Elution extraction efficiency

Extraction efficiency. The efficiency of extractions of imidacloprid from vegetables and crops decreases in the order acetonitrile > acetone > ethyl acetate. Acetonitrile is not a suitable extraction solvent because of the large number of co-eluting peaks on the chromatograms on HPLC at 210 or 270 nm. ... 

Relative extraction efficiencies of polar polymeric neutral, cation, and anion exchange sorbents (HLB, MCX, and MAX) for 11 beta antagonists and 6 beta agonists in human whole blood were probed.109 Initial characterization of MCX and MAX for acidic and basic load conditions, respectively, showed that both the agonists and antagonists were well retained on MCX, while they were recovered from MAX in the wash with either methanol or 2% ammonia in methanol (see Table 1.6). Blood samples were treated with ethanol containing 10% zinc sulfate to precipitate proteins and the supernatants loaded in 2% aqueous ammonium hydroxide onto the sorbents. After a 30% methanol and 2% aqueous ammonia wash, the analytes were eluted with methanol (HLB), 2% ammonia in methanol (MCX), or 2% formic acid in methanol (MAX). The best recoveries were observed with MCX under aqueous conditions or blood supernatant (after protein precipitation) spiked sample load conditions (see Table 1.7). Ion suppression studies by post-column infusion showed no suppression for propranolol and terbutaline with MCX, while HLB and MAX exhibited suppression (see Figure 1.6). 

Elution with two aliqots instead of one improves extraction efficiency and recovery. The collected eluents can be analyzed directly, or dried and reconstituted. 

Studies on solid supports have shown that tlie pore size of the silica-based sorbents is of little importance in MSPD, but it should be considered as could vary with the sample. Particle size is of greater importance since particles as small as 3-20 m can lead to extended solvent elution times and plugged MSPD columns. However, 40 m particles with 60 Angstrom pores have been used extensively and successfully. Sorbents that have a blended range of particle size such as 40-100 m work equally well and can be used in most applications (101, 103). These materials also tend to be less expensive. Depending on the application, analysts can also use non-end-capped materials and materials with a range of carbon loading. Different applications may benefit, suffer, or be unaffected by these parameters, but workers should consider them to obtain the best extraction efficiency and the cleanest sample. 

The cleanup procedure used was discussed in the section entitled Resin Elution Concentration. The extraction procedure was not the optimum procedure that would result from the observations. The data indicated that a base extraction at pH >12 and a base-to-solvent ratio of 15 1 with multiple extraction steps were needed to maximize removal of the matrix interferences. However, the extraction efficiency must be balanced against minimal sample destruction and operational ease. 

Analysis of data from the factorials indicates that pH has a consistently significant effect on compound recoveries. A summary of the effect of pH level on compounds used in the study is given in Table VI. There is also an interaction between pH and primary column sorbent type for some compounds. This interaction suggests that at low sample pH, a C18 column will produce the best extraction efficiencies for phenolic compounds. The effect of adding methanol to the sample before extraction clearly produced odd results when the recovery data from the 24 factorial was analyzed by using half-normal plots. This effect will be studied in future work. Additionally, different elution solvents will be examined as well as new sorbent phases as they become available. 

Bitteur and Rosset (23) have applied solid phase extraction for the recovery of black currant aroma compounds from waste water. They passed solutions of known compounds in water through three different extraction columns, eluted each with either ethanol or dichloromethane and then analyzed the eluant to determine extraction efficiency. While this study was aimed at the recovery of aroma compounds on a commercial basis, their results demonstrated that reverse phase polymers can effectively be employed in the recovery of aroma compounds from dilute aqueous systems. 

A unique property of LC/API/MS is the extent to which the analyte signal is affected by the sample matrix or the existence of co-eluting analytes. This property can have a profound influence on sensitivity and assay reproducibility. Because of matrix-ion suppression, it is not possible to estimate extraction recovery by comparison of the signal from a neat sample to an extracted sample. This is because the reduction in signal represents the combined effects of recovery and ion suppression. As first shown by Buhrman et al., quantitative assessment of extraction efficiency is made by spiking the neat sample into an extracted blank and comparison of the result to a similar sample spiked before extraction [120]. Conversely, the extent of ion suppression is obtained by the comparison of the signals for a neat unextracted sample to the same neat solution spiked into an extracted matrix blank. 

DNA purification on microdevices, as currently performed, appears to meet the needs of the forensics community. That is, extraction efficiencies and capacities comparable to the conventional methods have been demonstrated. Most notably, these methods typically result in elution volumes on the order of 10 p,L or less, negating the need for an additional concentration step (e.g., Microcon) and, thus, further diminishing DNA loss and additional processing time. Because the commercially available kits accept limited volumes of DNA, concentration of the eluted DNA is commonly required in forensic samples in order to maximize the amount of template DNA added to the STR amplification. In addition, because the target amount of template DNA added to an STR reaction is important in order to minimize possible PCR artifacts such as allelic dropout, off-scale alleles, and so forth, DNA quantification following extraction is necessary. 

MIP for diclofenac [DEC] was synthesized by precipitation polymerization [Dai et al., 2011]. The MIP showed high affinity toward DEC in aqueous solution and was used as SPE material for the quantitative enrichment of DEC in environmental water samples. The parameters such as washing solvent, elution solvent and breakthrough volume, which affects the extraction efficiency of the MIPS were evaluated to achieve the selective pre-concentration of DEC from water samples and to reduce non-specific interactions. Recoveries of DEC extracted from tap water, river water and wastewater samples were higher than 95%. The MIPs were found to be highly reusable as the stability of the MIP did not vary even after 30 adsorption and desorption cycles. 

Sample solutions flow evenly through the thin ( 0.5 mm thick) membrane making intimate contact with the extractive particles. It would be very difficult to avoid uneven flow (channeling) through a 0.5 mm bed of loose particles packed into a SPE tube. Studies with very dilute solutions of a dye show that the dye is taken up by the uppermost part of the membrane and that the dye uptake is very even over the entire area of the circular disk. Owing to the small volume and extraction efficiency of the membrane disk, elution of retained analytes requires a much smaller volume of eluting solvent than SPE cartridges. 

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