Buffer solution optimization for accurate fluoride ion detection in tap water

Polycrystalline (poly) lanthanum fluoride (LaF₃) Electrolyte-Insulator-Semiconductor (EIS) sensors can serve as a promising portable sensor platform for monitoring fluoride ion (F⁻) concentration due to their small size, fast response and simple fabrication method. The key to successful implementation is to consider and understand the effects of the measurement environment on the F⁻ detection performance of actual analyte samples. Here, we propose a pathway for accurate F⁻ analysis in tap water by using low concentration of the buffer solution. The F⁻ sensing characteristics of the sensors are extensively investigated by varying the concentration of the total ionic strength adjustment buffer solution (TISAB). The sensors exhibit a high sensitivity of 50.2 mV/pF, a low limit of detection of 1.4 ppb, a small hysteresis voltage of 0.9 mV and a small drift rate of 0.60 mV/h. in the 100-times diluted TISAB (0.01 × TISAB). In addition, the poly LaF₃ EIS sensors show highly selective detection of F⁻ over others. When F⁻ analysis of tap water is compared to a commercial F⁻ ion selective electrode, the result is only different by 6.1% for the 0.01 × TISAB compared to 11.2% for 1 × TISAB. Thus, the dilution of TISAB can provide better measurement conditions for highly accurate F⁻ analysis in actual sensor applications.