Extraction, recovery efficiency

The extraction method for prohexadione-calcium in soil was developed using alluvial soil and volcanic ash soil. Extraction by shaking the soil with a mixture of 1N sulfuric acid-acetonitrile (1 3, v/v) and/or of 1N sulfuric acid-acetone (1 3, v/v) showed an acceptable extraction recovery efficiency. 

Reclamation, Disposal, and Toxicity. Removal of poisons and inorganic deposits from used catalysts is typically difficult and usually uneconomical. Thus some catalysts are used without regeneration, although they may be processed to reclaim expensive metal components. Used precious metal catalysts, including automobile exhaust conversion catalysts, are treated (often by the suppHers) to extract the metals, and recovery efficiencies are high. Some spent hydroprocessing catalysts may be used as sources of molybdenum and other valuable metals. 

LLE has been used in the past for the extraction of pesticides from environmental water samples [17]. However, its application in the extraction of waste-water samples is scarce due to the low efficiency of extraction, especially for polar analytes. Because of the vast amount of surfactants and natural products present in wastewater samples, emulsions are formed which complicate the process of extraction and lead to low extraction recoveries. However, there have been some useful applications of LLE to wastewater analyses. For example, LLE was found to be effective for the isolation of herbicide and pesticide organic compounds from industrial wastewater samples and also from complex matrices [18]. 

Sonication helps improve solid-liquid extractions. Usually a finely ground sample is covered with solvent and placed in an ultrasonic bath. The ultrasonic action facilitates dissolution, and the heating aids the extraction. There are many EPA methods for solids such as soils and sludges that use sonication for extraction. The type of solvent used is determined by the nature of the analytes. This technique is still in widespread use because of its simplicity and good extraction efficiency. For example, in research to determine the amount of pesticide in air after application to rice paddy systems, air samples collected on PUF were extracted by sonication, using acetone as the solvent. The extraction recoveries were between 92% and 103% [21]. 

Solvents used in liquid membranes should have special characteristics such as low aqueous solubility, as a thin film of solvent is in contact with large volumes of aqueous solutions, and low viscosity to provide large diffusion coefficients in the liquid membrane. Furthermore, the analyte should have large partition coefficients between the donor and the membrane phase to give good extraction recovery and, at the same time, interfering substances in the sample should have low partition coefficients for efficient cleanup. 

Recoveries for soil and water samples spiked individually with the six commercial formulations at the 0.4 and 0.02% levels were 96 and 97%, respectively. Comparable recovery efficiencies were obtained for mixures of the pesticides. In addition, the ability to account for all the deposited pesticides in the analyses of the samples taken from the containers prior to any degradations was validation for the effectiveness of the extraction procedures. 

Samples of sand spiked with 36 nitroaromatic compounds, 19 haloethers, and 42 organochlorine pesticides, and a standard reference soil (certified for 13 polynuclear aromatic hydrocarbons, dibenzofuran, and pentachlorophenol) were extracted with supercritical carbon dioxide in a two- or four-vessel supercritical fluid extractor to establish the efficiency of the extraction and the degree of agreement of the parallel extraction recoveries. Furthermore, the many variables that influence the extraction process (e.g., flowrate, pressure, temperature, moisture content, cell volume, sample size, extraction time, modifier type, modifier volume, static versus dynamic extraction, volume of solvent in the collection vessel, and the use of glass beads to fill the void volume) were investigated. 

Table II. Net recovery efficiency of internal standards of plant growth substances after extraction and purification.

Brodtmann [120] carried out a long-term study on the qualitative recovery efficiency of the carbon adsorption method versus that of a continuous liquid-liquid extraction method for several chlorinated insecticides. Comparative results obtained by electron capture gas chromatography indicate that the latter method may be more efficient. 

The second ones are structural analogues with different masses or even the same mass. In the latter case, chromatographic separation between the analyte and its internal standard must be achieved when distinctive MRM (multiple reaction monitoring) transitions could not be found. It is preferable that the key structure and functionalities (e.g., -COOH, -S02, -NH2, halogens, and heteroatoms) of an internal standard are the same as those of the analyte and differ only by C-H moieties (length and/or position). Modifications in functionalities would result in significant differences in ionization efficiency and extraction recovery [8],... 

Application of LC-MS/MS techniques to the analysis of phthalate ester metabolites in urine have also been developed. For example, Blount et al. (2000b) have developed an assay to quantify the monoester metabolites (including MEHP) of eight phthalate diesters in urine, utilizing HPLC coupled with atmospheric pressure chemical ionization and tandem mass spectrometric (APCI-MS/MS) detection techniques. Urine samples were treated with -glucuronidase to release the free phthalate monoesters followed by a two-step solid phase extraction procedure. After evaporative concentration of the eluant, the analytes in the purified samples are further separated on a phenyl reverse phase HPLC column and quantified by APCI-MS/MS, following careful optizimation of the APCI-MS/MS instrument. The limits of detection for MEHP were determined to be 1.2 ng/ml urine with recovery efficiencies of between 78 and 91%. 

A similar study of the reproducibility of collection of 14c 9 tetrahydrocannabinol in plasma assayed by liquid scintillation after extraction and reverse-phase HPLC was also conducted. The amounts recovered were proportional to the amounts injected, and the HPLC recovery efficiency of the drug in the heptane extract was 95.7%. 

Sonication with a waterD methanol solution is the most popular method for the extraction of As species from rice powder [24, 25], algae, chicken meat [26], oyster tissue [27, 28], and baby foods [29]. Sample treatment with triBuoroacetic acid at 100°C was reported to be an efficient method for the extraction of As species present in different food matrices when compared with alternative methods that included sonication and accelerated solvent extraction. Extraction recoveries from 94 to 128 percent were obtained [29]. Low-molecular-weight Se compounds were extracted from nuts with HCIO4 to produce a fraction containing 3 to 15 percent of the total Se in different types of nuts [30]. 

Gas-liquid chromatography following reduction of paraquat to the mono- and diunsaturated derivatives (21) is of adequate sensitivity for most work when N-selective detectors are employed. Seiber and Woodrow (22.) modified this method for assaying paraquat in air samples. The method is time consuming and labor intensive, involving acid extraction and many concentration and evaporation steps. The maximum sample output per analyst per day is 6-8 with no duplicates. The reported recovery efficiency was 75% (22). although an efficiency closer to 50% is frequently encountered in practice. A modified acid extraction combined with analysis by the ELISA provides recoveries of 75% (Figure 3). This... 

---