Quantification of Fluorine in Plants by High Temperature Combustion Hydrolysis-Ion Chromatography

A new method for the determination of fluorine in plants was developed by high temperature combustion hydrolysis-Ion Chromatography. Chromatographic conditions were selected as Dionex IonPac AS18 separation column (4 mm×250 mm), Dionex IonPac AG18 protect column (4 mm×50 mm), ASRS ULTRA Ⅱ suppressor (4 mm) and conductivity detection. The fluorine ion was absorbed by pure water, which provided the same matrix between the sample solution and the standard solution. The sample solution was analyzed directly by Ion Chromatography with a simple procedure and low cost after filtration. The anions such as Cl^-, NO₃^-, SO₄^2-, PO₄^3-, CO₃^2-, HCO₃^- have no interferences with F^-, except the acetic acid produced in the process of pyrolysis. In order to eliminate the interference from acetic acid, 20 mmol/L NaOH solution was used as equal eluent for higher fluorine sample (xx-xxx μg/g) with the 25 μL sample volume, while for lower fluorine sample (0.x-x μg/g)with the 100 μL sample volume. The new method has wide linear range, high stability and a low detection limit as of 0.5 mg/kg. Four plant reference materials of shrub and tea with higher fluorine contents (xx-xxx μg/g) were studied as the relative error is lower than 10% and the relative standard deviation is lower than 6%. For wheat and rice samples which have lower fluorine content, the recovery by standard addition is 90%-110%. Compared with ion selective electrode and spectrophotometry, Ion Chromatography can be used for samples with a larger range of fluorine concentration, and has the advantages of high automation, easy operation and is environmentally friendly.