ISO/TS 16186 Footwear - Critical Substances Potentially Present in Footwear and Footwear Components - Determination of Dimethyl Fumarate (DMFU)

The standard "ISO/TS 16186 Footwear - Critical substances potentially present in footwear and footwear components - Determination of dimethyl fumarate (DMFU)" developed by the International Organization for Standardization (ISO) describes a method for the determination of dimethyl fumarate (DMFU) content using gas chromatography with single quadrupole mass spectrometry (GC-MS) or tandem quadrupole mass spectrometry (GC-MS/MS). This standard is applicable to all types of footwear and footwear components except metal parts.

In principle, the sample is removed using acetone at 60 degrees in an ultrasonic bath. In this step, two different procedures can be used depending on the material being tested:

• The standard procedure without purification and concentration of the extracted solution can be used for samples giving a simple chromatogram, for example textile shoe components.
• The complex matrix procedure with purification and concentration of extract can be used for samples with complex matrix effect such as skin.

An aliquot of the extract is analyzed using a gas chromatograph with single quadrupole mass spectrometry (GC-MS) or tandem quadrupole mass spectrometry (GC-MS/MS).

In addition to the usual laboratory equipment and laboratory glassware complying with the ISO 4787 standard, the following equipment is used in the tests:

• Analytical balance with a precision of at least 0,1 mg.
• Glass bottle (e.g. 40 ml volume) with a screw cap that can be closed tightly.
• Ultrasonic bath with adjustable temperature, suitable for operation at approximately 60 degrees.
• PTFE (Teflon) membrane filter with 0,45 µm pore width.
• GC bottle with cap (e.g. 2 ml volume).
• Volumetric flasks.
• Gas chromatography with mass selective detector (GC-MS or GC-MS/MS).
• Amber glass bottle (e.g. 10 ml volume) with a tightly closing screw cap.
• Activated magnesium silicate cartridge.
• Nitrogen vaporizer with conical tubes and adjustable temperature, suitable for operation up to 40 degrees.

The test sample shall consist of a single type of material (made of textile, leather, polymer or other organic material) which is tested separately. Cut homogeneous material samples into pieces with an edge length of approximately 3 mm to 5 mm. A maximum of three test samples (of equal mass) of the same type of material may be tested together, taking into account the limits of detection and quantification. The dryer may be a source of DMFU contamination of footwear. The dryer samples may be used without any further treatment.

According to standard procedure, 1,0 g plus/minus 0,1 g of the sample is weighed into a glass vial, the mass is recorded to the nearest 1 mg, 0,1 ml of the internal standard working solution and 9,9 ml of acetone are added and the vial is capped. The sample is held in an ultrasonic bath at 60°C plus/minus 5°C for 60 minutes plus/minus 5 minutes. Since the contents may be under pressure, the vial should not be opened without cooling. After cooling to at least 27°C, the solution is decanted and, if necessary, reduced to 1,0 ml under a gentle stream of nitrogen. This solution is filtered through a PTFE membrane filter. A portion of the extract is transferred to a GC vial and capped.

For extraction according to the procedure for complex matrix, weigh 1,0 g plus/minus 0,1 g of the sample into a glass vial, record the mass to the nearest 1 mg, add 0,1 ml of internal standard solution and 9,9 ml of acetone and cap the vial. The sample is extracted in an ultrasonic bath at 60 degrees plus/minus 5 degrees for 60 minutes plus/minus 5 minutes.

After cooling to at least below 27 degrees, 5 ml of the extract is transferred to a conical tube and reduced to approximately 0,2 ml under a gentle stream of nitrogen. The extract is reconstituted to 1 ml with n-hexane. The reconstituted extract is purified on an activated magnesium silicate cartridge.

When preparing calibration solutions, at least 3 calibration solutions of a mixture of dimethyl fumarate and dimethyl maleate, including the internal standard in acetone from the working solutions, are prepared at concentrations appropriate for analysis. Each solution should contain the internal standard at a concentration that matches the internal standard concentration in the final sample extract.

Extracted dimethyl fumarate (DMFU) is determined by GC-MS or GC-MS/MS. Adequate separation of dimethyl fumarate and dimethyl maleate is required to avoid false positive results caused by dimethyl maleate.

When calculating dimethyl fumarate in the sample, a calibration graph of the response against the known standard concentration is plotted. From the calibration graph, the dimethyl fumarate concentration in mg/l is interpolated. The dimethyl fumarate level is calculated as the mass fraction of the tested material according to the given formula.

If the limit of quantification needs to be below 0,1 mg/kg, it can be lowered by the concentration of the sample solution.

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 16186 Footwear - Determination of critical substances potentially present in shoes and shoe components - Dimethyl fumarate (DMFU)”.