HPLC has established itself as a versatile analysis technique in research, industrial and commercial testing laboratories. The area of applications is increasing by the day as is evidenced by journals and publications on the subject. However, high reliability on results can be placed only if high purity grade materials are used in addition to adherence to regular calibration and maintenance schedules.
Solvents play an important role as components of mobile phase and help in transport of injected sample to the detector after passing through the separation column. Solvents are available commercially under different purity grades for meeting different analysis requirements. HPLC analysis requires use of highest purity grade solvents keeping in mind cost and availability considerations. Critical considerations need thorough evaluation before selection of solvents to make up the mobile phase.
HPLC Grade solvents
HPLC grade solvents are manufactured specially for majority of HPLC grade separations. Such solvents essentially involve one or more distillations for removal of volatile impurities followed by filtration for removal of solid suspended impurities that may be present.
Characteristic properties of HPLC grade solvents
HPLC grade solvents are generally over 99.9% pure and the level of other impurities present are mentioned on the bottle label. Impurities can result in extraneous peaks which interfere with the main peaks in the chromatogram.
No solvent is 100% transparent over the entire UV- visible range of wavelengths. Commonly used HPLC solvents show transparency upto a certain wavelength range below which they absorb strongly. As UV detectors are used in most of the applications it is desirable that the selected solvent has as low UV cut-off wavelength as possible so that most of the sample components can show measurable absorbance at wavelengths above the cut-off value.
Higher the viscosity higher will be the back pressure due to resistance by stationary phase in the packed column so the solvents selected should have low viscosities.
Majority of solvents are stable in sealed bottles but some solvents have limited shelf life. Only limited quantities of such solvents should be procured and stored and available stocks should be consumed on priority after confirming the printed shelf life.
As a final word of advice all solvents should be filtered through 0.22μ filter and degassed before use. Such precautions will enhance useful lifespan of HPLC systems and also help place high reliance on results.