flowinjection

Flow injection (often called flow injection analysis, FIA) is an automated analytical technique in which a liquid sample is introduced into a continuously moving carrier stream and transported through a reaction manifold to a detector. The injected zone mixes and disperses with reagents in controlled conditions, producing a transient signal that is related to analyte concentration. The method emphasizes rapid processing, minimal reagent use, and easy coupling to a variety of detectors such as spectrophotometers, electrochemical sensors, and mass spectrometers.

Introduced in the 1970s, flow injection is characterized by its simple hardware: a pump to move the carrier, an injection device, mixing/coiling tubing to allow reactions and dispersion, and a detector. Key parameters include carrier flow rate, coil length (residence time), dispersion coefficient, and the sequence of reagent addition. These factors are adjusted to optimize sensitivity, precision, and throughput.

Flow injection is used in environmental monitoring, clinical chemistry, pharmaceutical quality control, and industrial process analysis. Its strengths are high sample throughput, reduced reagent consumption and waste, reproducible timing, and ease of automation. Variants and related approaches include segmented flow, sequential injection analysis, lab-on-valve systems, and microfluidic flow injection, which adapt the core concept to different scales and automation levels.

Limitations include potential carry-over between samples, reduced suitability for very slow reactions without additional incubation, and the need for careful calibration and control of dispersion effects. Despite these constraints, flow injection remains a versatile tool for routine and high-throughput chemical analysis.