Flow-injection assemblies

Fig. 4.14 Flow-injection assemblies for ion-exchange preconcentration of metal traces prior to introduction into an atomic absorption spectrometer. (A) Single-line manifold (B) three-valve system for upstream elution (C) automated assembly with intermittent pumping. (Reproduced from [11] with permission of the Royal Society of Chemistry).

Figure 5 (A) Flow-injection assembly. (B) Detail of gas diffusion unit.

Developments in the sensor fabrication techniques coupled to a flow injection assembly have been incorporated in real-time monitoring of biospecific interactions. The assembly utilizes screen-printed... 

I Gil Torro, JV Garcia Mate, J Martinez Calatayud. Spectrofluorimetric determination of vitamin K3 by a solid phase zinc reactor immobilized in a flow injection assembly. Analyst 122 139-142, 1997. 

Finally, FIA is an attractive technique with respect to demands on time, cost, and equipment. When employed for automated analyses, FIA provides for very high sampling rates. Most analyses can be operated with sampling rates of 20-120 samples/h, but rates as high as 1700 samples/h have been realized. Because the volume of the flow injection manifold is small, typically less than 2 mb, consumption of reagents is substantially less than with conventional methods. This can lead to a significant decrease in the cost per analysis. Flow injection analysis requires additional equipment, beyond that used for similar conventional methods of analysis, which adds to the expense of the analysis. On the other hand, flow injection analyzers can be assembled from equipment already available in many laboratories. 

The lack of selectivity can be circumvented by coupling a postcolumn flow system to a liquid chromatograph. This has promoted the development of a number of efficient liquid chromatography-CL approaches [16, 17]. Eluted analytes are mixed with streams of the substrate and oxidant (in the presence or absence of a catalyst or inhibitor) and the mixed stream is driven to a planar coiled flow cell [18] or sandwich membrane cell [19] in an assembly similar to those of flow injection-CL systems. Many of these postcolumn flow systems are based on an energy-transfer CL process [20], In others, the analytes are mixtures of metal ions and the luminol-hydrogen peroxide system is used to generate the luminescence [21],... 

The instrumentation used for FIA with CL detection is usually simple and is composed of the components depicted in Figure 2. These components are readily assembled to form the analytical manifold, although there are also commercially available flow injection systems with CL detection. Spectrophotometric or fluo-rimetric flow injection systems can often be used for CL measurements after some modifications. 

M. Badea, A. Curulli and G. Palleschi, Oxidase enzyme immobilisation through electropolymerised films to assemble biosensors for batch and flow injection analysis, Biosens. Bioelectron., 18(5-6) (2003) 689-698. 

Micro flow control devices open new possibilities for the miniaturization of conventional chemical and biochemical analysis systems. The micro total analysis system (pTAS) including microfabricated detectors (e.g. silicon based chemical sensors, optical sensors), micro flow control devices and control/detec-tion circuits is a practical micro electro mechanical system (MEMS). pTAS realize very small necessary sample volume, fast response and the reduction of reagents which is very useful in chemical and medical analysis. Two approaches of monolithic and hybrid integration of these devices have been studied. Monolithic and hybrid types of flow injection analysis (FIA) systems were already demonstrated [4, 5]. The combination of the partly integrated components and discrete components is useful in many cases [6]. To fabricate such systems, bonding and assembling methods play very important roles [7]. 

The sensors of the electronic nose are assembled in an array. The array is normally a small electronic unit that integrates the different sensors into a practical circuit card or another appropriate system that is easy to insert into the electronic nose instrument. If the array is to be used in a flow injection setup the unit also comprises a flow cell compartment with minimal volume. The system depicted in Fig. 2 shows how MOS and MOSFET arrays are integrated in a flow injection system [11]. Larger arrays can be integrated into silicon chips, as described for CP sensors where, for example an ASIC chip with 32 sensors has been fabricated with BiCMOS technology and having an area of 7 x 7 mm [18]. If the array is be inserted in the headspace volume of a bioreactor, the technical solution is a remote array probe that can be placed in a gas sample container [19]. 

Since ISEs can be used in continuous flow systems or in flow systems with sample injection (flow injection analysis, FIA)21 their application is wide, not limited to discrete samples. Analysis time becomes shorter, with faster recycling. Additionally, in flow systems the experimental assembly and data analysis can be controlled automatically by microcomputer, including periodic calibration. Another development is the use of sensors for the detection of eluents of chromatographic columns in high-pressure liquid chromatography (HPLC). Miniaturization has permitted an increase in the use of sensors in foods, biological tissues, and clinical analyses in general. 

Liu, G., Lin, Y. (2006). Biosensor based on self-assembling acetylcholinesterase on carbon nanotubes for flow injection/ amperometric detection of organophosphate pesticides and nerve agents. Anal. Chem. 78 835 3. 

A flow-injection analyzer can be assembled from readily available components 15, 25). The minimum requirements are an injection valve, pump, detector, recorder, and manifold tubing and connectors. Peristaltic pumps are most often used in FIA to propel the liquids. The flow produced by the pump should be steady and have low pulsation. A peristaltic pump should have 8-10 rollers on the pump head. A recently developed (25) low-cost FIA system uses air pressure to propel the liquid streams. This pressure produces a virtually pulse-free flow, but it may be prone to motion-related problems at sea. 

Figure 4.18 depicts a typical flow-injection pervaporation assembly. Solid lines represent fixed parts and the dashed lines, parts included when liquid samples are to be processed. 

Figure 12.2. Microcolumn flow-through manifolds for fractionation analysis in environmental solids (ti) continuous-flow system with either fraction collection or online detection (Jj) flow-injection setup with discrete injection of extractant (c) sequential injection system as assembled for fully automated sequential or single extractions. MC microcolumn, C coil, SP syringe pump, PP peristaltic pump, R reagent, D detector, W waste, SV selection valve, IV injection valve. (Adapted from Mir6 et al., 2005a.)...

Y. Suzuki, H. Hori, M. Twatsuki, T. Yamane, A four-wavelength channel absorbance detector with a light emitting diode-fibre optics assembly for simplifying the flow-injection analysis system, Anal. Sd. 19 (2003) 1025. 

Assemble the flow injection apparatus in the single-line mode as described by the manufacturer or your instructor. Use 0.89-mm i.d. pump tubing for the carrier and the sampling tubes (orange-orange color-coded stops on the peristaltic punip tubing). This should provide a flow rate of about 1.15 mL/min when using 25 rpm for the peristaltic pump. 

Flow-injection analysis Is also an excellent substitute for manual methods involving classical problems. Thus, the possibility of incorporating reducing columns into the system allows the use of strong reductants (e.g. Cr2+ or v2+) with no special precautions. The ease with which typical analytical instruments such as photometers and pH-meters can be incorporated into FIA assemblies further adds to its versatility. 

Fig, 18 Flow injection amperometric glucose biosensor based on LbL assembly of GOD on a... 

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