Chemical Forums
Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: tealswell on August 12, 2005, 04:06:20 PM
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When performing a titanium dioxide assay using a NIST standard that is 99.59% pure, do you add the purity to the calculation?
For example:
(Vol KMnO4 titrant)(equivalency factor)(Normality of KMnO4)(100)
/(weight sample)(purity)
I was told that the purity is not used b/c we are titrating for the assay value. But in LC/GC analysis, the purity of spl and std are entered into assay calculations. It seems to me that entering the known purity would normalize the calculation, since you know you did not start with 100% pure titantium dioxide.
Please advise!! ???
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[I was told that the purity is not used b/c we are titrating for the assay value.]
Thats quite right. When you assay a CRM you are determining how accurate your assay method is relative to the CRM you are using. If your assay of the CRM comes out at 96.60% TiO2 rather than the certified 99.59%, then you can say that the method is either within the acceptable limits of the method used or not. You may also use the ratio of determined:certified value to "correct" for the discrepancey in the samples determined by the same method. Although this mathematical correction may be erroneous.
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Please advise!! ???
Here goes my advice: don't crosspost.