High-Basicity Determination in Mixed Water−Alcohol Solutions by a Dual Optical Sensor Approach

Abstract

The activity of NaOH is known to be significantly affected by the presence of an alcohol in aqueous solutions. A novel linear relationship between (deltaA/deltaC(alcohol)) and C(base) was found in the highly alkaline, mixed H2O-ROH solutions (R = Me, Et, i-Pr). The use of this linear relationship led to a dual-transducer approach to decompose the optical signals of optical base sensors and to give base and alcohol concentrations in concentrated NaOH-H2O-ROH solutions ([OH-] = 0.05-3.6 M). The scope of the new dual-sensor approach was evaluated, and errors in C(base) and C(alcohol) were analyzed. The optical base sensors consist of sol-gel SiO2-ZrO2-organic polymer composites doped with high-pKa indicators. The pKa(s) of the indicators encapsulated in the composite films were determined and found to be affected by the composition of the sol-gel composites. Optical sensors and their uses in multicomponent systems are of intense current interest.( 1-7) In the multicomponent systems, the activity of the analyte and sensor response are often affected by change in ionic strength. For optical sensors that are based on indicator equilibria involving the analyte as their transducing mechanism, such effect is particularly significant. The concentrations of both the analyte and other chemicals affect ionic strength, and the sensor response to concentration of the analyte is thus often indistinguishable from those of other chemicals. An accurate measurement of each component in these multicomponent systems is actively studied. Several approaches have been developed to correct ionic strength in optical sensing for the pH region and solutions of low-to-medium ionic strength. (1-9) We recently reported a dual-transducer approach to measure acid concentrations (2-9 M HCl) in salt-containing, concentrated strong acids such as MClx-HCl (M = Li, Ca, Al) solutions. (10) This approach was shown to reduce the error in C(acid) from, for example,

Nickel oxide screen printed electrodes for the sensing of hydroxide ions in aqueous solutions

“…Reliable sensors for the monitoring of hydroxide ion concentrations which can operate in harsh environments are urgently sought. [1][2][3] Hydroxide is used worldwide in many industrial processes and rapid and reliable methodologies for the sensing of hydroxide ions for quality control purposes and monitoring during industrial processing are required. 4 Problems arise quite simply due to the corrosive nature of the concentrated alkali and glass pH electrodes become insensitive and unstable at high concentration levels.…”

Optical and electrochemical sol-gel sensors for inorganic species

“…Therefore, after the development of sensors responsive to highly concentrated acids and bases, our attention was shifted to dual-sensor approaches for measuring C acid and C salt in the salt-containing acid solutions [5,19] and C base and C alcohol concentrations in the basic mixed solvent systems [20,21] .…”

“…One of the most important features for optical sensing is that they are transparent in the visible region [13] . Sol-gels have found applications in the optical monitoring of pH [3,5,8,9,[14][15][16][17][18][19][20][21][22] , metal ions [23][24][25][26][27] , and various other analytes [28][29][30] . Sol-gels have also found use in electrochemical [31 -38] and spectroelectrochemical [39] sensing applications.…”

A Phenanthroline-Based Fluorescent Probe for Highly Selective Detection of Extreme Alkalinity (pH > 14) in Aqueous Solution

“…In extreme alkalinity detection filed, Thakur [10], Khalil [24], Xue [25–27], and Sadik [28] carried out pioneering and excellent work. At present, several fluorescent probes which can detect extreme alkalinity (pH > 14) have been reported [8, 22–26]. However, studies in this filed are still in the initial stage and many problems exist, such as (1) fluorescent probes which can detect pH > 14 are rare, (2) most of these fluorescent probes need organic solvents to assist their detections and few fluorescent probes can detect extreme alkalinity in pure water [22, 24, 25], and (3) for many fluorescent probes, the principle of sensing extreme alkalinity is measuring their absorbance changes and this brings about low sensitivity [22, 23, 26].…”