Preconcentration system

Figure 5.12. Hg cold-trap preconcentration system for the determination of mercury by gas-phase absorption. Source [477]... 

Chang et al. [952] used a miniature column packed with a chelating resin and an automatic online preconcentration system for electrothermal atomic absorption spectrometry to determine cadmium, cobalt, and nickel in seawater. Detection limits of 0.12,7 and 35 ng/1 were achieved for cadmium, cobalt, and nickel, respectively, with very small sample volume required (400-1800 xl). 

Beck et al. [61] used flow injection magnetic sector ICP-MS to determine cadmium, copper, nickel, zinc, and manganese in estuarine waters. The online preconcentration system used Toyopearl A-T Chelate 650 H as chelating resin, and was validated for an alkaline water standard reference material (SLEW-2). 

Fig. 5.11 Flow diagram of preconcentration system described by Knapp et al. [41].

For method development and display of the run status, a flow-chart of the TraceCon preconcentration system is used to visuahze the current system state. During the execution of a method the flow chart displays the current activity of the TraceCon apparatus in the run mode. Run errors can also be easily identified, so that runs can be aborted if parts of the system fail. 

Fig. 7.16 Calibration graph of vapour generator linked to gold amalgam preconcentration system.

Experimental designs were used to set up a held flow preconcentration system (six important variables were considered) coupled to a minicolumn concentration system filled with Chelite P... 

A solid -phase preconcentration system was implemented. Several chemical and flow-related parameters potentially influencing the enrichment factor were studied, of which only three were revealed to be significant... 

FI) preconcentration system for determination of trace gold in ore samples was studied by simplex... 

S. Cerutti, S. L. C. Ferreira, J. A. Gasquez, R. A. Olsina and L. D. Martinez, Optimisation of the preconcentration system of cadmium with 1 -(2-thiazolylazo)-7 -cresol using a knotted reactor and flame atomic absorption spectrometric detection, J. Hazard. Mater., 112(3), 2004, 279-283. 

M. C. Yebra and A. Moreno-Cid, Optimisation of a field flow preconcentration system by experimental design for the determination of copper in sea water by flow-injection-atomic absorption spectrometry, Spectrochim. Acta, Part B, 57(1), 2002, 85-93. 

C. R. Teixeira-Tarley, A. F. Barbosa, M. Gava-Segatelli, E. Costa-Figueiredo and P. Orival-Luccas, Highly improved sensitivity of TS-FF-AAS for Cd(II) determination at ng L levels using a simple flow injection minicolumn preconcentration system with multiwall carbon nanotubes, J. Anal. At. Spectrom., 21(11), 2006, 1305-1313. 

E. I. Vereda Alonso, L. P. Gil, M. T. Siles Cordero, A. Garcia de Torres and J. M. Cano Pavon, Automatic on-line column preconcentration system for determination of cadmium by electrothermal atomic absorption spectrometry, J. Anal. At. Spectrom., 16, 2001, 293-295. 

C. Mendiguchia, C. Moreno and M. Garcia-Vargas, Determination of copper in seawater based on a liquid membrane preconcentration system. Anal. Chim. Acta, 460(1), 2002, 35-40. 

In some cases, ultrasonic nebulization or preconcentration is used to enhance detection limits. As, Se, and Sb were measured in cloud water detection limits were 20, 100, and 20 pg/mL, respectively, using pneumatic nebulization and four to five times lower using ultrasonic nebulization [311]. In another study [312], activated charcoal from a 1-L sample volume was used to preconcentrate Pd and Pt in fresh waters. Detection limits were 0.3-0.8 ng/L. An automated online preconcentration system based on a cationic resin (AG50W-X8) was used to measure Cd, Pb, Ni, Cu, and Zn. A preconcentration factor of 30 was obtained even with a sample throughput of 20 samples per hour [313]. 

Matsumura T, Ito H, Yamamoto T, Morita M (1994), Organohalogen Compounds 19 109-112. development of a preconcentration system for PCDDs and PCDFs in seawater", Eds. University of Kyoto, Japan... 

Bosch, O.C., Sanchez, R.F., Cano, P.J., Garcia de Torres, A. Automated on-line separation-preconcentration system for platinum determination by electrothermal atomic absorption spectrometry. Anal. Chlm. Acta 494, 97-103 (2003)... 

The technology of GC-MS can be downsized for field usage and is now commercially available. Inficon (USA) manufactures a field-portable GC-MS, Hapsite. Vapor is withdrawn for 30 s into the Tenax preconcentration system, thermally desorbed into the apolar capillary colmnn with elevated temperature control, and the separated components are finally analyzed by the electron ionization quadrupole mass spectrometer. GB, GD, GA, and HD are detected and identified within 12 min with postulated LOD values of 0.2, 0.5, 8, and 0.3 pg/m (Sekiguchi et al, 2006). Gaseous and weakly volatile (boiling temperature >250°C) CWAs cannot be detected. 

Ultrasonic nebulizers have also been employed in continuous flow systems as interfaces between sample preparation steps in the analytical process and detection by virtue of their suitability for operating in a continuous mode. Thus, preconcentration devices have commonly been coupled to atomic spectrometers in order to increase the sensitivity of some analytical methods. An enhancement factor of 100 (10 due to USNn and 10 due to preconcentration) was obtained in the determination of platinum in water using a column packed with polyurethane foam loaded with thiocyanate to form a platinum-thiocyanate complex [51]. An enhancement factor of 216 (12 with USNn and 18 with preconcentration) was obtained in the determination of low cadmium concentrations in wine by sorption of metallic complexes with pyridylazo reagents on the inner walls of a PTFE knotted reactor [52]. One special example is the sequential determination of As(lll) and As(V) in water by coupling a preconcentration system to an ICP-AES instrument equipped with a USN. For this purpose, two columns packed with two different resins selective for each arsenic species were connected via a 16-port valve in order to concentrate them for their subsequent sequential elution to the spectrometer [53]. 

Although the automated, trace-metal preconcentration system has undergone a number of design changes, the major characteristics are summa-... 

Off-line preconcentration systems are less expensive and easier to handle, but often require very large sample volume (500-1000 ml), in some cases hampering the analytical determination due to the low amount of sample available. Furthermore, off-line methods are more contamination-prone, since they require a great number of subsequent steps of sample treatment. In order to reduce sample... 

In the first case, the voltammetric response can mainly be associated to reduc-tive/oxidative dissolution processes and topotactic or epitactic solid-to-solid transformations, eventually confined to thin surface layers of the parent material (Scholz and Meyer, 1998 Grygar et al., 2000 Scholz et al., 2005). In the second case, among other possibilities, the solid can act as a preconcentrating system for enhancing the signal of the electroactive probe in solution, but also as a catalyst with regard to this process. 

C.R.T. Tarley, S.L.C. Ferreira, M.A.Z. Arruda, Use of modified rice husks as a natural solid adsorbent of trace metals characterisation and development of an on-line preconcentration system for cadmium and lead determination by FAAS, Microchem. J. 77 (2004) 163. 

Fang, Z. L., A sequential injection on-line column preconcentration system for determination of cadmium... 

The second ORNL microcantilever project, funded by the ATF and technically co-directed hy TSA, involves polymer-coated micro cantilevers. In this case, the explosive molecule would be adsorbed on the surface of the polymer, and the swelling or change in physical properties would be measured indicating the presence of an explosive. Several polymers are currently being developed to provide the necessary selectivity for the different types of explosives signatures. The sensitivity is similar to the non-coated cantilever estimated limit of detection of low parts-per-billion (with proper collection and preconcentration system, LOD should approach low parts-per-trillion). Figure 6 illustrates two modes of detection for the coated cantilevers beam stress response and beam resonant frequency response. 

Chen, H., Jin, J. and Wang, Y., 1997, Flow- injection on-line Coprecipitation-preconcentration System Using Copper (II) diethyldithiocarbamate as Carrier for Flame Atomic Absorption Spectrometric Determination of Cadmium, Lead and Nickel in Environmental Samples, Analytica Chimica Acta, 353, 181-188. 

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