Chemical Indicating Devices

Abstract

Most people remember a chemical indicator from their high school chemistry. This kind of indicator is a material that changes color to signify the end point of a titration or to provide a relative indication of the acidity or alkalinity of a chemical substance. The use of indicators extends far beyond this. For example, food, cosmetic, pharmaceutical, and other chemical formulations undergo complex chemical, enzymatic, and microbial interactions when they are exposed to UV light or temperature fluctuations over time. Consequently, product quality may be degraded and may lead to additional safety concerns. The challenges facing the produce industry include successful implementation of Good Manufacturing Practices (GMP), Hazard Analysis and Critical Control Point (HACCP), Total Quality Management (TQM) programs, and other regulations that demand compliance. To address these issues and increase consumer confidence in product quality, safety, and authenticity, many manufacturers incorporate inexpensive monitoring devices into their products during production, packaging, or storage. A large number of consumer‐readable indicators are available commercially. Generally, chemical indicators may be defined as stimulus responsive materials that can provide useful information about changes in their environment. Organic dyes, hydrogels or “smart polymers,” shape‐memory alloys, thermochromic or photochromic inks, and liquid crystals are some examples. They may function by forming structurally altered ionic or molecular complexes with species in their environment through chemical or physical interactions involving proton exchange, chelation, hydrogen bonding, dipole–dipole interactions, or van der Waal forces. The resulting characteristic biochemical, chemical, optical, magnetic, thermal, or mechanical changes can be tailored to provide the desired indication response. This article focuses on inexpensive disposable chemical indicating devices such as pH indicators, temperature indicators, time–temperature indicators (TTI), and tampering and counterfeit indicators. The temperature and TTIs are widely used in the food and pharmaceutical products where date coding on a package may sometimes be inadequate.