Colorant analysis

Colorants beautify the physical objects surrounding us by giving them color. Apart from fulfilling aesthetic purposes, surface-adhering films are applied on substrates to provide protection against mechanical and chemical impacts (e.g., corrosion).

Cans of liquid paint

According to the definitions in DIN 55943, ISO 4617 and 4618, and ASTM D16-84, the term colorants is applied to pigments, dyes, and extenders. These are mixed with binders, resins, and plasticizers to produce the desired visual and functional effects (e.g., corrosion protection) as a surface coating.

Depending on the challenges posed by the surface characteristics of the substrate, the composition of coating systems has to be meticulously monitored. To characterize your colorants, we offer you a variety of analytical techniques, from ion chromatography, titration, and voltammetry to spectroscopy.

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Analyze colorants in line with international standards

Standards

Colorant analysis is regulated by a large body of international standards.

Click the link below to find an overview of standards relating to colorant, pigment, and dye analysis, including the analyte, matrix, and the analytical method applied.

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Anions in dyes

Dyes in different colors dissolving in a liquid medium

The ion concentration in aqueous dyes has a strong impact on the physical chemistry of dyeing, in particular on the binding capacity of the dye to the substrate. Ion chromatography is ideally suited to rapidly determine the content of ionic impurities in dyes. Additionally, it facilitates the analysis of heavy metal pigments such as chromate.

> Learn more about Metrohm ion chromatography

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Nitrobenzene traces in aniline

Mauve dye

Another important colorant class are the azo dyes, which make up at least two thirds of all colorants. Their first synthesis was an accident. While trying to synthesize quinine as a remedy for malaria, Henry Perkin accidentally discovered aniline purple (mauveine, also Perkin’s mauve), the first ever synthetic dye.

Today, industrial dye production starts with aniline, which itself is made by nitration of benzene to nitrobenzene, followed by reduction. For accurately determining nitrobenzene traces in aniline, voltammetry is the method of choice.

> Learn more about voltammetry

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Dye, diethylene glycol, water, and surfactant in writing ink

Dye content in writing ink

Most inks can be described as complex colloidal suspensions of pigment particles in a solvent. Instead of pigments, writing inks use water-soluble dyes and solvents, such as diethylene glycol (DEG). Surfactants are crucial for stabilizing the suspension and for adjusting the surface tension and the wetting characteristics. Moreover, they tune the ink–surface interaction.

Vis-NIR spectroscopy covers the analysis of practically all types of ink ingredients. Using the example of a writing ink, the application below describes the straightforward analysis of dye, diethylene glycol, surfactant, and water content.

> Learn more about Metrohm NIR spectroscopy systems

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Further applications and products

Indigo dyeing machine and process monitoring of chemical dying of textiles

Indigo textile dyeing in the process

In indigo textile dyeing, many parameters have to be monitored to ensure high quality dyeing. Our process analyzers facilitate the analysis of pH value, temperature, redox potential as well as the concentrations of hydrosulfite and indigo.

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System for fully automated preparation of solid samples for titration applications

Quality control of sulfonamides

Sulfonamides (e.g., sulfanilamide) are important base products for azo dyes. Download the application to see how you can determine sulfanilamide as part of quality control using automated potentiometric titration.

Go to the application Learn more about titration