Flow Injection Analysis (FIA)
Definition and meaning of Flow Injection Analysis (FIA) in chemistry.
Flow injection analysis (FIA) is an automated technique in which a small, discrete volume of liquid sample is injected into a continuously flowing, unsegmented carrier stream and carried through reaction coils to a flow-through detector.
In more detail
As the injected sample plug travels downstream, it mixes with the carrier and any merging reagent streams by controlled dispersion, forming a reproducible concentration gradient rather than a fully homogenized, equilibrated solution. The detector (commonly a spectrophotometer, electrode, or fluorometer) records a transient peak whose height or area is proportional to analyte concentration, calibrated against standards run under identical timing. Because results depend on precisely reproducible timing and dispersion rather than on reaching chemical equilibrium, FIA achieves high sample throughput, low reagent consumption, and excellent precision. Developed by Jaromír Růžička and Elo Harald Hansen in 1975, it is widely used for routine, repetitive assays in water quality, clinical, and industrial laboratories.
Key facts
| Field | Analytical Chemistry |
|---|---|
| Developed by | Jaromír Růžička and Elo Harald Hansen, 1975 |
| Common detectors | UV-visible spectrophotometer, ion-selective electrode, fluorometer |
| Typical throughput | 60-300 samples per hour |
In FIA determination of phosphate in river water, a sample is injected into a carrier stream that merges with ammonium molybdate reagent and a reducing agent (such as ascorbic acid); the molybdate first forms a pale phosphomolybdate species, which the reducing agent converts to the intensely blue phosphomolybdenum (molybdenum blue) complex, and the resulting absorbance peak at 660 nm is measured and compared to a calibration curve.
Frequently asked questions
Does FIA separate the components of a mixture like chromatography?
No. FIA does not chromatographically separate species; it relies on a single, reproducible reaction/dilution step and precise timing, not physical separation, to generate an analyzable signal.
Why doesn't the sample need to reach full chemical equilibrium?
Because every injection experiences identical, tightly controlled flow rates, tubing lengths, and timing, the partial (non-equilibrium) reaction state is perfectly reproducible, so peak height still correlates reliably with concentration via calibration.