Microcolumn preconcentration

Sperling, M., Yan, X., Welz, B. Electrothermal atomic absorption spectrometric determination of lead in high-purity reagents with flow-injection on-line microcolumn preconcentration and separation using a macrocycle immobilized silica gel sorbent. Spectrochim. Acta Part B 51, 1875-1889 (1996)... 

Liang, P., Zhao, E., Ding, Q., Du, D. Multiwalled carbon nanotubes microcolumn preconcentration and determination of gold in geological and water samples by flame atomic absorption spectrometry. Spectrochim. Acta B 63, 714—717 (2008)... 

Furuta N., Brushwyler K. R. and Hieftje G. M. (1989) Flow-injection analysis utilizing a spectrally segmented photodiode array ICP emission spectrometer I. Microcolumn preconcentration for the determination of molybdenum, Spectrochim Acta, Part B 44 (1989) 349-358. 

Z.H. Wang, Z.P. Zhang, Z.P. Wang, L.W. Liu, X.P. Yan, Acrylic acid grafted poly-tetrafluoroethylene fiber as new packing for flow injection on-line microcolumn preconcentration coupled with flame atomic absorption spectrometry for determination of lead and cadmium in environmental and biological samples, Anal. Chim. Acta 514 (2004) 151. 

Water (tap, river water, coastal seawater), Water SRMs Cu None [N/MT] On-line microcolumn preconcentration, elute into flame [SEP/CONC-FAAS] [N/MT-SEP/ CONC-FAAS] Anthemidis etal. (2001)... 

Limbeck A, Puls C, Handler M (2007) Platinum and palladium emissions from on-road vehicles in the Kaisermtihlen tunnel (Vienna, Austria). Env Sci Technol 41 4938 945 Liu P, Su Z, Wu X, Pu Q (2002) Application of isodiphenylthiourea immobilized silica gel to flow injection on-line microcolumn preconcentration and separation coupled with flame atomic absorption spectrometry for interference-free determination of trace silver, gold, palladium and platinum in geological and metallurgical samples. J Anal At Spectrom 17 125-130... 

Olsen et al. [660] used a simple flow injection system, the FIAstar unit, to inject samples of seawater into a flame atomic absorption instrument, allowing the determination of cadmium, lead, copper, and zinc at the parts per million level at a rate of 180-250 samples per hour. Further, online flow injection analysis preconcentration methods were developed using a microcolumn of Chelex 100 resin, allowing the determination of lead at concentrations as low as 10 pg/1, and of cadmium and zinc at 1 pg/1. The sampling rate was between 30 and 60 samples per hour, and the readout was available within 60-100 seconds after sample injection. The sampling frequency depended on the preconcentration required. 

In some applications, additional components acting as reactors for specific chemical pretreatment are incorporated within the flow manifold. Typical examples are ion-exchange microcolumns for preconcentration of the analyte or removal of interferences and redox reactors, which are used either to convert the analyte into a more suitable oxidation state or to produce online an unstable reagent. Typical examples of online pretreatment are given in Table 2. Apart from these sophisticated reactors, a simple and frequently used reactor is a delay coil (see also Fig. 4), which may be formed by knitting a segment of the transfer line. This coil allows slow CL reactions to proceed extensively and enter into the flow cell at the time required for maximum radiation. The position of the reactors within the manifold is either before or after the injection port depending on the application. 

Online trace enrichment by flow injection using a microcolumn of activated alumina and mass spectrometric determination of uranium in mineral, river and sea water is relevant for analyzing small sample volumes.80 Flow injection with online preconcentration using solid... 

Xan et al. [124] described a highly selective method for the determination of traces of lead in soils and sediments. It is based on the preconcentration of lead on a microcolumn packed with a macrocycle immobilised on silica gel. 

Emteborg, H., Baxter, D.C. and Freeh, W. (1993) Speciation of mercury in natural waters by capillary gas chromatography with a microwave emission detector following preconcentration using a dithiocarbamate resin microcolumn installed in a closed flow injection a system. Analyst, 118, 1007-1013. 

Saito, Y., M. Imaizumi, T. Takeichi, and K. Jinno. 2002. Miniaturized fiber-in-tube solid-phase extraction as the sample preconcentration method for microcolumn liquid-phase separations. Anal. Bioanal. Chem. 372 164-168. 

Cox and Mcleod66 passed their water samples through activated alumina microcolumns in the field, isolating and retaining both Cr(III) and Cr(VI) species. The microcolumns were then returned to the laboratory and inserted into a flow injection inductively coupled plasma-emission spectrometry (FI-ICP-ES) system for elution and quantification (the lowest results reported are around 40 nM). The pretreatment of the microcolumns and the FI-ICP-ES method was, however, complicated and time-consuming. Recently, Dogutan et al.67 and Latif et al.68 preconcentrated the Cr species on an exchange column and first eluted one species, and subsequently both of them. 

Munaf, E., H. Haraguchi, D. Ishii, T. Takeuchi, and M. Goto. 1990. Speciation of mercury compounds in waste water by microcolumn liquid chromatography using a preconcentration column with cold-vapour atomic absorption spectrometric detection. Anal. Chim. Acta 235 399 404. 

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. 

X. P. Yan, Y. Li, Y. Jiang, Selective measurement of ultratrace methylmercury in fish by flow injection on-line microcolumn displacement sorption preconcentration and separation coupled with electrothermal atomic absorption spectrometry, Anal. Chem., 75 (2003), 2251-2255. 

Chromatographic method The determination of silicate based upon the adsorption of preconcentrated phosphomolybdic and silicomo-lybdic heteropoly acid (HPA) in the dynamic mode on a microcolumn packed with an Amberlite XAD-8 polyacrylate adsorbent is reported [49]. The method is based on the adsorption of HPAs followed by desorption with acetonitrile and determination by reversed-phase HPLC. Another highly sensitive HPLC method for the simultaneous determination of soluble silicate and phosphate in environmental waters is used in ion-pair liquid... 

The presence in drinking water of phenol, cresol and various antioxidants (109-113) used for synthetic rubber preservation was tested by SPE with a Cig cartridge followed by RP-HPLC on a Cig column with UVD at 280 nm °. An automatic LC system was devised for determination of trace amounts of phenols in water, based on SPE preconcentration, RP microcolumns, isocratic methanol-water mobile phase and ELD in the autoincrement mode. LOD was 40-600 ngL, for eleven priority phenols . ... 

Schramel P., Xu L., Knapp G. and Michaelis M. (1993) Multi-elemental analysis in biological samples by online preconcentration on 8-hydroxy-quinoline—cellulose microcolumn coupled to simultaneous ICP-AES, Fresenius J Anal Chem 345 600-606. 

On-line preconcentration by chelation and C,x microcolumn elution with ethanol ETAAS detection (Lab. 16)... 

Q.-S. Pu, P. Liu, Q.Y. Sun, Z.X. Su, Flame atomic absorption spectrometric determination of gold and palladium using microcolumn on-line preconcentration and separation, Microchim. Acta 143 (2003) 45. 

J.-H. Wang, E.H. Hansen, Coupling on-line preconcentration by ion-exchange with ETAAS. A novel flow injection approach based on the use of a renewable microcolumn as demonstrated for the determination of nickel in environmental and biological samples, Anal. Chim. Acta 424 (2000) 223. 

Moldovan M, Gomez MM and Paiacios MA (2003) On-line preconcentration of Pd on alumina microcolumns and determination in urban waters by ICP-MS. Anal Chim Acta 478 209-217. Mooee W, Malanchuk M, Ceockee W, Hysell D, Cohen A and Staea JF (1975) Whole body retention in rats of different compounds following... 

Figure 4.38. Principle of the FIA preconcentration method. A large sample volume (top) is injected and after appropriate dispersion let pass through a microcolumn (shown as boxed area). Thus, locally, concentration of analyte is increased and may be sensed there directly (optosensing) or eluted into a smaller volume (cf. Fig. 4.39).

More advanced designs of the on-line preconcentration technique use sophisticated ion-exchange materials [576, 683, 684, 1217], time-based injection rather than valve injection [576, 712, 1228], and, most importantly, a countercurrent operation of the microcolumn [684, 712], an operation mode that prevents any matrix material from entering the flowthrough detector even during the preconcentration period. Thus, in Fig. 

Munaf et al. (1990) utilized microcolumn technique for preconcentration and LC separation of mercury compounds in waste water samples, using cystein-acetic acid as the mobile phase. After separation, the mercury compounds were digested on-line" with peroxodisulphate at room temperature, using Cu(ll) as a catalyst. The mercury was then reduced by alkaline Sn(ll) and determined by CV-AAS. The detection limit was calculated at 5 ng/L. 

Flow injection is a method using on-line discrimination chemical reactions. Direct selective preconcentration is performed on microcolumns, the analytes being concentrated up to three to four orders of magnitude and injected into the detector. Usually as separation techniques ion-exchange, liquid-liquid extraction, gas diffusion are used. Flow injection systems are connected either to ETA AS or ICP-AES detection systems. These methods have been used for determinations of redox species such as Crflll)/ Cr(IV), Fe(II)/Fe(III), As(III)/As(V), Se(IV)/Se(VI) in soil extracts and water samples. 

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