Synchronous scanning fluorescence

Pharr D, McKenzie J, Hickman A. 1992. Fingerprinting petroleum contamination using synchronous scanning fluorescence spectroscopy. Ground Water 30(4) 484-489. 

White et al. have reported a rapid fluorimetric determination of chlorpromazine by an in situ photochemical oxidation [139]. Variable-angle synchronous scanning fluorescence spectroscopy has also been applied to the determination of chlorpromazine and its sulfoxide [140]. 

Sikorska, E., Gorecki, T., Khmenlinskii, I.V., Sikorski, M., and Koziol, J. 2005. Classification of edible oils using synchronous scanning fluorescence spectroscopy. Food Chem. 89, 217-225. 

Peuravuori, J., Koivikko, R., and Pihlaja, K. (2002b). Characterization, differentiation and classification of aquatic humic matter separated with different sorbents synchronous scanning fluorescence spectroscopy. Water Res. 36,4552-4562. 

Synchronous-scanning fluorescence (SSF) relies on the inherent spectra behavior of some PAHs [4]. In many PAHs (those with a strong 0 to 0 transition) the highest wavelength excitation band is only a few nanometers lower than the lowest-wavelength emission band. These two bands are also the most intense in each of their respective spectra. This difference... 

Figure 6. Synchronous-scanning fluorescence spectrum of a mixture of standard PAHs.

The use of modem analytical methods has led to the determination of the PAHs which are produced in catalytic hydrocrackers. A variety of HPLC-DAD, fluorescence, and UV absorbance methods were developed to determine the occurrence of the PAHs. These PAHs result from a small number of reactions. These are either a new ring forming through two-or four-carbon addition or the condensation of pyrene, coronene, or ovalene. The latter reactions result in very large PAHs which cause process problems because of their low solubilities. Their production rates (and eventual precipitation in the process streams) can be monitored through the use of UV absorbance and fluorescence spectrometries. A synchronous-scanning fluorescence method was developed to monitor the production of dicoronylene during process operation. The results of these analyses can then be used to determine process performance. 

Fixed wavelength and synchronous scanning fluorescence suffer from non-selectivity and are generally Ineffective in structural elucidation (particularly for mixtures). Despite the ability to select both the excitation and emission wavelengths, the conventional luminescence methods have limited applicability since most spectra of complex mixtures often cannot be satisfactorily resolved. The use of a computer-controlled total scanning fluorometer can overcome many of the limitations of previous methods. 

J. C. Fetzer, The Use of Synchronous-Scanning Fluorescence Spectrometry for Detection of Dicoronylene in Hydrocracker Streams, Polycyclic Aromatic Compounds 7 269-274 (1995). 

Patterson, H. H., C. S. Cronan, S. Lakshman, B. J. Plankey, andT. A. Taylor. 1992. Comparison of soil fulvic acids using synchronous scan fluorescence spectroscopy, FTIR, titration and metal complexation kinetics. Science of The Total Environment 113, no. 1-2 179-196. doi 10.1016/0048-9697(92)90024-M. 

The EEM profiles of fractions obtained by the isolation procedure of the DOM by the XAD resins showed that a fractionation was effective and the XAD-8 eluate is highly representative of the original DOM. Emission scan spectra of DOM and its fractions are featureless, whereas synchronous scan spectra show that the isolation procedure is efficient in separating the original DOM into fractions with different fluorescence properties. The synchronous scan spectra obtained with a wavelength offset of 20 nm present multicomponent samples such as the DOM fractions from landfill leachate. 

Wakeham [14] has discussed the application of synchronous fluorescence spectroscopy to the characterization of indigenous and petroleum derived hydrocarbons in lacustrine sediments. The author reports a comparison, using standard oils, of conventional fluorescence emission spectra and spectra produced by synchronously scanning both excitation and emission monochromators. 

Bidimensional fluorescence spectra are commonly obtained in the three modes of emission, excitation, and synchronous-scan excitation, whereas tridimensional fluorescence (or total luminescence) spectra are obtained in the form of excitation-emission matrix (EEM) plots by measuring the fluorescence intensity emitted as a function of the wavelength over a range of excitation wavelengths. This technique allows to obtain more detailed information than that obtained by using conventional monodimensional fluorescence (Mobed et al., 1996). Fluorescence spectroscopy has provided valuable information on the molecular structure, functionalities, conformation, and intramolecular and intermolecular interactions of HS from organic amendments and unamended and amended soils (Senesi et al., 1990,1996, 2007 Mobed et al., 1996 Chen et al., 2003 Senesi and Plaza, 2007). 

Synchronous Scan. Emission and excitation monochromator scan at the same speed with a determined wavelength difference. This kind of scan is usually applied to study complex materials with several fluorophors or in mixtures of several fluorescent substances. The result of a synchronous scan is a product of excitation and emission spectra. This tool produces more defined peaks for interpreting the behavior of chemical structures during a dynamical process. 

Figure 16.37. Typical examples of fluorescence spectra of humic acids from Brazilian soil (Hapludox) under different tillage systems. The samples were prepared in aqueous solutions (20 mg liter-1, pH 8). (a) Fluorescence emission (Xexc = 240nm). (b) Fluorescence synchronous-scan excitation spectra (AX = 55 nm). (c) Fluorescence excitation spectra (Xem = 517 nm). (d) Fluorescence emission spectra (Xoxc = 465 nm).

Figure 16.39. Data showing correlation among fluorescence methods to determine humification degree of HA. A4AX is the humification index proposed by Zsolnay et al. (1999) it is calculated through the ratio between areas of the upper quarter of emission spectra (435-480nm) and the lower quarter (30( M45 nm) when excitation is made at 240nm. Iv is the humification index proposed by Kalbitz et al. (1999) it is calculated through the ratio of peak intensities in 465 and 399 nm measured in fluorescence synchronous-scan excitation spectra. A46S is the humification index proposed by Milori et al. (2002) it is calculated by fluorescence area of emission spectra when the excitation is made at 465 nm.

Fig. 7. Excitation, fluorescence, and synchronously-scanned spectra of oestrone in ethanol, and their second derivatives. A, excitation spectrum monitored at a fluorescence wavelength, Af B, fluorescence spectrum obtained at an excitation wavelength, Aex C, synchronously-scanned spectrum obtained with a constant interval, AA, between the excitation and emission monochromators. (From A. F. Fell, in Proc. 1st Symp. Anal. Steroids, Eger, Hungary, S. Gorog (Ed.), Amsterdam, Elsevier Press, 1982, pp. 495-510.)...

A number of less commonly used analytical techniques are available for determining PAHs. These include synchronous luminescence spectroscopy (SLS), resonant (R)/nonresonant (NR)-synchronous scan luminescence (SSL) spectrometry, room temperature phosphorescence (RTP), ultraviolet-resonance Raman spectroscopy (UV-RRS), x-ray excited optical luminescence spectroscopy (XEOL), laser-induced molecular fluorescence (LIMP), supersonic jet/laser induced fluorescence (SSJ/LIF), low- temperature fluorescence spectroscopy (LTFS), high-resolution low-temperature spectrofluorometry, low-temperature molecular luminescence spectrometry (LT-MLS), and supersonic jet spectroscopy/capillary supercritical fluid chromatography (SJS/SFC) Asher 1984 Garrigues and Ewald 1987 Goates et al. 1989 Jones et al. 1988 Lai et al. 1990 Lamotte et al. 1985 Lin et al. 1991 Popl et al. 1975 Richardson and Ando 1977 Saber et al. 1991 Vo-Dinh et al. 1984 Vo- Dinh and Abbott 1984 Vo-Dinh 1981 Woo et al. 1980). More recent methods for the determination of PAHs in environmental samples include GC-MS with stable isotope dilution calibration (Bushby et al. 1993), capillary electrophoresis with UV-laser excited fluorescence detection (Nie et al. 1993), and laser desorption laser photoionization time-of-flight mass spectrometry of direct determination of PAH in solid waste matrices (Dale et al. 1993). 

Lin CH, Fukii H, Imasaka T, et al. 1991. Synchronous scan luminescence techniques monitoring resonance and non-resonance fluorescence in supersonic jet spectrometry applied to anthracene derivatives. Anal Chem 63(14) 1433-1440. 

Synchronous scanning techniques have also been applied to the quantitative analysis of fluorescent substances. Synchronous scanning involves scanning both the excitation and emission monochromators simultaneously, while maintaining a constant wavelength interval between them. The technique has been employed in the analysis of multicomponent preparations. The technique is reported to simplify the spectra of multicomponent samples and reduce the bandwidths of fluorescence spectra. The equation relating the measured fluorescence to concentration is given by... 

Fluorescence applied to oil identification has been an active field, with 17 papers presented on the subject at the last three Pittsburgh Conferences. A number of interesting developments for fluorescence and low-temperature luminescence (LTL) are described by Eastwood et al. (58). These include synchronous scanning, difference spectrofluorometry, synchronous difference spectroscopy, derivative spectroscopy, and total luminescence (or contour) spectroscopy and combinations of these techniques. In a recent presentation, Eastwood and Hendrick (59) reported an extension of their low-temperature luminescence studies to include polarized excitation and emission spectroscopy, and time-resolved phosphorescence. Preliminary studies of polarization effects indicate that differences exist in low-temperature polarized luminescence spectra of oils, which may aid in oil identification. In the time-resolved phosphorescence spectra of oils, the most significant difference observed was enhancement of the vanadyl porphyrin signal at approximately 700 nm for short delay times (20 fxsec). 

Extraction and Separation. After cooling, the product mixture was an amorphous solid. The product mixture and the reaction vessel were ground and placed in a 250-mL Soxhlet thimble. The mixture could not be easily broken up, removed from the vessel, and extracted separately thus, a small reaction vessel was sacrificed for each reaction to ensure that all product PAHs were collected. The material was exhaustively extracted in a Soxhlet apparatus with 500 mL of dichloromethane. The solution fluoresced an intense green when UV light was shown on it with a handheld light (Ultraviolet Products). This method was used to monitor the extent of extraction. The extraction typically lasted 75 h, and one Soxhlet cycle occurred every 10 min. After the dichloromethane extraction, the Soxhlet thimbles were immersed in 1,2,4-trichlorobenzene at 175 °C for 1 day to ensure that all the PAHs were removed. Synchronous scanning spectrofluorometry showed only traces of PAHs that were already seen in the dichloromethane extract. 

---