nitrogen doped graphene quantum dots as selective and sensitive flourcent prob for detection of humic acid

Humic substances are known to play an important role in plant growth as well as in several environmental and geochemical reactions; and these are ubiquitous in natural environments.humic substances are not toxic to human life. since humic acid (ha) and fulvic acid concentrations in natural water samples are low, powerful techniques are required to analyze them. different analytical methods have been developed for the etermination of ha and fulvic acid at low concentrations, generally involving an extraction and/or preconcentration step previous to detection. generally, a direct determination of ha and fulvic acid is limited by the relatively higher detection limits of existing spectrophotometric and fluorescent techniques. this procedure involves synthesis via the pyrolysis of citric acid, as a source of carbon, and tris-hydroxymethylaminomethane, as a surface passivation agent. to examine the most important parameters including volume of n-gqds, ph of the solution, ultrasonic time, ionic strength and their interactions on the fluorescence intensity, a four factor central composite design (ccd) combined with response surface modeling (rsm) was implemented. under optimal conditions, the method showed a response to ha within a concentration range of 0.3– 15 ppm with a good linear relationship and the relative standard deviation for ha was 5.3%. the developed probe was successfully applied for the determination of ha in beverage samples with quantitative recoveries from 94.0 % to 101.4 %.