ISO/TS 16179 Footwear - Critical Substances Potentially Present in Footwear and Footwear Components - Determination of Organotin Compounds in Footwear Materials

The standard “ISO/TS 16179 Footwear - Critical substances potentially present in footwear and footwear components - Determination of organotin compounds in footwear materials” developed by the International Organization for Standardization (ISO) describes a test method to determine the presence of organotin compounds. This test method can be applied to all types of footwear materials.

In principle, organotin substances are extracted from the shoe material with a methanol-ethanol mixture under a moderately acidic condition, using tropolone as a complexing agent. The polar and high-boiling organotin is then converted to the corresponding volatile tetra-alkyl derivative by reaction with sodium tetraethylborate. Finally, it is detected by a gas chromatograph equipped with a mass selective detector (GC-MS).

The table titled “List of target compounds that can be analyzed with this technical specification” contains the list of target compounds that can be analyzed with this test method.

The equipment and materials used in this test method include:

• GC-MS gas chromatograph equipped with mass selective detector (MS).
• Analytical balance capable of measuring mass with an accuracy of 0,1 mg.
• A glove bag, box or isolation chamber containing gloves, with side and front openings and means of closing the openings, such as tape, that allows work in a completely isolated and controlled environment.
• Polypropylene sample tubes with screw caps and a volume of 50 ml.
• Micropipettes (ranging from 10 µl to 500 µl, with disposable tips).
• Pipette (capacity 1ml to 10ml).
• Calibrated pH meter with glass combination electrode and range 0 to 14.
• 10 ml, 25 ml and 100 ml volumetric bottles.
• Ultrasonic bath with adjustable temperature.
• Disposable glass Pasteur pipettes.
• Glass beaker.
• Centrifugal.
• Mechanical shaker (minimum 50 min.⁻¹ frequency).

When preparing the test piece, the test piece consists of a single piece of material taken from the shoe, such as leather, textile, polymer, coated material or other. Preparation of the sample should include removing individual materials from the shoe and preparing a test piece that results in particles with a maximum diameter of 4 mm or less.

Sodium tetraethylborate solution should be prepared in an inert atmosphere as it is air sensitive and will spontaneously combust in the presence of air. To minimise fire risks the solution should be prepared in an empty fume cupboard using the method given. Organotins are both toxic and known endocrine disruptors. Therefore, they should be handled with extreme caution. All chemicals stored below room temperature should be allowed to reach room temperature before aliquoting.

The preparation of the sodium tetraethylborate solution should be carried out in an inert medium. The analytical balance is placed in the inert medium, the power cable is passed through one of the small side openings, and the opening around the cable is sealed with tape. The following items are placed in the inert medium: a small beaker, a sealed bottle of sodium tetraethylborate, a large spatula containing THF, a small spatula and a small beaker, and a disposable pipette. Using an inert gas source connected to the side of the inert medium, the bag is filled with gas, allowing the mixed air and inert gases to be expelled through the front opening for several minutes. This ensures that the remaining oxygen is at a concentration low enough to not support combustion. The front opening of the inert medium is closed and the inert gas source is turned off. Using gloves next to the bag, weigh 2,0 g of sodium tetraethylborate into the beaker, then add enough THF to dissolve the borate. The top of the sodium tetraethylborate bottle is resealed. The front of the bag is opened and all items are removed, then left in the fume cupboard for cleaning. The sodium tetraethylborate solution is transferred from the beaker to a 10 ml volumetric flask and made up to the mark with THF. To minimize evaporation of the solvent, the reagent is stored in a refrigerator for up to three months when not in use.

When preparing standard solutions, organotin compounds are commercially available under their chloride forms, but for the calibration curve and the result the concentration is expressed as mg/kg of organotin cations. The table titled “Weight factor for recalculation of organotin chloride amount and organotin cations” gives the organotin chloride amount and the weight factor for recalculation of organotin cations (for 100 percent chloride form purity).

When preparing the tropolone solution, 0,500 g of tropolone is placed in a glass beaker using the analytical balance and dissolved in approximately 20 ml of methanol. Dilute to 100 ml in a volumetric flask. This solution can be used for up to one month after preparation and can be stored in a refrigerator at approximately 4 degrees.

When preparing the buffer solution, for example, 1 M sodium acetate solution is prepared by weighing 16,4 g of sodium acetate in 0,2 l of water and the pH value is adjusted to 4,5 with acetic acid.

Our organization, which has been trying to support businesses from every sector with its testing, measurement, analysis and evaluation studies carried out in a wide range for years, has a strong staff that closely follows the developments in the world in the field of science and technology and constantly improves itself. In this context, testing services are also provided to businesses in accordance with the standard “ISO/TS 16179 Footwear - Critical substances potentially present in shoes and shoe components - Determination of organotin compounds in shoe materials”.