Extraction for GC analysis

Smoke from forest fires may be collected by various means for subsequent laboratory analysis. The most applicable approach is to trap emissions from biomass burning on absorbent material. The absorbent material is then either solvent-extracted for GC analysis or directly desorbed onto a GC. For example, smoke is pulled with an air pump at a rate of 10-50mLmin through triple-layer glass cartridges with separate... 

Extraction for GC Analysis. The method was adapted from Muir and Baker (4). Sodium chloride (5 g) was dissolved in 500 mL of the water sample. The water was extracted with one 100-mL portion and two 50-mL portions of ethyl acetate. After each extraction, the organic layer was transferred to a 10 x 300 ram chromatography column containing 10 g of anhydrous sodium sulfate. The column effluent was collected in a 250-mL round-bottom flask and was concentrated to 1-2 mL on a rotary evaporator with the bath at 35 C. The concentrate was transferred to a small culture tube with three 1-mL rinses of acetone. The solvent was removed with a stream of gas while warming at 30 C. The residue was dissolved in 1.0 mL of toluene and stored at 4 C until analysis by GC. 

Teske, J., J. Efer, and W.Engewald, Large Volume PTV Injection Comparison of Direct Water Injection and In-Vial Extraction for GC Analysis of Triazines,... 

Teske, J., Efer, J., and Engewald, W., Large volume PTV injection Comparison of direct water injection and in-vial extraction for GC analysis of triazines, Chromatographia, 47, 35,1998. 

Uhler and Miller [39] developed a GC multiple headspace extraction technique for the determination of volatile hydrocarbons in butter [39]. In a related procedure to determine styrene and its dimer in milk, acetone was used to precipitate proteins and extract fat and the residues from the packaging material. Using direct injection of these extracts for GC analysis, detection limits were 0.16 mg/kg for styrene and 0.28 mg/kg for the dimer [40]. 

The method using GC/MS with selected ion monitoring (SIM) in the electron ionization (El) mode can determine concentrations of alachlor, acetochlor, and metolachlor and other major corn herbicides in raw and finished surface water and groundwater samples. This GC/MS method eliminates interferences and provides similar sensitivity and superior specificity compared with conventional methods such as GC/ECD or GC/NPD, eliminating the need for a confirmatory method by collection of data on numerous ions simultaneously. If there are interferences with the quantitation ion, a confirmation ion is substituted for quantitation purposes. Deuterated analogs of each analyte may be used as internal standards, which compensate for matrix effects and allow for the correction of losses that occur during the analytical procedure. A known amount of the deuterium-labeled compound, which is an ideal internal standard because its chemical and physical properties are essentially identical with those of the unlabeled compound, is carried through the analytical procedure. SPE is required to concentrate the water samples before analysis to determine concentrations reliably at or below 0.05 qg (ppb) and to recover/extract the various analytes from the water samples into a suitable solvent for GC analysis. 

Diphenyl ether herbicides are generally extracted from 10 to 50 g of air-dried soil with an organic solvent such as acetone, methanol and benzene by sonication, mechanical shaking or Soxhlet extraction. If necessary, the extracts are then cleaned by column chromatography or SPE. The extract is evaporated completely to dryness and the residue is dissolved in an appropriate volume of the solvent for GC analysis. The reduced amine metabolites are extracted under alkaline conditions. 

For soil samples, sufficient sample cleanup could be conducted even if the alumina column was changed to a Sep-Pak Alumina N cartridge (Waters) by the following process. The entire sample of the dried n-hexane extract (Section 6.2) is introduced into a Sep-Pak Alumina N cartridge, and the column is washed with 50 mL of n-hexane. Subsequently, pyriminobac-methyl is eluted with 3 mL of ethyl acetate, the solvent is evaporate to dryness under reduced pressure and the residue is dissolved in an appropriate volume of acetone for GC analysis. 

Table 4.15 fists the many possibilities for solid sampling for GC analysis. In general, sample preparation should be considered in close conjunction with injection. Robotic sample processors have been introduced for automatic preparation, solvent extraction and injection of samples for GC and GC-MS analyses. Usually, facilities are included for solvent, reagent, and standard additions and for derivatisation of samples. 

David et al. [184] have shown that cool on-column injection and the use of deactivated thermally stable columns in CGC-FID and CGC-F1D-MS for quantitative determination of additives (antistatics, antifogging agents, UV and light stabilisers, antioxidants, etc.) in mixtures prevents thermal degradation of high-MW compounds. Perkins et al. [101] have reported development of an analysis method for 100 ppm polymer additives in a 500 p,L SEC fraction in DCM by means of at-column GC (total elution time 27 min repeatability 3-7 %). Requirements for the method were (i) on-line (ii) use of whole fraction (LVI) and (iii) determination of high-MW compounds (1200 Da) at low concentrations. Difficult matrix introduction (DMI) and selective extraction can be used for GC analysis of silicone oil contamination in paints and other complex analytical problems. 

Shang et al. [5] used ASE for the extraction of NP and NPEO from estuarine sediments. A sample of 15-25 g was extracted three times using hexane/acetone at 100°C and 103 atm. This was followed by a clean-up step using CN-SPE. A blank sample was extracted between all samples to avoid contamination. Hexane/acetone was also used in the ASE method for alkylphenols and NPEO by Heemken et al. [12]. Extraction conditions for samples of 0.5-1 g were 100°C, 150 atm, with a static extraction step of 15 min, and a rinse step with 20 mL solvent. After a clean-up by HPLC, the analytes were derivatised with heptafluorobutyric acid anhydride for GC analysis. 

Reactions were followed and analyzed by GC. For GC analysis, samples were extracted with an equal volume of ethyl acetate and analyzed. Peak assignment was performed with an authentic standard of the product and confirmed by GC-MS (instrument Finnigan SSQ7000, GC-EI, achiral GC method described below). 

Gas Chromatography Analysis of Water for Pesticides. All analyses for pesticides in water were done by gas chromatography. Solvents used for extraction were checked by gas chromatography for purity and interferences and all glassware used in the extraction was cleaned in a chromic acid/sulfuric acid mixture. Standards consisted of mixtures of various pesticides (actual commercial formulations) suspended or dissolved in water. These aqueous standards were extracted in the same manner as unknown solutions. The standard concentrations encompassed the concentration of unknowns to be determined. A standard curve normally consisted of a set of four pesticide concentrations. Blanks were run and an internal standard (eicosane) was used. The internal standard concentration was kept constant for all analyses. The conditions for GC analysis were guided by the pesticides expected in the water. For the more complex mixtures, such as those employed in the synthetic waste and those encountered in the field, a 6 ft., 3 percent SE-30 on GAS CHROM Q column sufficed. A typical chromatogram of a complex pesticide mixture is shown in Figure 2. ( )... 

The most variable aspect of carbon tetrachloride analysis is the procedure used to separate carbon tetrachloride from the medium and prepare a sample suitable for GC analysis. As a volatile organic compound of relatively low water solubility, carbon tetrachloride is easily lost from biological and environmental samples, so appropriate care must be exercised in handling and storing such samples for chemical analysis. Brief summaries of the methods available for extraction and detection of carbon tetrachloride in biological and environmental samples are provided below. 

Lipids can be identified and quantified using thin-layer chromatography (TEC) and gas chromatography (GC) (Galliard, 1968). Extraction of lipids is achieved by homogenizing potato tubers with isopropanol in a blender, followed by a series of filtrations and extractions with chloroform-methanol (2 1). Chloroform is removed by rotary evaporation and the residue is redissolved in benzene-ethanol (4 1). This extract is passed through a DEAE-cellulose column, and the fractions collected are subjected to TEC on 250 p,m layers of silica gel G, using three solvent systems. Fatty acid methyl esters for GC analysis are prepared by transmethylation of the parent lipids, or by diazomethane treatment of the free fatty acids released by acid... 

Atmospheric pressure apparatus. Isomerization experiments at atmospheric pressure were carried out in an all-glass system equipped with greaseless values, a flow meter, a U-shaped silica reactor, a double TCD system recording the pressure of reactant (provided by a saturator) before the reactor and the pressure of the products after the reactor, a system to extract the products for GC analysis and a needle valve to regulate gas flow. The catalyst was placed on a silica fritted disc and the reactor was operated as a fixed bed at constant pressure and temperature. Hydrocarbons were introduced at a set pressure and hydrogen was used as complement to the atmospheric pressure on the catalyst. 

Aqueous samples are extracted with methylene chloride by liquid-liquid extraction in a separatory funnel or a liquid-liquid extractor. The extract is concentrated to 1 mL for GC analysis. If HPLC analysis were to be performed, methylene chloride should be exchanged to acetonitrile by evaporating the solvent extract with a few mL of acetonitrile and adjusting the final volume to 1 mL. 

Aqueous samples are extracted with methylene chloride. If the sample is not clean or if the presence of organic interference is suspected, a solvent wash should be performed. For this, the pH of the sample is adjusted to 12 or greater with NaOH solution. The sample solution made basic is then shaken with methylene chloride. Organic contaminants of basic nature and most neutral substances partition into the methylene chloride phase, leaving phenols and other acidic compounds in the aqueous phase. The solvent layer is discarded. The pH of the aqueous phase is now adjusted to 2 or below with H2S04, after which the acidic solution is repeatedly extracted with methylene chloride. Phenols and other organic compounds of acidic nature partition into the methylene chloride phase. The methylene chloride extract is then concentrated and exchanged into 2-propanol for GC analysis. For clean samples, abasic solvent wash is not necessary however, the sample should be acidified before extraction. It may be noted that basic solvent wash may cause reduced recovery of phenol and 2,4-dimethylphenol. 

Baguacu berry DG, CG, PtG, PG, MG, PgG Extraction with acidified ethanol, filtration, partitioning, SPE with Amberlite, acid hydrolysis, SPE with C18, derivatization with MSTFA for GC analysis Cellulose DB-5 C-18 EtAc-n-butanol- H20-acetic acid-HCI He ACN-H20-phosphoric acid-acetic acid TLC (254, 365 nm) GC/MS HPLC/MS/MS/ ESI(+) or NMR 69... 

Mulberry CG, CR Extraction with acidified aqueous MeOH, filtration, SPE with polyamide, paper chromatography, alkaline or acid hydrolysis, derivatization for GC analysis SPB C-18 He h2o-thf-tfa GC/MS/EI HPLC/DAD (520 nm)/MS/MS/ ESI(+) 51... 

Urine analysis for illegal drugs is increasingly performed in forensic laboratories (especially in Japan). Gas chromatography-mass spectrometry (GC-MS) is extensively used because of its versatility and reliability. By way of sample preparation for GC analysis, conventional liquid-liquid extraction has a widespread use, but it is not only laborious but also environmentally unfriendly due to the consumption of considerable amounts of organic solvents. Therefore, microintegration of the sample preparation procedure is required. 

Other mass spectral techniques that use LC and capillary electrophoresis (CE) as the sample introduction method make it possible to analyze chemicals that should otherwise be derivatized for GC analysis, and also those nonvolatile and nonderiva-tizable chemicals that cannot be analyzed at all with GC. Many of these chemicals could be analyzed with FUR without GC separation, but in the environment, they may be in, for example, water or soil samples (which possibly have to be extracted with water). Water samples are difficult to analyze with FTIR since water is quite a poor solvent for FTIR due to very high molar absorptivity. 

Dlflubenzuron. The benzoylphenyl urea Insect growth regulators, for example, pose a formidable residue analysis problem. The compounds are nonvolatile and thus must be derivatized for GC analysis by a rather arduous chemical procedure. The immunoassay developed in this laboratory is much more sensitive and reproducible at a fraction of the cost and can be used to analyze the more difficult matrices such as milk. For instance, a sensitivity of 1 ppb is routinely obtained when milk is added directly to the assay ( .). A series of partition steps can also be added to further clean dlflubenzuron milk extracts yielding a sensitivity in the low ppt range (4). However this increase in sensitivity may not be needed since methods in current use provide a detection limit of only 10-50 ppb. 

The Stringfellow Superfund site in California poses analytical problems similar to those encountered with most waste sites across the United States and that may be best addressed via LC/MS based methods. Most of the organic compounds in aqueous leachates from this site cannot be characterized by GC/MS based methods. Analysis of Stringfellow bedrock groundwater shows that only 0.78% of the total dissolved organic materials are identifiable via purge and trap analysis (IQ). These are compounds such as acetone, trichloroethylene etc, whose physical properties are ideally suited for GC/MS separation and confirmation. Another 33% of the dissolved organic matter is characterized as "unknown", i.e., not extractable from the aqueous samples under any pH conditions and thus not analyzed via GC. Another 66% is 4-chlorobenzene sulfonic acid (PCBSA), an extremely polar and water soluble compound that is also not suitable for GC analysis. This compound, a waste product from DDT manufacture, is known to occur at this site because of the history of disposal of "sulfuric acid waste from industrial DDT synthesis. 

Sample preparation and derivatization methods for GC analysis of BAs have been also proposed. In a method developed by Daudt and Ough (1980), amines are distilled from the alkalized grape juice or wine sample and trapped in an acidified solution. After concentration under vacuum, methylamine, dimethylamine, ethylamine, diethylamine, n-propylamine, isobutylamine, a-amylamine, isoamylamine, pyrrolidine, and 2-phenethylamine in their salt form are derivatized with triflu-oroacetic (TFA) anhydride. TFA derivatives are extracted with ethyl ether and analyzed by GC-MS with a capillary fused silica poly( ethylene) glycol (PEG) column and the following oven temperature program 8 min at 70 °C, l°C/min to 160 °C, isotherm for 90 min. 

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