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Kromasil technical evidence

analysis

You are working with HPLC for the separation and identification of analytical substances in laboratories. Challenge the selectivity of Kromasil for your most sensitive analysis.

development

You need to quickly purify substances for further studies in the development of pharmaceuticals. Kromasil will help you achieve your goals with ease and efficiency.

production

You are using preparative chromatography for high efficiency purification in a pilot or up to industrial-scale production. The robustness of Kromasil is available in ton quantities to meet your process demands.

 
 

What you should know about chemical stability

Some silica-based materials may be sensitive to hydrolysis and dissolution under low and high pH conditions respectively.

What influences hydrolysis of bonded phases at low pH?

Surface silanols

The surface of Kromasil consists of uniformly distributed, relatively neutral silanol groups. The number of unwanted, acidic silanols are minimized.

Coating density of the silane

High surface coverage gives higher chemical stability. In this respect it is interesting to remember that modification of the silica surface with monofunctional silanes also gives higher surface coverage and reproducibility than with polyfunctional silanes. Kromasil bonded phases are manufactured with monofunctional silanes. In figure 1, Kromasil C8 is compared with other commercial materials in terms of chemical stability under low pH conditions.

fig1 - chemical stability at low pH

Fig. 1 - Values of k' for butylbenzene plotted against the number of column volumes of purge.

What influences dissolution of silica material at high pH?

The manufacturing method

Materials produced by the sol-gel technique are more stable than "spongy" ones which are produced by reacting organo-silicates under basic conditions and gelling the resulting silicic acid in situ.

Surface treatment of the silica

The methods are many and generally patented.

Coating density of the silane

See the previous comments under "Stability at low pH conditions".

Kromasil fulfils high requirements for excellent chemical stability at high pH conditions, which is demonstrated by the ability of the material to withstand treatment under extremely harsh conditions for silica-based packings.

This is exemplified in figure 2 for the regeneration of a column used for the purification of insulin, with NaOH at pH > 13.

fig2 - regeneration of Kromasil at high pH

Fig. 2 - Regeneration of a Kromasil column contaminated with polymeric insulin, at pH>13.

Table 1 - leakage of silica and bonded phase after the treatment at pH >13
Phase Purged volume
(column volumes)		 Amount of Si in eluted
mobile phase (ppm)
C4
C8		 1 - 2 105
93
C4
C8		 3 - 4 74
71
C4
C8		 5 - 6 64
61
C4
C8		 7 - 8 58
56
C4
C8		 9 - 10 55
54

The advantages of using chemically stable silica-based materials are:

In table 2 you can see the low degree of leakage of bonded phase and silica from Kromasil phases under different mobile phase conditions.

Table 2 - leakage of bonded phase and silica from Kromasil phases under different mobile phase conditions
Mobile
phase		 Purged volume
(column volumes)		 Amount of Si in eluted
mobile phase (ppm)
pH 8 pH 2
1
1		 17
83		 1.1
0.5		 <0.5
<0.5
2
1		 17
83		 2.3
<0.5		 0.7
<0.5
2
1		 17
83		 1.8
<0.5		 0.7
<0.5
2 17 3.6 0.6
Conditions at pH 8:
Column: 4.6 × 250 mm (new column)
Mobile phase 1: n-propanol/buffer (10/90)
Mobile phase 2: n-propanol/buffer (70/30)
Buffer: NH 4Ac (0.2 M)/NH 3, pH=8.0
Conditions at pH 2:
Column: 4.6 × 250 mm (new column)
Mobile phase 1: n-propanol/H2O/TFA (10/90/0.1)
Mobile phase 2: n-propanol/H2O/TFA (70/30/0.1)
Common conditions:
Flow rate: 0.5 ml/min.
Total volume: 1 315 ml (317 column volumes)
Detection method: Atomic abs. (Si)
Detection limit: 0.5 ppm
· Eka Chemicals, Separation Products · SE–445 80 Bohus, Sweden · Phone +46 31 58 70 00 · Fax +46 31 58 77 27 ·
· E-mail kromasil@akzonobel.com ·