The retanning process is the main application of formaldehyde in the tanning industry since formaldehyde participates in two groups of synthetic organic tanning agents: syntans and resins. Resins can be hydrolysed with the result that formaldehyde is released. Thus, formaldehyde in leather can be free or from hydrolysis of resins. Due to the carcinogenic character of formaldehyde, its presence in leather should be avoided or should be below allowable limits. The EN ISO 17226 Standard is the Official Standard for the determination of formaldehyde content in leather, which, in the authors’ opinion, presents certain ambiguities in the wording of some operations included in their analysis methods and, some of these operations, are susceptible of improvement. Therefore, a revision of the EN ISO 17226 Standard (Parts 1 and) 2 is carried out in this work and, in particular, of the extraction phase of formaldehyde present in leather (possible use of alternative surfactant and shaking method); reaction time between the extracted formaldehyde with the dinitrophenylhydrazine solution (Part 1 of the Standard) and stability of the acetylacetone solution (Part 2 of the Standard).

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