C18A columns for polar reversed phase applications with 100 % aqueous mobile phase (USP L1)

C18 stationary phase for the analysis of more polar and hydrophilic compounds in reversed phase mode (USP L1). Silica gel based columns with C18 modification with hydrophilic endcapping. Because of their modification, C18A phases can be operated under 100 % aqueous conditions without destroying the stationary phase, what is not recommended for classical C18 phases caused by their hydrophobicity.

These phases are ideal for the analysis of:

• Water soluble vitamins
• Organic acids
• Proteins and peptides

Hydrophobic / pH stable C18 Columns for more unpolar analytes in Reversed Phase (USP L1)

C18 stationary phase with a special, high efficiency or polymeric unpolar endcapping style. Because of the high carbon content and the protection of the Silica gel these materials are also suited for the use of mobile phase in an extended pH range from typically pH 1–12.

While a high endcapped C18 phase is characterized mostly by the high carbon content. A polymeric endcapped phase also provides an increased steric selectivity.

C18 columns with trifunctional modifications (USP L1): 
Hydrophobic and stearic interactions

KNAUER´s most unpolar C18 phase with excellent shape selectivity. It features polymeric, high efficiency endcapping of 99 % and 20 % carbon content, exceptional pH stability in the range of 1–12, and outstanding mechanical and chemical stability.

Classical and hydrophilic/aqueous C8 columns for HPLC and UHPLC (USP L7)

C8 is a silica gel based stationary phase in reversed phase mode with alternative selectivity compared to C18 phases.

Compared to C18 phases, these columns show less retention due to the lower hydrophobicity.

These phases are ideal for the analysis of:

• Water soluble vitamins
• Steroids
• Catecholamines
• Sedatives

Hydrophilic C8A phase offers an alternative, more polar selectivity. It is suited for highly polar reversed phase applications with up to 100 % aqueous mobile phases. 

C4 columns for Reversed Phase in HPLC and UHPLC (USP L26)

C4 stationary phases (USP L26) are often used in reversed phase (RP) mode for different application areas. They are  also suitable for Hydrophobic Interaction Chromatography (HIC mode).

• Analysis of biomolecules like proteins and peptides

DNPH columns for polar reversed phase applications with 100 % aqueous mobile phase (USP L1)

C18 stationary phase for the analysis of more polar and hydrophilic compounds in reversed phase mode (USP L1). Silica gel based columns with C18 modification with hydrophilic endcapping, designed for DNPH analysis. Because of their modification, DNPH phase can be operated under 100 % aqueous conditions without destroying the stationary phase, what is not recommended for classical C18 phases caused by their hydrophobicity.

These phases are ideal for the analysis of:

• DNPH-derivates of aldehydes and ketones

Phenyl columns for Reversed Phase in HPLC and UHPLC  (USP L11)

Phenyl stationary phases (USP L11) in reversed phase mode with alternative selectivity for:

•     Aromatic and moderately π-π interaction polar analytes
•     Mixtures with varying polarity and aromaticity

The polarity is similar to C8 modification but with different selectivity for polar aromatics, polycyclic aromatic hydrocarbons, fatty acids etc.

Phenyl phases with a classical slightly hydrophobic endcapping or without endcapping.

Zwitterionic and polar columns for HILIC applications

Based on ultra-pure Silica gel, zwitterionic HILIC phases are ideal for the analysis of polar and ionizable compounds. Stronger interaction of more polar compounds with stationary aqueous layer.

Faster elution of nonpolar compounds is possible due to minor hydrophobic interactions. Retention increases with the charge of the analyte.

Recommended for the analysis of hydrophilic compounds like:

• Polar organic acids and bases
• Natural polar compounds
• Nucleosides
• Oligonucleotides
• Amino acids
• Peptides
• Water soluble vitamins

Amino columns for Normal Phase and for HILIC applications (USP L8)

Amino (NH2) bonded silica gel phases can be used ideally in the normal phase (NP) and HILIC mode but also with reversed phase (RP) mode. They show alternative NP selectivity to unbonded silica, especially for aromatics. Furthermore, the selectivity is influenced by hydrogen bond interactions with the analyte. The amino group is bonded to the silica support via a propyl linker.

Amino columns can also be used in the HILIC mode for carbohydrate analysis and for other polar compounds. Their weak anion-exchange properties can be used in the analysis of anions and organic acids.

The amino group is bonded to the silica support via a propyl linker.

Diol columns for Normal Phase in HPLC and UHPLC (USP L20)

Diol packing material can be universally used in different polar modes (NP, RP and HILIC). Diol bonded phases are a versatile alternative to unbonded silica for normal-phase separations with shorter equilibration times.

The hydroxyl groups provide good selectivity without excessive retention, caused by the weaker H-bonding of the diol layer than of silanols. Some diol bonded phases have been developed specifically for applications in the HILIC mode.

Cyano or CN for Normal Phase and Reversed Phase (USP L10)

CN is one of the most versatile stationary phases that can be used in reversed phase (RP) mode as well as in normal phase (NP) mode.

The cyano modification supports the π-π interaction as well as polar and hydrophobic interactions with low polarity solvents. These phases are preferred for compounds with double bonds and aromatic groups. Cyano bonded phases show unique selectivity for polar compounds and are more suitable than bare silica for normal-phase gradient separations. The cyano functional group is a strong dipole that can interact with other dipoles or induce dipoles on solutes. These phases also exhibit moderate hydrophobicity due to the alkyl linker.

Due to the quick equilibration time of the CN bonded phase, it is the best choice for gradient elution in normal phase mode. CN phases can be used as a less polar alternative to Si phases.

The material is typically preferred for

•  Compounds with double bonds
•  Aromatic analytes
  
•  Cyclic antidepressants

Si columns for Normal Phase and HILIC applications (USP L3)

Unmodified Silica gel materials were the first ones used for chromatography. This is the reason the mode is called "normal phase" (NP). They are still used in HPLC, although reversed phase (RP) is by far the most often used HPLC mode today.

A wide range of porous Si materials are available, characterized by:

•     Surface area
•     Pore size
•     Particle size
•     Purity
•     Metal content