Correlation techniques, wavelength analysis

It is important to note that although multivariate techniques such as PCR and PLS appear to allow the development of more accurate calibrations, single-wavelength analysis also demonstrated acceptable results. Therefore, after having identified a wavelength region that correlates well with reference method results, it may be possible to employ less expensive filter type spectrometers for at-line applications. 

One of the most important considerations is the concentration of the component being measured. The larger the concentration, the more options for the analyst. When considering vibrational spectroscopic analyzers, a major component will have numerous wavelengths at which it may be anal)rzed. Minor components require the analyst to seek wavelengths at which they have major absorbances and, almost invariably, use multiple wavelength correlation techniques such as partial least squares (PLS) or principle component analysis. 

Direct correlation between thermal radiation spectroscopic techniques and thermocouple temp measurements have been obtained for a pyrot mixt containing the agent CS and the simulant 1-methylaminoanthraquinone (Ref 28). Using rapid-scan spectroscopy for time resolution of the reaction, together with two-line analysis and max radiant energy wavelength techniques, the spatial, temporal and thermal history is documented... 

Faix et al. [34] analyzed the phenolic hydroxyl contents of milled wood lignins from 42 plant species. Aminolysis [35,36] was the most accurate and reprodncible technique. The H NMR and FTIR techniqnes were similar to each other in their correlations with the aminolysis results (correlation coefficient R = 0.77 and 0.75, respectively). The correlation of the As techniqne (analysis wavelength 250 nm) was poorer, with R = 0.57. 

Atomic absorption spectroscopy involves beaming light of an appropriate wavelength into a flame into which the sample has been sprayed, and thus contains an atomic vapour of the metal. The diminution in the intensity of the radiation is correlated with the concentration of the element. The majority of atoms in the flame remain in the ground state, so the technique is potentially more sensitive than flame photometry. The first application of atomic absorption in quantitative analysis was the determination of mercury by Hewlett in 1930, but it was not until after A. Walsh introduced the hollow cathode lamp as the light source in 1955 that the method came into general use. Today, it is the most widely used method of estimating metals in solution, but is likely to be overtaken in the future by inductively coupled plasma spectroscopy. 

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