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Some Applications of Acid-Base Equilibria
Published in Harry L. Pardue, Chemical Equilibria, 2018
Figure 6.1A includes titration curves for NaOH volumes from 0 to 100 mL. The dashed horizontal lines on the figure represent pH's at the start and end of the yellow to blue color change, pH = 6.0–7.6, for bromothymol blue. You can superimpose dashed lines representing the transition range for any indicator on any set of titration curves by setting D45 to “Yes” and Cells G45 and I45 to pH's at the beginning and end of the transition range for the indicator.
pH Measurement
Published in John G. Webster, Halit Eren, Measurement, Instrumentation, and Sensors Handbook, 2017
Norman F. Sheppard, Anthony Guiseppi-Elie
Indicator papers are a simple, rapid, and inexpensive means of measuring pH when the precision of an instrumental measurement is not necessary. These are constructed from a strip of paper or plastic that has been impregnated with one or more absorption indicator dyes chosen to span the pH range of interest. The dyes are generally covalently attached to the strip, to prevent contamination of the sample by leaching of the dyes. A strip for indicating pH in the range of 5.5–9.0 can be constructed using the dyes bromocresol purple, bromothymol blue, and phenol red [1]. The pH of a sample is determined to a precision of typically 0.5 units by comparing the color of the strip to a color calibration chart provided by the manufacturer.
Microfluidic Contact Lenses for Ocular Diagnostics
Published in Raju Khan, Chetna Dhand, S. K. Sanghi, Shabi Thankaraj Salammal, A. B. P. Mishra, Advanced Microfluidics-Based Point-of-Care Diagnostics, 2022
Antonysamy Dennyson Savariraj, Ammar Ahmed Khan, Mohamed Elsherif, Fahad Alam, Bader AlQattan, Aysha. A. S. J. Alghailani, Ali K. Yetisen, Haider Butt
Tear pH in a healthy person ranges between 6.5 to 7.6 (Abelson et al. 1981) and a deviation from this towards the alkaline window (pH ≈ 8) is an indication of the early stage of rosacea, a chronic dermatosis causing corneal melting and stromal scarring (Abelson et al. 1980, An et al. 2005). Its occurrence in the ocular environment prior to skin will go unnoticed unless the variation in tear pH is detected. A deviation in pH is not only found in rosacea patients (8.0 ± 0.32) but also in cataract patients in pre- (7.26 ± 0.23) and post- (7.50 ± 0.23) operation stages (Thygesen and Jensen 1987). Also tear pH and buffering capacity are the important yardsticks to evaluate the extent of ocular penetration of drugs (Ahmed and Patton 1984) indicative of the pressing need to monitor tear pH. Most techniques used to date involve electrodes (Fischer and Wiederholt 1982), microelectrodes (Carney et al. 1990), glass probes (Abelson et al. 1981), or fluorescent probes (Chen and Maurice, 1990) to be in contact with the cornea which all could cause inconvenience to the patient and lack continuity in monitoring. Benzenedicarboxylic acid (Yetisen et al. 2020) and anthocyanin (Riaz et al. 2019) functionalized CL pH sensors were truly minimally/noninvasive with the ability to continuously monitor pH in a short range (pH 7.0–8.0) (Yetisen et al. 2020) and pH 6.5–7.5 (Riaz et al. 2019)) limiting them from detecting pH beyond this window. At this juncture MCLs with colorimetric sensing units comprising of a methyl red, bromothymol blue, and phenolphthalein to suit a range of pH both in acidic and alkaline windows (Figure 12.5(G)(i), (H)(i)) (Moreddu et al. 2020b) help in close monitoring of tear pH. Methyl red, a carboxylic acid group, and an amine functional group can work in both acid and base media to detect pH in the range of 4.3–6.2. On the contrary, phenolphthalein is colorless in acidic media, and shows a color shift in alkaline media from pink to fuchsia, due to the formation of quinoid-carboxylated structure with the ability to detect pH from 8.2 to 12.0. Bromothymol blue, being a weak acid, exhibits a color shift from yellow to blue in alkaline media due to the formation of triphenylmethane. This pH sensor assay with the combination of methyl red, bromothymol blue, and phenolphthalein show a green color in neutral environments and its color intensity varies based on the pH. The wearer can capture the color change with a smartphone and the RGB values can be analyzed to detect the pH. Green color indicates a healthy eye and yellow color represents mild acidic condition ascribed to changes in tear buffering capacity (Norn 1985) but an alkaline pH exhibited with blue color indicates rosacea disease (Abelson et al. 1980). This sensor has a quick response of 15 s and has a high sensitivity of 12.23 nm/pH unit.
Magnetic Fe3O4-chitosan micro- and nanoparticles for wastewater treatment
Published in Particulate Science and Technology, 2019
Deniz Akın Sahbaz, Arzu Yakar, Ufuk Gündüz
In the adsorption experiments, bromothymol blue sodium salt (chemical formula: C27H27Br2NaO5S, MW: 646.36 g/mol) used as a model anionic dye was purchased from Sigma-Aldrich. Phosphate buffered saline (PBS, Sigma-Aldrich) was used to prepare buffer solutions. To adjust the pH of the solutions, nitric acid (HNO3, Merck), and sodium hydroxide (NaOH, Merck) were used, and Bromothymol Blue solutions were prepared at different pH values. All other chemicals were of analytical grade, and no further purification was required.