In this study, we applied an innovative approach of green
analytical
chemistry to develop a novel and eco-friendly chromogenic agent for
fluoride determination by making use of the nontoxic Al(III)-flavonoid
complex in a natural extract from St. John’s wort plant. The
initial intensely yellow-colored Al(III)-flavonoid complex formed
in the plant extract was converted to a colorless AlF6
3– complex with increasing amounts of fluoride, and
color bleaching of the Al-flavonoid chromophore (measured as absorbance
decrement) was proportional to fluoride concentration. The developed
method gave a linear response within the F– concentration
range of 0.11–1.32 mM with the LOD and LOQ values of 0.026
mM (0.5 mg L–1) and 0.079 mM (1.5 mg L–1), respectively. The LOD value for fluoride was below the WHO-permissible
limit (1.5 mg L–1) and the US-EPA-enforceable limit
(4 mg L–1) in water. The possible interference effects
of common anions (Cl–, Br–, I–, NO3
–, HCO3
–, SO4
2–, and PO4
3–) and cations (K+, NH4
+, Ag+, Ca2+, Mg2+, Mn2+, Fe2+, and Fe3+) were investigated;
the observed interferences from Fe2+, Fe3+,
and PO4
3– were easily eliminated by masking
iron with the necessary amount of Na2EDTA without affecting
the blank absorbance of the Al(III)-flavonoid complex, precipitating
phosphate with Ag(I) salt, and partly neutralizing alkaline water
samples to pH 4 with acetic acid. The developed method was applied
to real water samples and also validated against a reference spectroscopic
method at the 95% confidence level.
In this study, anthocyanin-rich fermented black carrot juice (şalgam/shalgam) was used as a chromogenic agent in order to develop eco-friendly, low-cost, simple, fast, and practical both visible spectrophotometric and smartphone-based methods for the determination of Al(III) ions in water samples. Formation of Al(III)-anthocyanin complex results in a color change from red to purple in direct proportion to the increasing Al(III) concentration. For the spectrophotometric analysis, the analytical response of the developed method between absorbance and logarithm of Al(III) concentration exhibits a satisfying wide linear concentration range from 37.0 to 1850.0 µM. The LOD and LOQ values are 6.67 µM and 22.0 µM, respectively. For smartphone-based analysis, the analytical response of the developed method between B values and Al(III) concentration obtained a linear concentration range from 18.5 to 111.0 µM. The LOD and LOQ values are 4.40 µM and 14.5 µM, respectively. LOD values are below the acceptable limit of Al(III) in water according to WHO (7.41 µM) for both methods. The interfering effect of common water ions was investigated, and the observed interferences from Sn2+, Fe2+, and Fe3+ were easily eliminated using enough concentration of Na2EDTA without affecting the blank absorbance/B value of the Al(III)−anthocyanin complex for two monitoring methods. The selectivity of the developed method was investigated in the presence of possible species such as benzoic acid, lactic acid, amino acids, and salt. Developed spectrophotometric and smartphone-based methods applied to real water samples and validated against the reference ICP-OES method at 95% confidence level using Student’s t- and F-tests.
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