Hysteresis in optical sensing and its impact on the analytical error of a calibration-free acid sensor

Durability tests and statistical analyses of errors have been conducted for an indicator-doped optical sol-gel sensor for concentrated strong acid. During the 9-month tests with no recalibration, the sensor response was steady in 2, 6, and 10M HCl. The studies here revealed that the major component of the analytical error was the hysteresis of the sensor response for this bromocresol purple (BSP) doped sol-gel sensor. The contribution of hysteresis to the total variance Shyst2/ST2 is 54 (11)% and 62 (13)% for 2 and 6M HCl, respectively.