Extraction recovery

In general, the sulfolane extraction unit consists of four basic parts extractor, extractive stripper, extract recovery column, and water—wash tower. The hydrocarbon feed is first contacted with sulfolane in the extractor, where the aromatics and some light nonaromatics dissolve in the sulfolane. The rich solvent then passes to the extractive stripper where the light nonaromatics are stripped. The bottom stream, which consists of sulfolane and aromatic components, and which at this point is essentiaHy free of nonaromatics, enters the recovery column where the aromatics are removed. The sulfolane is returned to the extractor. The non aromatic raffinate obtained initially from the extractor is contacted with water in the wash tower to remove dissolved sulfolane, which is subsequently recovered in the extract recovery column. Benzene and toluene recoveries in the process are routinely greater than 99%, and xylene recoveries exceed 95%. 

Fig. 4. Liquid extraction recovery process for citric acid.

FIG. 22-38 Tbe variation of adsorption density, oil-droplet contact angle, and oil-extraction recovery of bematite as a function of pH. To convert gram-moles per square centimeter to pound-moles per square foot, multiply hy 2.048. [From Raghavan and Fuerstenau, Am. Inst. Cbem. Eng. Symp. Ser., 71(150), 59... 

X 0 absorption density A or extraction recovery 0 contact angle ... 

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. 

Third, the bulk of the items in Table 1 address method performance. These requirements must be satisfied on a substrate-by-substrate basis to address substrate-specific interferences. As discussed above, interferences are best dealt with by application of conventional sample preparation techniques use of blank substrate to account for background interferences is not permitted. The analyst must establish a limit of detection (LOD), the lowest standard concentration that yields a signal that can be differentiated from background, and an LOQ (the reader is referred to Brady for a discussion of different techniques used to determine the LOD for immunoassays). For example, analysis of a variety of corn fractions requires the generation of LOD and LOQ data for each fraction. Procedural recoveries must accompany each analytical set and be based on fresh fortification of substrate prior to extraction. Recovery samples serve to confirm that the extraction and cleanup procedures were conducted correctly for all samples in each set of analyses. Carrying control substrate through the analytical procedure is good practice if practicable. 

An example of adequate sample homogenization is given in Table 4. The experiment was conducted with two replicate treated soil samples. Each replicate was analyzed in duplicate. Three different sample aliquots (2, 5 and 10 g) were used from each replicate. Analyses of controls and fortified samples were also conducted concurrently with treated samples to evaluate method performance (i.e., extraction recoveries). These results show that residue values are the same regardless of sample size. Thus, thorough homogenization of soil samples coupled with mgged analytical methodology provides for satisfactory residue analysis. 

Validation of extraction procedures is frequently lacking. A good assessment of quality assurance implies that the extraction recoveries are verified, e.g. by spiking of standard addition. A major drawback is that the spike is not always bound the same way as the compounds of interest. For the development of good extraction methods, materials with an incurred analyte (i.e. bound to the matrix in the same way as the unknown), which is preferably labelled (radioactive labelling would allow verification of the recovery), would be necessary. Such materials not being available, the extraction method used should be validated by other independent methods, e.g. by verification against known samples and by use of a recovery SPC chart. A mere comparison of extraction methods is no validation. 

Ealy [ 75 ] also used conversion to alkyl mercury iodides for the gas chromatographic determination of organomercury compounds in benzene extracts of water. The iodides were then determined by gas chromatograph of the benzene extract on a glass column packed with 5% of cyclohexane-succinate on Anakron ABS (70-80 mesh) and operated at 200 °C with nitrogen (56 ml min-1) as carrier gas and electron capture detection. Good separation of chromatographic peaks was obtained for the mercury compounds as either chlorides, bromides, or iodides. The extraction recoveries were monitored by the use of alkylmer-cury compounds labelled with 203 Hg. 

FIGURE 1.23 Dependency of extraction recovery of ABT-869 and acid metabolite AB849529 on buffer pH and proportion of ethyl acetate in organic solvent.137 (Reproduced with permission from John Wiley Sons.)... 

Extraction Recovery of Compound I from Supported Liquid-Liquid Extraction... 

Plasma proteins decreased extraction recoveries from SPME by irreversible adsorption onto the fiber. PPT prior to SPME by addition of acid or methanol was used to overcome this problem. SPME sensitivity may also be improved by dilution of plasma samples with buffer or water. 

Recovery — Recovery control (RC) solutions were prepared in 10/90 v/v ACN/water. Recovery evaluation (RE) samples were prepared in human plasma. Aliquot of RC solutions into assay plates followed sample preparation procedure steps 1 and 2. Instead of adding 50 pL of diluent, wells containing RC solutions were dried down under a steady stream of room temperature N2. The dried wells were then reconstituted with 250 pL of diluent. Reconstituted RC solutions were directly injected onto an HPLC analytical column, bypassing the extraction column. RE samples were aliquoted into an assay plate following normal sample preparation. RE samples were analyzed using the full extraction procedure (with extraction column). The analyte was tested at three concentration levels and the internal standard was tested at one. Mean extraction recovery for fenofibric acid varied from 93.2 to 111.1%, and mean extraction recovery for the Pestanal internal standard was 105.2%. 

An online filter was also used to protect the analytical column. A guard column was used before the T to prevent breakthrough. A restrictor was used to balance the pressure before, during, and after the valve switches. After sample transfer, the valve was switched back. With this method, both water-insoluble retinoids and water-soluble retinoic acid were extracted simultaneously. Because of the minimal light exposure of these light-sensitive analytes during the procedure, an extraction recovery of 97 to 100% was achieved with a quantitation range of 100 fmol to 3 nmol. 

Calibration curves for voriconazole were constructed in concentration ranges of 0.1 to 10 jUg/mL. Correlation coefficients exceeded 0.9998. Intra-day and inter-day coefficients of variation were less than 3.8 and 6.1%, respectively. The average extraction recovery was 94.6%. The limit of detection and the limit of quantification were 15 and 50 ng/mL, respectively. 

A linear calibration curve for epirubicin ranged from 0.50 to 100.0 ng/mL with a correlation coefficient of 0.999. Intra-day and inter-day coefficients of variation were less than 5.2 and 11.7%, respectively. Limit of detection and limit of quantification were 0.1 and 0.5 ng/mL, respectively. The extraction recoveries ranged from 89.4 to 101.2%. The validated method was successfully applied to the routine analysis of plasma samples from patients treated with epirubicin. 

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]. 

Tsukioka et al. [187] determined these contact herbicides in soil by mass fragmentography. The method is based on the reaction of l-benzyl-3-p-polytriazene with an extract of Frenock and Dalapon from strongly acidified sample solutions to form benzylated species. In the analysis of soil samples, steam distillation was applied prior to extraction. Recoveries were >92% and precision <5%. 

The LLE of relatively polar and water-soluble organic compounds is, in general, difficult. The recovery obtained from 11 of water with dichloromethane is 90% for Atrazine but lower for its more polar, degradation products, i.e., di-isopropyl- (16%), di-ethyl- (46%),andhydroxy-atrazine (46%). By carrying out LLE with a mixture of dichloromethane and ethyl acetate with 0.2 mol/1 ammonium formate, the extraction recoveries for the three degradation products were increased to 62 %, 87 %, and 65 %, respectively [437]. 

Duverneuil and coworkers (2003) have developed a method for the determination of 11 of the most commonly prescribed non-tricyclic antidepressants and some of their metabolites these include paroxetine, fluoxetine, norfluoxetine, sertraline, citalopram, fluvoxamine mirtazapine, venlafaxine, and 0-des-methylvenlafaxine. The method involves an LLE procedure followed by an HPLC separation with photodiode-array UV detection at three different wavelengths (220, 240, and 290 nm). The total run time was 18 min. The extraction recoveries were calculated to be in the range of 74-109% and the lower limit of detection (LLOD) reported was 2.5-5 ng/ml. A method published by Tournel and associates (2001) also reported the simultaneous determination of several newer antidepressants by RP-HPLC with UV detection. The compounds were isolated from human serum using an LLE process. The LLOQ ranged from 15-50 ng/ml depending on the analyte of interest. The total run time for all compounds eluted was approximately 20 min. 

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