Analytes quantitative recovery

In the present work, the technique of XO and MTB immobilization onto silica gel in the form of its complexes with Fe(III) and Bi(III) respectively were found. The acid - base and chemical-analytical characteristics of solid-phase reagents were examined. The optimal conditions of quantitative recovery of Pb(II) and Zn(II) from diluted solutions, such as acidity of aqueous phase, the mass of the sorbents, the volume of solutions and the time of equilibrium reaching, were found. The methods of and F" detenuination were based on a competitive reactions of Zr(IV) with immobilized MTB and or F". Optimal conditions of 0,0 and F" determination in solution using SG, modified ion associates QAS-MTB (pH = 1,5, = 5-10 mol/1). 

Low-level interferences are present in ground- and surface water samples. The water-methanol (4 1, v/v) wash in the SPE phase of the sample workup is intended to minimize these interferences while maintaining quantitative recovery of the analytes. A solvent blank may be injected with the samples as part of an analytical set to confirm the cleanliness of a solvent used. 

Isotope dilution techniques are attractive because they do not require quantitative recovery of the analyte. One must, however, be able to monitor specific isotopes which is possible by using mass spectrometry. 

One of the advantages of the isotope dilution technique is that the quantitative recovery of the analytes is not required. Since it is only their isotope ratios that are being measured, it is necessary only to recover sufficient analyte to make an adequate measurement. Therefore, when this technique is used in conjunction with graphite furnace atomic absorption spectrometry, it is possible to determine the efficiency of the preconcentration step. This is particularly important in the analysis of seawater, where the recovery is very difficult to determine by other techniques, since the concentration of the unrecovered analyte is so low. In using this technique, one must assume that isotopic equilibrium has been achieved with the analyte, regardless of the species in which it may exist. 

Elution This final step is to recover retained analytes, otherwise the matrix-free solution and rinsings from the second and third steps are combined for quantitative recovery of the analyte before completion... 

Presently, FAB-MS spectra are routinely used to characterize synthetic tyrosine O-sulfate peptides.152,57,63-671 Since partial hydrolysis of the sulfate ester occurs in the gas phase, quantification of the tyrosine O-sulfate residue by mass spectrometry is not possible, but combined with one-peak assignment in HPLC, FAB-MS represents a powerful analytical tool. On the other hand, partial hydrolysis in the gas phase excludes the presence of sul-fonated species which should be perfectly stable. In early studies the presence of such species were excluded by quantitative recovery of tyrosine upon acid hydrolysis or upon hydrolysis with arylsulfatase.1361 Recently, even MALDI-TOF-MS spectra of CCK-peptides1441 and of conotoxins a-PnIA and a-PnlB 138 were reported which show that in the positive-ion mode the [M + H-S03]+ ions represent the base peaks, while in the negative-ion mode, [M-H]-ions consistently correspond to the base peaks. In the CCK peptides intramolecular salt bridging of the sulfate hemi-ester with proximal positive charges of arginine or lysine side chains was found to reduce the extent of hydrolysis in the gas phase significantly.144,1491... 

Liquid-liquid partitioning has been used for many years for Ure purification of sulfonamides and diaminopyrimidine potentiators. When partitioning from an organic into an aqueous phase, the adjustment of the pH of Ure aqueous phase is critical to obtain quantitative recoveries.. Sulfonamides are generally extracted from Ure primary organic sample extract into strong acidic (238, 239, 242, 249, 252-254) or basic (241, 248, 255) aqueous solutions. For better sample cleanup, back-extraction of Ure analyte(s) into dichloromethane (241, 253, 254), or ethyl acetate (256), after pH adjustment of the aqueous phase at values between 5.1... 

In analytical work on speciation, methods of wet sample preparation are very important parts of the overall scheme of analysis. Constraints on preparation methods include low concentrations of analytes, often less than 0.1 mgg-1, stabilities of the analytes, and the need for suitable solutions for instrumental techniques of elemental determinations. Volume of sample and type of matrix must be considered. Procedures for the quantitative recoveries of organometallic compounds from sediments and organic matrices can be time-consuming. Their efficiencies and reliabilities must be thoroughly tested for each type of sample for analysis. 

Often, the matrix spike cannot be carried out at the same time as the analysis. The spiking is carried out separately on either the same matrix or on one that resembles the samples. In the example above, clean soil can be spiked with regular chlorophenol and then the recovery is measured. However, one should be careful in choosing the matrix to be spiked. For instance, it is easy to extract different analytes from sand, but not so if the analytes have been sitting in clay soil for many years. The organics in the soil may provide additional binding for the analytes. Consequently, a matrix spike may be extracted more easily than the analytes in real-world samples. The extraction spike may produce quantitative recovery, whereas the extraction efficiency for real samples may be significantly lower. This is especially true for matrix-sensitive techniques, such as supercritical extraction. 

Collection of metal complexes of the analytes on suitable adsorbing materials is often employed as an enrichment step in combination with flame methods. In a procedure proposed by Solyak et al. [20], five metals [Co(II), Cu(II), Cr(III), Fe(III), and Pb(II)] were complexed with calmagite 3-hydroxy-4-[(6-hydroxy-m-tolyl)azo]-naphthalenesulfonic acid and subsequently collected on a soluble cellulose nitrate membrane filter. In this way an effective separation from alkaline and alkaline earth metals was achieved, based on the differences in their complex formation constants and those of the transition elements. The experimental parameters were optimized for the quantitative recovery of the elements. After hot dissolution of the filter with HNO3, the analytes were determined by FAAS. Minimum detectable concentrations ranged from 0.06 pg l-1 for Cu to 2.5 pg l-1 for Cr. 

TLC can be applied to the preliminary isolation of the compound under analysis from complex mixtures or to the purification of the products after a derivatization reaction. Several examples of TLC conditions for various substances and/or derivatives are given in Table 2.1. In all instances TLC must be carried out in such a way that it will contribute to the solution of a given analytical problem and that it should not become a source of difficulties and errors. As in the preceding instance, contamination of the sample with incidental impurities from the solvents used should be prevented. Chromatographic materials should also be tested for the presence of substances that could interfere with the compounds under analysis in the chromatogram. The quantitative recovery of individual zones from the layer for further treatment is obviously a prerequisite for reliable results. 

In the absence of suitable reference materials, the procedure should be tested using different sample weights and also measuring recoveries of element added at the beginning of the procedure. It must be remembered, however, that these criteria although necessary, are not sufficient, for the complete demonstration of the validity of the analytical procedure. The application of an independent (different in all respects of sample treatment and analyte quantitation) analytical method to a homogeneous practice sample would provide very useful confirmation of method reliability. 

A further advantage of combining IPC and MS is that isotope-labeled internal standards may be used for accurate quantification of analytes. No recovery check is needed for analytes because the labeled analogues of the analytes that serve as internal standards are added to the samples before the extraction step. This allows sample mixtures to be analyzed without pretreatment because the labeled internal standards share the fate of the un labeled analyte during sample processing without differences in extraction efficiency between the labeled standards and unlabeled analytes. This method achieved excellent precision and improved linearity of calibration lines despite interference from sample matrices in the quantitative analysis of important secondary intracellular metabolites in a complex biological sample solution from cultured cells. The technique is a valuable strategy for metabolomics [75],... 

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