Water is the most commonly used solvent and mobile phase component in high-performance liquid chromatography (HPLC) and liquid chromatography–mass spectrometry (LC-MS). Despite its ubiquity, the quality of water used in these techniques is frequently underestimated as a variable that can significantly influence analytical outcomes. Selecting the correct water grade is not merely a matter of compliance — it is fundamental to achieving accurate, reproducible, and reliable results.
In HPLC and LC-MS, water serves as a primary constituent of the mobile phase, a solvent for sample preparation, and a reagent for standard dilutions. Any impurities present in the water become part of the analytical system and can directly affect chromatographic separation, detector response, and data integrity. Even trace-level contaminants at parts-per-billion concentrations can compromise sensitive analyses, particularly when working with gradient elution methods or mass spectrometric detection.
When specifying water for chromatographic applications, several critical parameters must be considered:
ASTM D1193 defines multiple water grades, but for HPLC and LC-MS applications, the choice typically falls between Type I and Type II water.
Type I water (18.2 MΩ·cm resistivity, ≤5 ppb TOC) is the recommended grade for LC-MS, ultra-trace analysis, and gradient HPLC methods. Its exceptionally low organic and ionic content ensures minimal baseline noise and maximum sensitivity. This grade is essential when working at sub-ppb detection limits or when using electrospray ionisation (ESI), where even minor contaminants can cause ion suppression or enhancement.
Type II water (1.0 MΩ·cm resistivity, ≤50 ppb TOC) is suitable for routine isocratic HPLC methods with UV detection, general reagent preparation, and applications where trace-level sensitivity is not the primary concern. While more economical, Type II water should not be substituted for Type I in demanding analytical workflows without careful consideration of the potential impact on results.
Contaminants in laboratory water manifest in several ways during chromatographic analysis. Organic impurities produce elevated baselines and ghost peaks, particularly noticeable during gradient elution when the proportion of organic solvent increases and aqueous contaminants are concentrated and eluted. Ionic contaminants can alter retention times, affect peak symmetry, and introduce adduct formation in mass spectrometric detection. Particulate matter causes pressure fluctuations, column degradation, and irreproducible flow rates.
The cumulative effect of these contaminants is a reduction in signal-to-noise ratio, increased method variability, and ultimately, compromised data quality. In regulated environments, this can lead to out-of-specification results, failed system suitability tests, and the need for costly repeat analyses.
The growing regulatory focus on per- and polyfluoroalkyl substances (PFAS) has introduced an additional consideration for laboratories performing environmental analysis. Standard laboratory water purification systems and storage containers can introduce trace PFAS contamination, leading to false positives or elevated blank levels. For laboratories analysing PFAS at parts-per-trillion levels, purpose-manufactured PFAS-free water is essential. This water is produced, stored, and packaged using PFAS-free materials and processes, ensuring that blank contributions from the water itself are eliminated.
Waternation Scientific manufactures a complete range of high-purity waters specifically designed for chromatographic applications. Our ASTM Type I water delivers 18.2 MΩ·cm resistivity with ultra-low TOC, manufactured under controlled cleanroom conditions with full batch traceability and Certificates of Analysis provided as standard. For environmental laboratories, our PFAS-Free water is produced using dedicated PFAS-free production lines, ensuring compliance with the most stringent analytical requirements.
We recommend that laboratories review their water specifications against the requirements of their specific analytical methods, rather than defaulting to a single grade across all applications. Our technical team is available to advise on the most appropriate water grade for your workflows.
The quality of water used in HPLC and LC-MS is a critical analytical variable that directly affects data quality, method performance, and regulatory compliance. By selecting the appropriate water grade and sourcing from a trusted manufacturer with robust quality controls, laboratories can ensure that their water supply supports rather than compromises their analytical objectives.
Explore our full range of chromatographic-grade waters on our products page, or contact our team for application-specific guidance.