Aqueous solutions spectral-analysis technique

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 . 

The intense absorption of water over most of the infrared spectrum restricts the regions where aqueous solutions of carbohydrates can be usefully studied. Absorbance subtraction makes it possible to eliminate water absorbance and magnify the remaining spectral features to the limit of the signal-to-noise ratio. Many other data-processing techniques, such as the ratio method,4 the least-squares refinement,5 and factor analysis,6 should be of benefit in the study of carbohydrate mixtures. 

The Raman spectra of neat glacial acetic acid and its aqueous solutions at different temperatures were studied in detail by Semmler and Irish [165] using factor analysis, difference spectroscopy, and band resolution techniques. The complex spectral region between 800 and 1850 cm" is discussed assuming the presence of up to four different species monomer (M), cyclic dimer (C), open (or linear) dimer (L), and chain polymers (P) whose concentrations change under the effect of both the temperature and the concentration, as can be observed in Fig. 11. In glacial acetic acid, the effects of the temperature rise are (1) the progressive disappearance of the polymeric forms, (2) the presence, above 150°C, of monomeric species, and (3) the transformation of closed dimers into lineal... 

Compared with other spectroscopic methods, these techniques include advantages of nondestructive analysis, easy spectral measurement, high sensitivity, and simple spectral analysis. These studies show that FUV and DUV spectroscopy are the promising analytical method not only for aqueous solutions but also for analyses of organic components such as polymer films. 

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