Extracts , contaminated, analysis

Commonly used methods for the determination of petroleum hydrocarbon contamination in soil are modifications of Environmental Protection Agency method 418.1, which use sonication or a Soxhlet apparatus for analyte extraction and either infrared spectrometry [5] or gas chromatography with flame ionization detection [6-7] for extract analysis. Regardless of the analytical method following the extraction, both modifications use Freon-113, which has been implicated as a cause of ozone depletion. Therefore, alternative methods are being sought for the determination of hydrocarbon contamination in environmental samples that reduce the need for this halogenated solvent. 

For example, if gasoline is suspected to be the sole contaminant, the method will use purge-and-trap sample introduction. If higher-boiling petroleum fractions (diesel, middle distillates, motor oil) are the contaminants, the analysis will use direct injection and hotter oven temperatures. Mixtures or unknown contamination may require both volatile range and extractable range analyses. Alternatively, a single injection can be used to analyze the entire sample, but the extraction method must not use a solvent evaporation step. 

In addition to extractive analysis techniques, other analytical and process metrics are routinely used to characterize and profile the hazard level of chemical agent in secondary waste at chemical agent disposal facilities. These include the short-term exposure limit (STEL), the vapor screening level (VSL), the shortterm limit (STL), and the Army s 0, IX, 3X, and 5X designations for various levels of agent contamination. These metrics are explained briefly below and summarized in Table 3-3. 

The objective of our work was to produce extracts which, contained a wide range of organic contaminants for analysis by GCMS. Two extraction techniques were used micro steam distillation and liquid-liquid extraction using high-speed homogenisation. 

In case of hydrophobic compounds, which strongly adsorb to particles, e.g. pentabro-modiphenylether or 5 and 6 ring polycyclic aromatic hydrocarbons, special care is required to ensure complete extraction of the particle bound fraction. Separate analysis of SPM and of the liquid would be a good option. If it can be justified, for example, by consideration of contaminant partitioning, analysis of the SPM fraction as surrogate for whole water might be appropriate. Nevertheless, in water bodies with extremely low SPM content (<3mg/L) the dissolved fraction of those contaminants contributes significantly to the total concentration, and hence, has to be taken into account. 

No information on analysis of tetrachloroethylene in soil or sediment was located. Several procedures for determination of the chemical in plants and food were located. GC/ECD and GC/HSD are most commonly used to analyze solid samples for tetrachloroethylene contamination. Extraction, purge-and-trap, and headspace analysis have all been used to prepare samples. Analysis of headspace gases by GC coupled with ECD, MS, or HSD has proven relatively sensitive (low- to sub-ppb range) and reproducible for a variety of foods (Boekhold et al. 1989 Entz and Hollifield 1982 EPA 1982c Pocklington 1992 ... 

The oil should be less soluble In water than the contaminant. The analysis of the contamlnant/extraction oil system should be an accurate and straightforward process. 

See also Bloassays Microbial Tests. Food and Nutritional Analysis Overview Contaminants. Pharmaceutical Analysis Plant Extracts. Thin-Layer... 

Other alternative options for PAHs extraction coupled to flow injection are static, dynamic, and static-dynamic-pressurized liquid extraction. They have been applied to contaminated soils analysis, allowing the partial automation of the proposed approaches. Efficiencies close to 100% have been obtained with the three operational modes. However, the static-dynamic mode has proved as the most suitable alternative providing the shortest extraction time (25 min) versus the static (30 min) and the... 

The total blank is determined by extracting 100 g of ultrapure water and has usually been found not to differ from the reagent blank (of the order of 0.01 nmol/L). Random sources of contamination during analysis under clean-room conditions therefore can be neglected. 

It should be emphasized that the routine use of GC-MS for post-explosion analysis is not without problems. Highly contaminated extracts from the debris often decrease the efficiency of the GC-MS analysis. This is especially true for some nitrate esters and nitramines, where a significant decrease in sensitivity has been observed. 

In order to insure accurate and reproducible isotopic analyses, the compounds to be analyzed must be rigorously purified. The usual methods of purification of organic and inorganic materials are used, bearing in mind that often only very small quantities are available. Thus microtechniques (Cheronis, 1954) are usually employed for distillation or even recrystallization. In recrystallization as in extraction, hydroxylic solvents should not be used in order to reduce the possibility of exchange, and to reduce isotopic contamination in analysis. 

Analytical Procedures. Standard methods for analysis of food-grade adipic acid are described ia the Food Chemicals Codex (see Refs, ia Table 8). Classical methods are used for assay (titration), trace metals (As, heavy metals as Pb), and total ash. Water is determined by Kad-Fisher titration of a methanol solution of the acid. Determination of color ia methanol solution (APHA, Hazen equivalent, max. 10), as well as iron and other metals, are also described elsewhere (175). Other analyses frequendy are required for resia-grade acid. For example, hydrolyzable nitrogen (NH, amides, nitriles, etc) is determined by distillation of ammonia from an alkaline solution. Reducible nitrogen (nitrates and nitroorganics) may then be determined by adding DeVarda s alloy and continuing the distillation. Hydrocarbon oil contaminants may be determined by ir analysis of halocarbon extracts of alkaline solutions of the acid. 

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)... 

Analytical Supercritical Fluid Extraction and Chromatography Supercritical fluids, especially CO9, are used widely to extrac t a wide variety of solid and hquid matrices to obtain samples for analysis. Benefits compared with conventional Soxhlet extraction include minimization of solvent waste, faster extraction, tunabihty of solvent strength, and simple solvent removal with minimal solvent contamination in the sample. Compared with high-performance liquid chromatography, the number of theoretical stages is higher in... 

The procedure of simultaneous extracting-spectrophotometric determination of nitrophenols in wastewater is proposed on the example of the analysis of mixtures of mono-, di-, and trinitrophenols. The procedure consists of extraction concentrating in an acid medium, and sequential back-extractions under various pH. Such procedures give possibility for isolation o-, m-, p-nitrophenols, a-, P-, y-dinitrophenols and trinitrophenol in separate groups. Simultaneous determination is carried out by summary light-absorption of nitrophenol-ions. The error of determination concentrations on maximum contaminant level in natural waters doesn t exceed 10%. The peculiarities of application of the sequential extractions under fixed pH were studied on the example of mixture of simplest phenols (phenol, o-, m-, />-cresols). The procedure of their determination is based on the extraction to carbon tetrachloride, subsequent back-extraction and spectrophotometric measurement of interaction products with diazo-p-nitroaniline. 

Although SFE and SFC share several common features, including the use of a superaitical fluid as the solvent and similar instrumentation, their goals are quite distinct. While SFE is used mainly for the sample preparation step (extraction), SFC is employed to isolate (chr-omatography) individual compounds present in complex samples (11 -15). Both techniques can be used in two different approaches off-line, in which the analytes and the solvent are either vented after analysis (SFC) or collected (SFE), or on-line coupled with a second technique, thus providing a multidimensional approach. Off-line methods are slow and susceptible to solute losses and contamination the on-line coupled system makes possible a deaease in the detection limits, with an improvement in quantification, while the use of valves for automation results in faster and more reproducible analyses (16). The off-line... 

On-line LC-GC has frequently been used as a clean-up technique for the analysis of trace levels of contaminants (pesticides, plasticizers, dyestuffs and toxic organic chemicals) in water and food products. Several different approaches have been proposed for the analysis of contaminants by on-line LC-GC. Since pesticide residues occur at low concentration in water, soil or food, extraction and concentration is needed before GC analysis is carried out. 

Multidimensional gas chromatography has also been used in the qualitative analysis of contaminated environmental extracts by using spectral detection techniques Such as infrared (IR) spectroscopy and mass spectrometry (MS) (20). These techniques produce the most reliable identification only when they are dealing with pure substances this means that the chromatographic process should avoid overlapping of the peaks. 

---