Reversible and high accuracy pH colorimetric sensor array based on a single acid-base indicator working in a wide pH interval

Highlights

• Reversible pH CSA working within 7 pH units by using only one pH indicator.

• Use of a suitable surfactant to vary the pKa of the indicator over 7 pH units.

• Error minimization (0.01 pH units) with a model computing the optimal spots number.

• A pH CSA with analytical performance comparable to the glass electrode.

Abstract

A pH colorimetric sensor array (CSA) with fast response time (<1 min) using only one acid-base indicator, Bromothymol Blue (BB), was prepared and characterized by modulating the amount, C, of the surfactant Hexadecyltrimethylammonium p-toluenesulfonate between 0 and 0.3725 gCTApTs/gprecursor with a constant amount of the OrMoSil precursors. The effect of the C increase is a continuous acidic shift of the calibration position, i.e. a huge variation of the pKa value of BB in the pH range 5.80-13.50. The precision error decreased with increasing C from 0.096 pH units (lower C values) to 0.023 pH units (larger C values). This result led to the development of a model to determine the number of spots with suitable C values required for having a similar value of precision in the entire working interval of the CSA. By selecting only 4 spots the precision error is < 0.100 pH units in the pH range 5.80–13.50. With 256 spots (diameter of each spot ≈ 3 mm), the model predicted an error almost constant (≈0.010) in the entire pH range.

Pastore A., Badocco D. & Pastore P., 2020. Reversible and high accuracy pH colorimetric sensor array based on a single acid-base indicator working in a wide pH interval. Talanta 219: 121251. doi: 10.1016/j.talanta.2020.121251. Article (subscription required).

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