There are many organic solvents used in liquid phase testing. Acetonitrile and methanol are two common solvents. However, due to the difficulty of separation in some tests, tetrahydrofuran plays an irreplaceable role. It can be noted that there are 2 different products of tetrahydrofuran, one with stabilizer and one without stabilizer. What is the difference between these two products?
First, let’s introduce tetrahydrofuran: Tetrahydrofuran (THF) is a colorless, water-miscible organic liquid with a small viscosity at normal temperature and pressure. Because of its long liquid range, it is a commonly used medium polar aprotic solvent, and it is also often used as a precursor of high molecular polymers.
Tetrahydrofuran is unstable in nature and has one thing in common with many other ether solvents. When it comes into contact with oxygen or air for a long time, a small amount of peroxide will be generated. The peroxide in the solvent will have a certain impact on experimental tests. If the peroxide content exceeds 1%, tetrahydrofuran can no longer be used. Adding stabilizers to tetrahydrofuran can slow down the formation of peroxide. Common stabilizers that inhibit the formation of peroxides include hydrogenated hydroquinone, 3,5-di-tert-butyl-p-cresol (BHT) and butylated hydroxybenzyl pyridinium ether (BHA). Generally, 0.01-0.04% BHT is added to tetrahydrofuran as a stabilizer. Because tetrahydrofuran is unstable, the shelf life of tetrahydrofuran without adding stabilizers is relatively short. Adding stabilizers can effectively extend the shelf life of tetrahydrofuran. So, what impact does adding stabilizer have on the use of tetrahydrofuran in tests?
We know that commonly used detectors for HPLC are UV detectors and photodiode array detectors. Usually, UV absorption data will be indicated on the label or COA of HPLC solvents, as shown in the figure below:
Figure 1 COA without stabilizer tetrahydrofuran (part)
Figure 2 COA containing stabilizer tetrahydrofuran (part)
Comparing the two pictures, we can see that tetrahydrofuran containing a stabilizer, which is also suitable for HPLC, has no UV data. Why is this? To this end, we used UV spectroscopy to test the UV transmittance of two kinds of tetrahydrofuran. The spectra are as follows:
Figure 3 UV spectrum of tetrahydrofuran without stabilizer
Figure 4 UV spectrum of tetrahydrofuran containing stable mica fixative
It can be seen from the two spectra that tetrahydrofuran with stabilizer added has obvious absorption at 260~290 nm, which will affect the signal of the target compound at 260~290 nm. Therefore, tetrahydrofuran containing stabilizer is not suitable for UV detectors and photoelectric detectors. Detection of some wavebands by diode array detectors. For detection and analysis methods that do not involve UV absorption, such as GPC, etc., tetrahydrofuran containing stabilizer can be used.
It can be seen that tetrahydrofuran without stabilizers has a wider application range, and the specific selection principles can be selected based on testing needs and frequency of use. In addition, tetrahydrofuran will cause certain damage to the pipeline materials of liquid chromatography. When using it, it is necessary to control the proportion of tetrahydrofuran and maintain the instrument well.
