Flow Injection - Spectrophotometric Detection

Mahrous et al. [27] described the colorimetric determination of mefenamic acid with potassium ferricyanide in NaOH medium. The orange product is measured at 464 nm, and the molar absorptivity is 1.9 x 103 L/mol cm. The method was applied successfully to the determination of mefenamic acid in capsules. Garcia et al. [28] reported a flow injection spectrophotometric method for the determination of mefenamic acid in bulk samples and pharmaceuticals, also based on the reaction of mefenamic acid with potassium ferricyanide in NaOH media. The absorbance of the product obtained was measured at 465 nm, and the corresponding calibration graph was linear over the range of 1.00-100 mg/L, with a limit of detection of 0.18 mg/L. 

Attempts to improve selectivity and sensitivity of spectrophotometric measurements by using new chromogenic reagents, e.g. of 2-(5-nitro-2-pyridylazo)-5-(A -propyl-A-sulfopropylamino)phenol for flow-injection-spectrophotometric determination of trace V in river water [3], Af-butyl-A -(sodium p-amino benzenesulfonate) thiourea to determine Pd in minerals and catalysts [4], benzeneacetaldehyde-4-hydroxy-oxo-aldoxime to determine Co in pharmaceuticals, biological materials and steels [5], 2,6-dichloroarsenazo for the determination of Bi in copper alloys [6], lV-undecyl-A-(sodium p-aminobenzenesulfonate)-thiourea to identify and determine Cu in alloy, liver and wheat [7], dimethoxyhydroxyphenylflurone for the determination of trace amounts of Mo in steel and pure iron [8] and 5-(6-methoxy-2-benzothiazole-azo)-8-aminoquinoline for the detection of Co in drainage sediment and Ni in A1 alloy [9] have recently been reported. 

An alternative flow injection spectrophotometric method for the determination of h in the ground and surface water was reported by Kamavisdar and Patel (Kamavisdar Patel, 2002). The method was based on the catalytic destruction of the colour of the Fe(lll)-SCN"-CF -nBPy quarternary complex. The detection limit of the method was reported to be 0.1 ng ml"i of iodide. Another redox reaction between chloramine-T and N,N -tetramethyldiaminodiphenylmethane (Feigl s Catalytic Reaction) was applied for the determination of traces of iodine in drinking water (Jimgreis Gedalia, 1%0). 

DeBorba BM, Rohrer JS, Bhattacharyya L (2004) Development and validation of an assay for citric acid/citrate and phosphate in pharmaceutical dosage forms using ion chromatography with suppressed conductivity detection. J Pharm Biomed Anal 36 517-524 Perez-Ruiz T, Lozano C, Tomas V, Sanz A (1998) Flow-injection spectrophotometric determination of oxalate, citrate and tartrate based on photochemical reactions. Anal Lett 31 1413-1427... 

Traces of boron in seawater have been determined by flow injection analysis with spectrophotometric detection at 415 nm using G 30 methine H. The linear range was 1 -10 mg/1 boron with a detection limit of 0.017 mg/1 [3]. 

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. 

Flow injection analysis is based on the injection of a liquid sample into a continuously flowing liquid carrier stream, where it is usually made to react to give reaction products that may be detected. FIA offers the possibility in an on-line manifold of sample handling including separation, preconcentration, masking and color reaction, and even microwave dissolution, all of which can be readily automated. The most common advantages of FIA include reduced manpower cost of laboratory operations, increased sample throughput, improved precision of results, reduced sample volumes, and the elimination of many interferences. Fully automated flow injection analysers are based on spectrophotometric detection but are readily adapted as sample preparation units for atomic spectrometric techniques. Flow injection as a sample introduction technique has been discussed previously, whereas here its full potential is briefly surveyed. In addition to a few books on FIA [168,169], several critical reviews of FIA methods for FAAS, GF AAS, and ICP-AES methods have been published [170,171]. 

A. A. Ensafi and G. B. Dehaghi, Ultra-Trace Analysis of Nitrite in Food Samples by Flow Injection with Spectrophotometric Detection, Fresenius J. Anal. Chem. 1999,363, 131. 

FIA systems are used to investigate the kinetics of homogeneous chemical reactions and for the analytical determination of many components by means of spectrophotometric detection, amongst other applications. In the latter method, a certain concentration of reagent (component forming a coloured complex with the component to be determined) is added (injection), to a constant liquid flow of the solution in which the component to be determined is situated (flow).The resulting solution subsequently passes a reaction chamber, after which detection occurs by means of a spectrophotometer (analysis). 

Spectrophotometric techniques combined with flow injection analysis (FIA) and on-line preconcentration can meet the required detection limits for natural Fe concentrations in aquatic systems (Table 7.2) by also using very specific and sensitive ligands, such as ferrozine [3-(2-bipyridyl)-5,6-bis(4-phenylsulfonic acid)-l,2,4-triazine], that selectively bind Fe(II). Determining Fe(II) as well as the total Fe after on-line reduction of Fe(III) to Fe(II) with ascorbic acid allows a kind of speciation.37 A drawback is that the selective complexing agents can shift the iron redox speciation in the sample. For example, several researchers have reported a tendency for ferrozine to reduce Fe(III) to Fe(II) under certain conditions.76 Most ferrozine methods involve sample acidification, which may also promote reduction of Fe(III) in the sample. Fe(II) is a transient species in most seawater environments and is rapidly oxidized to Fe(III) therefore, unacidified samples are required in order to maintain redox integrity.8 An alternative is to couple FIA with a chemiluminescence reaction.77-78... 

Sakai et al. reported a novel flow injection method for the selective spectrophotometric determination of acetylcholine using thermochro-mism of ion associates [38]. Samples (0.14mL) containing acetylcholine were injected into a flow injection system with a buffered (pH 11) carrier stream and a reagent stream (10 mM tetrabromo-phenolphthalein ethyl ester in dichloroethane) at 0.8 mL/min. The temperature of the flow cell was 45°C which reduced interference and improved recovery, and the detection was at 610 nm. 

Measures Cl, Yuan J, Resing JA (1995) Determination of iron in seawater by flow injection analysis using in-line preconcentration and spectrophotometric detection. Mar Chem 50 3-12... 

Fig. 4 Optimized SdFFF fractogram of ES Cells. Representative fractogram of ES cell suspensions after SdFFF elution. Elution conditions Flow injection of 100 pL of ES suspension flow rate, 0.6 mL/min (sterile PBS, pH 7.4) and external multigravitational field, 40 (O.lg spectrophotometric detection at 254 nm). Fractions were collected as follows PFl, 3 min 40 sec/4 min 15 sec PF2, 4 min 20 sec/4 min 50 sec PF3, 5 min 0 sec/5 min 50 sec. ER corresponds to the end of channel rotation. In this case, the mean externally applied field strength was equal to zero gravity thus RP, a residual signal, corresponds to the release peak of reversible cell accumulation wall sticking. (View this art in color at www.dekker.com.)...

ISO/TR 11905-2). Another method oxidizes nitrogen forms into nitrates which can be then estimated (NF EN ISO 11905-1). Lastly, an ISO/CD 29441 method, under development, uses UV digestion, followed by flow injection analysis (FIA), continuous flow analysis (CFA) with spectrophotometric detection, and allows automation of the method. 

The system combines the advantageous characteristics of flow injection analysis, such as a high sample throughput and low detection limits, with those of sequential injection analysis such as robustness and versatility. It was initially exploited for industrial process control, with spectrophotometric detection, for the determination of highly acidic or alkaline protolytes using an ingenious titration procedure [109], free... 

I.Y. Kolotyrkina, L.K. Shpigun, Y.A. Zolotov, G.I. Tsysin, Shipboard flow injection method for the determination of manganese in sea-water using in-valve preconcentration and catalytic spectrophotometric detection, Analyst 116 (1991) 707. 

P.L. Kempster, H.R. van Vliet, J.F. van Staden, Prediction of FIA peak width for a flow-injection manifold with spectrophotometric or ICP detection, Talanta 36 (1989) 969. 

A U-shaped glass tube was used in the first segmented flow analysers with spectrophotometric detection but is now rarely used due to the pronounced radiation losses at the curved portions and in the cylindrical walls of the tube. A single tube axially traversed by the radiation incident beam can be used instead of a typical flow cell in situations requiring a short optical path, as originally demonstrated in the spectrophotometric determination of the major constituents of fertilisers in a flow injection system [84] this approach avoided the need for manual sample dilutions. 

D. Vendramini, V. Grassi, E.A.G. Zagatto, Spectrophotometric flow injection determination of copper and nickel in plant digests exploiting differential kinetic analysis and multi site detection, Anal. Chim. Acta 570 (2006) 124. 

A.R.A. Nogueira, S.M.B. Brienza, E.A.G. Zagatto, J.L.F.C. Lima, A.N. Araujo, Flow injection system with multisite detection for spectrophotometric determination of calcium and magnesium in soil extracts and natural waters, J. Agric. Food Chem. 44 (1996) 165. 

The feasibility of using a portable flow injection system for the in situ monitoring of river water was demonstrated by the design and deployment of a field instrument with spectrophotometric detection for the determination of phosphate [4], Solid-state technology (LED source and photodiode detector) was used to construct a compact, battery-operated analyser that could operate without maintenance for several weeks, yielding reliable, pseudo-continuous results. The monitor was further applied to the determination of nitrate [5] and ammonium [6] in river waters. Details of the instrumentation were also reported [7,8]. 

An alternative sampling approach is to deploy a submersible analyser [14,15]. Water is sucked from the exterior environment by an on-board pump in order to fill the sampling loop, with excess sample directed back to the exterior. The flow system is remotely controlled and the results can be either stored in the analyser or transmitted back to the ship via a cable. In this context, a small submersible flow injection analyser, with solid-state spectrophotometric detection, was conceived for the in situ determination of nitrate (Fig. 8.2). Its performance and versatility were assessed by results from laboratory, shipboard (North Sea IMPACT Cruise) and in situ (Tamar Estuary, UK) analysis. Excellent temporal and spatial resolutions were reported and this aspect is crucial for investigating dynamic processes in estuarine, coastal and open ocean waters. 

Bromine. Convergence of bromide, bromate and hydrochloric acid streams leads to formation of the unstable bromine reagent that can be added to the main analytical channel of a flow injection system. The approach was exploited for the spectrophotometric determination of acetylcysteine in sachets [100]. A noteworthy feature is that in-line waste treatment involving elimination of excess bromine was performed by adding an ascorbic acid stream to the main channel after detection. 

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