Automatic analytical methods for environmental monitoring and control

Although, non-segmented flow systems have existed for a long time, only in 1975 J. Ruzicka and E. Hansen and K.K. Stewart et al, independently demonstrated that flow injection systems can be used for rapid and precise automated analysis if the proper flow conditions are selected. This approach is known as flow-injection analysis; term coined by J. Ruzicka and E. Hansen.

Since FIA was born, it found many applications both in the laboratory and in process control and became known simply as FI as it was realized that FI is not only a tool for analysis, but also a generally applicable solution handling technique. Its ability to control and monitor kinetic aspects of automated assays has been recognized, and identified as “kinetic advantage”.

By now its scope is broadening into environmental research and into a tool of biotechnology and for the study of the chemistry of life. FI’s versatility, or self-adaptation, and perfect computer compatibility makes it an ideal interface between a computer and a (bio)chemical system.

Flow-injection analysis is based on the insertion/injection of a liquid sample into a moving non-segmented carrier stream of a suitable liquid. The injected sample forms a zone, which is transported by the carrier through a coil of tubing to a detector. The detector measures a physical parameter of the sample (absorbance, electrode potential, pH, etc.) that changes continuously as a function of time as the sample passes through the flow cell. This means that the concentration of the species being monitored is continuously changing with time. The carrier may contain a reagent that reacts with the analyte to yield a detectable product, or may consist of an inert solution and in this case the carrier serves as a means of transporting the sample to the detector. Thus, the FIA response curve is a result of two processes, both of kinetic nature, the physical process of dispersion of the sample zone within the carrier stream, and the chemical process of the formation of chemical species.

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  a pump (P) that is used to propel the carrier stream through a thin tube;
  
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  an injection device (V_i) that introduces into the carrier a well-defined volume of sample solution (S) in a very reproducible manner;
  
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  a coil of tubing also named reaction coil (RC) in which the sample zone disperses and reacts with the components of the carrier, forming species that are detected by a flow-through detector;
  
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  a
  recorder which registers the FIA typical signals. A typical recorder output has a form of a peak, its height (H) being related to the analyte concentration.
  

(b)
Figure III.2.11. (a) Diagram of a FIA system. (b) Typical recorder output. P – pump; V – injection device; RC – reactor (reaction coil); D – detector; C – carrier; S – sample; R – reagent; W – waste; H – peak height; T – residence time; t_b – peak width, time that sample zone passes through flow-cell.

In addition to such higher sampling rate and very rapid availability of the analytical response, the most important aspect of the FIA method is the concept of controlled dispersion of the sample zone, an entirely new concept in analytical chemistry at that time, and which allows the design of a FIA system suited to automate a given analytical procedure.