Excitation-emission matrix concentrations

Figure 16.41. Fluorescence excitation-emission matrix spectra of humic acids (HA) isolated from municipal solid waste compost (MSWC), from soil amended with MSWC at 40tha 1yr 1 (MSWC40), and from the corresponding unamended control soil (MSWC0), in the absence and presence of Cu2+, Zn2+, Cd2+, and Pb2+ ions at a total concentration of 40 xmol liter-1. EEWPmax denotes the excitation/emission wavelength pairs at maximum fluorescence intensity (Plaza et al., 2006).

Fig. 2. A three-dimensional excitation/emission matrix for coastal surface seawater (Florida Bay, South Florida) showing excitation/emission maxima at 240/385 nm, 240/435 nm, 320/400 nm and 350/450 nm. Concentrated by ultrafiltration (500 Dalton cut-off membrane) pathlength = 1 mm Hewlett Packard 1100 FLD (G1321 A)...

Fig. 9. ODMR investigations at T = 1.4 K of Pd(2-thpy)2 dissolved in an n-octane Shpol skii matrix. Concentration = 10 mol/1 cw excitation Ag c = 330 nm (30.3 x 10 cm 0- Detection of the emission at 18418 cm (Tj —> Sq transition), (a) Zero-field ODMR (optically detected magnetic resonance) spectrum (b) Zero-field microwave recovery ODMR signal after pulsed microwave excitation with a microwave frequency of 2886 MHz. The best fit of the recovery signal is obtained with Eq. (4). (Compare Ref. [61])...

Figure 6.8. Example of the use of rank annihilation factor analysis for determining the concentration of tryptophane using fluorescence excitation-emission spectroscopy. In the top left plot the unknown sample is shown. It contains three different analytes. The standard sample (only tryptophane) is shown in the top right plot. In the lower right plot, it is shown that the smallest significant (third from top) singular value of the analyte-corrected unknown sample matrix reaches a clear minimum at the value 0.6. In the lower left plot the unknown sample is shown with 0.6 times the standard sample subtracted. It is evident that the contribution from the analyte is practically absent.

Up to this point, regression has been restricted to two blocks of two-way data Y and X. In chemical analysis, however, a growing number of problems can be cast as three-way regression analysis. Consider the calibration of chemical constituents on the basis of their fluorescence excitation/emission spectrum or of gas chromatography/mass spectrometry (GC/MS) data. For each sample, two-dimensional measurements are available that constitute a three-way data array, X. This data array has to be related to sample concentrations of one, vector y, or several analytes, matrix Y. Cases can be imagined where even the matrix Y constitutes a three-way data array. 

Standardizing the Method Equations 10.32 and 10.33 show that the intensity of fluorescent or phosphorescent emission is proportional to the concentration of the photoluminescent species, provided that the absorbance of radiation from the excitation source (A = ebC) is less than approximately 0.01. Quantitative methods are usually standardized using a set of external standards. Calibration curves are linear over as much as four to six orders of magnitude for fluorescence and two to four orders of magnitude for phosphorescence. Calibration curves become nonlinear for high concentrations of the photoluminescent species at which the intensity of emission is given by equation 10.31. Nonlinearity also may be observed at low concentrations due to the presence of fluorescent or phosphorescent contaminants. As discussed earlier, the quantum efficiency for emission is sensitive to temperature and sample matrix, both of which must be controlled if external standards are to be used. In addition, emission intensity depends on the molar absorptivity of the photoluminescent species, which is sensitive to the sample matrix. 

The quantification algorithm most commonly used in dc GD-OES depth profiling is based on the concept of emission yield [4.184], Ri] , according to the observation that the emitted light per sputtered mass unit (i. e. emission yield) is an almost matrix-independent constant for each element, if the source is operated under constant excitation conditions. In this approach the observed line intensity, /ijt, is described by the concentration, Ci, of element, i, in the sample, j, and by the sputtering rate g, ... 

With analytical methods such as x-ray fluorescence (XRF), proton-induced x-ray emission (PIXE), and instrumental neutron activation analysis (INAA), many metals can be simultaneously analyzed without destroying the sample matrix. Of these, XRF and PEXE have good sensitivity and are frequently used to analyze nickel in environmental samples containing low levels of nickel such as rain, snow, and air (Hansson et al. 1988 Landsberger et al. 1983 Schroeder et al. 1987 Wiersema et al. 1984). The Texas Air Control Board, which uses XRF in its network of air monitors, reported a mean minimum detectable value of 6 ng nickel/m (Wiersema et al. 1984). A detection limit of 30 ng/L was obtained using PIXE with a nonselective preconcentration step (Hansson et al. 1988). In these techniques, the sample (e.g., air particulates collected on a filter) is irradiated with a source of x-ray photons or protons. The excited atoms emit their own characteristic energy spectrum, which is detected with an x-ray detector and multichannel analyzer. INAA and neutron activation analysis (NAA) with prior nickel separation and concentration have poor sensitivity and are rarely used (Schroeder et al. 1987 Stoeppler 1984). 

Fig. 3. Emission spectra of Pd(2-thpy)2 (a) in an n-octane Shpol skii matrix (line spectrum) and (b) in butyronitrile (broad band spectrum) at T = 1.3 K, Aexc = 337.1 nm (N2-Laser). The energies of the vibrational satellites are specified relative to the electronic origin at 18,418 cm f The structures marked by asterisks on the high energy side of the electronic origin result from other sites and vanish with a site-selective excitation, e.g. at 19,113 cm (18,418 cm i -1-695 cm vibrational satellite). Concentration of Pd(2-thpy)2 10 mol/1. Note Fora better comparison, the broad band spectrum is shifted by 200 cm to lower energy. (Compare Ref. [56])...

Fig. 27. Emission spectrum of (b) Pt(2-thpy-h6)(2-thpy-d6) at T=1.3 K of site A. For comparison, the spectra of (a) Pt(2-thpy-hg)2 and (c) Pt(2-thpy-d6)2 are also reproduced. (Compare Fig. 25.) The compounds are dissolved in an n-octane matrix (= Shpol skii matrix) with a concentration of c = 10 mol/1. The compounds (a) and (c) are excited at Aexc = 457,9 nm (A 21,839 cm while the partially deuterated compound (b) is site-selectively excited at the elec-...

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