Jul
News
HPLC solvent selection: acetonitrile, methanol or purified water?
Comparing acetonitrile, methanol and purified water for HPLC: column pressure, UV cut-off, selectivity and the solvent grade each detector needs.
In HPLC, the solvent is not merely the medium that carries the mobile phase. It has a direct effect on baseline stability, retention time, peak resolution and column lifetime. Choosing the right solvent makes a method run more reliably, reduces repeat failures and limits the cost of having to re-run samples.
Start with the right analytical grade
For HPLC, use an HPLC-grade solvent, or a higher grade such as LC-MS grade when the method demands very high sensitivity. General-purpose solvents may carry organic impurities, non-volatile residues or fine particulates that raise baseline noise, produce ghost peaks and foul the system.
Acetonitrile or methanol?
Acetonitrile generally has the lower viscosity of the two, so system backpressure tends to be lower under the same conditions. It also produces sharp peaks in many reversed-phase methods. Methanol is usually easier to optimise on cost and offers a different selectivity from acetonitrile, which can be useful when you need to separate compounds of closely related structure.
Check the UV cut-off and your detector
With a UV/Vis detector, pay attention to the wavelength range you are working in. A solvent with a high UV cut-off can produce a noisy baseline at low wavelengths. With an MS detector, the solvent and any additives must be suitably volatile, low in non-volatile salts and free of impurities that cause ion suppression or interference.
Quality of the aqueous phase
Water used for HPLC should be purified water suitable for chromatographic analysis, correctly filtered and correctly stored. Poor-quality water can cause baseline noise, raise backpressure through particulates, or allow microbial growth if it sits in the mobile-phase reservoir too long.
Practical recommendations
- Filter and degas the mobile phase before running if your system requires it.
- Do not top up a bottle by mixing fresh solvent with old solvent unless the quality is under control.
- Record the opening date, lot number and the name of the person who prepared it on the reservoir label.
- Check the COA and SDS before use to confirm the grade is right for the intended purpose.
A suggestion from QEMIX: when choosing an HPLC solvent, start from what the method requires — detector, column, sample, detection limit and operating budget. The QEMIX team can advise on solvents, containers and consumables suited to each laboratory application.
References
- PubChem LCSS: pubchem.ncbi.nlm.nih.gov/docs/lcss
- OSHA Laboratory Safety: osha.gov/laboratories
Send the product name with its CAS Number, grade and pack size. QEMIX helps you look up the Specification and SDS, and supplies the COA for the exact Lot No. once the batch is confirmed.
See the brands QEMIX distributes