What Is Azo?
Azo dye analysis in leather determines whether the dyes used release banned aromatic amines under reducing conditions. The specimen is reduced with sodium dithionite, the released amines are extracted, and they are identified and measured by GC-MS.
Purpose of Azo
The purpose is to determine whether the leather product contains azo dyes that release aromatic amines banned under REACH Annex XVII Entry 43.
Which Products Is Azo Applied To?
- Dyed leather and synthetic leather
- Footwear uppers and linings
- Leather bags, belts and gloves
- Leather clothing
- Upholstery leather
In Which Sectors Is Azo Used?
Standards Related to Azo
- TS EN ISO 17234-1 (aromatic amines from azo dyes in leather)
- TS EN ISO 17234-2 (4-aminoazobenzene)
- TS EN ISO 4044 (sample preparation)
Azo Conditions
- Reduction
- With sodium dithionite in citrate buffer, at the temperature defined in the standard
- Measurement
- Identification by GC-MS, confirmation by a second method
- Unit
- mg/kg
Equipment for Azo
- GC-MS
- HPLC-DAD or LC-MS/MS
- Water bath
- Solid-phase extraction system
- Mill
Sample Requirements for Azo
- A separate specimen for each colour
- Ground specimen (ISO 4044)
- Upper leather and lining must be analysed separately
- Approximately 1 g specimen
Duration of Azo
Because of the reduction, extraction and chromatographic measurement steps, analysis takes several working days; duration increases with the number of colours.
Azo Procedure
- 1The specimen is separated by colour and component, ground, and weighed.
- 2It is reduced with sodium dithionite in citrate buffer.
- 3The released amines are extracted.
- 4The extract is concentrated.
- 5Identification is carried out by GC-MS.
- 6Amines found are confirmed by a second method and their amount is calculated.
Azo Acceptance Criteria
REACH Annex XVII Entry 43 sets a threshold concentration for the listed aromatic amines; a result above the threshold is non-compliant. The current threshold and list of amines are confirmed from the regulatory text.
Evaluation of Results
Each amine is reported separately. Interference is more likely in the leather matrix than in textiles; a positive finding is not reported without confirmation by a second chromatographic method.
Azo Report
- Specimen identification and colours analysed
- Part of the standard applied
- Result (mg/kg) and limit of quantification for each amine
- Confirmation method
Accreditation
EUROLAB holds internationally recognised accreditation obtained from accreditation bodies party to the IAF and ILAC multilateral recognition arrangements, under ISO/IEC 17025 for laboratory testing, ISO/IEC 17020 for inspection and surveillance, and ISO/IEC 17021-1 and ISO/IEC 17065 for system and product certification. This chain ensures the reports and certificates issued are accepted worldwide.
Whether this test can be offered within accredited scope depends on your product and the standard applied; since accreditation is method-based, the scope is confirmed in writing at the quotation stage.
Scope and authorisationsRelated Regulations
- (EC) 1907/2006 REACH Annex XVII Entry 43
Footwear and Leather Testing — What Does This Testing Field Cover?
The section below describes the field that the Azo test belongs to; the conditions and acceptance criteria of this particular test are given in the sections above. The scope specific to your product is confirmed in writing at the quotation stage.
Footwear and leather testing assesses the physical durability and chemical safety of a product together. Footwear is a MULTI-COMPONENT product: the sole, upper, lining, insole, heel and bonding line are tested both individually and together. One component being good does not mean the product is good; failure usually appears where components join.
On the physical side, the most common field failure is SOLE-UPPER SEPARATION. Bond strength is therefore the most critical measurement in the field and is a direct indicator of the bonding process (surface preparation, adhesive selection, pressing conditions). Next come sole abrasion and flex resistance: a shoe is flexed hundreds of thousands of times over its life.
Slip resistance is the most important parameter for safety and its measurement depends on the surface: wet ceramic, oily steel and dry floor give different results. Slip resistance is therefore reported not as a single number but with the surface and the direction of slip stated.
A separate body of work applies to protective footwear, and this is the most commercially critical distinction. Toe protection (impact and compression), penetration resistance, antistatic behaviour, heat and cold insulation, electrical insulation and fuel resistance are assessed under personal protective equipment requirements. CE is mandatory for these products and the category must be chosen correctly; an ordinary footwear test report does not satisfy that file.
On the chemical side, CHROMIUM (VI) has a special place in leather. The chromium (III) used in tanning can oxidise into chromium (VI) during storage and ageing; that is, a leather that was compliant at production may exceed the limit months later. The time of measurement and the history of the sample therefore affect the result, and measurement after ageing may be required.
Other chemical items are aromatic amines from azo dyes, pentachlorophenol, short-chain chlorinated paraffins, dimethyl fumarate and phthalates. These items come from REACH restrictions and brand restricted substance lists.
There is NO CE marking on consumer footwear; the obligation runs through material composition labelling, compliance with chemical restrictions and general product safety. Labelling has a rule of its own: the type of material used for the upper, the lining and insole and the outer sole is shown by pictograms.
Comfort and functional claims (waterproofness, moisture management, breathability) are supported by separate tests, and these claims require evidence if used in marketing copy.
Method groups in this field
Bonding and strength
Sole-upper bond strength, seam strength, heel attachment strength, strap and buckle strength.
Abrasion and flexing
Sole abrasion, flex resistance (dry and at low temperature), insole abrasion.
Slip resistance
Forward and backward slip measurements on wet ceramic, oily steel and dry floor.
Protective properties
Toe impact and compression resistance, penetration resistance, antistatic behaviour, heat and cold insulation, fuel and chemical resistance.
Leather chemistry
Chromium (VI), azo dye amines, pentachlorophenol, short-chain chlorinated paraffins, pH and fat content.
Comfort and function
Waterproofness, water vapour permeability, moisture management, colour fastness and the effect of perspiration.
Commonly confused in this field
- Footwear claiming a protective function falls under PPE legislation and requires CE; a consumer footwear test report does not satisfy that file.
- A chromium (VI) result depends on the age of the sample and its storage conditions; leather compliant at production may exceed the limit later.
- Slip resistance is not a single number; it cannot be interpreted without stating the surface and the direction.
- A result obtained for one component does not cover the whole product; the joints are tested separately.
- Labelling rules run on material pictograms; an incorrect pictogram causes problems in customs and market surveillance.
- A waterproofness claim is not verifiable unless the test used and the number of flex cycles after which it was measured are stated.
Which decisions these results support
- Compliance with the brand restricted substance list
- The PPE category and CE file for protective footwear
- Supplier and lot-based acceptance control
- Root cause analysis of field complaints (bond opening, sole separation)
- Substantiation of functional claims
Related Tests
Frequently Asked Questions About Azo
If the upper leather is clean, is the lining assumed clean too?
No. The lining comes from a different supplier and different dyes. It also has closer skin contact, so it must be analysed separately.