Application of Fluorescence Spectroscopy in Chemical Oceanography
Application of Fluorescence Spectroscopy in Chemical Oceanography: Tracing Colored Dissolved Organic Matter (CDOM) Erika Mae A. Espejo
3rd year, BS Chemistry, University of the Philippines, Diliman
Abstract Dissolved organic matter (DOM), the fraction passing through a 0.45 µm membrane filter, is considered poorly understood mixture of organic polymers because of its complexity. Although it largely influences a lot of biogeochemical processes in aquatic environments, its characterization is not that simple. However, due to the fact that it comprises optically active fraction called colored dissolved organic matter (CDOM) together with the help of its colloidal components, tracing of DOM can be possible. Through different methods and instruments such as fluorescence excitation-emission spectroscopy, parallel factor analysis (PARAFAC), isolation-fractionation technique (pairing of fluorescence and absorbance spectroscopy), and satellite remote sensors, analysis of DOM can be done which can help elucidate its dynamics in aquatic environments. Introduction When a molecule absorbs light (energy), an electron is excited and promoted to an unoccupied orbital. Figure 1 shows a Jablonski diagram which describes what happens when an electron is excited:
Fig. 1 Jablonski diagram
The energy difference between the ground (S 0) and excited singlet states (S1, S2 or higher) determines the wavelengths at which light is absorbed. Absorption (excitation) can result in a range of transitions to various vibrational sublevels of excited singlet states, which is then followed by nonradiative relaxation to the lowest sublevel of the S 1 state, via vibrational relaxation and internal conversion. Internal conversion, singlet–triplet intersystem crossing and fluorescence then compete for relaxation to the ground state (S 0). The wavelength of the fluorescence emission is determined by the difference in energy between S1 and S0 states. The greater the conjugation in the molecule,
3rd year, BS Chemistry, University of the Philippines, Diliman
Abstract Dissolved organic matter (DOM), the fraction passing through a 0.45 µm membrane filter, is considered poorly understood mixture of organic polymers because of its complexity. Although it largely influences a lot of biogeochemical processes in aquatic environments, its characterization is not that simple. However, due to the fact that it comprises optically active fraction called colored dissolved organic matter (CDOM) together with the help of its colloidal components, tracing of DOM can be possible. Through different methods and instruments such as fluorescence excitation-emission spectroscopy, parallel factor analysis (PARAFAC), isolation-fractionation technique (pairing of fluorescence and absorbance spectroscopy), and satellite remote sensors, analysis of DOM can be done which can help elucidate its dynamics in aquatic environments. Introduction When a molecule absorbs light (energy), an electron is excited and promoted to an unoccupied orbital. Figure 1 shows a Jablonski diagram which describes what happens when an electron is excited:
Fig. 1 Jablonski diagram
The energy difference between the ground (S 0) and excited singlet states (S1, S2 or higher) determines the wavelengths at which light is absorbed. Absorption (excitation) can result in a range of transitions to various vibrational sublevels of excited singlet states, which is then followed by nonradiative relaxation to the lowest sublevel of the S 1 state, via vibrational relaxation and internal conversion. Internal conversion, singlet–triplet intersystem crossing and fluorescence then compete for relaxation to the ground state (S 0). The wavelength of the fluorescence emission is determined by the difference in energy between S1 and S0 states. The greater the conjugation in the molecule,
References: [1] Andy Bakera, Robert G.M. Spencer. Characterization of dissolved organic matter from source to sea using fluorescence and absorbance spectroscopy [2] C.A. Stedmon*, S. Markager . Behaviour of the optical properties of coloured dissolved organic matter under conservative mixing [3] S.P. Tiwari, P. Shanmugam. An optical model for the remote sensing of coloured dissolved organic matter in coastal/ocean waters [4] Colin A. Stedmona, Stiig Markagera, Rasmus Bro. Tracing dissolved organic matter in aquatic environments using a new approach to fluorescence spectroscopy [5] Claude Belzile, Laodong Guo. Optical properties of low molecular weight and colloidal organic matter: Application of the ultrafiltration permeation model to DOM absorption and fluorescence [6] C. Romera-Castillo, M. Nieto-Cid, C.G. Castro , C. Marrasé, J. Largier, E.D. Barton, X.A. Álvarez-Salgado. Fluorescence: Absorption coefficient ratio — Tracing photochemical and microbial degradation processes affecting coloured dissolved organic matter in a coastal system [7] http://neptune.gsfc.nasa.gov/science/slides.php?sciid=73