Quantitation recovery of analytes

Ensuring high-quality analytical performance in trace analysis, if separation of sample components by extraction is indispensable, requires implementation of the appropriate extraction method and establishment of suitable operational parameters to ensure a high efficiency of extraction. Selection of extraction conditions is crucial for quantitative recovery of analyte, or at least for sufficient effectiveness. If an aqueous solution is one of the extraction phases, problems such as complex-ation, hydrolysis, and solvation can play an important role. Extraction of elements from aqueous to organic phase often requires selection of appropriate ligands and control of pH. 

An important difference between the batch and the continuous mode of precipitation is the available reaction time. Different standing times are normally used in batch procedures to ensure the completeness of the precipitation reaction or/and the form of the precipitate to facilitate filtration and minimize contamination. Standing times of IS min to a few hours are typical, occasionally with elevated temperatures. Such procedures are obviously not feasible in continuous on-line precipitation systems where reaction times are typically in the range of a few seconds to a few tens of seconds. Quantitative recovery of analyte through precipitate collection is therefore not likely unless the precipitation (or coprecipitation) process is extremely fast. 

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). 

Residue study protocols typically either include quality specifications for analytical procedures or refer to a written analytical method that includes such specifications. The protocol for an LSMBS should also include analytical quality specifications, either directly or by reference to a method. Analytical specifications usually include minimum and maximum recovery of analyte from fortified control samples, minimum number of such fortifications per set of samples, minimum linearity in calibration, minimum stability of response to injection of calibration solutions, and limits of quantitation and of detection. 

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. 

HPLC/MS and HPLC/MS/MS analyses are susceptible to matrix effects, either signal enhancement or suppression, and are often encountered when the cleanup process is not sufficient. To assess whether matrix effects influence the recovery of analytes, a post-extraction fortified sample (fortified extract of control sample that is purified and prepared in the same manner as with the other samples) should be included in each analytical set. The response of the post-extraction fortified sample is assessed against that of standards and samples. Matrix effects can be reduced or corrected for by dilution of samples, additional cleanup, or using calibration standards in the sample matrix for quantitation. 

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... 

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. 

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. 

Alkaline oxidizing fusion is an effective way of dissolution of metallic powders, particularly of metals resistant to direct wet acid treatment (Ru, Os, and Ir), but is rarely used for decomposition of complex noble metal samples because of low recoveries (e.g., 34—84 % Pt, Pd, and Au from silicate materials) [64]. Low stability of the complexes formed under dissolution (water, HCl) of the melt and difficulties with quantitative conversion of analytes into complexes of strictly defined composition (suitable for subsequent separation) limit the applicability of the alkaline fusion method. Hydroxocomplexes easily formed in the solutions can cause problems with quantitative separation and preconcentration of the metals, particularly when using ion-exchange chromatography. 

One major advantage of stable Isotope dilution methodology Is that quantitative recovery of the analyte Is not required Both the analyte and the added spike are Identical chemically, so Incomplete recoveries will affect both analyte and spike In the same way In this regard the enriched spike serves not only as... 

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