Wet chemistry, also called wet chemical analysis, is a form of analytical chemistry that uses classical methods, such as Colorimetry, Gravimetry and Titration to analyze elements and compounds in liquid samples. Wet chemistry is a form of analytical chemistry that uses classical methods such as observation to analyze materials. It is called wet chemistry because most of the analyzing are done in the liquid phase. Wet chemistry is also called bench chemistry since many tests are performed at lab benches.
Why wet chemical analysis?
Analytical chemistry has developed exponentially in the last three decades, still, the wet chemical analysis is an integral part of the modern analytical chemistry lab because the wet chemical methods are proven and less expensive. Often, modern instrumentation cannot determine results which many specific wet chemical tests provide. Wet chemistry includes basic experimentation techniques, such as measuring, mixing, and weighing chemicals, conductivity, density, pH, specific gravity, temperature, viscosity, and other aspects of liquids.
Historically, titrimetric method has been the most common method of wet chemical analysis. Titration is based on the use of a burette, from which a titrant (standard solution) is added to the sample until an "endpoint" is reached. The endpoint is generally indicated by a color change. In modern methods, manual titrations are replaced by auto titration in which the titration endpoint is detected by a potentiometric device.
Visual colorimetric comparison tests are the second most commonly performed test. Even today many of the regulatory methods recommend visual colorimetric comparison tests for quick checking and it is common in field applications. Photometric or spectrophotometric measurements provide the most accurate means of measuring the color of a reacted sample. Many of the chemical parameters commonly tested using titration are also measured using photometric methods.
Automated Wet Chemical Analysis
Wet chemical methods of analysis are labor-intensive, consume large quantities of reagents and generate chemical waste. Wet chemical methods are automated with modern instrumentations to minimize some of the pain points, improve precision and accuracy, and eliminate manual errors. Single wet chemical parameters are commonly determined using standalone instruments such as colorimeter, photometer or pH, conductivity, Ion-Selective Electrode (ISE) meters or auto titration. In field-analysis applications, simple filter-based photometers have been used in place of monochromator-based spectrophotometers. When a high throughput solution is necessary, one or many of these instruments are combined with automation.
Fully-automated wet chemical methods based on photometric measurements are accomplished with Discrete Analyzers or flow analyzers such as a Flow Injection Analyzer (FIA) or Segmented Flow Analyzer (SFA). I will review the difference between these techniques, their advantages and limitations in my future blog post.
Automated Wet Chemical Analysis and Regulatory Methods
Basic pH and conductivity measurements find uses in almost all industrial applications and are the most recommended wet chemical analysis method by the national and international regulatory bodies. The next important and most-commonly used wet chemical method is the titration method followed by photometric/colorimetric measurements.
When it comes to water analysis, many of the drinking and wastewater analyses, as per the USEPA, ASTM, ISO methods, are based on wet chemical method of analysis. In the world of food and beverage analysis, many of the fruit juices, milk, beer, wine, cider and other alcoholic beverage test methods recommended by international standard methods, AOAC, ISO are based on automated wet chemical analysis.
Visual colorimetric tests are the recommended method of analysis for identification and limit tests for commonly-used salts in pharmaceutical applications. Many pharmacopeias including the United States Pharmacopeia recommends visual colorimetric tests for the identification and limit tests. Part of the Monograph modernization process, these visual tests are being replaced by instrumentation techniques such as ion chromatography. I will present a detailed overview in my future blogs.
US EPA – 40 CFR Part 136 - Guidelines Establishing Test Procedures for the Analysis of Pollutants
US EPA - 40 CFR Part 141 - NATIONAL PRIMARY DRINKING WATER REGULATIONS