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Chemistry LibreTexts

Basic Instrumentation

You now have an outline of the basic ion chromatography process. The loading of the sample onto the column varies with the instrument. The sample is eluted off of the column, through the detector. The signal from the detector is converted into the chromatograph. Lastly, considering you have the eluent flowing through a column with very fine particles. How can you force water through a column containing very fine particles?

When a water filter is used in a pitcher, the force of gravity is used, and when a water filter is used on a tap, the water pressure in the pipes is used. In our situation, a much higher pressure is required, since the solid phase particles are much smaller that a water filter on a household tap.

The pressures required for most IC instruments is at least 600 psi. In order to achieve this pressure a double piston high pressure pump is used, one such example is shown in the picture.

The injection of the sample onto the column is performed using a multiport valve that is inline with the eluent tubing. Different instruments have slightly different styles, with the most common a direct port for injection.

Another example is where an autosampler is used. In the photo to the right, an autosampler is shown, where a peristaltic pump (image below) pulls the sample up the autosampler tube and into the sample loop on a six-port valve. This is the setup used in the Lachat 8500 QuickChem series with an ion chromatography channel.

Software controls the six-port valve and at the appropriate time the valve switches to have the sample flow onto the column.

The six port valve works by first having the flow of the sample go through the sample loop (figure on the left) and then to the waste. This fills the sample loop with the sample. At a set period, the valve turns connecting different lines coming in. The eluent now forces the sample from the sample loop onto the column.

One instrument, a Lachat 8500 QuickChem with IC, is shown below illustrating a guard column, analytical column, and the suppressor cartridge. The guard column is used to protect the analytical ion column from contamination.