VDSpher® Reversed Phases

Reversed phase (RP) chromatography is the unique method of HPLC used most frequently. Therefore, the number of available reversed phases is increasing steadily, so that as far as possible, a matching stationary phase is available for each separation problem. For example, C18 stopped being just C18 long time ago: many different approaches of modification and endcapping result in a large bandwidth of very different C18 phases.

Even our brand VDSpher is going through this development and can offer many different modifications and variations. Numerous phases can be selected for C18, C8, C4, phenyl and CN modifications. The available VDSpher Classic & PUR reversed phase modifications and their physical properties are shown in the appropriate Tables.

Reversed Phase Modifications: VDSpher® Classic & PUR

Phase Modification Endcapping USP Code

C18-E (1)

C18 yes L1
C18-NE C18 no L1
C18-SE C18 yes (special) L1
C18-M C18 no L1
C18-M-E C18 yes L1

C18-M-SE (1)

C18 yes (special) L1

C18-H (1)

C18 yes (polar) L1

C8-E (1)

C8 yes L7
C8-SB C8 yes L7
C8-NE C8 no L7
C8-SE C8 yes (special) L7
C8-M C8 no L7


C8 no L7
C8-M-E C8 yes L7
C8-M-SE C8 yes (special) L7
C8-H C8 yes (polar) L7
C4-E C4 yes L26
C4-SE C4 yes (special) L26

Phenyl-E (1)

Alkylphenyl yes L11
Phenyl-SE Alkylphenyl yes (special) L11


Alkylphenyl yes L11

CN-RP (1)

Alkylnitrile yes L10
CN-SE-RP Alkylnitrile yes (special) L10

(1) Also available as U-VDSpher® PUR Phases for UHPLC.


Below, C18 phases are used to show how the individual modifications and variants of endcapping differ from one another.

Depending on the type of reagents used, a single (“monomeric”) or a multiple (“polymeric”) bonding at the surface silanol groups of the basic silica gel is achieved in the modification step, which then results either in a brush-like or a branched out structure. For steric reasons however, all silanol groups cannot be modified in both cases, so that the phases still show a noticeable silanophilic activity. To reduce this or to avoid it altogether, an endcapping with Trimethylchlorosilane is carried out in a subsequent step. The reaction guidance of the endcapping also plays a role here: in the liquid phase, only approx. 40% of the remaining silanoles can react with Trimethylchorosilane, while in the gas phase, it is up to 99%.

In another variant, a reagent is used in addition to the monomer modification which carries a polar group and therefore functions as ‘polar spacer” between the C18 chains. The special properties of this phase are described in detail further down.

The different VDSpher C18 phases arise from the combination of the modification and endcapping methods described above:

C18-NE monomeric bonding no endcapping
C18-E monomeric bonding liquid phase endcapping
C18-SE monomeric bonding gas phase endcapping
C18-M polymeric bonding no endcapping
C18-M-E polymeric bonding liquid phase endcapping
C18-M-SE polymeric bonding gas phase endcapping
C18-H single bonding polar spacer

Bonding and endcapping have a decisive influence on the hydrophobicity of a phase. The higher carbon load in a multiple bonded phase ensures a more hydrophobic behaviour than for a single bonded phase. On the other hand, free silanol groups have a hydrophilic effect. The behaviour of the VDSpher C18 phases can therefore be displayed schematically. For orientation, two VDSpher OptiAqua and OptiBio phases are considered in the Figure below as well.

Hydrophobicity of VDSpher® C18 modifications.

Two examples are given in Figures, which illustrate the different separation behaviour of VDSpher reversed phases. The standard separation of Benzene, Naphthalene and Anthracene differ according to the carbon content in each column. The most hydrophobic phase C18-M-SE retards Anthracene for the longest duration as compared to phases with medium hydrophobicity C18-E, while the most hydrophilic phase C18-H enables a significant lesser retention of the analytes.

Besides, the polar group of the phase VDSpher C18-H can also be used to achieve a different selectivity: the purification of insulin (Peak 2) with the phases VDSpher Classic 100 C8-E and VDSpher Classic 100 C18-H is shown in the Figure below. For this example, the phase VDSpher C8-E was selected, because it has a carbon load comparable with that of VDSpher C18-H. It is to be noted that on using VDSpher C8-E, insulin elutes between its impurities, while in the “polar” phase VDSpher C18-H, insulin retardation is longer than for its impurities.

Normally, the standard phase VDSpher C18-E is a very good starting point for many separation problems. It is of medium hydrophobicity and shows a low silanophilic activity. VDSpher C18-E has therefore proved its worth in many applications e.g., for the isolation of natural substances, for the determination of caffeine in coffee, tea and other caffeine containing drinks and even for the determination of amino acids.

The phase VDSpher C18-SE, which does not show any silanophilic activity is slightly more hydrophobic. Hydrophobic substances are therefore retarded more by this phase. Besides, due to the complete endcapping and the resulting inertness, the analysis of alkaline substances is implemented better and an increased stability of the phase is achieved in strong acids and slightly alkaline media.

On the other side, the not endcapped phase VDSpher C18-NE is available, if importance is given to silanophilic activity during separation. The free silanol groups also increase the water mobility as compared to the endcapped phases.

For working in 100% water as mobile phase, we recommend the very hydrophilic phase VDSpher C18-H. The polar spacer ensures that the C18 chains do not collapse despite the high water content. VDSpher C18-H is therefore ideal for the analysis of polar analytes and smaller water-soluble biomolecules.

The three phases VDSpher C18-M, VDSpher C18-M-E and VDSpher C18-M-SE can be selected for very hydrophobic applications. These phases have a very high carbon load due to their multiple bonding. The branched surface structure shields the surface of the silica gel effectively, so that despite high hydrophobicity, working with 100% water as eluent is possible. As in the single bonding phases, not endcapped VDSpher C18-M, in the liquid phase endcapped VDSpher C18-M-E and in the gas phase encapped VDSpher C18-M-SE modifications are available, so that the influence of the silanol groups and carbon content can be considered for the desired application.

The described modifications and their effects are not limited to just C18: a large number of different VDSpher phases are available for C8 and C4 modifications as well. Because of the low carbon load as compared to C18 phases, C8 and especially C4 phases are less hydrophobic. Moreover, the silanophilic activity is more pronounced due to the better accessibility of the silica gel surface.

VDSpher Phenyl-E with liquid phase endcapping and VDSpher Phenyl-SE with gas phase endcapping are alternatives to the aliphatically modified reversed phases. π-π interactions influence the separation due to the alkylphenyl modification and other selectivities are enabled e.g., for polar and non-polar aromatic hydrocarbons or fatty acids.

VDSpher PUR Phenyl-B is a special phase, which enables aliphatic as well as aromatic interactions and therefore represents an interesting alternative to many Phenyl-Hexyl phases on the market.

The product portfolio is rounded off with the reversed phases by the alkyl nitrile-modified separation phases VDSpher CN-RP and CN-SE-RP, which are e.g., ideal for the separation of alkaline molecules.

Physical Properties: VDSpher® Classic & VDSpher® PUR Reversed Phases

Phase Available pore sizes
Carbon content
Nitrogen content
pH range

Classic: 75, 100, 150
PUR: 100, 150

75 Å: 21.0
100 Å: 16.8
150 Å: 10.5
0 2 - 7.5
C18-NE Classic & PUR: 100 16,3 0 2 - 7.5

Classic: 75, 100
PUR: 100

75 Å: 21.3
100 Å: 17.0
0 2 - 9
C18-M Classic & PUR: 100 17.5 0 2 - 8
C18-M-E Classic & PUR: 100 19.0 0 2 - 8
C18-M-SE Classic & PUR: 100 20.0 0 2 - 10
C18-H Classic & PUR: 100 11.5 0 2 - 7.5

Classic: 75, 100, 150
PUR: 100, 150

75 Å: 13.8
100 Å: 10.0
150 Å: 5.9
0 2 - 7.5

Classic: 75, 100
PUR: 100

75 Å: 13.0
100 Å: 11.3
0 2 - 8.5

PUR: 100

9.9 0 2 - 7.5

Classic: 75, 100, 150
PUR: 100

75 Å: 13.9
100 Å: 10.4
150 Å: 6.1
0 2 - 9

Classic: 100


0 2 - 8

PUR: 100

8.2 0 2 - 8

PUR: 100

10.7 0 2 - 8

PUR: 100

11.0 0 2 - 10
C8-H Classic & PUR: 100


0 2 - 7.5
C4-E Classic & PUR: 100 7,0 0

2 - 7.5

C4-SE Classic & PUR: 100 7.1 0 2 - 9
Phenyl-E Classic & PUR: 100 10.0 0 2 - 7.5

PUR: 100

10.7 0 2 - 9

PUR: 100

12.0 0 2 - 7.5
CN-RP Classic & PUR: 100 6.5 1.3 2 - 8

PUR: 100, 150

100 Å: 7.0
150 Å: 5.0
100 Å: 1.5
150 Å: 1.2
2 - 9

The available particle sizes can be obtained from our current price list.


© VDS optilab Chromatographietechnik GmbH    |    Webdesign:NIKNET