3.3.6 Six-Port Injector
High pressure systems require a special type of sample injection since injections with standard syringes are not possible. Four-, six-, and eight-port valves are used for high pressure systems. These systems are equipped with a fixed volume loop of tubing that serves as the sample loop that is loaded with a standard blunt-tipped syringe. These multiple port systems allow un-interrupted flow to the column during the loading of a sample on a sample loop and during injection of a sample under high pressure. As with a dual reciprocating HPLC pump, it is easier to show how a six-port valves works through an animation. Animation 3.4 shows the alignment of the valves during the loading of a sample onto a sample loop, switching of the values, and injection of the contents of the sample loop onto an HPLC column. View the animation by clicking on the figure below.
Animation 3.4 Operation of a six-port sampling/injection valve for an HPLC.
The sampling loop of a six-port valve can be loaded by a syringe or by pumping liquid sample into the valve by an automatic sampler. Sample loop sizes range from 5 - 100 μL for analytical-scale HPLC to milliliter volumes in preparatory-scale HPLC. The advantage of a syringe (manual) injection is that less sample volume is required (since filling of the tubing in an automatic sampler is not required). The obvious advantage of an automatic sampler is that numerous samples can be automatically analyzed by a computer-controlled system.
In-Line Filter:
Although samples and solvents are filtered prior to injection or use with an HPLC, an in-line filter is usually present immediately after the injection valve. This filter removes any remaining particles in the mobile phase that may clog the guard or analytical column. In-line filters are one of the most commonly maintained items for HPLC systems.
| Frank's Homepage |
©Dunnivant & Ginsbach, 2008