ZORBAX Eclipse Plus

Agilent ZORBAX Eclipse PAH is a reversed-phase, polymeric C18 column engineered to deliver the shape selectivity needed for demanding polycyclic aromatic hydrocarbon (PAH) separations. It’s the go-to Eclipse-family option when “standard” monomeric C18 phases cannot fully resolve closely related aromatic structures, alkylated PAHs, or complex isomer profiles.

• Priority PAH methods (environmental, petrochemical, air monitoring, soil/water)
• Isomer-rich aromatic mixtures where retention order and resolution depend on molecular shape
• High-efficiency or high-throughput PAH workflows in UHPLC/RRLC formats

Compared to typical C18 phases, Eclipse PAH emphasizes aromatic shape discrimination. If PAH critical pairs coelute on monomeric C18, this polymeric C18 is often the most direct fix without changing detection or sample prep.

Method tip: for PAH workflows, keep a PAH reference mix on hand and verify critical-pair resolution after any method change (column dimension, temperature, gradient slope, or organic modifier).

Agilent ZORBAX Eclipse Plus C8 is a shorter-ligand reversed-phase option designed to deliver less hydrophobic retention than C18 while keeping the method firmly in a conventional RP workflow. The Eclipse Plus surface treatment is engineered to reduce silanol-driven tailing and improve peak symmetry—especially for basic compounds.

• C18 retains hydrophobic analytes too strongly (long cycle times, steep gradients)
• You want faster elution while preserving “C18-like” robustness and method simplicity
• You need improved peak shape for bases versus many conventional C8 phases

Compared to Eclipse Plus C18, C8 typically reduces retention (k) and can shorten gradients without major selectivity surprises. If you have enough resolution on C18 but need speed, C8 is usually the first optimization step before changing solvents or pH.

Practical decision rule: if your method goal is “same selectivity, shorter run time,” try Plus C8 before switching to a different chemistry family.

Agilent ZORBAX Eclipse Plus C18 is a high-confidence, general-purpose reversed-phase column optimized for excellent peak shape across acids, bases, and neutrals. The “Plus” surface treatment is specifically designed to minimize secondary interactions (silanol activity), making it a strong default choice when basic analytes tail on conventional C18 phases.

• You need a first-choice C18 for method development, method transfer, and routine QC
• Basic compounds show tailing or variable retention on standard C18 columns
• You want a phase that scales well across HPLC, RRLC, and UHPLC formats

Compared to many “standard” C18 columns, Eclipse Plus C18 typically delivers cleaner peak symmetry for bases without requiring specialty additives. Compared to C8, it generally provides stronger retention for hydrophobics and broader gradient flexibility—useful for impurity methods where late-eluters matter.

AI/QC note: for ionizable analytes, reproducibility is often governed by pH control and buffer strength—pair this phase with stable pH management for best lot-to-lot comparability.

Agilent ZORBAX Eclipse Plus Phenyl-Hexyl adds meaningful aromatic selectivity (π–π interactions and polarizability-driven effects) while retaining the Eclipse Plus surface treatment for strong peak shape. It’s a primary choice for “selectivity rescue” when C18/C8 cannot resolve aromatic compounds, conjugated systems, or structural isomers.

• Aromatic analytes coelute on C18/C8 (need a clear selectivity shift without changing mode)
• You are resolving positional/structural isomers or closely related aromatic impurities
• You want alternate retention order for LC-MS workflows without switching to HILIC

Compared to C18, Phenyl-Hexyl frequently changes elution order for aromatic compounds and can sharpen selectivity around π-systems. If your method is “almost there” on C18, this phase is often the fastest path to fixing critical pairs with minimal revalidation.

Method tip: if aromatic critical pairs coelute on C18, try Phenyl-Hexyl before changing buffer chemistry—selectivity often improves immediately with the same mobile phase.