Chromium is a multivalent metal ion, common form of six valence chromium and trivalent chromium, Cr six is 100 times as toxic as the trivalent chromium, has the very strong carcinogenic and skin damage, according to statistics, over 80% of the world's leather is leather, easy to remain six chromium. Therefore, countries all over the world especially in the EU and other developed countries, there is limited strictly to six chromium content in leather, generally requiring less than 5 mg/kg, the EU EN420:1994 regulations glove leather soluble chromium six maximum limits for 2mg/kg.
Test on six valence chromium in leather reported more [1-4], but the real as a standard method of detection based on the commonly used are: Chinese SN/T0704 1997, EU EN420:1994, several German DIN53314 - 1996, the detection method of 1997 and EN420:1994 in the SN/T0704 agreement, this paper focuses on the discussion of EN420:1994 and DIN53314 - 1996 two a detection method, for your reference.
One, introduction to the standard
1, EN420:1994EN420:1994 is the March 2, 1994 European Standards Committee on through the "gloves General requirements specified in article 4.4.3," in which the six chromium content in leather gloves should be less than 2mg/kg, 6.1 test methods are introduced, as follows: 10g crushing water 99ml water and 1ml potassium hydrogen phosphate two sample buffer (2mol/l 2), oscillation hours after filtration, the filtrate pH value should be between 7.5 - 8. The filtrate is 25ml to 100ml volumetric flask, add 2ml phosphoric acid solution (68%), add water to 40ml, plus ml of the phosphoric acid solution, 2ml two phenyl hydrazine acetone solution (Kaba 1%), water volume, 5 - 20 minutes to 550mm absorbance was measured, using a reagent blank as reference, the six prices chromium content in the sample by using the standard curve.
2, DIN53314 - 1996 DIN53314 is made by German Chemists Association (GDCH), the International Leather Chemists Association of Engineers (IULTCS) and chemical analysis (IUC) established the Joint Committee on the "detection" six valence chromium in leather, the main contents are as follows: 2.000g crushed samples to a 250ml volumetric flask, adding potassium hydrogen phosphate 100ml beforehand by argon gas to adjust the pH two buffer (0.1mol/l, pH value of 8 ± 0.1), argon gas after gasser, control the temperature of 18-28 ℃, shaking for 3 hours, filtering, filtrate pH value should be 7.5 - 8, otherwise it should reduce weighing redo. The filtrate of 10ml in 2 50ml volumetric flask, add water to 40ml, then add 1ml phosphoric acid solution (68%), adding two 1ml benzene hydrazine acetone solution of Kaba in a volumetric flask (1%), add water to the scale; another is directly added to the scale, 10 - 20 minutes to 540mm absorbance, to a reagent blank as reference, the two absorbance difference, obtains six chromium content in leather by using the standard curve.
Similarities and differences between the two standards, methods and the advantages and disadvantages through the above introduction, we can see the basic principle of the two methods are the same, all is the use of phosphate buffer solution extraction soluble CR six, at the same time the filtrate pH was 7.5 - 8, with two carbazide as chromogenic agent, chromogenic in acidic conditions, spectrophotometric method for the determination of hexavalent chromium content of six. But in the specific operation is different, after the comparative analysis we can find, EN420:1994's 6.1 method is simple, sample volume, concentration of buffer solution is small, and can be directly from the standard curve to get results. Disadvantages of method is too simple, without considering the effect of the general color leather itself the pH and leather extracts, the application is restricted greatly.
Method of DIN53314 - 1996 in the sample amount is small, buffer solution concentration is larger, the extraction liquid pH in the 7.5 - 8; extraction process of argon protection, prevent the transformation of six chromium and trivalent chromium; and the results of calculation to deduct the sample itself to eliminate the effects of color, color dyeing leather. Disadvantage of this method is less sampling amount, considering the influencing the color of leather, method does not stipulate the general detection limit, recommend the detection limit was 3mg/kg, unable to meet the EU EN420 requirements; at the same time method applies to samples extraction was less than 0.600A (cuvette as 2cm), for the dark samples exceeded the absorbance to treatment did not make clear a regulation, standard application brings certain restrictions.
Comparison of three, conclusion through two standard method and we nearly several years of practical work experience, found that because of finished leather by acid dyes, dyeing and finishing, acidic, high concentration of buffer solution, according to DIN53314 standard, sample weight smaller conditions to ensure the basic extraction pH in 7.5 - 8, at the same time by influence of leather and their color, the results need fully consider the sample absorbance factors. But the EN420:1994 6.1 method, the sample volume, concentration of the buffer is small, almost no buffer capacity, leachate pH was 5.5 - 6.5, can not guarantee the filtrate pH value reached 7.5, 8, and six chromium relation extraction solution of pH values and the extract significantly; at the same time without deducting sample color the results of a large error. Therefore, we believe that the 6.1 methods in EN420:1994 suitable for the detection of special leather gloves, which extract colorless, neutral leather, mainly is the artificial leather; and for the dyeing of leather, detected by DIN53314 standard method is more reasonable. At the same time, because of the defect of two standard method, the relevant departments should as soon as possible strength, standard test method six chromium new in leather, in order to adapt to the needs of international trade.