Switches liquid flow instrumentation

Fig. 4 Instrumental setup (a) and representative peaks (b) of echo-peak technique. An unknown sample is first injected and the mobile phase flows directly to the separation column. Within a short delay, a reference standard solution is injected and the switching valve turns to a different position to allow the mobile phase to flow through a short precolumn (as shown by dashed arrows) prior to passing through the same separation column. Two chromatographic peaks are therefore recorded, one for the unknown sample (solid line) and the other for the reference solution (dotted line). A and B mobile phases, LC liquid chromatograph, MS mass spectrometer...

Originally, the basic idea was realized without an FC switch by a continuous or one-tum rotation of the sample perpendicular to the external magnetic field direction, in order to induce a flow but such a mechanical rotation is, similar to a mechanical FC switch, much too slow to establish reproducible states of motions in common, low-viscosity anisotropic liquids such measurements were therefore restricted to high-viscosity liquid crystalline polymers. Fast electronic FC eliminates these restrictions, but to date the new tedmique has only been used with proton spin signals owing to instrumental limitations. ... 

TPR has been carried out in a Micromeritics Autochem 2910 instrument equipped with the CryoCooler system for reaching subambient temperature by means of liquid nitrogen. A molecular sieve trap has been put between the sample holder and the detector in order to absorb water that is formed dining the rednction process. 100 mg of wet sample has been introduced in the sample holder, dried in situ by a nitrogen flow at 393 K for two h. Then the sample was cooled down to 153 K under Ar flow (50 cm min" ) after which, the flow was switched to 5% H2 in Ar (50 cm min ) and maintained throughout the analysis. After a baseline had been established, the temperature was started at a rate of 5 K min up to 623 K. A TPR experiment on sample Pduns reference was carried out on 10 mg of sample following the same procedure described above for the catalysts. 

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