Injection analysis sequential

Sequential injection analysis was conceived in 1990 by Ruzicka Marshall [75] as a novel approach to process analysis and laboratory assays, as well as to the development of sensors. A flow diagram of the simplest analyser is shown in Fig. 2.8. 

Sequential injection analysis relies on three cornerstone features sequential aspiration, flow reversal, and controlled dispersion under reproducible timing. 

The versatility, ruggedness and simplicity of sequential injection systems have been often recognised [76—78]. In fact, different analytical procedures could be carried out using the same manifold, commutation could be better exploited, and reagent addition was carried out only in the presence of the sample, thus reducing reagent consumption and waste generation. 

it is interesting to mention the stepwise injection system [79], a variant of sequential injection analysis (without a holding coil), which permits the accomplishment of all the steps involved in a specific application as if they were stationary. The related instrument is very robust and amenable to gas analysis. 

FIGURE 2.8 Flow diagram of a simple sequential injection analyser. S = sample C = carrier/ wash stream R = reagent Rc = holding coil SV = selection valve D = detector arrow = site where pumping is applied. 

While SFA usually requires that the analytical reaction reaches chemical equilibrium, FIA does not. In fact, FIA only requires the extent of reaction to be constant and reproducible, which is facilitated by the high reproducibility provided by the hydrodynamic behavior of the system. Moreover, since FIA uses much thinner tubing and lower flow rates, it consumes samples and reagents much more sparingly than does SFA. 

In addition, FIA is much more flexible than SFA allowing the implementation of analytical methodologies unaffordable to the latter, e.g. kinetic methods, stopped-flow methods. 

Another major advantage of FIA over SFA is its ease of implementation. In fact, a dedicated manifold can be readily assembled from fairly inexpensive parts, viz. a peristaltic pump, injection valves, flow-cells. Teflon tubing, connectors and available measuring instruments, e.g. spectrophotometers, potentiometers, ammeters, atomic absorption spectrometry equipment. This propitiated a vast expansion of FIA among research laboratories and led to the development of a large number of applications relative to other, more recent techniques within a few years after its inception. 

The central port of the valve is connected to a two-way piston pump via a holding coil, to address the peripheral ports of the unit, for sequential aspiration of the various constituents, and also to the detector, via the central communication channel. Side ports can also be used for other purposes such as discharging waste or connection to other devices, e.g. a microwave oven, photooxidation system or mixing chamber. 

Schematic depiction of a typicai SiA system. HC hoiding coii, RC reaction coii, SV selection valve. 

---

Table 6 Examples of Sequential Injection Analysis with CL Detection...

Motz SA, Klimundova J, Schaefer UF, Balbach S, Eichinger T, Solich P, Lehr C-M (2007) Automated measurement of permeation and dissolution of propranolol HC1 tablets using sequential injection analysis. Anal Chim Acta 581 174—180... 

Gutes and coworkers presented an automated electronic tongue based on sequential injection analysis (SIA) and linear sweep voltammetry, for the simultaneous determination of glucose and ascorbic acid, by means of ANN regression. The models were evaluated with an external test set (Gutes et al., 2006). 

Christian, G. D., Sequential injection analysis for electrochemical measurements and process analysis, Analyst, 119, 2309-2314, 1994. 

Miro, M. and Hansen, E. H., Solid reactors in sequential injection analysis Recent trends in the environmental field, Trends Anal. Chem., 25, 267-281, 2006. 

R. C. C. Costa, M. I. Cardoso, A. N. Araujo, Metals determination in wines by sequential injection analysis with flame atomic absorption spectrometry, Am. J. Enol. Vitic., 51 (2000), 131-136. 

R. Cerdeira de Campos Costa, A. Nova Araujo, Determination of Fe(III) and total Fe in wines by sequential injection analysis and flame atomic absorption spectrometry, Anal. Chim. Acta, 438 (2000), 227-233. 

M. A. Segundo, J. L. F. C. Lima, A. O. S. S. Rangel, Automatic flow system based on sequential injection analysis for routine determinations in wines, Anal. Chim. Acta, 513 (2004), 3 -9. 

Kefala, G. and Economou, A. (2006), Polymer-coated bismuth film electrodes for the determination of trace metals by sequential-injection analysis/anodic stripping voltammetry. Anal. Chim. Acta, 576(2) 283-289. 

Fluorimetric methods [34] Fluorimetric sequential injection analysis of magnesium in commercial drinking waters is based on the complexation of magnesium (II) with 8-hydroxyquinoline-5-sulfonic acid in the presence of ethylene glycol-bis(6-aminoethyl ether)-N,N,N, N -tetra-acetic acid as a masking agent and cetyltrimethylammonium chloride as the fluorescence enhancer. 

An amperometric immunosensor using sequential injection analysis techniques to detect the herbicide 2,4-D in water was described by Wilmer and Trau [102,103]. This rapid competitive EIA used an alkaline phosphatase-labelled monoclonal antibody directed against the herbicide and an immunoreactor with 2,4-D immobilized via BSA, either to Eupergit in a column or directly to the surface of a glass capillary. A detection limit of the immunosensor at 0.1 (jLg 2,4-D 1, without enrichment of the analyte, pointed to the feasibility of making automatic measurements of 2,4-D in drinking and ground water. 

To increase the percentage of dialysis, as well as the dialysis time, multiple flow reversals with a time of 20 s between each flow reversal is selected. Similar results are obtained by using a sequential injection system with the stopped-flow period around 150 s. The advantage of utilizing the stopped-flow mode over multiple flow reversals in the sequential injection analysis systems is that it needs less programming and, also, it reduces the strain on the pump. 

The concentration step is very easy to implement in sequential injection analysis. The system is very simple and the results are reproducible. Most of the time, this step is not necessary for HPLC. When it is necessary, it can easily be done in the same time with the extraction step. 

---