原文由 graymice 发表:
救你们指定的方法而言,Negative就是未检出(萃取液浓度<0.02mg/kg),如果是Positive就会给出具体的检出液浓度值,不管结果是阴性还是阳性,都不代表镀层的浓度,只代表萃取液的浓度。不过目前很多大公司默认阴性代表合格,阳性代表不合格。
f) If the absorbance value obtained in B.5.2.d is equal to or greater than that obtained in B.5.2.e, the sample is considered to be positive for Cr(VI). If not, the test result is negative.
g) A positive boiling water extraction test result indicates the presence of Cr(VI). The Cr(VI)concentration detected in the boiling water extraction solution is equal to or greater than
0,02 mg/kg with a sample surface area of 50 cm2 used. However, it shall not be interpreted as the Cr(VI) concentration in the coating layer of the sample and shall not be used as a method detection limit for this qualitative
请看标准原文,金属中的六价铬无论是点测试,还是沸水萃取测试,都只给出Negative,positive.Negative 表示的是由表面积为50cm2的样品所萃取出来的溶液中的六价铬的浓度等于或大于0.02mg/kg,一定要加上是50CM2,所以这个0.02mg/kg也不是MDL,目前测试金属中的六价铬一般都不会给出MDL。
但总有些同志老想知道如果是POSITIVE,想知道值是多少或者大概是多少,所以就有了提供镀层厚度,密度,有些机构会给出具体的数值,但这个数值仅供参考,因为厚度,密度,表面积都很难保证准确性。所以一般检测机构是不愿给数值的