Spectrophotometric Analysis of Fulvic Acid Solutions - A Second Look

Elham A. Ghabbour, Northeastern University
Geoffrey Davies, Northeastern University


Standard fulvic acid (FA), spectrophotometric measurements, optical absorbance, absorption coefficient, FA concentrations, commercial FA

Date of Submission


Date of Acceptance


Publication Date


Subject Areas

Environmental Analysis, Humic Substances, Fulvic Acids


This paper re-evaluates and modifies a previously proposed, simple method of estimating the concentration of aqueous fulvic acid solutions. Spectrophotometric measurements of aqueous solutions of three International Humic Substances Society (IHSS) standard fulvic acids (FAs) at pH 1.0 and pH 4.0 in the wavelength range 350 – 500 nm at 20°C indicate that a) the optical absorbances in this wavelength range decrease exponentially with increasing wavelength; b) the spectrum of each standard FA is independent of pH in the range 1.0 to 4.0; c) plots of absorbance vs. FA concentration at fixed wavelength are linear up to at least 135 mg FA/L; d) the absorption coefficients at each wavelength derived from the linear plots cover a small range for the three standard FAs and average to 5.3 ± 0.3, 3.4 ± 0.3, 1.9 ± 0.2 and 0.89 ± 0.10 Lcm-1g-1at 350, 370, 400 and 450 nm, respectively. The averages at 350, 370 and 400 nm are close to the actual absorption coefficients for IHSS standard FA 1S101F and are substantially lower than the absorption coefficients of IHSS standard FA 2S103F employed in the previous work; and e) substitution of the absorption coefficients of this study in the previously observed linear correlation of measured carbon concentrations and spectrophotometrically estimated FA concentrations results in a predicted average carbon content of 52% for five commercial FA samples. This estimate is similar to the average measured %C values of the standard FAs used to develop this simple analytical method, which has potential value for the certification and regulation of humic substances.

Permanent URL


Recommended Citation

Ghabbour, Elham A. and Davies, Geoffrey (2009) "Spectrophotometric Analysis of Fulvic Acid Solutions - A Second Look," Annals of Environmental Science: Vol. 3, Article 10.
Available at: http://hdl.handle.net/2047/d1001892x