New Chrome VI Method Imminent

New Chrome VI Method Imminent

An updated version of BS EN ISO 17075, the internationally recognised method for the analysis of chrome VI in leather, is due to be published by the end of February 2017.

The updates will see the method being split into 2 parts; part 1 being the colorimetric method (technically unchanged from the current version of the method) and part 2 using a new technique – Ion Chromatography.

 

New Chrome VI Method

BS EN ISO 17075-1

This method is often referred to as the ‘colorimetric’ method. The leather is cut into small pieces and placed in a phosphate buffer at pH 7.5-8.0 (the pH is crucial to ensure that chrome VI is not generated or reduced during the analytical procedure). Any chrome VI present in the leather leaches into the solution.

The laboratory then adds a reagent called 1,5-diphenylcarbazide which, in the presence of chrome VI, oxidises to 1,5-diphenylcarbazone turning the solution a pink/purple colour. The solution is filtered using Solid Phase Extraction (SPE) to remove any interfering dyestuffs from the solution that may generate a false positive.

The colour complex is quantified photometrically at 540nm using a UV-Vis spectrophotemeter to measure the intensity of the pink i.e. the amount of chrome VI detected.

The limit of detection for this method is 3mg/kg

 

BS EN ISO 17075-2

This method uses Ion Chromatography and is considered an ‘improved analytical technique’.

The leather is cut in to small pieces and placed in a phosphate buffer at pH 7.5-8.0 (again, the pH is crucial to ensure that chrome VI is not generated or reduced during the analytical procedure). Any chrome VI present in the leather leaches into the solution.

An aliquot of the filtered extract is analysed for CrVI using ion-exchange chromatography with UV-VIS detection. The advantage of this method is that there are no interferences from the colour of the extract, eliminating the risk of false positives.

The method states that if a leather sample is tested to both 17075-1 and 17075-2 and there is a difference in the results, the result from 17075-2 (ion chromatography) should be considered as the reference.

BLC would recommend that the Ion Chromatography method (17075-2) is specified.

 

What Is Ion Chromatography?

Ion chromatography is the separation and quantitative analysis of anions and cations in an ionic solution using the ion exchange method of liquid chromatography. The chromatographic process separates the different ions within the sample (i.e. a separation of chrome III and chrome VI).

 

Further Updates on the Horizon – Chrome VI Ageing

There are two primary methods for chrome VI ageing – the use of heat and UV. These methods are either technical standards (committee documents) or laboratory/brand in house methods and have not been formally published as international standards

For the heat ageing – the leather is aged for 24 hours at a high temperature and low relative humidity; the conditions can vary but typically these are 80ºC and <5% RH before going on to conduct the procedure described above in 17075 (either part 1 or part 2)

For the UV ageing – the leather is aged for 24 hours according EN ISO 105-B02:2013 Part B02: Colour fastness to artificial light: Xenon arc fading lamp test, Exposure Cycle A1  before going on to conduct the procedure described above in 17075 (either part 1 or part 2).

These ageing methods are designed to assess the propensity for chrome VI to form in leather. There is ongoing work to publish the ageing method as international standards, proposing to become 17075-3. We will be keeping an eye on this at BLC and will keep our members informed.

For further information on chrome VI testing, please view our Chrome VI webpage or contact us via info@blcleathertech.com or +44 (0) 1604 679999.

28 February 2017

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