CEN/TC 289/WG 1 - Chemical test methods

This document provides lists of chemicals that have already been detected in leather and guidelines for applying the available chemical test methods for leather. This information can be used by those involved in setting specifications for leather, especially for those parameters relating to restricted chemical substances.
Generic lists of restricted chemicals used on the market contain many substances that are not relevant to the leather industry. Those chemical substances that are not mentioned in this document do not need to be determined, thus avoiding unnecessary analytical costs.
NOTE            Due to the constantly changing legal requirements and toxicological evaluation of chemical substances, this document cannot address all potentially critical substances.

This document specifies a method for determining the total content (solvent extractible) of the following bisphenols in leather:
—     bisphenol A;
—     bisphenol B;
—     bisphenol F;
—     bisphenol S.
This method requires the use of liquid chromatography (LC) with either a single quadrupole mass spectrometer (MS), a triple quadrupole mass spectrometer (MS/MS), an ultraviolet (UV) detector, a diode array detector (DAD) or a fluorescence detector (FLD) to identify and quantify the bisphenols.
NOTE            This method can also be used for other bisphenols if they are validated by the laboratory.

This document specifies a test method for detection and quantification of extractable non-volatile per- and polyfluoroalkyl substances (PFAS) in leather and coated leather by solvent extraction and liquid chromatography coupled with mass spectrometry.
This document, taking into account the three-dimensional distribution of the fibres within leather, makes the evaluation of the PFAS with respect to the mass.
PFAS substances categories and applications are listed in Annex A, Table A.1. Classes of PFAS regulated compounds listed in Annex B, Table B.1, include acids, telomers, sulfonates and sulphonamide alcohols. Classes of other non-regulated compounds that can be determined by this document are listed in Annex C, Table C.1.
NOTE 1        By applying the method specified in this document, the concentration of free fluorotelomer alcohols (FTOH) in a sample cannot be correctly quantified if perfluoropolymers that release FTOH due to transesterification with the extraction solvent methanol are present in the sample.
NOTE 2        Some regulations (e.g. Reference [4]) also restrict perfluoropolymers having a linear or branched perfluoroheptyl group with the moiety (C7F15)C as one of the structural elements that can degrade to PFOA, e.g. polymers containing 2-perfluorooctylethanol (8:2 FTOH, CAS Registry Number® 678-39-7) bonded as esters. To determine whether these perfluoropolymers are intentionally present, it could be necessary to introduce an alkaline hydrolysis method to remove the 8:2 FTOH side-chain from the polymer. In addition, other FTOH, e.g. 6:2 FTOH or 10:2 FTOH, will be released from relevant perfluoropolymers by alkaline hydrolysis.

This document is a method for determining ethoxylated alkylphenols (APEO) [nonyphenol ethoxylate (NPEOn, where 2 ≤ n ≤ 16) and octylphenol ethoxylate (OPEOn, where 2 ≤ n ≤ 16)] in leather. This direct method is especially suitable when a larger number of leather samples are to be checked for the presence of ethoxylated alkylphenols.
This method requires the use of liquid chromatography (LC) with a triple quadrupole mass spectrometer (MS/MS) to identify and quantify the ethoxylated alkylphenols.
NOTE 1        In the leather industry, the most commonly used ethoxylated alkylphenol is the NPEO, with an average of 9 EO. It has an optimum cloud point in water for the typical leather processing temperatures of 40 °C to 55 °C.
NOTE 2        This document and ISO 18218-2 use different solvents for the extraction of the ethoxylated alkylphenols from leather. Consequently, the two analytical methods are expected to give similar trends but not necessarily the same absolute result for the ethoxylated alkylphenol content in leather.

This document specifies a method for the determination of the total metal content in leather using digestion of the leather and subsequent determination with inductively coupled plasma optical emission spectrometry (ICP-OES), inductively coupled plasma mass spectrometry (ICP-MS), atomic absorption spectrometry (AAS) or spectrometry of atomic fluorescence (SFA).
This method determines the total metal content in leather. It is not compound-specific or specific to the oxidation state of the metals.

This document specifies a quantitative test method to determine 24 kinds of pesticide residues in leather by gas chromatography-mass spectrometry (GC-MS).
This document is applicable to all types of leather that could release pesticides.

This document specifies a thermal pre-ageing procedure for leather to obtain indications about the tendency to the formation of hexavalent chromium under specified conditions and the determination of hexavalent chromium according to ISO 17075‑1 or ISO 17075‑2.
This thermal pre-ageing procedure does not simulate any real condition in leather production or use.
It is applicable to all types of chromium tanned leather.

This document specifies a chromatographic method to determine the amount of middle-chain chlorinated paraffins (MCCPs) C14 to C17 in processed and unprocessed leathers.

This document specifies a chromatographic method to determine the amount of short-chain chlorinated paraffins (SCCPs) C10 to C13 in processed and unprocessed leathers.

This document specifies a method for the determination of free formaldehyde, which is released under dynamic conditions when the sample is heated in an inert dry atmosphere, in process auxiliaries for leather. The analytical result obtained according to this procedure is expressed in milligrams per kilogram (mg/kg) sample.

This document specifies a method for the determination of free and released formaldehyde in leathers. This method, based on high-performance liquid chromatography (HPLC), is selective and not sensitive to coloured extracts and is intended to be used for precise quantification of formaldehyde.
The formaldehyde content is taken to be the quantity of free formaldehyde and formaldehyde extracted through hydrolysis contained in a water extract from the leather under standard conditions of use.

This document specifies a method for determining the use of certain azo colourants which can release certain aromatic amines.

This document specifies a test method by acetonitrile solvent extraction for the determination of the total content (solvent extractible) of the following preservative agents in leather by liquid chromatography:
—     2-(thiocyanomethylthio)-benzothiazole (TCMTB);
—     4-chloro-3-methylphenol (PCMC);
—     2-phenylphenol (OPP);
—     2-octylisothiazol-3(2H)-one (OIT);
This method can also be used to determine breakdown products of these preservative agents, which protect leather from microbiological attack.

This document specifies a test method by artificial perspiration solution aqueous extraction for the determination of the aqueous extractable content of the following preservative agents in leather by liquid chromatography:
—     2-(thiocyanomethylthio)-benzothiazole (TCMTB);
—     4-chloro-3-methylphenol (PCMC);
—     2-phenylphenol (OPP);
—     2-octylisothiazol-3(2H)-one (OIT);
This method can also be used to determine breakdown products of these preservative agents, which protect leather from microbiological attack.

This document specifies a test method to determine the degree and rate of aerobic biodegradation of hides and skins of different animal origin, whether they are tanned or not, through the indirect determination of CO2 produced by the degradation of collagen.
The test material is exposed to an inoculum (activated sludge from tannery wastewater) in an aqueous medium. If there is not a tannery nearby then urban wastewater can be used as the inoculum.
The conditions established in this document correspond to optimum laboratory conditions to achieve the maximum level of biodegradation. However, they might not necessarily correspond to the optimum conditions or maximum level of biodegradation in the natural medium.
In general, the experimental procedure covers the determination of the degradation degree and rate of the material under controlled conditions, which allows the analysis of the evolved carbon dioxide produced throughout the test. For this purpose, the testing equipment complies with strict requirements with regard to flow, temperature and agitation control.
This method applies to the following materials:
—     natural polymers of animal stroma (animal tissue/skins);
—     animal hides and skins tanned (leather) using organic or inorganic tanning agents;
—     leathers that, under testing conditions, do not inhibit the activity of microorganisms present in the inoculum.

This document specifies a test method for the determination of tanning agents through filtration of all vegetable and synthetic tanning products.

This document specifies a method for determining alkylphenols (nonylphenol and octylphenol) and alkylphenol ethoxylates (nonylphenol ethoxylate and octylphenol ethoxylate) in leather and process auxiliaries. The analysis is based on high-performance liquid chromatography (HPLC) or gas chromatography-mass spectrometry (GC-MS).
The analysis of the alkylphenol ethoxylate is made by cleaving the alkylphenol ethoxylate and measuring the released alkylphenol.
NOTE       ISO 18218-1 and this document use different solvents for the extraction of the ethoxylated alkylphenols from leather. Consequently, the two analytical methods are expected to give similar trends but not necessarily the same absolute result for the ethoxylated alkylphenol content in leather.

This document specifies a method for the determination of extractable metals in leather using extraction with an acid artificial-perspiration solution and subsequent determination with inductively coupled plasma optical emission spectrometry (ICP-OES), inductively coupled plasma mass spectrometry (ICP-MS), atomic absorption spectrometry (AAS) or spectrometry of atomic fluorescence (SFA).
This method determines extractable metals in leather; it is not compound-specific or specific to the oxidation state of the metals. This method is especially suitable for determining the extractable chromium in chromium-tanned leathers.

This document specifies a method for the determination of free and released formaldehyde in leathers. This method, based on colorimetric analysis, is not intended to be used for a precise quantification of formaldehyde.
The formaldehyde content is taken to be the quantity of free-formaldehyde and formaldehyde extracted through hydrolysis contained in a water extract from the leather under standard conditions.
This process is not absolutely selective for formaldehyde. Other compounds such as extracted dyes could interfere at 412 nm.

This document describes a method for the determination of chromium in aqueous solution obtained from leather. This is an analysis for total chromium in leather; it is not compound specific or specific to its oxidation state.
This method describes the determination of chromium by inductively coupled plasma (ICP) and is applicable to leathers which are expected to have chromic oxide contents in excess of 1 mg/kg. Two techniques for the preparation of the solution to be analysed are included. In the event of dispute, the wet oxidation technique is intended to be used.

This document describes a method for the determination of chromium in aqueous solution obtained from leather. This is an analysis for total chromium in leather; it is not compound specific or specific to its oxidation state.
This method describes the determination of chrome by iodometric titration and is to be applicable to chromium-tanned leathers which are expected to have chromic oxide contents in excess of 0,3 %. Two different methods are described as alternatives for obtaining chromium in a suitable solution. It is appropriate to use either method.

ISO 4098 | IULTCS/IUC 6:2018 specifies a method of determination of water-soluble matter, water-soluble inorganic matter and water-soluble organic matter.
ISO 4098 | IULTCS/IUC 6:2018 is applicable to all leather types. The result obtained by this analysis depends on factors such as:
-      the degree to which the leather is ground;
-      the extraction temperature;
-      the extraction period;
-      the ratio of leather to water.
To obtain comparable results, it is consequently imperative that test conditions be accurately reproduced.
In all cases, any ammonium salts in the filtrate are included as part of the water-soluble matter and are then decomposed on ignition. Thus they contribute towards the result for water-soluble organic substances. The concentration of the ammonium salts can be determined in the filtrate separately if required.

ISO 17075-2:2017 specifies a method for determining chromium(VI) in solutions leached from leather under defined conditions. The method described is suitable to quantify the chromium(VI) content in leathers down to 3 mg/kg.
ISO 17075-2:2017 is applicable to all leather types.
The results obtained from this method are strictly dependent on the extraction conditions. Results obtained by using other extraction procedures (extraction solution, pH, extraction time, etc.) are not comparable with the results produced by the procedure described in this document.
If a leather sample is tested with both ISO 17075-1 and this document, the results obtained with this document are considered as the reference. The advantage of the method described in this document is that there are no interferences from the colour of the extract. Nevertheless, interlaboratory trials do not show significant differences (see Annex D) and the results are comparable between both methods.

ISO 17075-1:2017 specifies a method for determining chromium(VI) in solutions leached from leather under defined conditions. The method described is suitable to quantify the chromium(VI) content in leathers down to 3 mg/kg.
ISO 17075-1:2017 is applicable to all leather types.
The results obtained from this method are strictly dependent on the extraction conditions. Results obtained by using other extraction procedures (extraction solution, pH, extraction time, etc.) are not comparable with the results produced by the procedure described in this document.
If a leather sample is tested with both this document and ISO 17075-2, the results obtained with ISO 17075-2 are considered as the reference. The advantage of the method described in ISO 17075-2 is that there are no interferences from the colour of the extract. Nevertheless, interlaboratory trials do not show significant differences (see Annex C) and the results are comparable between both methods.

ISO 4044:2017 specifies how to prepare a test sample of leather for chemical analysis. The test sample can be either ground or cut into small pieces. Unless specified in this document, the method to be used depends on the size of leather sample available for testing.

ISO 19070:2016 specifies a method to determine the amount of N-methyl-2-pyrrolidone (NMP) in leather and leather components.
This method may also be used for the determination of N-ethyl-2-pyrrolidone (NEP) in leather.

ISO 19071:2016 specifies a test method for the determination of chromium (VI) content in chromium tanning agents. The results give information about the reductive potential of the chromium tanning agent.

ISO 17070:2015 specifies a method for determining the content of tetrachlorophenol-, trichlorophenol-, dichlorophenol-, monochlorophenol-isomers, and pentachlorophenol, its salts, and esters in leather.

ISO 17489:2013 specifies a simple and practical method of determining the adsorbable fraction of synthetic tanning agents using a polymer-based product. It is particularly suitable for measuring the batch-to-batch consistency of synthetic tanning agents.

ISO 17226-3:2011 specifies a method for determining the emission of formaldehyde from leathers. This method is based on high performance liquid chromatography (HPLC). It is selective and also allows the emission of other low molecular aldehydes and ketones to be observed.
ISO 17226-3:2011 deals with the release of formaldehyde to the gas phase. Therefore, the obtained results are not comparable with the results of methods described in ISO 17726-1 and ISO 17226-2 which are based on extraction with liquid water.

ISO 17234-2:2011 is supplementary to ISO 17234-1 and describes a special procedure to detect the use of certain azo colorants in commodities, which can release 4-aminoazobenzene. The procedure also detects 4-aminoazobenzene (Solvent Yellow 1) which is already available as free amine in commodities without reducing pretreatment.
Azo colorants that are able to form 4-aminoazobenzene generate, under the conditions of ISO 17234‑1, the amines aniline and 1,4-phenylenediamine. The presence of these 4-aminoazobenzene colorants cannot be reliably ascertained without additional information (e.g. the chemical structure of the colorant used) or without a special procedure.

ISO 5398-2:2009 describes the determination of chrome by colorimetric means. It is applicable to leathers which are expected to have chromic oxide contents in excess of 0,05 %. This is an analysis for total chromium in leather; it is not compound specific or specific to its oxidation state.

ISO 4684:2005 specifies a method of determination of volatile matter which is applicable to all leather types.
It is not possible to determine the exact moisture content of leather by this method. This is because at elevated temperatures other volatile substances escape and tannins and fats can be oxidized. Some absorbed water may be left in the leather after drying.

ISO 20137:2017 gives guidelines to apply the available chemical test methods for leather. This information can be used by those involved in setting specifications for leather, especially for those parameters relating to restricted chemical substances.
Lists of restricted chemicals contain many substances that are not relevant to the leather industry. Those chemical substances that are not mentioned in this document do not need to be determined, thus avoiding unnecessary analytical costs.

This document specifies a test method for detection and quantification of extractable neutral, ionic, long, medium and short chain perfluorinated and poly-fluorinated substances in leather and coated leather.
This document, taking into account the three-dimensional distribution of the fibres within leather, makes the evaluation of the perfluorinated and poly-fluorinated substances with respect to the mass.
Classes of regulated compounds listed in Annex A, Table A.1, include acids, telomers, sulfonates and sulphonamide alcohols. Classes of other non-regulated compounds that can be determined by this document are defined in Annex B, Table B.1.

ISO 18218-1:2015 is a method for determining ethoxylated alkylphenols (nonyphenol ethoxylate [NPEOn with 1 ≤ n ≤ 16] and octylphenol ethoxylate [OPEOn with 1 ≤ n ≤ 16]) in leather. This direct method is especially suitable where a larger number of leather samples are to be checked for the presence of ethoxylated alkylphenols.
This method requires the use of high-performance liquid chromatography (HPLC) with triple quadrupole mass spectrometer (MSMS) to identify and quantify the ethoxylated alkylphenols.
NOTE 1       In the leather industry, the most commonly used commercial ethoxylated alkylphenol is the NPEO with an average of 9 EO. It has an optimum cloud point in water for the typical leather processing temperatures of 40 °C to 55 °C.
NOTE 2       ISO 18218-1 and ISO 18218-2 use different solvents for the extraction of the ethoxylated alkylphenols from leather. Consequently, the two analytical methods are expected to give similar trends but not necessarily the same absolute result for the ethoxylated alkylphenol content in leather.

This document specifies a method for the determination of the total metal content in leather using digestion of the leather and subsequent determination with inductively coupled plasma optical emission spectrometry (ICP-OES), inductively coupled plasma mass spectrometry (ICP-MS), atomic absorption spectrometry (AAS) or spectrometry of atomic fluorescence (SFA).
This method determines the total metal content in leather; it is not compound-specific or specific to the oxidation state of the metals.

ISO 18219:2015 specifies a chromatographic method to determine the amount of short-chain chlorinated paraffins (SCCP) C10-C13 in processed and unprocessed leathers.
Annex A is for information only.

ISO 27587:2009 specifies a method for the determination of free formaldehyde in process auxiliaries for leather. The analytical result obtained according to this procedure is expressed in milligrams per kilogram sample. The upper limit of quantification of the method is given by the capacity of the cartridge (total carbonyls 6 400 µg/cartridge).

ISO 17234-1:2015 specifies a method for determining the use of certain azo colorants which can release certain aromatic amines.

ISO 13365:2011 specifies a test method for the determination of the content of the following preservative agents:
2-(thiocyanomethylthio)-benzothiazole (TCMTB);
4-chloro-3-methylphenol (PCMC);
2-phenylphenol (OPP);
2-octylisothiazol-3(2H)-one (OIT);
in leather by liquid chromatography.
Preservative agents are necessary to protect leather from microbiological attack.

ISO 20136:2017 specifies a test method to determine the degree and rate of aerobic biodegradation of hides and skins of different animal origin, whether they are tanned or not, through the indirect determination of CO2 produced by the degradation of collagen.
The test material is exposed to an inoculum (activated sludge from tannery wastewater) in an aqueous medium.
The conditions established in this document correspond to optimum laboratory conditions to achieve the maximum level of biodegradation. However, they may not necessarily correspond to the optimum conditions or maximum level of biodegradation in the natural medium.
In general, the experimental procedure covers the determination of the degradation degree and rate of the material under controlled conditions, which allows the analysis of the evolved carbon dioxide produced throughout the test. For this purpose, the testing equipment complies with strict requirements with regard to flow, temperature and agitation control.
This method applies to the following materials:
- natural polymers of animal stroma (animal tissue/skins),
- animal hides and skins tanned (leather) using organic or inorganic tanning agents,
- leathers that, under testing conditions, do not inhibit the activity of microorganisms present in the inoculum.

ISO 14088:2012 specifies a test method for the determination of tanning agents through filteration of all vegetable and synthetic tanning products.

ISO 18218-2:2015 is a method for determining alkylphenols (nonylphenol and octylphenol) and alkylphenol ethoxylates (nonylphenol ethoxylate and octylphenol ethoxylate) in leather and process auxiliaries. The analysis is based on high-performance liquid chromatography (HPLC) or gas chromatography-mass spectrometry (GC-MS).
The analysis of the alkylphenol ethoxylate is made by cleaving the alkylphenol ethoxylate and measuring the released alkylphenol.
NOTE ISO 18218‑1 and this part of ISO 18218 use different solvents for the extraction of the ethoxylated alkylphenols from leather. Consequently, the two analytical methods are expected to give similar trends but not necessarily the same absolute result for the ethoxylated alkylphenol content in leather.

ISO 17072-1:2011 specifies a method for the determination of extractable metals in leather using extraction with an acid artificial-perspiration solution and subsequent determination with inductively coupled plasma/optical emission spectrometry (ICP-OES), or inductively coupled plasma/atomic emission spectrometry (ICP/AES), or inductively coupled plasma/mass spectrometry (ICP/MS), or atomic absorption spectrometry (AAS) or spectrometry of atomic fluorescence (SFA).
This method is especially suitable for determining the extractable chromium in chromium tanned leathers.
This method determines extractable metals in leather, it is not compound-specific or specific to the oxidation state of the metals.
This method is also applicable for the determination of many extractable metals, including aluminium (Al), antimony (Sb), arsenic (As), barium (Ba), cadmium (Cd), calcium (Ca), chromium (Cr), cobalt (Co), copper (Cu), iron (Fe), lead (Pb), magnesium (Mg), manganese (Mn), mercury (Hg), molybdenum (Mo), nickel (Ni), potassium (K), selenium (Se), tin (Sn), titanium (Ti), zinc (Zn), and zirconium (Zr).
The quantification limit of extractable lead is 3 mg/kg.

ISO 17072-2:2011 specifies a method for the determination of the total metal content in leather using digestion of the leather and subsequent determination with inductively coupled plasma/optical emission spectrometry (ICP/OES), or inductively coupled plasma/mass spectrometry (ICP/MS), or atomic absorption spectrometry (AAS) or spectrometry of atomic fluorescence (SFA).
This method determines the total metal content in leather; it is not compound-specific or specific to the oxidation state of the metals.
The method is applicable for determining aluminium (Al), antimony (Sb), arsenic (As), barium (Ba), cadmium (Cd), calcium (Ca), chromium (Cr), cobalt (Co), copper (Cu), iron (Fe), lead (Pb), magnesium (Mg), manganese (Mn), mercury (Hg), molybdenum (Mo), nickel (Ni), potassium (K), selenium (Se), silicon (Si), sodium (Na), tin (Sn), titanium (Ti), zinc (Zn), and zirconium (Zr).
The quantification limit of total lead is 8 mg/kg.
ISO 17072-2:2011 is not applicable to chromium-tanned leathers. In this case, ISO 5398-1, or ISO 5398-2, or ISO 5398-3, or ISO 5398-4 are used.

ISO 17234-1:2010 specifies a method for determining the use of certain azo colorants which may release certain aromatic amines.