coils with respect to their placement around the sample-containing NMR tube. A normal coil configuration locates the broadband coil closer to the sample, while an inverse configuration locates the highband (normally tuned to H, but possibly F) closer to the sample. 

Since the sample must be placed onto the filament before it is inserted into a heated chamber with carrier flow, placement of fibers and fine powders presents a problem. If these materials may not be melted onto the filament, they may fall off or blow off in the carrier gas stream before pyrolysis. Consequently, these sample types are generally analyzed using a small quartz tube, which is inserted into a coiled filament. The sample may be placed into the tube, held in position using plugs of quartz wool, weighed, and then inserted into the coiled element for pyrolysis. It... 

Apparatus. A suitable gas chromatograph has been described by Lysyj"Ll5,The Beckman valve used to introduce the sample is modified by removing one loop and replacing it with two 1.5 inch long stubs of pressure tubing. This arrangement allowed placement of the microcell in or out of the carrier gas stream. The remaining loop of the valve is used for calibration. 

---