Chemical Forums
Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: STM on June 20, 2017, 04:34:36 AM
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please i need simple definitions of the above terms and their implications in a water sample. I have checked the internet and obtained some information but I cant find a clear-cut definition on what they are and how they can be obtained experimentally.
What are they? How can they be obtained? What information does the result give?
Thank you
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Did you find this paper? http://onlinelibrary.wiley.com/doi/10.4319/lo.2012.57.5.1453/pdf. It uses both terms:
"Absorbance corrected for offset was then converted to Napierian absorption coefficient, ag(λ) (m-1). The dependence of ag(λ) on λ is typically described using Eq. 1:
ag(λ) = ag(λ0)e-S(λ-λ0) (1)
where λ0 < λ and S is the spectral slope coefficient in the λ0–λ-nm spectral range. Spectral slope coefficients were estimated using a linear fit of the log-linearized ag(λ) spectrum over their respective spectral range and are reported here with units of nm-1. Measurements of DOC and ag(350) were used to calculate DOC-normalized absorption coefficients (ag(350) : DOC), expressed here in units of L mol-1 cm-1."
From this I take it that Napierian absorption coefficient is the absorbance per unit length of the sample. (Napierian means using natural logs rather than log10.) Thus A = ln(I0/It) and a = A/l, where l is the path length.
Spectral slope coefficient is a measure of how the absorption coefficient changes with wavelength. In appropriate circumstances, over a relatively narrow wavelength range, it can be described by Eq. 1, i.e. it varies exponentially with wavelength.
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Thank you for response. It was highly helpful.