Indicator Reagents

Abstract

The article contains sections titled: 1. Introduction 2. pH Indicators 2.1. Theory 2.2. Errors 2.3. Color‐Change Transition 2.4. Classification 2.4.1. Azo pH Indicators 2.4.2. Nitro pH Indicators 2.4.3. Phthalein pH Indicators 2.4.4. Sulfonephthalein pH Indicators 2.4.5. Triphenylmethane pH Indicators 2.4.6. Benzein pH Indicators 2.4.7. Fluorescent pH Indicators 2.4.8. Miscellaneous pH Indicators 2.4.9. Mixed Indicators 2.5. pH Indicator Papers 2.6. pH Indicators for Nonaqueous Solutions 3. Adsorption Indicators 4. Fluorescent Indicators 5. Chemiluminescent Indicators 6. Redox Indicators 7. Metal Indicators 7.1. Volumetry (Complexometry) 7.2. Colorimetry and Photometry 7.3. Structure 7.4. Ligand Classes 7.4.1. Ligands Forming Five‐Membered Chelate Rings 7.4.2. Ligands Forming Six‐Membered Chelate Rings 8. Analytical Test Kits

A review on colorimetric indicators for monitoring product freshness in intelligent food packaging: Indicator dyes, preparation methods, and applications

“…These dyes can be synthesized easily with many possible substitutes on the azo group (Gürses et al., 2016; Hunger, 2003). Azo dyes are often functioning as pH indicators, where they are generally red in acid form and yellow in basic form (Sabnis et al., 2011). Another group of synthetic colorants is phthalein dyes (e.g., sulfonephthalein), which are mostly water‐insoluble but soluble in alcohol (Sabnis et al., 2011).…”

“…Azo dyes are often functioning as pH indicators, where they are generally red in acid form and yellow in basic form (Sabnis et al., 2011). Another group of synthetic colorants is phthalein dyes (e.g., sulfonephthalein), which are mostly water‐insoluble but soluble in alcohol (Sabnis et al., 2011). Phthalein dyes possess diverse color profiles, depending on different aromatic substituents.…”

“…They are widely used as pH indicators, due to clear color transition caused by the protonation/deprotonation of the phenolic hydroxyl groups (Sabnis et al., 2011). Phthalein indicators have been explored by researchers for the detection of pesticides, viable cells, and inorganic electrolytes (De Meyer et al., 2014; Sabnis et al., 2011). Apart from azo and phthalein dyes, other pH indicators explored for intelligent packaging applications include phenazine and quinone dyes (Sabnis et al., 2011).…”

A chemical reaction controlled by light-activated molecular switches based on hetero-cyclopentanediyls

“…Interconversion can be induced by external stimuli such as temperature, chemical modifications, redox reactions, electric fields, or irradiation with photons 2–5. The most commonly known type of molecular switches are pH indicators, which are based on acid–base equilibria and therefore belong to the group of chemically activated compounds 6,7. Other chemically switchable systems may, for example, find application in the field of gas or ion sensing,5,8 or be used as redox indicators 7…”

“… 6 , 7 Other chemically switchable systems may, for example, find application in the field of gas or ion sensing, 5 , 8 or be used as redox indicators. 7 …”