Preconcentration and extraction

Ashton and Chan [ 1 ] have reviewed the techniques for the collection of seawater samples preservation, storage, and prevention of contamination are all discussed. The most appropriate measurement techniques, preconcentration and extraction, method validation, and analytical control are all covered. The apparent aluminium content of seawater stored in ordinary containers such as glass and polyethylene bottles decreases gradually, e.g., to half in 2.5 h. But if the samples are acidified with 0.5ml/l concentrated sulfuric acid the aluminium content remains constant for at least one month. Accordingly, samples should be acidified immediately after collection. However, the aluminium could be recovered by acidifying the stored samples and leaving them for at least five hours. 

The other techniques used are less sensitive and could require preconcentration by extraction by the chloroform-dithizone method (6, 45, 64), non-boiling evaporation (39) or by adsorption on W wire loops (44, 65). Preconcentration and extraction methods require great care to be taken in order to avoid contamination and are often time-consuming, and require a fairly large volume of samples. 

FIA techniques for AAS are described in detail in the reference by Tyson. In addition to automated CVAAS and HGAAS, FIA has been used to automate online dilution for the preparation of calibration curves, online matrix matching of solutions, online preconcentration and extraction for GFAAS, automated digestion of samples, and much more. Commercial FIA systems are available for most AAS instmments. 

The concentrations of individual PAH in water systems range from less than 1 ppt (pg per g) in pure ground water supplies to greater than 1 ppm (pg per g) in heavily contaminated sewage. Therefore, some preconcentration and extraction techniques are required to raise the concentrations to levels at which identification and quantitative analysis are possible. Because PAHs may only represent as little as 0.01% of the total organic fraction present in the water sample, the analytical scheme must be devised so that the PAHs can be analyzed without the interference from the other pollutants. Since the concentrations are so low, serious errors may occur from losses or contamination during sampling or the analytical... 

J. Ricanyovd, R. Gadzala-Kopciuch, K. Reiffova, Y. Bazel and B. Buszewski, Molecularly imprinted adsorbents for preconcentration and extraction combined with HPLC, Adsorption, 16 (4-5) 473-483, 2010. 

Used in preconcentration and extraction separation of heavy metal ions gives colour reactions with many metals in extraction-photometric detn. of Ag 462 nm, e 31000), Bi, Pb, Zn 538 nm, e 93000), Cd, Cu, Pd, Hg 485 nm, e 71000), T1 and other elements. Bluish-black cryst. (EtOH aq.). Sol. aq. 

Recent publications indicate the cloud-point extraction by phases of nonionic surfactant as an effective procedure for preconcentrating and separation of metal ions, organic pollutants and biologically active compounds. The effectiveness of the cloud-point extraction is due to its high selectivity and the possibility to obtain high coefficients of absolute preconcentrating while analyzing small volumes of the sample. Besides, the cloud-point extraction with non-ionic surfactants insures the low-cost, simple and accurate analytic procedures. 

Recently, SPE cartridges and disks have been widely and successfully used in preconcentration processes [1-3]. They reduce solvent usage, disposal costs, and extraction time for sample preparation and obtain large enrichment factors. 

First procedure consists of several stages. 11-molybdo-bismuthphosphate (MBP) is formed and extracted with butyl acetate, stripped with ammonia or acetate buffer solution and determined in aqueous solution using reaction of MBP with Astro Floxine (AF) or other polymethine dyes. Full separation from molybdate excess is not necessary in this procedure as spectiaim of lA differs considerable from dye spectiaim. Therefore sepai ation is simplified and used only as preconcentration step. Concentration factor 50 and good reproducibility make possible determination of low P(V) concentrations at 10 mol/1 level and lower. 

Theoretical and applied aspects of microwave heating, as well as the advantages of its application are discussed for the individual analytical processes and also for the sample preparation procedures. Special attention is paid to the various preconcentration techniques, in part, sorption and extraction. Improvement of microwave-assisted solution preconcentration is shown on the example of separation of noble metals from matrix components by complexing sorbents. Advantages of microwave-assisted extraction and principles of choice of appropriate solvent are considered for the extraction of organic contaminants from solutions and solid samples by alcohols and room-temperature ionic liquids (RTILs). 

Actually, the successful use of cationic surfactants (cSurf), as flotation reagents, frothers, metal corrosion inhibitors, pharmaceutical products, cosmetic materials, stimulates considerable increase in their production and as a result increases their content in natural water. As cationic surfactants are toxic pollutants in natural water and their maximum contaminant level (MCL) of natural water is 0.15-4.0 mg/dm, it is necessary to use methods for which provide rapid and reliable determination with sensitivity equal to at least 0.1 of MCL. Practically most sensitive methods of cationic surfactant determination include the preconcentration by extraction or sorption. Analytical methods without using organic solvents are more preferable due to their ecological safety. 

The aqueous micellai solutions of some surfactants exhibit the cloud point, or turbidity, phenomenon when the solution is heated or cooled above or below a certain temperature. Then the phase sepai ation into two isotropic liquid phases occurs a concentrated phase containing most of the surfactant and an aqueous phase containing a surfactant concentration close to the critical micellar concentration. The anionic surfactant solutions show this phenomenon in acid media without any temperature modifications. The aim of the present work is to explore the analytical possibilities of acid-induced cloud point extraction in the extraction and preconcentration of polycyclic ai omatic hydrocai bons (PAHs) from water solutions. The combination of extraction, preconcentration and luminescence detection of PAHs in one step under their trace determination in objects mentioned allows to exclude the use of lai ge volumes of expensive, high-purity and toxic organic solvents and replace the known time and solvent consuming procedures by more simple and convenient methods. 

Flow-injection (FI) on-line analyte preconcentration and matrix removal techniques greatly enhance the performance of atomic spectrometry [348], By using USN with membrane desolvation (MDS) as the interface, FI sorbent extraction can be directly coupled with ICP-MS for the analysis of organic solutions [349]. 

Statham [448] has optimised a procedure based on chelation with ammonium dithiocarbamate and diethylammonium diethyldithiocarbamate for the preconcentration and separation of dissolved manganese from seawater prior to determination by graphite furnace atomic absorption spectrometry. Freon TF was chosen as solvent because it appears to be much less toxic than other commonly used chlorinated solvents, it is virtually odourless, has a very low solubility in seawater, gives a rapid and complete phase separation, and is readily purified. The concentrations of analyte in the back-extracts are determined by graphite furnace atomic absorption spectrometry. This procedure concentrates the trace metals in the seawater by a factor of 67.3. 

In many applications, such as the analysis of mercury in open ocean seawater, where the mercury concentrations can be as small as 10 ng/1 [468,472-476], a preconcentration stage is generally necessary. A preliminary concentration step may separate mercury from interfering substances, and the lowered detection limits attained are most desirable when sample quantity is limited. Concentration of mercury prior to measurement has been commonly achieved either by amalgamation on a noble-metal metal [460,467, 469,472], or by dithizone extraction [462,472,475] or extraction with sodium diethyldithiocarbamate [475]. Preconcentration and separation of mercury has also been accomplished using a cold trap at the temperature of liquid nitrogen. 

Holm et al. [74] used a spectrometry for the determination of 237neptunium in seawater. The actinides are preconcentrated from a large seawater sample by hydroxide precipitation. The neptunium was isolated by ion exchange, fluoride precipitation, and extraction with TTA. 238Neptunium or 235neptunium was used to determine the radiochemical yield. 

With the aim of minimising the time taken in the preconcentration, and extending the chemical analysis of surfactants to more complex aqueous matrices in which very low detection limits are required, preconcentration techniques using solid-liquid extraction with various adsorbent materials, such as XAD [27] and anionic exchange resin [28] have been developed. 

Analytical methods for detecting phenol in environmental samples are summarized in Table 6-2. The accuracy and sensitivity of phenol determination in environmental samples depends on sample preconcentration and pretreatment and the analytical method employed. The recovery of phenol from air and water by the various preconcentration methods is usually low for samples containing low levels of phenol. The two preconcentration methods commonly used for phenols in water are adsorption on XAD resin and adsorption on carbon. Both can give low recoveries, as shown by Van Rossum and Webb (1978). Solvent extraction at acidic pH with subsequent solvent concentration also gives unsatisfactory recovery for phenol. Even during carefully controlled conditions, phenol losses of up to 60% may occur during solvent evaporation (Handson and Hanrahan 1983). The in situ acetylation with subsequent solvent extraction as developed by Sithole et al. (1986) is probably one of the most promising methods. 

Finally, when ultratrace determinations are being performed it is often necessary to preconcentrate the sample or separate the analyte of interest from the matrix. The most commonly employed methods for preconcentration and separation of water samples include evaporation, chelation, coprecipitation, extraction, ion-exchange, chromatography, and electrochemistry. The procedure adopted will depend on the analyte, the form in which it exists, and the sample matrix. 

PCBs in full-fat milk includes four main steps. This first step involves extraction of the PCBs from the matrix. The second step involves preconcentration and cleanup. The third step uses gas chromatographic separation. Finally, the last step involves detection. (5 sentences, 47 words)... 

Extraction can be nsed for separation or isolation of the analyte from the sample matrix or vice versa as well as a preconcentration method. Extraction of metal ions is based on the reaction of weak organic acids with metal ions that give nncharged complexes that are highly solnble in organic solvents as ethers, hydrocarbons, ketones and polychlorinated species (generally chloroform and carbon tetrachloride). The efficacy of the extraction is mainly dependent on the extent to which solntes distribnte themselves between two immiscible solvents. The amonnts of analyte can be determined spectrophotometrically as well as with other available analytical methods. 

In 1985, Ruzicka and Hansen established the principles behind flow injection optosensing [13-15], which has subsequently been used for making reaction-rate measurements [16], pH measurements by means of immobilized indicators [17,18], enzyme assays [19], solid-phase analyte preconcentration by sorbent extraction [20] and even anion determinations by catalysed reduction of a solid phase [21] —all these applications are discussed in Chapters 3 and 4. Incorporation of a gas-diffusion membrane in this type of sensor results in substantially improved sensitivity (through preconcentration) and selectivity (through removal of non-volatile interferents). The first model sensor of this type was developed for the determination of ammonium [13] and later refined by Hansen et al. [22,23] for successful application to clinical samples. 

More recently, some studies have reported the use of supercritical fluid chromatography (SEC) [479,480], Coupling SEC with SEE, sample extraction, preconcentration, and quantification can be performed in a single step. The mobile phase, carbon dioxide, can be modified by adding different... 

This technique of MEUF has also been successfully employed for the recovery of thuringiensin [258], removal of cresols [262], extraction of chromate anion [257], removal of dissolved organic pollutants [256], removal of -alcohols [263],preconcentration and removal of iron [260], and preconcentration of aniline derivatives [261].Kandori and Schechter [264] have given a detailed account of selecting surfactants for MEUF. The design characteristics of micellar enhanced utrafilters and cross-flow ultrafiltration of micellar surfactant solutions have been described by Markets et al. [265]. 

Several studies are devoted to the extraction of phenolic compounds. These compounds are particularly interesting from a practical viewpoint, as phenol derivatives are toxic pollutants that have marked detrimental effects on living organisms in general therefore, the development of effective methods of phenols recovery is a long-standing problem of analytical chemistry. To determine phenolic compounds at the trace level, typically preconcentration and separation from accompanying substances is required, but the extraction of phenolic compounds with conventional solvents is often not quantitative. From a more theoretical viewpoint, phenolic compounds exhibit a wide structural variability, thus, a study of their... 

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