Carrier gases high-speed

In precipitation reactions, powder characteristics depend on the speed of the nucleation of particles and their growth due to the mass flow to the surfaces. In freeze drying and spray drying, powder characteristics primarily depend on the size of droplets, which in turn is determined by the parameters of a nozzle and characteristics of the flow of a carrier gas. Both these methods enable one to obtain powders with very high surface area. 

Separation occurs as the vapor constituents equilibrate between carrier gas and the stationary phase. The carrier gas is a chemically inert gas available in pure form such as argon, helium, or nitrogen. A highly dense gas gives best efficiency since diffusivity is lower, but a low-density gas gives faster speed. The choice of gas is often dictated by the type of detector. 

A comprehensive GC X 2GC technique with differential flow modulation has been developed for rapid analysis of VOCs. " In comprehensive GC X 2GC, two secondary columns of different polarities are used, requiring a GC with two detectors to monitor the column effluents. The flow-switching device is a modification of the unit developed by Sacks and Akard " for high-speed chromatography. The flow of carrier gas to the columns is controlled by a three-port solenoid valve placed outside the GC oven and not in the sample flowpath. Parallel and serially positioned tee unions control the flows of carrier and auxiliary gases and interface the primary column effluent to the secondary columns. Bueno and Seeley " used a 5.0 m X 0.25 mm i.d. capillary column with a... 

Thermal desorption from the SPE cartridge is a further possibility [77,122]. In this approach, the sample is introduced at a controlled speed into the packed liner of a PTV injector set to a low temperature with the water eliminated via the split vent. Salts and involatile polar material are rinsed from the sorbent with water and the sorbent dried by purging with a high carrier gas flow rate. The trapped analytes are subsequently desorbed in the splitless mode by rapidly heating the PTV to the injection temperature. The most commonly used sorbents are Tenax and Carbofrit. The method is restricted to a narrow range of applications by the low breakthrough volume of polar analytes on the... 

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