Sample application aqueous solutions

In Fig. 16.32, application of a TSK PW SEC system consisting of a combination of precolumn + PWM + 6000 + 5000 + 4000 + 3000 demonstrates a possibility for analytical purposes to change from DMSO-dissolved glucans to an aqueous solution. An initially DMSO-dissolved potato starch sample was applied to the TSK PW system and because separated with an aqueous... 

Fixed pathlength transmission flow-cells for aqueous solution analysis are easily clogged. Attenuated total reflectance (ATR) provides an alternative method for aqueous solution analysis that avoids this problem. Sabo et al. [493] have reported the first application of an ATR flow-cell for both NPLC and RPLC-FUR. In micro-ATR-IR spectroscopy coupled to HPLC, the trapped effluent of the HPLC separation is added dropwise to the ATR crystal, where the chromatographic solvent is evaporated and the sample is enriched relative to the solution [494], Detection limits are not optimal. The ATR flow-cell is clearly inferior to other interfaces. 

Applications Quantitative dry ashing (typically at 800 °C to 1200°C for at least 8h), followed by acid dissolution and subsequent measurement of metals in an aqueous solution, is often a difficult task, as such treatment frequently results in loss of analyte (e.g. in the cases of Cd, Zn and P because of their volatility). Nagourney and Madan [20] have compared the ashing/acid dissolution and direct organic solubilisation procedures for stabiliser analysis for the determination of phosphorous in tri-(2,4-di-t-butylphenyl)phosphite. Dry ashing is of limited value for polymer analysis. Crompton [21] has reported the analysis of Li, Na, V and Cu in polyolefins. Similarly, for the determination of A1 and V catalyst residues in polyalkenes and polyalkene copolymers, the sample was ignited and the ash dissolved in acids V5+ was determined photo-absorptiometrically and Al3+ by complexometric titration [22]. 

EFFECT OF OIL. Titrations were performed in which small amounts of decane were added with the surfactant sample. The results were found to be insensitive to the presence of up to 2 cm3 of the decane. This allows the application of the method to both simple aqueous solutions and microemulsions containing significant quantities of decane. 

In view of this situation we studied a number of samples of Mn02 with different composition and various OH" contents in order to estimate the correlation between the activity of Mn02 and concentration of OH" ions. This compound can be electrochemically deposited on the anode from various aqueous solutions, but electrolytes with sulfate and ammonia sulfate have found widest application [3], It has been determined that the composition and structural parameters of the end-product are governed by the presence of fluoride ion in electrolyte. 

A convenient method is the spectrometric determination of Li in aqueous solution by atomic absorption spectrometry (AAS), using an acetylene flame—the most common technique for this analyte. The instrument has an emission lamp containing Li, and one of the spectral lines of the emission spectrum is chosen, according to the concentration of the sample, as shown in Table 2. The solution is fed by a nebuhzer into the flame and the absorption caused by the Li atoms in the sample is recorded and converted to a concentration aided by a calibration standard. Possible interference can be expected from alkali metal atoms, for example, airborne trace impurities, that ionize in the flame. These effects are canceled by adding 2000 mg of K per hter of sample matrix. The method covers a wide range of concentrations, from trace analysis at about 20 xg L to brines at about 32 g L as summarized in Table 2. Organic samples have to be mineralized and the inorganic residue dissolved in water. The AAS method for determination of Li in biomedical applications has been reviewed . 

Selecting the C-bound protons before performing a homonuclear two-dimensional experiment enables to measure small heteronuclear coupling constants [16]. Such an experiment with a sample of natural isotopic abundance was first published by Otting and Wuthrich in 1990, where the half-filter element with spin-lock purge pulse was used to select the C-bound protons in a small protein in aqueous solution [6]. Later applications illustrated the usefulness of the same half-filter element with smaller molecules [17, 18]. 

At least three methods have been found to be applicable to the solubilization of chemically modified wood. The first experiment (4) (Direct method) employed severe dissolution conditions. For example, in 20-150 min at 200-250°C, wood samples esterified by a series of aliphatic acids could be dissolved in benzyl ether, styrene oxide, phenol, resorcinol, ben-zaldehyde, aqueous phenol solutions, etc. For carboxymethylated, ally-lated and hydroxyethylated woods, the conditions provided for dissolution in phenol, resorcinol or their aqueous solutions, formalin, etc., by standing or stirring at 170°C for 30 to 60 min (5). 

Derivatization After Desorption. Alkanolamines, highly polar basic compounds, present a difficult analytical problem. Although direct gas chromatographic separations can be achieved, this technique is not applicable to trace analysis due to sorption problems at trace concentrations. A derivatization/gas chromatographic procedure has been developed for the determination of alkanolamines in air as low as 100 ppb (54,55). The samples are collected on activated alumina and desorbed with an aqueous solution of 1-octanesulfonic acid. The... 

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