Sampling valve basically supports the discrete volumes of the treated samples stream to periodically inject into the carrier gas stream of the chromatograph. Sampling valves are fitted with electric or pneumatic actuators which help them to be operated automatically. Switching valve are critical if binary pumps are used. It allows employment of different desired mobile phases. Switching valve consists of five parts: control unit, connecting device, valve body, a rotor and preloaded assembly.
Foreflushing allows you to separate low molecular weight compounds. In the example shown, C1-C5 hydrocarbons are rapidly eluted from Column 1 onto Column 2 (position A). When the valve is switched to position B, C6 and heavier compounds (which have moved slowly through Column 1) are eluted from Column 1 to the detector. C1-C5 hydrocarbons are eluted from Column 2 back onto Column 1, then to the detector.
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