Hi everyone.
I have developed a R package named eemR (https://github.com/PMassicotte/eemR and https://cran.r-project.org/web/packages/eemR/index.html) which aims at providing an easy way to manipulate fluorescence matrix.
One of the function in the package is used to extract peak values at different regions in the fluorescence matrix (Coble's peaks for instance). I have noticed that the reported locations of these peaks are not consistent in the literature.
In Coble's 1996 paper, peaks are reported as follow (these are the values I am using in the R package):
Coble, P. G. (1996). Characterization of marine and terrestrial DOM in seawater using excitation-emission matrix spectroscopy. Mar. Chem. 51, 325–346. doi:10.1016/0304-4203(95)00062-3.
Peak B: ex = 275 nm, em = 310 nm
Peak T: ex = 275 nm, em = 340 nm
Peak A: ex = 260 nm, em = 380:460 nm
Peak M: ex = 312 nm, em = 380:420 nm
peak C: ex = 350 nm, em = 420:480 nm
In Coble's 2007 paper, peaks are reported as follow:
Coble, P. G. (2007). Marine optical biogeochemistry: The chemistry of ocean color. Chem. Rev. 107, 402–418. doi:10.1021/cr050350+.
Peak B: ex = 275 nm, em = 305 nm
Peak T: ex = 275 nm, em = 340 nm
Peak A: ex = 260 nm, em = 260/400 - 460 nm
Peak M: ex = 290 nm, em = 310/370 - 410 nm
peak C: ex = 320 nm, em = 420:460 nm
On the USGS website (http://or.water.usgs.gov/proj/carbon/EEMS.html):
Peak B: ex = 270 nm, em = 306 nm
Peak T: ex = 270 nm, em = 340 nm
Peak A: ex = 260 nm, em = 450 nm
Peak M: ex = 300 nm, em = 390 nm
peak C: ex = 340 nm, em = 440 nm
At first, these differences seem to be minors but I was wondering what were your thoughts about that. Should I review my code to change or adjust peak positions?
Hi Philippe,
I agree that it's better to find maximum (or average) in the specific region, not the specific position.
There are some related references which may be helpful.
One is from Coble's new book: Aquatic Organic Matter Fluorescence (2014).
Another is Leenheer's EST paper (2003).
And you can also refer to Chen&Westerhoff&Leenheer's EST paper (2003) .
Best Regards
Penghui
Thank you I'll have a look to these. However it is just adding more possibilities ;-) I think that we are going to have a formal definition of these peaks (even thought I know it is difficult with current knowledge).
Yeah, it's difficult.
A lot of factors influence the position. First is the bias of spectra in some uncorrected spectra. And also there are some environmental factors (pH, ionic strength, solvent polarity etc.). And different biogeochemical processes could contribute the same direction of the shift. So I think it's better for the new definition not based on the sources. For example, traditional M peak have been attributed to marine derived, or phytoplankton derived, or photobleaching product of peak C.
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