Natural waters flow injection spectrophotometric

Table 4. Flow injection spectrophotometric determination of iron (III) in natural waters.

Complexation with PAN immobilized on a Dowex 50Wx4 cation exchanger makes a basis of the determination of Zn in human hair, natural water and pharmaceutical and cosmetic formulations [11]. Flow-injection solid-phase spectrophotometry using TAN immobilized on silica gel was proposed for the determination of Zn in pharmaceutical preparations [12]. Adsorption of the complex with PAR on Sephadex anion exchanger makes a basis of solid phase spectrophotometric method for the determination of Zn in environmental samples [13]. 

F.J. Krug, B.F. Reis, M.F. Gine, J.R. Ferreira, A.O. Jacintho, E.A.G. Zagatto, Zone trapping in flow injection analysis. Spectrophotometric determination of low levels of ammonium ion in natural waters, Anal. Chim. Acta 151 (1983) 39. 

The formation of liquid optical artefacts along the flowing sample is minimised by using less concentrated solutions, preferably involving chemical species with a high transport number. This approach was used when solid-phase extraction was implemented in a flow injection manifold for the spectrophotometric determination of ammonium in natural waters [113]. As pronounced concentration gradients are inherent to solid-phase extraction, a relatively dilute (0.5 mol L 1 NaOH) solution was selected as the eluent. 

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. 

Alternatively, the oxidising or reducing solid reagent can be immobilised on a suitable support, as demonstrated in the spectrophotometric and chemiluminometric flow injection determinations of manganese in natural waters using mini-columns of lead(IV) dioxide or sodium bis-muthate immobilised on silica gel beads [112] and paper pulp [113], respectively. 

The spectrophotometric determination of cadmium in natural waters involving in-line formation of an aqueous dithizone suspension [121] illustrates another application of in-line suspension addition. Solid dithizone reagent was packed in a mini-column through which a surfactant (Triton X-100) stream was allowed to flow. The emerging suspension formed was added by confluence to the main analytical channel of a flow-injection system. With this innovation, good sensitivity was achieved without the need for an analyte separation/concentration LLE step and the entire procedure was carried out in the aqueous phase. 

Sample dissolution and analyte conversion to a more easily detected species, e.g., the sequential injection determination of total nitrogen in wastewaters involving Kjeldahl oxidation and nitrate formation [141]. The spectrophotometric flow injection determination of organic phosphorus in natural waters [142], relying on the release of the different forms of phosphorus as orthophosphate, is another good example. 

I.D. McKelvie, B.T. Hart, T.J. Cardwell, R.W. Cattrall, Spectrophotometric determination of dissolved organic phosphorus in natural waters using in-line photooxidation and flow injection, Analyst 114 (1989) 1459. 

J. Mortatti, F. J. Krug, and H. Bergamin F, Spectrophotometric Determination of Lead in Natural Waters and Plant Material by Flow Injection Analysis [in Portuguese]. Energ. Nucl. Agric. (Piracicaba), 4 (1982) 82. 

Nitrite Nitrite is an important indicator of fecal pollution in natural waters as well as a potential precursor of carcinogenic species. A rush of flow and sequential injection spectrophotometric method based on Griess-type reactions has been proposed, also coupled to online sorbent enrichment schemes. The catalytic effect of nitrite on the oxidation of various organic species constitutes the basis of fairly sensitive spectrophotometric methods. Fluorometric methods based on the formation of aromatic azoic acid salts, quenching of Rhodamine 6G fluorescence, and direct reaction with substituted tetramine or naphthalene species have been also reported. Indirect CL methods usually involve conversion into nitric oxide and gas-phase detection as mentioned in the foregoing section. The redox reaction between nitrite and iodide in acidic media is the fundamental of a plethora of flow injection methodologies with spectrophotometric, CL, or biamperometric detection. New electrochemical sensors with chemically modified carbon paste electrodes containing ruthenium sites, or platinum electrodes with cellulose or naphthalene films, have recently attracted special attention for amperometric detection. 

L.J. Gimbert, P.M. Haygarth, P.J. Worsfold, Determination of nanomolar concentrations of phosphate in natural waters using flow injection with a long path length liquid waveguide capillary cell and soUd-state spectrophotometric detection, Talanta 71 (2007) 1624-1628. 

McKelvie, I.D. et al., Spectrophotometric determination of dissolved organic phosphorus in natural waters using in-line photo-oxidation and flow injection. Analyst 114, 1459, 1989. Aminot, A. and Kerouel, R., An automated photo-oxidation method for the determination of dissolved organic phosphorus in marine and fresh water. Marine Chemistry 76, 113, 2001. Solorzano, L. and Strickland, J.D., Polyphosphate in seawater. Limnology and Oceanography 13, 515,1968. 

FIGURE 1,6 Example of manifolds developed for flow injection speciation analysis, (a) Manifold of the reversed FIA system for speciation of chromium with pH measurements and spectrophotometric detection, q—peristaltic pumps, V—injection valves, L— reaction coil, M.E.—pH glass electrode. (Adapted from Ruz, J. et al. 1986. J. Autom. Ghent. 8 70-74.) (b) Manifold of branched FIA system for simultaneous biamperomet-ric determination of nitrate and nitrite. (Cd)Cu—reductive column with copperized cadmium, L—mixing coils. (Adapted from Trojanowicz, M., W. Matuszewski, and B. Szostek. 1992. Anal. Chim. Acta 261 391-398.) (c) Example signal recordings obtained in the FIA system shown in (b) 1-6—standard solutions, A-I—natural water samples. Concentration in standard solutions 1—0.075 2—0.050 3—0.025 mM nitrate and 4—7.5 5—5.0 6—2.5 pM nitrite. 

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