Extraction Methods in Trace Analysis

Wiestaw Zyrnicki, Jolanta Borkowska-Burnecka, and Anna Lesniewicz 

Extraction processes and phenomena commonly occurring and easily observed in nature and the environment are of extreme importance and of enormous potential. Therefore, extraction processes have been widely applied in many areas of daily life, with special utilization in chemical and related technologies as well as chemical analysis. 

Extraction techniques are universal, standardized, and commonly applied sample preparation methods (see for example [1 ]). Development of extraction methodology in the past 20 years has been eventful and impressive. Universalism of these techniques is associated with applicability to analyses of a great diversity of organic compounds (including DNA and RNA) and elements and their speciation forms, which are present in different sample matrices both in trace and macro quantities. 

Extraction can be used as an efficient and selective sample preparation method before analysis by chromatographic, spectroscopic, electroanalytical, or electrophoretic methods (see for example [5-10]). International norms from the International Standards Organization, US Food and Drug Administration, and US Environmental Protection Agency recommend application of extraction methods in analysis of food products and environmental and pharmaceutical samples. Novel ideas and new views concerning extraction have led to many controversies about terminology and to reallocation and softening of the boundaries between extraction and other analytical sample treatment techniques. 

Extraction is a mass exchange process in a multiphase and multicomponent system that involves transfer and distribution of one or more components into two 

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Extraction or dissolution almost invariably will cause low-MW material in a polymer to be present to some extent in the solution to be chromatographed. Solvent peaks interfere especially in trace analysis solvent impurities also may interfere. For identification or determination of residual solvents in polymers it is mandatory to use solventless methods of analysis so as not to confuse solvents in which the sample is dissolved for analysis with residual solvents in the sample. Gas chromatographic methods for the analysis of some low-boiling substances in the manufacture of polyester polymers have been reviewed [129]. The contents of residual solvents (CH2C12, CgHsCI) and monomers (bisphenol A, dichlorodiphenyl sulfone) in commercial polycarbonates and polysulfones were determined. Also residual monomers in PVAc latices were analysed by GC methods [130]. GC was also... 

The method detection limit is, in reality, a statistical concept that is applicable only in trace analysis of certain types of substances, such as organic pollutants by gas chromatographic methods. The method detection limit measures the minimum detection limit of the method and involves all analytical steps, including sample extraction, concentration, and determination by an analytical instrument. Unlike the instrument detection limit, the method detection limit is not confined only to the detection limit of the instrument. 

Di Bonito, M., Breward, N., Crout, N., Smith, B., and Young, S. (2008). Soil pore water extraction methods for trace metals determination in contaminated soils. In Environmental Geochemistry Site Characterization, Data Analysis, and Case Histories (B. De Vivo, H. E. Belkin, and A. Lima, eds.). Elsevier Science Publishers, Amsterdam, The Netherlands. 

Ensuring high-quality analytical performance in trace analysis, if separation of sample components by extraction is indispensable, requires implementation of the appropriate extraction method and establishment of suitable operational parameters to ensure a high efficiency of extraction. Selection of extraction conditions is crucial for quantitative recovery of analyte, or at least for sufficient effectiveness. If an aqueous solution is one of the extraction phases, problems such as complex-ation, hydrolysis, and solvation can play an important role. Extraction of elements from aqueous to organic phase often requires selection of appropriate ligands and control of pH. 

Another example of ultrasound use is leaching of organic impurities from different kinds of samples. The main analytes of interest are PAHs, which are widespread in soil, sediment, dust, and particulate samples [55]. USE is recommended as a fast, efficient, and direct environmental sample preparation method for determination of PCBs, nitrophenols, pesticides, or polymer additives. Organometallic and biologically active compounds (such as vitamins A, D, and E) present in samples in trace quantities, can be extracted from animal and plant tissues with the aid of ultrasonic wave energy [59]. Table 6.6 presents some typical applications of USE in trace analysis of biological and environmental samples [60]. 

The currently most used method comprises an initial step in which the compound of interest is retained by the sorbent-containing column, followed by the elimination, through rinsing, of the greatest possible number of undesired substances for the subsequent measurement. The analyte is then recovered in a small volume of an appropriate solvent as a solution strongly enriched. This extraction procedure allows not only isolation of the analyte but also its pre-concentration, which is particularly useful in traces analysis. 

The feasibility of extracting selectively and rapidly herbicide residues, including some phenylureas, in soil by water heated at 90°C and collecting analytes with a Carbograph 4 SPE cartridge set online with the extraction cell (Figure 25.8) was evaluated.Recovery of neutral and acidic herbicides ranged between 81 and 93%, except for two acidic herbicides (63%). For the analytes considered, comparison of methods showed hot water extraction was overall more efficient than Soxhlet and sonication extraction techniques. Rapid trace analysis of polar and... 

As mentioned previously, many instrumental methods can handle a sample as it is. Sometimes processing is called for to comply with standardized procedures or to create conditions for the specific determination of a substance. In trace analysis, sample processing is performed to concentrate a trace constituent to a level at which it can be determined by a given instrumental technique or to eliminate interfering constituents, or both. Some of the techniques used are solvent extraction, evaporation, distillation, precipitation and ashing. 

Many of the clean-up methods used in trace analysis exploit HPLC mobile and stationary phases in a somewhat different way. For example, a crude sample extract can be loaded onto a small cartridge packed with a suitable adsorbent under conditions such that the analyte (and its internal standard if present) are strongly retained. Washing the loaded cartridge removes many of the coextracted compounds and the analyte plus SIS can then be eluted from the cartridge by a suitable change of solvent in effect this is a kind of binary chromatography, i.e., a compound is either retained on the stationary phase or it is not. This approach (solid phase extraction... 

This simple principle is still apphed in trace analysis, often in miniaturized form, as either an extraction procedure per ie or as a clean-up method (or both). Classical LLE uses large amounts of organic solvent (an environmental concern) and is slow, while the various miniaturized methods use much smaUer amounts of solvent, are much faster and more amenable to automation, and... 

In the past, lanthanides were almost exclusively analyzed with element-specific methods such as AAS and ICP. However, spectral interferences are observed in trace analysis of lanthanides in geological samples, so that time-consuming extractions or group separations on ion exchangers have to be carried out first. In many cases, pre-concentrations are necessary, because the detection... 

Different kinds of partition equilibria are found in chemical sensors. In sensors on the basis of ion-selective electrodes with liquid membranes, specific ligands are dissolved which form complexes with sample ions. In this way, at the sensor surface a concentration-dependent galvani potential difference is formed which can be measured potentiometrically. The principle of extraction photometry is applied, in modified manner, in optical sensors. Extraction photometry is a classical method of trace analysis, where the sample solution is extracted using a water-immiscible solution of a ligand which is able to... 

A number of techniques have been developed for the trace analysis of siUcones in environmental samples. In these analyses, care must be taken to avoid contamination of the samples because of the ubiquitous presence of siUcones, particularly in a laboratory environment. Depending on the method of detection, interference from inorganic siUcate can also be problematic, hence nonsiUca-based vessels are often used in these deterrninations. SiUcones have been extracted from environmental samples with solvents such as hexane, diethyl ether, methyl isobutylketone, ethyl acetate, and tetrahydrofuran (THF)... 

An on-line concentration, isolation, and Hquid chromatographic separation method for the analysis of trace organics in natural waters has been described (63). Concentration and isolation are accompHshed with two precolumns connected in series the first acts as a filter for removal of interferences the second actually concentrates target solutes. The technique is appHcable even if no selective sorbent is available for the specific analyte of interest. Detection limits of less than 0.1 ppb were achieved for polar herbicides (qv) in the chlorotriazine and phenylurea classes. A novel method for deterrnination of tetracyclines in animal tissues and fluids was developed with sample extraction and cleanup based on tendency of tetracyclines to chelate with divalent metal ions (64). The metal chelate affinity precolumn was connected on-line to reversed-phase hplc column, and detection limits for several different tetracyclines in a variety of matrices were in the 10—50 ppb range. 

RAPID PHOTOMETRIC METHODS FOR WATER ANALYSIS IN FIELD. EXTRACTION-FREE RAPID PROCEDURES FOR THE DETERMINATION OF TRACES OF REGULATED METALS WITH l-(2-PYRIDYLAZO)-NAPHTOL-2... 

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