Flow injection systems basics

A BASIC FLOW INJECTION SYSTEM FOR CHEMILUMINESCENCE MEASUREMENTS... 

FIA analyzers or FIA components. One company produces a series of instruments that are flow injection systems with atomic absorption spectrometric detection dedicated to determination of mercury. Some companies produce flow injection analyzers for a large number of ions. One supplier has an analyzer that comprises three separate units a basic analytical module, an automatic sample module, and a data capture module, all these units being completely automated. The instrument is capable of analyzing nutrients, ions, and metals. It offers a wide analytical choice using ion-selective electrodes (ISEs), chemiluminescence, or fluorescence. With analysis speeds up to 120 samples per hour and detection limits down to parts per billion levels, this flow injection analyzer performs determinations well compared with other techniques. 

The basic instrumentation of flow injection systems consists of the manifold, a pump for the transport of the reagent, rotary sample injection valves, a flow-through cell, and a detector [6], which can be chemiluminescence-, mass spectrometric-, or electrochemical-based, among other possibilities. For example Figure 10.2 shows the block diagram of a flow injection system coupled to chemiluminescence detection. The sample is introduced into the flow injection analysis system via the injection valve or via an autosampler, while the carrier and reagent streams are pushed forward to the detector by the pumps. 

A flow scheme for the basic form of ion chromatography is shown in Fig. 7.3, which illustrates the requirements for simple anion analysis. The instrumentation used in IC does not differ significantly from that used in HPLC and the reader is referred to Chapter 8 for details of the types of pump and sample injection system employed. A brief account is given here, however, of the nature of the separator and suppressor columns and of the detectors used in ion chromatography. 

Enzyme linked electrochemical techniques can be carried out in two basic manners. In the first approach the enzyme is immobilized at the electrode. A second approach is to use a hydrodynamic technique, such as flow injection analysis (FIAEC) or liquid chromatography (LCEC), with the enzyme reaction being either off-line or on-line in a reactor prior to the amperometric detector. Hydrodynamic techniques provide a convenient and efficient method for transporting and mixing the substrate and enzyme, subsequent transport of product to the electrode, and rapid sample turnaround. The kinetics of the enzyme system can also be readily studied using hydrodynamic techniques. Immobilizing the enzyme at the electrode provides a simple system which is amenable to in vivo analysis. 

The flow system can be designed to produce mixing which minimizes concentration profiles. Such processes are discussed in any basic fluid mechanics or flow injection analysis text book 36 37). 

The basic experimental equipment for FFF is, except for the channel and its support, in general identical to the equipment used for liquid chromatography. It is usually composed of a solvent reservoir, a pump, and an injection system the chromatographic column is replaced by the FFF channel, followed by a detector. The FFF channel can require additional supporting devices, such as a centrifuge for sedimentation FFF or a power supply, and other electronic regulation devices for electrical FFF. If necessary, this basic equipment is complemented by a flow meter at the end of the separation system. For special semipreparative purposes, a fraction collector can be attached to the system. 

The basic components of the system are a liquid driver with only one carrier stream, a multi-port selection valve and a detector (Fig. 2.9). The valve is the heart of the sequential injection system and normally comprises 6—10 peripheral ports and a central port in a multi-position valve configuration. The central port is linked to a holding coil and the peripheral ports are connected to different solution aspiration tubes and transmission lines that are linked to different manifold components, e.g., detector and mixing chamber. Only one peripheral port is connected to the central port at any one time. Stream management inside the holding coil is accomplished by a bi-directional piston (or peristaltic) pump. The analyser is fully computer controlled and the injection volumes, residence times, delivery of solutions and analytical path lengths are selected based on a valve timing sequence and related flow rates. 

Fang, Z.-L, Liu, Z.-S., Shen, Q., Combination of flow injection with capillary electrophoresis. Part I. The basic system. Anal. Chim. Acta 1997, 346(2), 135-143. 

Flow-injection analysis can be implemented with the aid of closed systems of two basic types closed-loop and closed-open systems. 

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