Preconcentration organic compounds

Namiesnik et al. [33] have reviewed the analysis of soils and sediments for organic contaminants. They discuss methods of sample preparation and isolation-preconcentration prior to instrumental determination. Compound classes discussed include volatile organic compounds, polychlorobiphenyls, polyaromatic compounds, pesticides and polychlorodibenzo-p-dioxins and polychlorodibenzofurans. 

EPA. 1988g. Method T03. Method for the determination of volatile organic compounds in ambient air using cryogenic preconcentration techniques and GC with flame ionization and electron capture detection. Compendium of methods for the determination of toxic organic compounds in ambient air. Atmospheric Research and Exposure Assessment Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, RTP, NC. EPA/600/4-89/017. 

Another of the new techniques for extractive preconcentration, separation, and/or purification of metal chelates, biomaterials, and organic compounds is based on the use of surfactant micellar systems. 

Rhoderick GC, Miller WR. 1990. Multipoint calibration of a gas chromatograph using cryogenic preconcentration of a single gas standard containing volatile organic compounds. Anal Chem 62 810-815. 

McCaffrey, C. A., J. MacLachlan, and B. I. Brookes, Adsorbent Tube Evaluation for the Preconcentration of Volatile Organic Compounds in Air for Analysis by Gas Chromatography-Mass Spectrometry, Analyst, 119, 897-902 (1994). 

The handling and disposal problems associated with the use of liquid solvent extractors have resulted in increased attention to the separation and preconcentration of organic compounds in water by collection in synthetic polymers followed by elution with an organic solvent (2). For example, selective collection and concentration of organic bases on methylacrylic ester resin from dilute water samples have been reported (3). Such collection techniques are especially well-suited to flow-injection measurement techniques. In this study, ionizable organic analytes such as salicylic acid and 8-hydroxyquinoline (oxine) were extracted into a polymer and then back extracted by an aqueous solution. Amperometric measurement using a flow-injection technique was employed to monitor the process. 

T. Noy, E. Weiss, T. Herps, H. van Cruchten and J. Rijks, On-line combination of liquid chromatography and capillary gas chromatography. Preconcentration and analysis of organic compounds in aqueous sample , J. High Resolut. Chromatogr. Chromatogr. Commun. 11 181-186(1988). 

TO-12 Cryogenic preconcentration and direct flame ionization detection Nonmethane organic compounds... 

Environmental research interests have recently extended from persistent hydrophobic organic chemicals to more hydrophilic organic compounds. The latter include some polar pesticides, many pharmaceuticals and personal care products, microbial toxins, and endocrine disrupting compounds.4 Polar organic compounds are often present at low concentrations in the aquatic environment, which poses a problem for most conventional sampling and analytical procedures. Recently, considerable effort has been directed toward the development of extraction methods suitable for the preconcentration of polar organic compounds commonly found in water bodies. Many of these methods use... 

Creaser, C.S., D.J. Weston, and B. Smith. 2000. In-membrane preconcentration/membrane inlet mass spectrometry of volatile and semivolatile organic compounds. Anal. Chem. 72 2730-2736. 

A1 As Be Co, Mo, V Cu, Pb cio2 Ge Pb trace metals U, Th, Po, Ra Organic compounds in water include the following (122) spectrofluorometric, neutron activation hplc coupled to icp / aes AAS icp / aes potentiometric ion chromatography preconcentration reaction followed by spectrophotometry preconcentrated as various complexes OC-spectroscopy and liquid scintillation... 

Solid-phase microextraction (SPME) — is a procedure originally developed for sample preconcentration in gas chromatography (GC). In this procedure a small-diameter fused silica optical fiber, coated with a liquid polymer phase such as poly(dimethylsiloxane), is immersed in an aqueous sample solution. The -> analytes partition into the polymer phase and are then thermally desorbed in the GC injector on the column. The same polymer coating is used as a stationary phase of capillary GC columns. The extraction is a non-exhaustive liquid-liquid extraction with the convenience that the organic phase is attached to the fiber. This fiber is contained in a syringe, which protects it and simplifies introduction of the fiber into a GC injector. Both uncoated and coated fibers with films of different GC stationary phases can be used. SPME can be successfully applied to the analysis of volatile chlorinated organic compounds, such as chlorinated organic solvents and substituted benzenes as well as nonvolatile chlorinated biphenyls. 

The term solid-phase extraction was introduced by personnel of the J. T. Baker Company in 1982. The method consists of retention of the analytes from a liquid or gaseous sample to a solid stationary phase and subsequent removal of analytes using an appropriate eluent. The main purpose of SPE is isolation and preconcentration of compounds of interest or sample clean-up and simplification of the matrix. Application of this sample preparation technique also allows extract fractionation. As a result of significant reduction in the volume of organic solvents used, high recovery, and the possibility of process automation, SPE is a good alternative for conventional liquid-liquid extraction. According to their affinity for the compound of interest, stationary phases are classified as follows ... 

A GC equipped with an appropriate detector is the most frequently used analytical technique for determining the concentrations of 1,1-dichloroethane in air, water, soil, fish, diary products, and various foods. Volatile organic compounds in environmental samples may exist as complex mixtures or at very low concentrations (ppt to ppb range). Subsequently, the GC technique must be supplemented by some method of sample preconcentration. 

Blanchard and Hardy (1985, 1986) developed a method that allows for continuous monitoring or intermittent analysis of volatile organic priority pollutants in environmental media. The method is based on permeation of volatile organic compounds through a silicone polycarbonate membrane from wastewater sample matrix, into an inert gas stream and directed into a capillary GC/FID via a sampling loop (Blanchard and Hardy 1986). Advantages of this procedure are that it is simple, it does not require time-consuming preconcentration steps, and it can be used either in the field or in the laboratory. 

Supercritical fluid extraction (SFE), usually with carbon dioxide and, often, with a modifier, has become of increasing interest in the last few years because of its selectivity, preconcentration effect, efficiency, simplicity, rapidity, cleanness, and safety, mainly concerning the extraction of organic compounds prior to separation and detection by chromatographic techniques. It has several advantages over classical solvent extractions, in comparison with recent extraction techniques. Approaches to obtain quantitative extractions, including fluid choice, extraction flow rate, modifiers, pressure, and temperature, are presented, as well as the potential for SFE to extract polynuclear aromatic hydrocarbons (PAHs) from soils, sediments, and biota. Improvements and new environmental applications are also reported. 

An on-line technique coupling preconcentration via a precolumn packed with PGC and LC with a PGC analytical column has been applied to the trace-level determination of some polar and water-soluble organic pollutants from environmental waters.As these analytes are much more retained by the graphite surface than by silica Cig, preconcentration on the PGC precolumn cannot be coupled on-line with a widely used and more efficient Cjg silica analytical columns. In this study, applications were presented for the trace-level determination of 2-chloro-4-aminophenol, chloroanilines, amino-phenols, and cyanuric acid these organic compounds are included in the EC environmental priority pollutant list. The influence of the sample matrix was investigated with drinking and river water samples. 

The efficiency and selectivity of fuUerenes as adsorbents from aqueous solutions has resulted in a number of analytical applications of C g and C g as chromatography stationary phases, as chemical sensors and, especiaUy, as sorbents for the preconcentration of analytes. In the latter case, the adsorption properties of fuUerenes are more useful for inorganic and organometaUic compounds than for organic compounds. On the other hand, the fuUerenes exhibit a selectivity for aromatic compounds and planar molecules that makes them very attractive as stationary phases for liquid chromatography. 

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