Organic Chemicals: What's The Other 2% in 98% Purity Products?

As we all know, in 99.999% Aluminum metal, the total impurities are less than 10 ppm. The impurities may be listed as iron, silicon, etc.

I have been asked by many customers about our organic chemicals. What's the other 2% in 98% purity products? The purity you list is 98% HPLC and I’d like to know the other 2% impurities. If you only list your Dihydromyricetin as 98% HPLC, what are the other 2% impurities? Your highest pure sodium hyaluronate is only 95%, what are the other 5%? You just said you don’t know?
Actually, we may never know what the other 2% or 5% is, because it may never exist.

The main reason is the different test methods. Here I want to talk about the purity for organic chemicals.

The purity of organic chemicals is tested by totally different methods with inorganic materials. For example, ICP-MS can be used to test hafnia, while HPLC (High-performance liquid chromatography) is used for Dihydromyricetin. In the organic field, 98% means almost pure product. The other 2% can be small impurities or detection errors on a fully acceptable basis. If you are very very strict, you can require 99% HPLC purity. But most of the time, it doesn’t make any sense. We can never offer 100% HPLC product, even if the purity in the HPLC spectrum is 100%, a single peak, in the common test method it still can be 98%, which is caused by impurities in the test solvent or different machines.

Why is the purity of sodium hyaluronate only 95%? Sodium hyaluronate is a polymer. The test method is based on the method in European Pharmacopoeia. 95% is almost pure product.

In this case, we may find some products tagged as purity of 103%. How and why it can be 103%?
The answer is also in the test method. For instance, an external standard method could make this happen and this method is one of the most common approaches. Sometimes we can find the purity requirement is 95%~105% in many pharmacopeia.