Sampling and Preconcentration Techniques

Different analytical strategies have been employed to increase the sensitivity and specificity of IMS-based instruments for detection of CWAs and toxic indnstrial chemicals (TICs). Dopants, such as acetone, are utilized to enhance the performance of IMS instruments in several commercial instruments. A different approach to increase performance was to operate at pressures below or above the ambient pressnre. In the former case, it was reported that the reduced pressure doubled the resolution of the DMS, thus improving the specificity of the device. In the latter case, the IMS was operated at pressures up to 4,560 torr (6 bar) for detection of DMMP (commonly used as a simulant for nerve agents) and other compounds. Resolution increased, to a certain extent, with pressure (and the electric field strength), but once clnstering effects became dominant, the resolution did not increase as theory predicted.  

The combination of a SPME device with a pyrolysis gas chromatographic (GC) IMS system improved the limit of detection of tributylphosphate (TBP, which served as a simulant) in water by a factor of 20 compared to the same system without the SPME device. SPME fibers were also used to sample headspace vapors of several types of nerve agents, and the fibers were introduced directly into a modified ESI source for subsequent detection by IMS and mass spectrometry (MS). A SPME-IMS system, with thermal desorption, was also used to screen soil samples for precursor and degradation products of CWAs, and it was found that fibers of polydimethyl-siloxane (PDMS) were superior to PDMS-divinylbenzene fibers.  

Direct sampling of water sources or other liquid samples with an ESI inlet coupled to an IMS for detection of CWAs, their precursors, or degradation products has 

Several examples of the research involving detection of CWAs, their precursors, and degradation products were given in the previous discussion. Eor obvious reasons, the open literature does not contain reports about operational experience with CWAs and the performance of detection systems even in exercises. With regard to the actual detection limits for CWAs of IMS-based detectors, one can refer to the specifications presented by the manufacturers, which usually state that performance conforms to the operational requirements without giving actual substantiated quantitative results. A historical perspective of the development of CWA detectors based on IMS technology is given here and is followed by a state of the art overview. 

Programs to develop IMS-based detectors and monitors for CWAs were undertaken with the support of defense establishments in several governments, notably the United Kingdom and United States. In the United States, research toward the development of an automatic chemical agent detector and alarm (ACADA) was begun but later discontinued. Efforts were resumed by Smiths Detection, and the result has been placed into service as the GID-3 and its later models, like the GID-M. The intention for this analyzer is to continuously monitor the presence of CWAs in ambient air and sound the alarm when threshold values are exceeded. The GID-3 and all other IMS-based analyzers are regarded as point sensors and cannot determine chemical compositions at distances greater than a few meters in the absence of breezes. 

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Due to the high sensitivity of the UV-detection and less problematic UV-absorption maximum values (around 365 nm), simpler sample cleanup and preconcentration techniques were developed, as compared to the other antibiotic groups. 

For analysis of solutions, ICP-mass spectrometry (ICP-MS) is very promising (Houk et al., 1980 Houk, 1986 Bacon et al., 1990). Recent advances in separation and preconcentration techniques are discussed by Horvath et al. (1991). Bacon et al. (1990) report that although ICP-MS is a multi-element technique, recent papers tend to concentrate on a small number of target elements. With isotope dilution mass spectrometry (IDMS), detection limits are further reduced (Heumann, 1988) IDMS is also suitable for accurate speciation in very low concentration levels of elements (Heumann, 1990). For the direct analysis of solid samples, glow discharge mass spectrometry (GD-MS) (Harrison etal., 1986) is of interest. Tolg (1988) has suggested that a substantial improvement in the absolute detection power of GD-MS, as applied to micro analysis, can be expected, at least in comparison with the ICP as ion source. 

The separation performance and sensitivity of a capillary electrophoresis system coupled to a phosphorous-specific flame photometric detector (FPD) has been reported for the detection of alkylphosphonic acids l20 221. The liquid junction used to decouple the electric field from the FPD showed a negligible influence on the performance of the system as compared with online UV detection. The use of an on-column sample stacking preconcentration technique allowed for injection of 900 nL. With the large injection, the detection limits for the alkylphosphonic acids in water were 0.1-0.5 xgmL 1. 

Bruland and Franks [15] investigated the determination of Cu, Cd, Zn and Ni in seawater by graphite-furnace atomic absorption spectrometry, carrying out a strict comparison of sampling techniques and preconcentration techniques (solvent extraction and chelating resin methods) [15]. 

A method for analysis of polar pesticides in wine by the use of automated in-tube SPME coupled with LC/ESI-MS was proposed (Wu et al., 2002). In-tube SPME is a microextraction and preconcentration technique that can be coupled on-line with high-performance liquid chromatography (HPLC), suitable for the analysis of less volatile and/ or thermally labile compounds. This technique uses a coated open tubular capillary as an SPME device and automated extraction. Using a polypyrrole coating, six phenylurea pesticides (diuron, fluometuron, linuron, monuron, neburon, siduron) and six carbamates (barban, car-baryl, chlorpropham, methiocarb, promecarb, propham) were analyzed in wine. Structures of compounds are reported in Fig. 9.4. Due to the high extraction efficiency of the fiber toward polar compounds, benzene compounds, and anionic species, LODs ranging between 0.01 and 1.2pg/L were achieved, even if the sample ethanol content affects the recoveries of analytes. 

Since its introduction, SPME has found numerous applicahons in the analysis of different classes of compounds present in various matrices. Several analytical methods for the determination of OCPs in water samples which make use of SPME as extracting and preconcentrating technique have been described. Magdic and Pawliszyn analyzed environmental water samples for the determination of OCPs using a PDMS-coated hber (him thickness 100 /rm). PDMS was preferred to other commercially available coating, i.e., polyacrylate, the latter being... 

Liquid-liquid extraction (LLE) is among the oldest sample extraction and preconcentration techniques available in analytical chemistry. LLE is a method whereby two immiscible phases, generahy an organic solvent and an aqueous solution, are brought into contact in order to extract one or more analytes from one phase into the other. If the receiving phase has a smaller volume than the donor phase, preconcentration can be effected. The separation mechanism is, like SPE, based on partitioning. At equilibrium, the partition coefficient of analyte i (Ki) in a two-phase system is given by... 

EDCs in the aquatic environment are often present in complex matrices such as effluent samples. For this reason, wide ranges of sample preparation and preconcentration techniques have been employed in conjunction with analytical separations. Preconcentration is often necessary due to sensitivity limitations of the instrumental techniques. 

This is followed, in Chapter 3, by the description of the analytical procedures used for monitoring the presence of uranium in the environment air, water, soil, and plants. As there is a large variety of sample types, there is no universal procedure for all environmental samples. Therefore, we present a myriad of sample treatment procedures and preparation methods as well as some separation and preconcentration techniques. Several examples of analytical procedures, based on the sample preparation methods, are described to demonstrate the diversity required for characterizing environmental samples. 

SPME is a fast, simple, and green sample preparation technique that can easily combine the process of sample preconcentration and GC or HPLC determination. However, in some cases, it still has difficulty in the fabrication of SPME fibers. In 2006, Lee s group reported a novel extraction and preconcentration technique termed micro-solid-phase extraction (p-SPE), based on the packing of sorbent material in a sealed porous polypropylene membrane envelope. Recently, Lee s group reported... 

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). 

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... 

Many process mixtures, notably fermentations, require sample preconcentration, microdialysis, microfiltration, or ultrafiltration prior to analysis. A capillary mixer has been used as a sample preparation and enrichment technique in microchromatography of polycyclic aromatic hydrocarbons in water.8 Microdialysis to remove protein has been coupled to reversed phase chromatography to follow the pharmacokinetics of the metabolism of acetaminophen into acetaminophen-4-O-sulfate and acetaminophen-4-O-glucu-ronide.9 On-line ultrafiltration was used in a process monitor for Aspergillus niger fermentation.10... 

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. 

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. 

At present, inductively coupled plasma mass spectrometry provides a unique, powerful alternative for the determination of rare earths in natural samples [638,639]. Nevertheless, its application to the determination of rare earths at ultratrace concentration level in seawater is limited, because highly saline samples can cause both spectral interferences and matrix effects [640]. Therefore, a separation of the matrix components and preconcentration of the analytes are prerequisites. To achieve this goal, many preconcentration techniques have been used, including coprecipitation with... 

Winge et al. [730] have investigated the determination of twenty or more trace elements in saline waters by the inductively coupled plasma technique. They give details of experimental procedures, detection limits, and precision and accuracy data. The technique when applied directly to the sample is not sufficiently sensitive for the determination of many of the elements at the low concentrations at which they occur in seawater, and for these samples preconcentration techniques are required. However, it has the advantages of being amenable to automation and capable of analyzing several elements simultaneously. 

The application of the Chelex 100 resin separation and preconcentration, with the direct use of the resin itself as the final sample for analysis, is an extremely useful technique. The elements demonstrated to be analytically determinable from high salinity waters are cobalt, chromium, copper, iron, manganese, molybdenum, nickel, scandium, thorium, uranium, vanadium, and zinc. The determination of chromium and vanadium by this technique offers significant advantages over methods requiring aqueous final forms, in view of their poor elution reproducibility. The removal of sodium, chloride, and bromide allows the determination of elements with short and intermediate half-lives without radiochemistry, and greatly reduces the radiation dose received by personnel. This procedure was successfully applied in a study of... 

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