Abstract
Objectives: To validate use of fluoride ion-selective electrode (F-ISE; Orion™ 9609BNWP) methodology to quantify fluoride concentration of human milk.
Methods: Fluoride standards were prepared using a 1 ppm fluoride solution and 50% low-level total ionic strength adjustment buffer (TISAB). The F-ISE was calibrated with 0.0005 mg/L, 0.005 mg/L, and 0.05 mg/L. The concentrations of standards were 0.000313, 0.0005, 0.000625, 0.00125, 0.0025, 0.005, 0.01, and 0.05 mg/L fluoride. Human milk samples (0.5 mL) were combined with 0.5 mL low-level TISAB. A blank was also prepared by mixing 0.5 mL of distilled water with 0.5 mL low-level TISAB. The standards, human milk and blank were then placed on a shaker plate for 10 min prior to being evaluated for their fluoride concentrations. The electrode was cleaned with distilled water, dried after every measurement, and millivolts and mg/L were recorded. All standards and samples were run in duplicate, and the mean ± SD is reported.
Results: The r2 of the standard curve was 0.9938. Mean fluoride concentrations of human milk pools were 0.0097±0.0003 and 0.021±0.001 mg/L, respectively. Mean measured fluoride concentration in the standards reflected the known concentration for all but the 0.000313 mg/L fluoride standard which was measured as 0.0002±0.0002 mg/L. Importantly, this low concentration was below the lowest concentration of the calibration curve (0.0005 mg/L). Therefore, 0.000313 mg/L is the limit of detection for the described protocol.
Conclusions: The back-calculated concentrations produced results that reflected the known concentration of the standards. Also, our analysis of two pools of human milk found fluoride concentrations similar to those reported in the literature (0.005 mg/L–0.01 mg/L).