FIA-FAAS

Pump 1 FIA-valve Carrier Sample loop Burner  

An FIA system is especially useful in the analysis of solutions containing high levels of solids such as saturated salt solutions or dissolved fusion mixtures. The burner slot or nebulizer will not become blocked since the system is continuously and thoroughly rinsed with the carrier stream after each sample measurement. The FIA system requires less than 400 /zl of sample solution, which is much less than with continuous aspiration. Thus, FIA-FAAS is the preferred technique when only small sample amounts are available. Low sample consumption is also beneficial for routine analysis, since with fully automated sequential multi-element analysis more determinations can be performed with a given sample volume. 

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Cu, Fe FIA-FAAS Whole milk MW digestion HN03/ Triton X-100... 

FIA-FAAS. Figure 94 shows the principle of the FIA-flame atomic absorption spectrometer. The carrier stream (usually, deionized water or... 

Schematic diagram of an FIA-FAAS system. PP, peristaltic pump V, six-way valve V2, selection valve iji, Triton X-100 flow rate q2, diluent flow rate q, HCl (pH 4) sample, H2O (pH 7) and NaOH flow rates SRC, solid reagent column R, R2, and R3, reactors D, detector SBSR, single-bead string reactor. (From Di Nezio, M.S., Palomeque, M.E., and Fernandez Band, B.S., Talanta, 63, 405, 2004. With permission.)...

I.A. Kovalev, L.V. Bogacheva, G.I. Tsysin, A.A. Formanovsky, and Y.A. Zolotov. FIA-FAAS system including on-line solid phase extraction for the determination of palladium, platinum and rhodium in alloys and ores. Talanta 52 39-50, 2000. 

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]. 

The on-line interface of flow manifolds to continuous atomic spectrometric detectors for direct analysis of samples in liquid form typically requires a nebuliser and a spray chamber to produce a well-defined reproducible aerosol, whose small droplets are sent to the atomisation/ionisation system. A variety of nebulisers have been described for FAAS or ICP experiments, including conventional cross-flow, microconcentric or Babington-type pneumatic nebulisers, direct injection nebuliser and ultrasonic nebulisers. As expected, limits of detection have been reported to be generally poorer for the FIA mode than for the continuous mode. 

The advantage of the selective adsorption of a particular element oxidation state has been exploited for on-line element preconcentration and speciation analysis of Cr by FAAS. Cespon Romero et al. [21] described an FIA system employing a minicolumn made of a chelating resin containing poly(aminopho-sphonic) acid groups, able to selectively retain Cr(III) ions. An FIA manifold was employed for efficient preconcentration and subsequent elution of Cr(III) with a small volume of 0.5 M HC1. The original sample was also treated with ascorbic acid to reduce Cr(VI) to Cr(III) and total Cr is determined as Cr(III) after appropriate retention and elution. Eluates are introduced into an N20-acetylene flame connected to the column outlet. The concentration of Cr (VI) is obtained by difference. Employing a sample volume of 6.6 mL, LoD for total Cr is 0.2 pg l-1. A study of FI operational variables, interferences, and precision is reported for the analysis of tap, mineral, and river waters. 

As regards fractionation methodologies for the selective determination of Pb and other metals compounds in wines, Lemos et al. [57] have developed a FIA method for the direct determination of available free Pb(II) and total Pb content in wine samples. Lead (II) was chemically retained on a packed polyurethane foam microcolumn, modified by immobilization of 2-(2-benzothiazolyazo)p-cresol (BTAC) and eluted with 0.1 M HC1. The eluate was determined on-line by FAAS. Total Pb was quantified after sample digestion with HN03 and H202, whereas free Pb was determined by direct sample on-line preconcentration and elution. No effect of ethanol on the enrichment procedures was observed. With a preconcentration factor of 26 an LoD of 1 xg l-1 was reached. Four red and three white wines of different origins were analyzed and the total Pb content varied from 8 to 42 p,g 1 1. 

Obviously, cyanide cannot be directly measured by flame atomic absorption spectrometry (FAAS), but an indirect approach, as that schematically depicted in Figure 7.16, allows this possibility to be implemented, improving detection limits with regard to those reported previously for flow-based methods. The FIA manifold relies on the formation of soluble metal-cyanide complexes as the sample passes through a small column packed with soUd-phase reagent (SPR). Different SPR have been tested for indirect determination of cyanide using FIA. In all cases the eluted complex is measured by FAAS. Detection limits close to 0.05 mg/1 cyanide have been reported [28]. 

The measurement of Na, K, Mg, and Ca by FAES or EAAS techniques usually requires dilution of the water sample, considering that their natural concentrations exceed the linear range of the methods. The use of an FIA system with a dialysis imit for the automatic determination of Ca and Mg by FAAS, and Na and K by flame photometry in wastewater has been reported [121,126,127]. Other researchers [124,128,129] have used... 

A large diversity of instrumental techniques are also available to determine these elements, from those extremely simple such as volumetric, spectrophotometric, electrochemical or flame photometric ones, a second group of medium complexity, like FAAS, ICP-AES, ICP-MS, or even EASS, and a third group of greatest technological complexity which could include FIA-ETAAS-HPLC, FIA-HPLC-ICP-MS, etc. All these instrumental alternatives can also be coupled with different kind of preconcentration systems (chelating resins, matrix modifiers, LC, etc.) which allow to minimize the effect of impurities interferences, and consequently to obtain a better analytical signal. 

All FIA atomic absorption methodologies developed for indirect AA determination involve the utilization of flame atomic absorption spectrometry (FAAS) as detector, and are based on oxidation of AA to DHAA and reduction of a metallic specie (Fe(III) to Fe(II), Cr(VI) to Cr(III), Mn(VII) to Mn(II) and Mn(IV) to Mn(II)). Most of the methods apply a microcolumn with a solid phase (polymeric adsorbent Amberlite XAD4 [136], cation-exchange resin Amberlite IR120 [137,138], or poly(aminophosphonic acid) chelating resin [139,140]) to retain the reduced metallic species. The other possibility is the utilization of a solid-phase reactor filled with the substance to be reduced. Thus, Noroozifar et al. [141] propose a reactor filled with Mn02 suspended on silica gel beads. 

Note BA biamperometric titration CE-CCD capillary electrophoresis with contactless conductivity detection CL chemiluminescence EB electrochemical biosensor FAAS flame atomic absorption spectrometry FIA flow injection analysis HPLC-UV high-performance liquid chromatography with UV detection MC multicommutation P potentiometry SIA sequential injection analysis SP spectrophotometry TB turbidimetry. 

FIGURE 24.11 FIA manifold for the indirect atomic absorption determination of cyclamate. B blank F filter FAAS flame atomic absorption spectrometer P pump PC precipitation coil RC reaction coil S sample SVl and SV2 switching valves UW ultrapure water W waste. 

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