Trace analysis preconcentration

The first two aspects entail relatively high concentrations of surfactants. In the last case, trace amounts are to be determined. When performing surfactant analysis, preconcentration and/or separation of the different surfactant classes are prerequisites for identifying and quantifying the compound in question. Furthermore, the trend is to analyze the individual components of any surfactant mixture. 

The attractive features of spllti ess injection techniques are that they allow the analysis of dilute samples without preconcentration (trace analysis) and the analysis of dirty samples, since the injector is easily dismantled for cleaning. Success with individual samples, however, depends on the selection of experimental variables of which the most Important sample... 

Hot splitless WCOT 0.5 ppm (FID) without preconcentration Lower injection temperature than split Trace analysis Handles dirty samples Automation Flash vaporisation Optimisation required (splitless time, oven temperature, solvent) Limited number of solvents ( solvent effect ) Thermal degradation possible Discrimination possible Poor direct quantification Unsuitable for very polar substances... 

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. 

Energy Dispersive X-ray Fluorescence Analysis Preconcentration of Trace Elements Radionuclide X-ray Fluorecence Analysis Voltammetry... 

Complex matrixes typically cannot be analysed directly to obtain the selectivity and sensitivity required for most trace analysis applications. To circumvent this problem, solid-phase micro extraction techniques were used to preconcentrate analytes selectively prior to gas chromatography/ion trap mass spectrometry analysis. 

The SCE-GC combination began to be explored for trace analysis of organotin compounds and other pollutants. Its main advantage is that SCE accelerates the extraction-preconcentration operations involved in the analytical process95. 

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. 

P. Britz-McKibbin and S. Terabe, On-line preconcentration strategies for trace analysis of metabolites by capillary electrophoresis. J. Chromatogr.A 1000 (2003) 917-934. 

The advantages of CC in ultra trace analysis are shown to be unmistakable. The quantitative reliability of the method was demonstrated by the extension of a calibration graph for phenol to two decades of concentration more when compared with conventional chromatography. A considerable improvement of the signal-to-noise ratio can be achieved in a relatively short time. The method offers excellent prospects for ultra trace analysis in cases where preconcentration of the solute fails. 

Solid-phase microextraction (SPME) for preconcentration, followed by GC/ Ion Trap MS, was used for trace analysis of explosives and their metabolites in seawater [9]. NICI was used with methane as reagent gas. Compounds of interest included RDX, TNT and two of its metabofrtes 2-amino-4,6-dinitrotoluene (2ADNT) and 4-amino-2,6-dinitrotoluene (4ADNT). Although the instrument sensitivity was in low-ppb range, the detection limits for SPME with GC/ITMS... 

To determine ions at mid pg/1 to mg/1 (ppb to ppm) levels with IC, a sample size of 10 to 50/pi is sufficient. To determine ions at lower levels, then a preconcentration or trace enrichment technique has t3rpically to be utilized [20]. With this method, the analytes of interest are preconcentrated on another column in order to "strip" ions from a measured sample volume. This process concentrates the desired species resulting in lower detection limits. However, preconcentration has several disadvantages, compared with a direct method, additional hardware is required. A concentrator column is used to preconcentrate the ions of interest, a sample pump is needed for loading sample, an additional valve is often required for switching the concentrator column in and out-of line with the analytical column and extra time is required for the preconcentration step. It was of interest to explore the development of a high-volume direct-injection IC method that would facilitate trace ion determinations without a separate preconcentration step. This would represent a significantly simpler and more reliable means of trace analysis. 

A study of mercury in Lake Michigan found levels near 1.6 pM (1.6 X 10 12 M), which is two orders of magnitude below concentrations observed in many earlier studies.5 Previous investigators apparently unknowingly contaminated their samples. A study of handling techniques for the analysis of lead in rivers investigated variations in sample collection, sample containers, protection during transportation from the field to the lab, filtration techniques, chemical preservatives, and preconcentration procedures.6 Each individual step that deviated from best practice doubled the apparent concentration of lead in stream water. Clean rooms with filtered air supplies are essential in trace analysis. Even with the best precautions, the precision of trace analysis becomes poorer as the concentration of analyte decreases (Box 5-2). 

J. K. Robinson, M. J. Bollinger, and J. W. Birks, Luminol/H202 Chemiluminescence Detector for the Analysis of NO in Exhaled Breath, Anal. Chem. 1999, 71, 5131. Many substances can be analyzed by coupling their chemistry to luminol oxidation. See, for example, O. V. Zui and J. W. Birks, Trace Analysis of Phosphorus in Water by Sorption Preconcentration and Luminol Chemiluminescence, Anal. Chem. 2000, 72, 1699. 

Preconcentration by electrodeposition is one of the more valuable techniques for electroanalytical trace analysis. In this method the electroactive species to be determined is concentrated by electrodeposition into or onto an electrode placed... 

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. 

Da Silva, C.L., E.C. de Lima, and F.M. Tavares (2003). Investigation of preconcentration strategies for the trace analysis of multi-reside pesticides in real samples by capillary electrophoresis. J. Chromatog. A, 1014 109-116. 

The few articles currently available regarding trace analysis without preconcentration, use in general the graphite furnace technique [102,120, 138] with sample sizes of the order of microliters, and deal with the elements Sb [47, 83], Pb and Bi [48-50], As, Sb, Bi, Sn, Cd, Pb [10, 57, 116] as well as Al, Cr, Sn [6, 62], Co, and Mg [104]. Alkaline earths can be determined directly with the flame method [122, 147], Further techniques of atomic absorption by flame use concentration methods, for example for the determination of small concentrations of tin [17], Te [26], Co, Pb, and Bi [104], and W [106]. From the analytical viewpoint, it is only useful to remove the iron matrix. The extraction of the elements to be determined from the matrix always carries with it the danger of losses and therefore results showing concentrations that are too low. 

Minczewski, J., Chwastowska, J., Dybczyhski, R. Separation and Preconcentration Methods in Inorganic Trace Analysis. E. Horwood, Chichester (1982)... 

Membrane Extraction in Preconcentration, Sampling, and Trace Analysis... 

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