Testing acc. to ISO 19071: Leather - Chemical tests - Determination of chromium(VI) and the reductive potential for chromium tanning agents
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Testing methods
Our test laboratory performs testing according to DIN EN ISO 19071 as an accredited test method for the determination of chromium(VI) and the reductive potential of chromium tanning agents. The method examines chromium-containing tanning chemicals rather than leather samples. It takes into account that commercial chromium tanning agents may contain reducing constituents that can influence the direct determination of chromium(VI).
In addition to determining any chromium(VI) present, the test therefore indicates the extent to which the tanning agent is capable of reducing added chromium(VI). This provides a quantitative characterization of an important chemical property of chromium tanning agents.
Testing according to DIN EN ISO 19071
The chromium tanning agent is dissolved in water. Chromium(VI) reacts with 1,5-diphenylcarbazide to form a coloured complex, which is extracted with n-hexanol and subsequently determined photometrically at 540 nm.
Because chromium tanning agents can exhibit different levels of reductive potential, evaluation is performed using the standard addition method. Defined amounts of chromium(VI) are added to several test solutions, and measurements are carried out at a minimum of four concentration levels. The resulting standard addition curve is used to determine either the chromium(VI) content or the reductive potential of the tanning agent.
If the calculation produces a positive value, this is reported as the chromium(VI) content in mg/kg. A negative calculated value, on the other hand, represents the reductive potential of the chromium tanning agent. In this case, the chromium(VI) content is reported according to the standard as less than 3 mg/kg, while the magnitude of the reductive potential is stated separately.
Applications of the test
DIN EN ISO 19071 is particularly relevant to manufacturers, users and suppliers of chromium tanning agents. The method allows different tanning chemicals to be compared with regard to both their chromium(VI) content and their ability to reduce chromium(VI) that is present or introduced.
The test can therefore be used to characterize tanning-agent quality, compare different production or supply batches and investigate changes in formulations. It is also useful when investigating chromium(VI)-related problems in leather production, since the reducing behaviour of the chromium tanning agent can influence the chemical system during tanning.
Different test methods are required for examining the finished leather itself.
Distinction from chromium(VI) determination in leather
DIN EN ISO 19071 examines chromium tanning agents, not the leather produced with them. For direct determination of chromium(VI) in leather, FILK performs testing according to DIN EN ISO 17075-1 and DIN EN ISO 17075-2.
This makes it possible to investigate both the chromium tanning agent and the finished leather when dealing with questions concerning chromium chemistry in leather manufacture.
Related tests
The total chromium or chromic oxide content of leather can additionally be determined colorimetrically according to DIN EN ISO 5398-2. While this method determines total chromium, DIN EN ISO 17075-1 and DIN EN ISO 17075-2 specifically determine chromium(VI) in leather. DIN EN ISO 19071 complements these methods by examining the chromium tanning agents themselves and their reductive potential.
Here you will also find an overview of our range of tests according to DIN, CEN and ISO standards.
