Detection of trace fluoride in serum and urine by online membrane-based distillation coupled with ion chromatography

• A membrane-based distillation (MBD) module was fabricated for sample preparation.
• MBD module consists of a sample vessel and a lab-made membrane unit.
• MBD was hyphenated with IC to implement on-line detection of fluoride.
• Successful application of this method in serum and urine.

An online membrane-based distillation (MBD) coupled with ion chromatography (IC) method was proposed for automatic detection of trace fluoride (F−) in serum and urine samples. The system consisted of a sample vessel, a lab-made membrane module and an ion chromatograph. Hydrophobic polytetrafluoroethylene (PTFE) hollow fiber membrane was used in MBD which was directly performed in serum and urine samples to eliminate the matrix interferences and enrich fluoride, while enabling automation. The determination of fluoride in biological samples was carried out by IC with suppressed conductometric detection. The proposed method feasibly determined trace fluoride in serum and urine matrices with the optimized parameters, such as acid concentration, distillation temperature, and distillation time, etc. Fluoride exhibited satisfactory linearity in the range of 0.01–5.0 mg/L with a correlation coefficient of 0.9992. The limit of detection (LOD, S/N = 3) and limit of quantification (LOQ, S/N = 10) were 0.78 μg/L and 2.61 μg/L, respectively. The relative standard deviations of peak area and peak height were all less than 5.15%. The developed method was validated for the determination of fluoride in serum and urine with good spiked recoveries ranging between 97.1–101.9%. This method also can be proposed as a suitable alternative for the analysis of fluoride in other complex biological samples.