Reversed-phase liquid chromatography frequently employs organic solvents such as methanol, acetonitrile or tetrahydrofuran. Although HPLC grade products of these solvents are available, it seems some users have trouble when using a reagent grade solvent instead of HPLC grade. This leads them to waste considerable amounts of time. How do the two solvent grades differ?

--Methanol/acetonitrile--
Reagent grade solvents contain larger quantities of UV absorbing impurities than HPLC grade solvents. This makes it difficult to use reagent grade solvents for gradient elution or trace analysis due to these impurities being retained and eluted as peaks under gradient conditions. This is particularly so when detection is conducted at a short wavelength when significant differences appear in baseline noise or detection sensitivity. In some cases (or at certain specific wavelengths) it may be possible to use a reagent grade solvent but we recommend HPLC grade solvents in order to obtain a stable, reproducible chromatogram.

--Tetrahydrofuran--
Tetrahydrofuran easily generates peroxides. In order to prevent this antioxidants are frequently added. The antioxidants can cause a ghost peak so a solvent containing no antioxidants should be used in HPLC. The presence of peroxides in tetrahydrofuran will have very significant effect on the baseline stability (greater than for most other organic solvents), which results in a strong recommendation always to use HPLC grade solvents which have not been stored for extended periods.