Water for HPLC: why water quality changes your analytical results

What goes wrong with unsuitable water

• Baseline noise: organic or ionic impurities can raise the background signal.
• Spurious peaks: UV-absorbing impurities, or cleaning residues left in the reservoir, can produce unwanted peaks.
• Rising backpressure: fine particulates or microbial growth can block the frit, the guard column or the analytical column.
• Poor repeatability: water of inconsistent composition shifts retention times and signal response.

Matching the water to the application

For HPLC-UV, use water suitable for chromatographic analysis, of consistent purity and low in UV-absorbing impurities. For LC-MS, ionic impurities, additives and anything that interferes with the ion source need tighter control still.

ECS ultrapure water systemV-Pure R50V-Pure E50 (EDI)

Looking after the aqueous reservoir

Aqueous mobile phase should not stand on the system for long, particularly when it contains buffer or other components that support microbial growth. Reservoirs need cleaning on a regular schedule, and a reservoir should not be shared with solvents or solutions liable to leave residue.

Recommended practice

• Use a clean bottle with a suitable cap and a cleaned solvent inlet line.
• Filter the mobile phase through an appropriate membrane if the method requires it.
• Degas to limit air bubbles that disturb the pump and the detector.
• Record the preparation date, the composition, the pH where relevant, and the person who prepared it.
• Do not use water that has been standing, or that shows cloudiness, sediment or an unusual odour.

QEMIX recommends: when an HPLC run shows ghost peaks or an unstable baseline, check the water, the reservoir, the filter membrane and the solvent before you suspect the column or the detector.

References

• PubChem LCSS: pubchem.ncbi.nlm.nih.gov/docs/lcss
• OSHA Laboratory Safety: osha.gov/laboratories