An Introduction to FIA and SIA
- Lesson 1: Introduction
- Lesson 2: Fundamentals of Flow Injection Analysis
- Lesson 3: Membrane Sampling Devices
- Lesson 4: Dispersion
- Lesson 5: Enrichment
- Lesson 6: Chemistry
- Lesson 7: Sequential Injection Analysis
- Lesson 8: Zone Fluidics
FLOW INJECTION ANALYSIS
FIA (Flow Injection Analysis) was defined by Ruzicka and Hansen in 1975. Simultaneous patents by Ruzicka and Hansen in Denmark and Stewart in the USA launched a new technology that would quickly gain worldwide acceptance.
Three key attributes of this technology ensured its rapid acceptance:
- The fundamental principles are easy to understand and implement
- Instrumentation can readily be assembled from simple, inexpensive, off-the-shelf components.
- It provides a simple means of automating many manual wet chemical analytical procedures
The following diagram can be used to describe the basic components and principles of FIA
A typical FIA manifold is comprised of a pump, injection valve, detector, and tubing manifold. The pump is used to propel one or more streams through the Detector via narrow bore (0.5 - 0.8 mm ID) tubing. These streams may be reagents, solvents, or some other medium such as a buffer. The injection valve is used to periodically introduce a small volume (generally <100 ?l) of sample into the carrier stream. As this sample is carried to the detector, the fluid dynamics of flow through narrow-bore tubing mixes sample and reagent, leading to chemical reaction to form a detectable species. This species is sensed by the detector as a transient peak. The height and area of the peak are proportional to concentration, and are used to quantify the concentration of the compound being determined by comparison to samples of known concentration (calibration curve).
Although it is possible to carry out the above process in a manual system with detector output to a chart recorder, most current systems are computer controlled with appropriate data acquisition and manipulation capabilities.
Of course, the described manifold is the simplest case, and innovative researchers have integrated a wide range of different sample processing steps into FIA methodologies. These include dilution, trace enrichment, solvent extraction, matrix modification, gas permeation, dialysis, and reactions with immobilized reagents.
Detection is most frequently photometric (uv/vis and more recently ? ir). In the field of life sciences, different luminescence techniques are gaining popularity. Electrochemical techniques such as amperometry, and potentiometry, have gained new life by coupling them to flow-based sample handling techniques such as FIA and SIA. Even AAS, ICP-MS and ICP-AES, and even GC have been coupled to FIA and SIA manifolds.
SEQUENTIAL INJECTION ANALYSIS
Sequential Injection Analysis (SIA) is a new generation of FIA , and was defined by Ruzicka and Marshall in 1991. This approach to automated sample manipulation arose from a need to simplify manifolds and address the unique requirements of the field of process analysis. In SIA, a selection valve and bi-directional pump is used to draw up small volumes of sample and reagents, and then propel them through a coil to a detector. Again, the process causes mixing of the sample and reagent segments leading to chemistry that forms a detectable species before reaching the detector.
The main benefits of SIA are
- simpler hardware than FIA - one pump, one valve, one carrier stream
- its efficient use of reagents and minimization of waste
- simple and universal manifold q the ease with which different chemistries can be implemented in one manifold