Extraction conditions samples

Selection of the extraction conditions (sample preparation, types of solvents, further purification steps, etc.) is crucial to ensture complete extraction of phenolics from vegetal material without losses or modifications of their chemical structure. 

Principles and Characteristics A first step in additive analysis is the identification of the matrix. In this respect the objective for most polymer analyses for R D purposes is merely the definition of the most appropriate extraction conditions (solvent choice), whereas in rubber or coatings analysis usually the simultaneous characterisation of the polymeric components and the additives is at stake. In fact, one of the most basic tests to carry out on a rubber sample is to determine the base polymer. Figure 2.1 shows the broad variety of additive containing polymeric matrices. 

Brandt [200] has extracted tri(nonylphenyl) phosphite (TNPP) from a styrene-butadiene polymer using iso-octane. Brown [211] has reported US extraction of acrylic acid monomer from polyacrylates. Ultrasonication was also shown to be a fast and efficient extraction method for organophosphate ester flame retardants and plasticisers [212]. Greenpeace [213] has recently reported the concentration of phthalate esters in 72 toys (mostly made in China) using shaking and sonication extraction methods. Extraction and analytical procedures were carefully quality controlled. QC procedures and acceptance criteria were based on USEPA method 606 for the analysis of phthalates in water samples [214]. Extraction efficiency was tested by spiking blank matrix and by standard addition to phthalate-containing samples. For removal of fatty acids from the surface of EVA pellets a lmin ultrasonic bath treatment in isopropanol is sufficient [215]. It has been noticed that the experimental ultrasonic extraction conditions are often ill defined and do not allow independent verification. 

PFE is based on the adjustment of known extraction conditions of traditional solvent extraction to higher temperatures and pressures. The main reasons for enhanced extraction performance at elevated temperature and pressure are (i) solubility and mass transfer effects and (ii) disruption of surface equilibria [487]. In PFE, a certain minimum pressure is required to maintain the extraction solvent in the liquid state at a temperature above the atmospheric boiling point. High pressure elevates the boiling point of the solvent and also enhances penetration of the solvent into the sample matrix. This accelerates the desorption of analytes from the sample surface and their dissolution into the solvent. The final result is improved extraction efficiency along with short extraction time and low solvent requirements. While pressures well above the values required to keep the extraction solvent from boiling should be used, no influence on the ASE extraction efficiency is noticeable by variations from 100 to 300 bar [122]. 

Modifiers can be used very effectively in on-line SFE-GC to determine the concentration levels of the respective analytes. This presents an advantage in terms of the use of modifiers in SFE, since they appear as solvent peaks in GC separations and do not interfere with the target analyte determination. Although online SFE-GC is a simple technique, its applicability to real-life samples is limited compared to off-line SFE-GC. As a result, on-line SFE-GC requires suitable sample selection and appropriate setting of extraction conditions. If the goal is to determine the profile or matrix composition of a sample, it is required to use the fluid at the maximum solubility. For trace analysis it is best to choose a condition that separates the analytes from the matrix without interference. However, present SFE-GC techniques are not useful for samples... 

Raw Material Extraction Methods Feed (g) (i.c. %) Sample Preparation p.s. Ill Bioactive Compound T P Extraction Conditions f.r. t c-s. Recovery (%) Ref. 

Duplicate samples were processed onshore after a variety of storage procedures. All samples were analysed for copper and iron by GFA-AS. Only samples filtered (< 1 pm), acidified, and stored frozen gave extractable copper and iron results comparable with those for samples extracted immediately after collection. Cold storage with sample acidification in polyethylene containers appeared less satisfactory. Organic extracts from samples processed onboard are best retained in all-Teflon containers pending complete digestion and analysis onshore. Unless clean (ultra-filtered air) conditions can be ensured onboard, the estuarine water samples are best returned in a filtered, acidified, and frozen condition for onshore processing. 

Wash-elution and aspiration-dispensing cycle optimization experimental results are shown in Figures 1.14 and 1.15, respectively. A comparison of recovery yields between the tip experiment and a 96-well plate containing 15 mg of Varian SPEC C18 under the same extraction conditions gave a value of 70% for the latter, a figure obtained from three aspiration-dispensing cycles for the former. For intra-run accuracy of calibration standards, a %CV range from -3.6% to 3.5% was recorded, while for the QC samples, 7.7%, 1.3%, and 0% were obtained for QCL, QCM, and QCH (n = 18), respectively. Run precisions were 1.1 to 9.2% and 5.1 to 5.7%, respectively, for calibration and QC samples. An LLOQ of 10 ng/mL was established. 

FIG U RE 1.37 Effects of extraction time and fiber length on two-phase LPME of mirtazapine stereoisomers.156 Influence of extraction time (A) and acceptor-to-donor phases volume ratio (B) on the efficiency of LPME. Plots for the (+)-(5)-mirtazapine (white bars) and (-)-(R)-mirtazapine (black bars) enantiomers (response in area counts). Extraction conditions (A) 1 mL plasma sample 0.1 mL 10 M NaOH 3.0 ml deionized water 7.0 cm fiber length 22 /rL toluene (B) 30 min of extraction 1 mL plasma sample 0.1 mL 10 M NaOH 3.0 mL deionized water toluene. (Reproduced with permission from Elsevier.)... 

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. 

It is difficult to compare recoveries obtained by different laboratories because their extraction conditions (pH, phase ratio, number and time-length of extractions, salinity) are generally different. Sample volumes can be very high, up to 200 1 [433], and 50 1 of surface water [434] or 201 of sea water allow the extraction of 5 ng/1 of alkanes. When using a specific detection method, the sample volume can be lower 2 ng/1 of PAH was determined from 11 of river water using liquid chromatography and fluorescence detection [435]. Chlorophenols below the 10 ng/1 level were determined from 100 ml of sea water with electron capture detection (ECD) GC [436]. 

The aim of the present work was to design and operate an apparatus in which stationary combustion and flames can be produced and sustained to pressures of 2000 bar and with environmental temperatures up to 500°C. Visual observation of the interior of the reaction vessel should be possible. Arrangements had to be made by which a gas flow of only a few microlitres per second could be fed steadily into the reaction vessel at pressures to two kilobar. A similar provision was necessary to extract small samples for product analysis at constant conditions. The principle of design and operation will be described. First results will be given for experiments with oxygen introduced into supercritical water-methane mixtures. 

Under normal reaction conditions, phenolic compounds are the predominant antioxidants in hydrophilic extracts of samples that easily transfer one hydrogen to the peroxy radical (ROO ). 

Other sulfonamides. The fact that the extraction of one of these sulfonamides is only optimized at a totally different pH displays the compilations in relying on a single set of extraction conditions as representative for all members within each class of PPCPs. To trap acid components in the sample, the sample has to be acidified to pH < 2, passed through a conditioned column such as an RP C18 solid-phase extraction column, and then eluted with a volatile solvent. Neutral compounds are, on the other hand, extracted by adjusting the sample to pH 7-8 before ranning the sample through the extraction column, which has been conditioned with acetone, methanol, or distilled water. Basic compounds are extracted by initially adjusting the sample to pH > 12 with EDTA and KOH. 

The interlaboratory results obtained from the analysis of defined standard solutions, but also from the analysis of sediment extracts prepared either by the coordinator of the study or by the participants themselves, also provide a measure of the variation between laboratories. The results show that the interlaboratory reproducibility ranges from 6.5% for the defined dioxin sample to 27.9% for the sediment sample extracted by the participants themselves. As was mentioned before, the reproducibility for this last sample is relatively high and most presumably due to the introduction of extra handlings (extraction and cleanup) to the total procedure. In addition, the fact that not all the participants had prior experience with the extraction protocol to be used could have added to the increase in variability of the process. Furthermore, the dilution factor was not dictated. This also introduces a certain degree of variation. For the reproducibility of the DR CALUX bioassay itself and not caused by differences in operating extraction conditions, the maximum variation between laboratories was observed to be 18.0%. The results for the sediment extract samples can also be used to estimate the method variability for extracts, that is, based on samples of unknown composition. Again, given the intra-as well as the interlaboratory variations observed in this study, it appears justified to conclude that the standard deviation of the means provides a reasonable estimate of the method variability, based on the overall aver-... 

SFE Equipment. The extraction apparatus (Figure 1) used was manufactured by the Superpressure Division of Newport Scientific, Inc. (Jessup, MD) and modified by adding two more separators. Detailed extraction conditions were described by Chao et al. (21). For each test run, approximately 200 g of frozen and thawed ground beef sample containing about 18% fat or 100 g of animal fat was loaded into the extraction vessel and extracted with supercritical CO2. 

Trap conditioning Sample extraction Desorption from trap... 

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