Determination of extraction efficiency

For correct measurements, the extraction efficiency for each analyte must be known and compensated for. To determine the extraction efficiency, a natural seawater sample at a high concentration level is purged, and the water is left in the purge chamber after the flow of purge gas has been stopped. The first measurement is made using the method to be evaluated. Then, the purge gas is turned on again, the procedure is repeated and a second measurement is made. 

The original concentration C, the extraction efficiency A (0 /l S1), the concentration Ci recorded after the first, and C2 after the second measurement follow the equations 

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Often solvents do not extract 100% of the total radioactive residue. In this case, knowledge about the concentration of the target analyte(s) in the extract and the filter cake is necessary. Even if large amounts of radioactivity remain in the solid residual materials, the extraction efficiency may be sufficient if this unextracted radioactivity is permanently bound to the matrix or if it is associated with compounds which are not included in the residue definition. Finally, in all cases a well performed metabolism study can provide the answers needed, even where residues in the edible parts of treated crops or animals do not occur. If incurred residues do not occur, clearly the determination of extraction efficiency is not required. 

Consequently, separate experiments for the determination of extraction efficiency are often not required. An expert statement based on the results of metabolism studies is sufficient in most cases. These statements should also refer to the extraction solvent used for the analysis of samples of supervised trials. Residue levels found in these trials are the criterion for GAP and the basis for the setting of MRLs. Even if a solvent with insufficient extraction efficiency is used for samples from supervised trials, the later choice of better solvents would not result in lower safety for the consumer. 

The purge gas flow rate is kept constant at = 80 mL/min by a metal bellows flow controller (Porter Instruments, VCD-1000, see Fig. 23-1). A toggle valve downstream of the flow controller is used to stop the gas flow for maintenance of the system or for determination of extraction efficiencies, etc. The purity of the purge gas is checked by running the analytical programme without injection of seawater. 

Validation of true extraction efficiency normally requires the identification and quantitation of field-applied radiolabeled analyte(s), including resulting metabolites and all other degradation products. The manufacturer of a new pesticide has to perform such experiments and is able to determine the extraction efficiency of aged residues. Without any identification of residue components the calculation of the ratio between extracted radioactivity and total radioactivity inside the sample before extraction gives a first impression of the extraction efficiency of solvents. At best, this ratio is nearly 1 (i.e., a traceability of about 100%) and no further information is required. Such an efficient extraction solvent may serve as a reference solvent for any comparison with other extraction procedures. 

The concept of SPME was first introduced by Belardi and Pawliszyn in 1989. A fiber (usually fused silica) which has been coated on the outside with a suitable polymer sorbent (e.g., polydimethylsiloxane) is dipped into the headspace above the sample or directly into the liquid sample. The pesticides are partitioned from the sample into the sorbent and an equilibrium between the gas or liquid and the sorbent is established. The analytes are thermally desorbed in a GC injector or liquid desorbed in a liquid chromatography (LC) injector. The autosampler has to be specially modified for SPME but otherwise the technique is simple to use, rapid, inexpensive and solvent free. Optimization of the procedure will involve the correct choice of phase, extraction time, ionic strength of the extraction step, temperature and the time and temperature of the desorption step. According to the chemical characteristics of the pesticides determined, the extraction efficiency is often influenced by the sample matrix and pH. 

Determination of extractability of stabilisers is a substantial part of the rating of stabiliser efficiency where leaching is a common deterioration effect or where legislation requires quantitative data dealing with... 

In the supercritical phase, both temperature and pressure play a significant role in determining the extraction efficiency. After the short-lived retrograde solubility effect subsides at about 55-60°C, a transition of the system back to the mass transfer controlled situation will take place where increasing temperature will, once again, bring about a surge in the extraction efficiency. In fact, for the supercritical phase,... 

PTRs have received considerable attention as effective agents to facilitate the use of hydrogen peroxide, but require many parameters to be adjusted to obtain good selectivity. Among them are the nature and concentration of the PTRs, where in general, the length of the alkyl groups determines the extraction efficiency, the solvent, the pH of the aqueous phase, and the presence of salts like NaCl, which modifies the distribution of the species [154]. 

Known amounts of adipic acid and 1,4-butanediol were dissolved in acidic methanol and analyzed in order to determine the extraction efficiencies. Extraction efficiencies, 79% for adipic acid and 76% for 1,4-butanediol, were calculated by dividing the slope of the calibration curve for extracted samples by the slope of the calibration curve for non-extracted samples. Bearing in mind the different characters of the extracted compounds, the recoveries obtained by this single-step extraction were good. Flirschlag and KOster earlier used SPE to extract hydroxyacids and dicarboxylic acids from aqueous media [94]. Their recovery for adipic acid was 67% using a SDB-1 column from... 

From the pump the fluid travels to a heated zone, where it becomes supercritical, and then to an extraction vessel where the sample is contained. The extraction vessel and connecting tubes are housed in an oven, so the temperature is kept constant during extraction. Density determines the extraction efficiency and is dependent on pressure and temperature in the supercritical zone. It is essential to maintain a rigorous control of both parameters during the extraction. 

Determination HPLC extraction efficiencies of 60% or better 185 about 0.03 /ng/1 were obtained by extraction of 1.0 /ng/1... 

Because the extraction efficiency was determined by the direct comparison of dye concentration in the spiked dyebadi before and after the extraction, the higher SFE recoveries (e.g. efficiency >99%) should have relative standard deviations <1%. For the purpose of this study, >99% of recovery is sufficient to illustrate the effectiveness of the SFE technique. According to our experiments, no decomposition or breakdown of these disperse dyes was observed during SFE at the specified experimental conditions described atove. The restrictor flow rates of SC-CO2 often dominate the success of SFE, and can be varied to provide information on the dynamics of the extraction process. It is known that if the flow of supercritical fluid is sufficient to sweep the ceil void volume, the effectiveness of the extraction is enhanced. In fact, changing the flow rate is a simple way to determine the extraction efficiency (7). In this study, no obvious difference in extraction efficiency was observed at the SC-C02 flow rate of 2.0, and S.O mL/min. It is also noted that SFE of samples with high concentrations of water tends to plug fused silica restrictors 19). Therefore, a restrictor temperature controller was used in our experiments to avoid restrictor plugging. 

The glove juice method is considered to be an aggressive sampling technique however, results of experiments described above suggest that it does not recover 100% of bacteria placed on the skin. We conducted a smdy to specifically determine the extraction efficiency of the glove juice/plastic bag sampling procedure... 

It is important to know the efficiency of the solvent extraction process. Aliquots of solutions of perdeuterated chemical standards can be spiked onto the sorbents prior to extraction. The perdeuterated analogs of the analytes of interest have different retention times in chromatographic systems so that they are easy to detect. By evaluating the amount of standard extracted, one can determine the extraction efficiency of the compounds of interest. 

A simple method was described for the extraction and determination of ultratrace amounts of Cu(II) ions using octadecyl-bonded sihca membrane disks modified with a recently synthesized SchifPs base 2,2 -[l,2-ethane-diyl-hir-(nitriloethyhdyne)]-hir-(l-naphthalene). The pH effect, nature and amount of counter anions, flow rates, and type of stripping acid were evaluated as the important factors of extraction efficiency of metal ions. The capacity was found to be 396 p.g of copper for the membrane disks modified by 5 mg of the hgand. The limit of detection of the proposed method is 4 ng/lOOO ml. The structure of the organic modifier is given in Scheme 8. 

The recovery of an analyte in an assay is defined by the FDA in a strictly operational way as the detector response obtained Ifom an amount of the analyte added to and extracted from the biological matrix, compared to the detector response obtained for the true concentration of the pure authentic standard. Recovery pertains to the extraction efficiency of an analytical method within the limits of variability. Recovery of the analyte need not be 100 %, but the extent of recovery of an analyte and of the internal standard should be consistent, precise, and reproducible. Recovery experiments should be performed by comparing the analytical results for extracted samples at three concentrations (low, medium, and high) with unextracted standards that represent 100 % recovery (FDA 2001). In terms of the symbols used in Section 8.4, the recovery is thus defined as the ratio (R /R"), and is equivalent to determination of F provided diat no suppression or enhancement effects give rise to differences between R and R" and that the proportional systematic errors and 1 are negligible. The FDA definition of recovery also corresponds to that of the PE ( process efficiency ) parameter (Matuszewski 2003) discussed in Section 5.3.6a, since the former (FDA 2001) measures a combination of extraction efficiency and matrix effects (if any). 

The aromatic content of naphtha feeds to a BTX process can be measured by a procedure such as that described in ASTM method D4420 (19). Generally, a polar liquid phase is used on either an open tubular capillary or acid-washed Chromosorb P column. The aromatic content of the raffinate is used to determine the extraction efficiency and aromatic recovery of the process. A procedure similar to ASTM D4420 measures the trace levels in the raffinate (19). Stationary phases used here are also polar, and, in practice, the same chromatograph can be used for analyzing both the feed and raffinate if appropriate calibration procedures are used. The stationary phases used in ASTM D4420 are OV-275, SE-30, and OV-101. 

Sample preparation and limits of detection are also important determinants of the efficiency of such methods. In particular, non-selective extraction procedures are necessary for good recovery of molecules in a wide polarity range, including highly polar drugs not amenable to GC-MS. 

In a simple liquid-liquid extraction the solute is partitioned between two immiscible phases. In most cases one of the phases is aqueous, and the other phase is an organic solvent such as diethyl ether or chloroform. Because the phases are immiscible, they form two layers, with the denser phase on the bottom. The solute is initially present in one phase, but after extraction it is present in both phases. The efficiency of a liquid-liquid extraction is determined by the equilibrium constant for the solute s partitioning between the two phases. Extraction efficiency is also influenced by any secondary reactions involving the solute. Examples of secondary reactions include acid-base and complexation equilibria. 

For the extraction described in Example 7.14, determine (a) the extraction efficiency for two extractions and for three extractions and (b) the number of extractions required to ensure that 99.9% of the solute is extracted. 

In this work, a method based on the reduction potential of ascorbic acid was developed for the sensitive detennination of trace of this compound. In this method ascorbic acid was added on the Cr(VI) solution to reduced that to Cr(III). Cr(III) produced in solution was quantitatively separated from the remainder of Cr(VI). The conditions were optimized for efficient extraction of Cr(III). The extracted Cr(III) was finally mineralized with nitric acid and sensitively analyzed by electro-thermal atomic absorption spectrometry. The determinations were carried out on a Varian AA-220 atomic absolution equipped with a GTA-110 graphite atomizer. The results obtained by this method were compared with those obtained by the other reported methods and it was cleared that the proposed method is more precise and able to determine the trace of ascorbic acid. Table shows the results obtained from the determination of ascorbic acid in two real samples by the proposed method and the spectrometric method based on reduction of Fe(III). 

The effect of different pai ameters such as temperature, pressure, modifier volume, dynamic and static extraction time on the SFE of the plant were investigated. The orthogonal array experimental design method was chosen to determine experimental plan, (5 ). In this design the effect of five parameters and each at five levels were investigated on the extraction efficiency and selectivity [4]. 

As with urine, saliva (spumm) is easy to collect. The levels of protein and lipids in saliva or spumm are low (compared to blood samples). These matrices are viscous, which is why extraction efficiency of xenobioties amoimts to only 5 to 9%. By acidifying the samples, extraction efficiencies are improved as the samples are clarified, and proteinaceous material and cellular debris are precipitated and removed. Some xenobioties and their metabohtes are expressed in hair. Hair is an ideal matrix for extraction of analytes to nonpolar phases, especially when the parent xenobioties are extensively metabolized and often nondetectable in other tissues (parent molecules of xenobioties are usually less polar than metabolites). Hair is a popular target for forensic purposes and to monitor drug compliance and abuse. Human milk may be an indicator of exposure of a newborn to compounds to which the mother has been previously exposed. The main components of human milk are water (88%), proteins (3%), lipids (3%), and carbohydrates in the form of lactose (6%). At present, increasing attention is devoted to the determination of xenobioties in breath. This matrix, however, contains only volatile substances, whose analysis is not related to PLC applications. 

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