Structure and Function of FIA

The system is based on a peristaltic pump, which ensures that a solvent is pumped through the system at a flow rate which is both continuous and discontinuous. This makes the creation of small "chambers" in the liquid, so more samples can be dispatched without being mixed together. The system consists of:

• An automatic pipette to take many samples quickly.

• A peristaltic pump which ensures a constant and discontinuous flow of a solvent.

• Inserting samples into the solvent.

• A mixing coil, a column (a thin tube) capable of mixing the solvent and the samples after the solvent passes through the tube by the flow.

• A detector that can register the content of certain chemical substances.

• A waste container for the collection of samples and the solvent.

The figure shows the flow injection system structure. The detector may include a spectrophotometer if the chemicals have a color.

• Automatic pipetting is used in many types of analytical devices. This means that the system can handle many samples in succession.

• The peristaltic pump is capable of creating a flow which is both continuous and discontinuous in the thin tubing. It creates small spaces, so the individual samples are not mixed together and produces very accurate results. The equipment can easily be adjusted. This is important, as the flow rate determines whether the substances in the samples are either separated from each other or whether they have time to react with the reagent before they reach the detector. So you can increase and decrease the flow rate appropriately.

• It is easy to introduce samples directly in the solvent. The very slim tube also means that the apparatus can analyze very small quantities.

• The diameter and length can be adjusted for the column (mixing coil / tube). The length, diameter and flow of the pump is namely to control whether the substances must be separated or whether to undergo reactions in the flow.

• The detector must be able to handle very small quantities. This is permitted in most detectors as measurements take place in a very small space at the end of the mixing coil. Depending on the chemical substances to be measured, different detectors are used. If measuring a chemical compound which has a colour and thus can absorb light, a spectrophotometer can be used. Sometimes the chemical compound is not itself a color that is detectable in a spectrophotometer. So, one can add a reagent which forms a colored substance with the chemical compound. Alternatively, ion-selective electrodes can be used if you need to measure the concentration of nitrate.