Extraction, sampling

The thermospray process extracts sample molecules from a solvent and turns them into ions. Therefore, the system is both an inlet and an ion source, so a separate ion source is not necessary. 

Automated analyzers may be used for continuous monitoring of ambient poUutants and EPA has developed continuous procedures (23) as alternatives to the referenced methods. Eor source sampling, EPA has specified extractive sampling trains and analytical methods for poUutants such as SO2 and SO [7446-11-9] sulfuric acid [7664-93-9] mists, NO, mercury [7439-97-6], beryUium [7440-41-7], vinyl chloride, and VOCs (volatile organic compounds). Some EPA New Source Performance Standards requite continuous monitors on specified sources. 

Source sampling of particulates requites isokinetic removal of a composite sample from the stack or vent effluent to determine representative emission rates. Samples are coUected either extractively or using an in-stack filter EPA Method 5 is representative of extractive sampling, EPA Method 17 of in-stack filtration. Other means of source sampling have been used, but they have been largely supplanted by EPA methods. Continuous in-stack monitors of opacity utilize attenuation of radiation across the effluent. Opacity measurements are affected by the particle size, shape, size distribution, refractive index, and the wavelength of the radiation (25,26). 

Sampling from pneumatic conveyors parallels gas sampling. The exception is that soflds loadings can be as high as 50 kg of soHds per kg of gas. Commercially available samplers extract particles directly from a transport line. Fixed position samplers are mounted directly on the pneumatic conveyor pipe. Devices are available which extract samples from the product stream by the projection of a sample tube iato the flow. Particles impact on the tube and fill the open cavity. The tube is then withdrawn, and an internal screw discharges the collected material (20). In another model, the RX Sampler (manufactured by Gustafson) (29), samples are withdrawn usiag compressed air. 

Figure 2.16 Clirotnatograms of a pentane extract of a water sample containing 200 ppb of a naphtha fraction (a) sample extracted by using a continuous flow system, where a pressurized bottle was employed as the sample-delivery system (b) batch-extracted sample. Reprinted from Journal of Chromatography, A 330, J. Roeraade, Automated monitoring of organic Race components in water. I. Continuous flow exti action together with on-line capillary gas cliro-matography , pp. 263 - 274, copyrigth 1985, with permission from Elsevier Science.

The HMR/fractionatlon approach gives very good results When applied to ethylene-propylene copolymer fractions reported by Abls, et. al. (19) These authors extracted sample 5 (In Table VII) with hexane to get soluble and Insoluble fractions (5a and 5b), and with ether to get soluble and insoluble fractions (5c and 5d). The hexane set (5a and 5b) and the ether set (5c and 5d) can be separately analyzed by the HIXCO.TRIADX program. The results are shown In Table VIII. In the 2-state (B/B) model, we have 4 parameters and 12 values to fit to HMR data of pairwise fractions. In the 3-state (B/B/B) model, we have 7 parameters and 12 values to fit. Thus, the use of pairwise fractions Is absolutely essential for 3-state analysis. 

Various extraction methods for phenolic compounds in plant material have been published (Ayres and Loike, 1990 Arts and Hollman, 1998 Andreasen et ah, 2000 Fernandez et al., 2000). In this case phenolic compounds were an important part of the plant material and all the published methods were optimised to remove those analytes from the matrix. Our interest was to find the solvents to modily the taste, but not to extract the phenolic compounds of interest. In each test the technical treatment of the sample was similar. Extraction was carried out at room temperature (approximately 23 °C) for 30 minutes in a horizontal shaker with 200 rpm. Samples were weighed into extraction vials and solvent was added. The vials were closed with caps to minimise the evaporation of the extraction solvent. After 30 minutes the samples were filtered to separate the solvent from the solid. Filter papers were placed on aluminium foil and, after the solvent evaporahon, were removed. Extracted samples were dried at 100°C for 30 minutes to evaporate all the solvent traces. The solvents tested were chloroform, ethanol, diethylether, butanol, ethylacetate, heptane, n-hexane and cyclohexane and they were tested with different solvent/solid ratios. Methanol (MeOH) and acetonitrile (ACN) were not considered because of the high solubility of catechins and lignans to MeOH and ACN. The extracted phloem samples were tasted in the same way as the heated ones. Detailed results from each extraction experiment are presented in Table 14.2. 

The method procedures are very time-efficient by always using a well defined portion of the extracts, thus avoiding multiple extractions, time-consuming rinses and overloading of the chromatographic cleanup systems with co-extracted sample matrix. 

The development of a robust analytical method is a complex issue. The residue analyst has available a vast array of techniques to assist in this task, but there are a number of basic rules that should be followed to produce a reliable method. The intention of this article is to provide the analyst with ideas from which a method can be constructed by considering each major component of the analytical method (sample preparation, extraction, sample cleanup, and the determinative step), and to suggest modern techniques that can be used to develop an effective and efficient overall approach. The latter portion emphasizes mass spectrometry (MS) since the current trend for pesticide residue methods is leading to MS becoming the method of choice for simultaneous quantitation and confirmation. This article also serves to update previous publications on similar topics by the authors. ... 

Mixing, wrist shaking, or tumbling combinations offer a simple, effective, but time-consuming and not highly reproducible method of extraction. Sample-to-solvent ratios are similar to Soxhlet ratios. Although sample manipulation is reduced, this technique requires nearly as much time as the Soxhlet method. Shake-flask extraction is low cost. 

Figure 3.2 The three-step Soxhlet extraction process of the Soxtec extraction system (a) solubilisation of extractable matter from sample immersed in boiling solvent (b) rinsing of extracted solid and (c) concentration of extracted sample and collection of distilled solvent for reuse or disposal. Reproduced by permission of FOSS Analytical A/S, Hillerdd...

It is important that any method for surfactant analysis maintains the same oligomer distribution in the extracted samples. LLE and SPE are generally combined with chromatographic methods for separation and resolution of non-ionic surfactants into their ethoxamers. An alternative is the use of SPME-HPLC, recently reported by Chen and Pawliszyn [141]. Alkylphenol ethoxylate surfactants such as Triton X-100 and various Rexol grades in water were determined by means of SPME-NPLC-UV (at 220 nm) [142]. Detection limits for individual alkylphenol ethoxamers were at low ppb level. 

Equilibrium stress-strain dependences were determined in extension using a stress relaxation arrangement described earlier (21). Dry non-extracted samples were measured at 150 C in nitrogen atmosphere and extracted samples swollen in dimethylformamide were measured at 25 C. The equilibrium value of stress 6 e was reached within 2-4 min except of a few dry samples with the lowest tig, for which the equilibrium stress was determined using an extrapolation procedure described earlier (21). 

Factors Affecting Extraction Yield in SC-CO2 Extraction Sample Preparation... 

Three Zeeman-based methods for the determination of cadmium in seawater were investigated. Direct determinations can be made with or without the use of a pyrolytic platform atomisation technique. The wall atomisation methods presented were considerably faster than the platform atomisation technique. For extremely low levels of cadmium, indirect methods of analysis employing a preliminary analyte extraction can be employed. Background levels are minimal in extracted samples, and the total furnace programme time was the lowest of the methods examined. 

The dwell time was 200 msec for the analytes and 100 msec for the IS. At least 500 extracted samples were injected onto each column without any column regeneration. No solvent evaporation and reconstitution steps were involved. Ethyl acetate was preferred over methyl t-butyl ether (MTBE) because MTBE caused pulp-up of the mat. Six blank plasma lots were tested for matrix interference and none was detected in the analyte or IS region. When 100 ng/mL of the analytes were spiked into the blank plasma samples, the relative standard deviations were 1.0 and 1.5% for omeprazole and its metabolite, respectively. Precision and accuracy figures are given in Table 1.9. 

Vortex the injection plate to thoroughly dissolve the extracted samples. 

Recovery — Overall procedural recovery was evaluated. The results from spiked plasma QC (evaluation) samples that went through the analytical procedure were compared to the results from neat spiking (control) solution samples. The neat spiking solutions used to prepare the plasma evaluation samples were evaporated and reconstituted at the same volumes as the extracted samples. The analyte was tested at three concentration levels and the internal standard was tested at one. Mean recovery for the analyte was approximately 122.9% the level was 55.2% for the internal standard. 

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