Recovery yield

In trace organic analysis there is usually an extraction or clean-up process, rather than a sample dissolution. Here not only must the matrix effect be considered, but also the recovery yield of the extraction. Frequently an external spike standard is added, but there is often no way of knowing if the recovery of the spike standard matches the analyte in question. There is considerable evidence that the U S E P A method for VOA analysis (Minnich 1993) is subject to such error, as reported by Schumacher and Ward (7997). The analyst must always consider the possibility of such an error, especially when using CRMs to control methods that are applied in routine mode. 

C in a TH F-toluene-hexane mixture. After the mixture was cooled below —50 °C, ketone 41 was added. After 60min, the reaction was quenched with aqueous citric acid. The organic layer was then solvent switched into toluene, and the product 50 was crystallized by the addition of heptane (91-93% isolated yield, >99.5% ee). The chiral modifier 46 is easily recycled from the aqueous layer by basification with NaOH and extraction into toluene to recover 46 (>99% purity, 98% recovery yield). The modifier has been recycled up to nine times in subsequent chiral addition reactions without any problem. 

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. 

In Section III.D various methods were mentioned for determination of the 15N to 14N isotope ratio. Some applications to amines that appeared in the recent literature are presented here. Isotope dilution with a known aliquot of labelled compound allows solving some of the problems related to nonquantitative recovery yields of analyte in the analytical processing of a sample. However, the possibility of isotopic fractionation has to be taken into consideration. 

Although in several cases complex multicomponent mixtures are purified, the optimization problem can usually be reduced to the investigation of a binary mixture because there always exists a limiting impurity that elutes closest to the major component. The limiting impurity sets the constraint for the throughput, production rate, recovery yield, and other parameters. 

The maximum production rate, however, often results in nnacceptable recovery yields. Low recovery yield requires further processing by recycling the mixed fractions. The recovery yield at the maximum production rate strongly depends on the separation factor. In the cases of difficnlt separations, when the separation factor under linear conditions is aronnd or lower than a= 1.1, the recovery yield is not higher than 40%-60%. Even in the case of a=1.8, the recovery yield at the maximum production rate is only about 70%-80%. The situation is still less favorable in displacement chromatography, particularly if the component to be purified is more retained than the limiting impurity. In this case, from one side the impurity, whereas from the other side the displacer, contaminates the product. 

When the production rate, Pr, and the recovery yield, F, are simultaneously maximized via their product, Pr x F, the optimum conditions usually result in such a configuration in which the recovery yield is much higher with a small sacrifice in production rate [42]. 

The amount of solvent needed for the purification of a unit amount of target compound is conveniently described by the term specific production. Thus, the minimum solvent consumption can be determined for a given purification. The amount of solvent pumped through the column during one cycle is proportional to the mobile phase flow rate and the cycle time. The amount of purified product made in one cycle is the product of the amount injected and the recovery yield. Thus, the specific production can be written as [43]... 

Multiobjective optimization is an optimization strategy that overcomes the limits of a singleobjective function to optimize preparative chromatography [45]. In the physical programming method of multiobjective optimization, one can specify desirable, tolerable, or undesirable ranges for each design parameter. Optimum experimental conditions are obtained, for instance, using bi-objective (production rate and recovery yield) and tri-objective (production rate, recovery yield. 

FIGURE 10.22 Optimum separations for isocratic overloaded elution for the purification of the less retained component. The production rate (left) and the product of the production rate and the recovery yield (right) were maximized, respectively, a=1.2 k=2 C = C = lOOmg/mL. (Reproduced from Felinger, A. and Guiochon, G., J. Chromatogr. A, 752, 31, 1996. With permission from Elsevier.)... 

SPE methods with different cartridge packings have been employed for the pre-concentration and clean up of sulfonated azo dyes from waters and soil extracts [110,111], The extraction of solid samples has been carried ont by sonication or Soxhlet extraction and the extracts treated like the water samples. C18 cartridges and columns [111] were used followed by the elution with aqueous organic solvents in the presence of TEA with recovery yields always greater than 65% [93,111], Higher recoveries have been obtained by using C18 columns, pre-conditioned with an ammonium acetate buffer and elnted with methanol [111], The use of styrene-divinylbenzene [93,112], as well as of cross-linked polymeric sorbents with sulfonate functions, was shown to be suitable in the SPE of the more polar componnds [111],... 

In order to preclude this problem and the necessary frequent regeneration of the anion system s suppressor column, an ion chromatography exclusion scheme was utilized. Samples collected in a mine environment were reliably concentrated by freeze-drying and then analyzed on an ICE system with dilute hydrochloric acid eluent. The precision of the ICE method was experimentally determined to be 2.5% in a concentration range of 1 to 10 yg/mL. The accuracy was not independently determined but good precision and recovery yield confidence that measured values are within 5% of the true value. No interferences were observed in the ICE system due to strong acids, carbonic acid or other water soluble species present in mine air subject to diesel emissions. 

For a preparahve applicahon, focus is on recovering the targeted products while ophmizing produchon costs. The object of the separation is to reach the purity and recovery yield required for one or more specific components of the feed mixture. To maximize produchon, injechons are made as often as possible. The amount of stahonary phase used is set in order to minimize the costs of the product, equipment, and eluent consumption. Figure 12.2 presents the preparahve chromatogram of the same compounds as in Figure 12.1, where the injected amount is maximized in order to ophmize the process [5]. 

Solvent absorption using cresol gives a good recovery yield, but large quantities of cresol are required. This is a drawback, and so is the costly installation required. 

The diagram of the micro steam distillation-extraction apparatus is given. The recovery yield is given for test compounds. 

The diagram of the apparatus is given. The effect of pH and the recovery yield in function of time are described. 

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