The Nature of Rest Silanol Groups on the Surfaces of Silica Based Solid Phase Extraction Materials

Abstract

Abstract. Chemically bonded solid phase materials are very important in separation chemistry. The chemically modified silica gel contains rest silanol groups that can affect the retention properties when they are used for separation of compounds. Some commercially available solid phase extraction (SPE) materials based on silica gel were analysed for rest silanol groups by near infrared spectroscopy. The combination frequency of the water molecules in the 5500-5000 cm -1 region was used in identifying the nature of water molecules on the surface and the information was used to identify the types of silanol groups on the surface. Second derivative technique was employed in the detailed analysis.Nine different SPE materials including C18, C8, C 6 H 5 , NH 2 , OH, CN, SiOH, SA (SCX) and SB (SAX) were examined by near infrared spectroscopy for rest silanol groups. The results show that the non-polar and polar stationary phases contain vicinal silanol groups and the ion exchange solid phase materials contain free, vicinal and geminal silanol groups. IntroductionSolid phase extraction (SPE) columns are important tools of an analytical chemist in pre-concentrating analyte from solutions containing the analyte. The separation is carried out by passing the solution containing the component of interest through a column containing a suitable SPE material. When suitable SPE material used, the separation is based on the fact that the solid phase has greater affinity to the solute or components a chemist wants to separate from the solution matrix. This fact helps a chemist to preconcentrate either analyte from a solution matrix (isolation) or get rid of unwanted components (interference retention) in the solution matrix so that the filtrate is free from interfering components in the determination of the analyte. When the retained components on the SPE material are of interest then the components are eluted from the stationary SPE material using a suitable eluent (elution). Solid phase extraction is very widely used in isolating the analyte of interest from a variety of samples such as urine, blood serum, water etc. The mechanism of interaction of the components in the solution matrix and the solid stationary phase includes non polar, polar interactions, van der Waals interactions etc.

Fragment‐based approach to calculate hydrophobicity of anionic and nonionic surfactants derived from chromatographic retention on a C18 stationary phase

“…The similarity of the curves indicates that this likely results from changes in the silica surface of the stationary phase. The silica surface of a C 18 stationary phase can contain several forms of acidic silanol groups that affect elution of anionic compounds by ion exclusion . When these groups are protonated at low pH, the ion‐exclusion effect disappears and the silica surface allows for more interaction of the anionic compound with the stationary phase, thereby increasing retention .…”

Immobilized Grubbs catalysts on mesoporous silica materials: insight into support characteristics and their impact on catalytic activity and product selectivity

“…S6 †). 85 As this dehydration step led to the sharpest increase in activity, as visualized by the blue arrows in Fig. 5, not only is the presence of water clearly disadvantageous for metathesis catalysis, but it can also be concluded that the type of silanol is less crucial for the catalytic activity.…”

Characterization of Silica Extracted from Rice Husk by NIR Spectroscopy and its Application in Separation Science

“…The hydrogen bonded vicinal silanol groups are highly acidic compared to other silanol groups on the surface and can be modified in several different ways. The hydrogen in acidic silanol groups can also be chemically treated with suitable chlorosilanes to modify the silanol groups into polar or non-polar materials that can be used in separation science [7]. Silica and modified silica based stationary phases are used as stationary phases in liquid chromatography.…”

“…Silica in several different materials and forms have been successfully characterized by Near infrared spectroscopy. Christy [7] has studied several silica gel samples and their water adsorption evolutions using gravimetry and near infrared transflectance spectroscopy with the help of second derivative techniques and showed that the hydrogen bonded silanol groups adsorb water readily compared to free silanol groups. A completely dry silica gel sample gives a very simple near infrared spectrum in the region 11000-4000 cm -1 .…”