HPLC/Spectro Grade n-Hextane,95% – the Secret behind the Purity Value

n-Hexane is an important chemical raw material and solvent, which is widely used in medicine, chemical analysis and chemical production industries. At the same time, it is also an organic solvent commonly used in chromatographic analysis. I wonder if you have noticed that the purity of n-Hexane marked on many chromatographic grade n-Hexane labels is greater than 95%? What is the remaining 5%? Will it affect our experimental results?

Now let’s use the experiment to find out for you.

Another indicator of n-Hexane reagent is the content of hexane containing isomers. Generally, this indicator is greater than 99%. It can be seen that the impurity source in n-Hexane may be mainly hexane isomers.

Firstly, several Hexane isomers were separated by preparing hexane isomer mixed standard. Weigh a certain amount of n-Hexane, 2-METHYLPENTANE, 3-methylpentane, 2,3-dimethylbutane and 2,2-dimethylbutane to prepare isomer mixed standard. The separation results are shown in the chromatogram of Figure 1:

It can be seen from the chromatogram that the main isomer impurities in HPLC grade n-Hexane are 3-methylpentane and a small amount of 2-METHYLPENTANE, and the other non isomer impurities are C7 and cycloalkanes (the peak time is after 7min), i.e. 2,2-dimethylpentane, 2,4-dimethylpentane and METHYLCYCLOPENTANE. According to the preparation process of n-Hexane, the boiling points of the main impurities methyl cyclopentane and 3-methylpentane are 71.8 ° C and 63.3 ° C. they are close to that of n-Hexane. It is difficult to separate them from the main component n-Hexane in the production process, so they become impurities and remain in n-Hexane reagent.

It is determined that n-Hexane impurities are hexane isomers. Will these impurities affect the experimental results? For liquid phase test, improper solvent selection will produce baseline instability or “pseudo peak”. HPLC grade reagent is a kind of solvent with the least particles and the lowest UV absorption produced by special methods, in which the UV absorption of solvent is a more concerned index. Therefore, we further tested the UV transmittance t (%) of HPLC grade n-Hexane at different wavelengths.

At the wavelength of 220 ~ 400 nm, the transmittance of HPLC n-Hexane is more than 80%, and the transmittance is close to 100% at 280 ~ 400 nm. It can be seen that the isomer impurities in HPLC n-Hexane basically will not affect the UV absorption.

Therefore, although the content of n-Hexane in chromatographic grade n-Hexane reagent is greater than 95%, the isomer impurities in it will not affect the test. As long as the UV absorption value of n-Hexane reagent meets the requirements, it can be used safely.