SiliaSphere™- Bonded Spherical Silica Gel
Every year, various companies release new chromatographic phases to the market and claim that their phases are the most efficient. Choosing the right phase along with the right supplier is becoming a challenging task.
For the past 18 years, SiliCycle has been dedicated to the development of silica-based products and has acquired extensive experience in grafting technology.
This outstanding expertise, combined to tightly controlled proprietary functionalization processes, allows SiliCycle to be the supplier of choice for all chromatographic applications.
Silica surface possesses active silanols (Si-OH, free OH groups of the silica), which permits the modification of the surface chemistry by grafting silane moieties. This property allows the control of the surface polarity useful in separation techniques. Various types of silanes can be grafted on the surface to afford monomeric or polymeric bonded phases which both have pros and cons as described below.
Main Differences Between Monomeric and Polymeric Bonded Phases
By grafting a monofunctional alkylsilane reagent, only one bond can be formed with the silica surface. This type of grafting is called monomeric. The dimethyl groups help to protect the surface by creating steric hindrance, which, at the same time, prevent from reaching the highest possible silane density. The residual silanol groups are inhibited by the grafting of a capping agent. Usually, even after the endcapping, a small portion of the initial silanols is still present due to steric hindrance.
Monomeric phases present a very high stability, batch-to-batch reproducibility and good hydrophobic properties. The fact that the silane possesses only one bond with the surface makes this phase less stable at low pH, which may lead to silane hydrolysis and consequently leaching. For low pH, the polymeric phase
Historically, trichloroalkylsilanes were the first to be employed for economic reasons. By grafting a di- or trifunctional alkylsilane reagent, it is possible to form multidimensional bondings with the surface and also between silane molecules. This grafting method is called polymeric functionalization. The silica surface is more hydrophobic, has greater stability in strong acidic condition (pH 2-3) and has a longer lifetime. However, polymeric phases present major disadvantages over monomeric ones: lower homogeneous surface coverage due to cross-polymerization reactions, poorer batch-to-batch reproducibility leading to variation in retention even for the same molecule.
Homogeneous Surface Coverage
SiliCycle developed a new and innovative grafting technique which is characterized by a homogeneous coverage of the alkyl chains on the surface. This proprietary process can be used with all silane types and ensures greater chemical stability as well as better performance due to the greater homogeneity of the surface coverage.
When functionalizing silica, it is impossible to react with every silanol group, so endcapping technology is often used to prevent peak tailing caused by non-specific interactions and thus improve separations. Furthermore, more sophisticated methods lead to strong layer protection offering very high sorbent durability in harsh conditions.
The endcapping step can be done using various methodologies. The easiest one is to treat the surface with a small silylating agent, such as trimethylchlorosilane (TMSCl). However, at SiliCycle, we always try to improve and control this critical step to afford highly deactivated silanol phases. For some phases, we use the conventional single endcapping step technique, for others we use our proprietary endcapping processes which can include multistep methods, use of specific silylating agents or other special treatments.