Trace preconcentration system

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

Detection - Accepts a sample from the preconcentrator and makes an analysis. Several types of detectors are currently incorporated in trace portals. These detectors include ion mobility spectrometers or mass spectrometers. The detection subsystem needs to be reliable and rugged to perform hundreds to thousands of analyses per day with the necessary sensitivity and specificity required in the trace portal system. Most detectors are concentration-sensitive devices. 

Trace detection portal systems can be mathematically modeled [8], The model provides the basis for describing trace portal subsystems and is independent of the specific sampling technique, preconcentration technology, or detector. Through the model, a relative measure of a trace portal system can be determined, which provides a means for comparing trace detection portals. 

The mathematical model demonstrates the importance of sample collection (r/T), preconcentration (tjc), concentration (C), and detection (k) in a complete trace portal detection system. Of these three subsystems, the detector is the most understood. Considerable information is available that quantifies the sensitivity, specificity, and limits of detection (LOD) for a particular detection method when used for trace explosives detection [13-15], For trace detection portals, the selection of the detection method is based on performance, initial cost, and maintenance issues. The remaining subsystems (sample collection and preconcentration) are the most variable and least understood for their contribution to trace portal performance. Optimizing the explosive removal and transport in sample collection along with preconcentration will enhance the performance of the entire trace detection system. The sensitivity of the detector will help determine the performance needed from the sample collection and preconcentration. 

The preconcentrator is a critical subsystem in a trace detection system because of its ability to collect minute amounts of explosive material. Without preconcentration, the amount of material available to detect would be well below the LOD for many detectors. In addition, the preconcentrator serves as an impedance-matching device between the airflow of the sample collection subsystem and the airflow to the detector. The characteristics of a well-designed preconcentrator include... 

Solid materials are commonly used to retain either analytes or interferents in solution in continuous analytical systems on account of their advantages. Thus, they afford efficient trace preconcentration in a convenient manner, thereby lowering detection and quantification limits and enabling the determination of the target analytes at the required levels. Also, they facilitate the removal of interferents (leachate clean-up) and the storage of analytes as the retained species remain unaltered over long periods due to the inert... 

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

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. 

Amberlite XAD polymeric adsorbents have been used for the preconcentration of trace elements in batch procedures followed by AAS or photometric measurements. The adsorbent series also shows promise in on-line preconcentration systems. Plantz et al.[24] used XAD-4 (polystyrene divinyl benzene based) to collect the bis(carboxymethyl)-dithiocarbamate complexes of Co, Cu, Cr, Ni, Mo, Pt, and V by reversed phase adsorption, and eluted the complexes with 0.1 M NH4OH, with the subsequent determination made by ICP-MS. Xu et al.[25] used the polyacrylate adsorbent XAD-8 to collect the chloro-complex of gold, which was subsequently eluted by ethanol and determined by flame AAS. 

M. Khajeh, Application of modified organo-nanoclay as the sorbent for zinc determination by FAAS An optimisation study of an online preconcentration system, Biol. Trace Elem. Res., 2012, 145(1), 118 125. 

Martinis, E.M Olsina, R.A. Altamirano, J.C., Wuilloud, R.G. (2009) On-line ionic liquid based preconcentration system coupled to flame atomic absorption spectrometry for trace cadmium determination in plastic food packaging materials, Talanta, 78 857 - 862. 

Integration of sample preparation and chromatography by on-line coupling aims at reduction of analysis time. It is apparent from Section 7.1 that these hyphenated techniques are not yet contributing heavily to the overall efficiency of polymer/additive analysis in industry. On-line SFE-SFC requires considerable method development, and MAE-HPLC is off-line. Enhancement of sensitivity for trace analysis requires appropriate sample preparation and preconcentration schemes, as well as improved detection systems. 

Fang et al. [661] have described a flow injection system with online ion exchange preconcentration on dual columns for the determination of trace amounts of heavy metal at pg/1 and sub-pg/1 levels by flame atomic absorption spectrometry (Fig. 5.17). The degree of preconcentration ranges from a factor of 50 to 105 for different elements, at a sampling frequency of 60 samples per hour. The detection limits for copper, zinc, lead, and cadmium are 0.07, 0.03, 0.5, and 0.05 pg/1, respectively. Relative standard deviations are 1.2-3.2% at pg/1 levels. The behaviour of the various chelating exchangers used was studied with respect to their preconcentration characteristics, with special emphasis on interferences encountered in the analysis of seawater. 

Aniline, methyl aniline, 1-naphthylamine, and diphenylamine at trace levels were determined using this technique and electrochemical detection. Two electrochemical detectors (a thin-layer, dual glassy-carbon electrode cell and a dual porous electrode system) were compared. The electrochemical behavior of the compounds was investigated using hydrodynamic and cyclic voltammetry. Detection limits of 15 and 1.5nmol/l were achieved using colourimetric and amperometric cells, respectively, when using an in-line preconcentration step. 

Three methods for trace metal preconcentration were examined liquid-liquid extraction aided by a chelating agent, concentration on a synthetic chelating resin and reductive precipitation with NaBTLt. The latter method gave 1000-fold preconcentration factors with total recovery of Pb and other elements17. Preconcentration of nanogram amounts of lead can be carried out with a resin incorporating quinolin-8-ol (3)18. Enhancement factors of 50-100 can be achieved by such preconcentration procedures followed by determination in a FLA (flow injection analysis) system limits of detection are a few pg Pb/L19. 

J.E. Parmeter, G.A. Eiceman andJ.E. Rodriguez, Trace Detection of Narcotics Using a Preconcentrator/ Ion Mobility Spectrometer System, NIJ Report 602-00, April 2001. 

Liquid chromatography cleanup on a LiChrosorb Diol column has been further proposed for the offline purification of chloramphenicol residues from bovine muscle and eggs (32). An online approach based on reversed-phase principles has also been described for isolation of chloramphenicol residues from swine kidney by an automated column switching system (63). Use of a protein exclusion column (Hisep) has been also suggested in an online trace-enrichment method for the determination of chloramphenicol in animal tissues (52). By employing a column-switching system, all chloramphenicol that eluted from the protein exclusion column was trapped at the entry of a 5 m Supelcosil LC-18 preconcentration column, to be subsequently back-flashed into the analytical column. 

S. Cancela and M. C. Yebra, Flow-injection flame atomic absorption spectrometric determination of trace amounts of cadmium in solid and semisolid milk products coupling a continuous ultrasound-assisted extraction system with the online preconcentration on a chelating ami-nomethylphosphoric acid resin, J. AO AC Int., 89(1), 2006, 185-191. 

Every coupling application favors one part of the coupling system. A dominating chromatography part leads to the speciation analysis [5,6,26,27]. The elemental specific detection facilities of atomic spectrometry are strongly favored over the multielement capabilities. An inversion of this construction leads to multielement trace analysis in complex matrices with the use of chromatographic equipment as powerful preconcentration and matrix elimination tool [13k The ability of chromatography for a further time resolution between the separated traces is not really required because of the excellent elemental specific detection capabilities of atomic spectrometry. 

As pointed out above, IC is a well-established method for the analysis of inorganic anions and has become the method of choice in many application areas. Many techniques are available using singlecolumn [46] or dual-column systems with various detection modes. IC can be used both for analytical and preparative purposes. Large sample volumes, up to 1300 pul, can be injected to determine trace anions and cations and to attain detection limits of 10-400 ng/1. For determinations at a pig/1 to mg/1 level, a sample size of 10-50 xl is sufficient. Preconcentration is necessary for lower concentrations (an additional column, a sample pump, an extra valve and an extra time are the disadvantages of this approach [47]). With an IEC column and isocratic... 

Katarina, R.K., N. Lenghor, and S. Motomizu. 2007. On-line preconcentration method for the determination of trace metals in water samples using a fully automated pretreatment system coupled with ICP-AES. Anal. Sci. 23 343-350. 

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