Silica gels carbon content

Phosphoric acid esters having a low content of arsenic can be obtained by treating with 0.1-10% adsorbents such as activated clay, active carbon, alumina, and silica gel to decrease the arsenic content. Thus, 100 parts lauryl phosphate containing 10.3 ppm As and 2 parts activated clay were mixed at 60-70°C for 2 h and filtered to give lauryl phosphate only containing 0.6 ppm As [28]. 

The carbon content of a stationary phase is measured by an elemental analyser, as a weight balance before and after heating at 800 °C. Particle size, pore size, and surface area are measured by specific instruments, such as a particle size analyser, nitrogen adsorption porosimeter, and mercury depression analyser, respectively. The precision of the measurement of carbon content is high however, that of the other measurements is relatively poor. Therefore, it is difficult to relate the surface area of different silica gels to analyte retention factors. 

Organic groups are bound to the silica surface after grinding silica in organic liquids (277). A more controlled substitution of surface silanol groups was reported by Wartmann and Deuel (194). Silica gel which had been treated with thionyl chloride was allowed to react with phenyl lithium. Silicon-phenyl bonds could be detected by infrared spectroscopy. The phenyl content of Aerosil treated in this way as estimated from carbon analysis corresponded to 85% of the silanol groups (188). However, it is not certain whether the reaction... 

Figure 3.10—Formation of bonded organosilanes at the interface of silica gel. Representation of organic monomers and polymers at the surface of silica gel. The arrangement Si-O-Si C is more stable than Si O C. This reaction leads to a carbon content of 4 or 5%. Other reactions can also be used (hydrosilylation in particular). When a monolayer of hydrocarbons is bonded to the surface of silica, they orient in a particular manner at the interface due to their lipophilic and hydrophilic character.

Method. The corticosteroid is dissolved in 0.1 ml of dry acetone. A 0.2-ml volume of a solution of EDTN (S mg/ml in dry acetone) is added followed by 0.025 ml of 0.1 M sodium carbonate. The tube is stoppered and incubated at 45 °C for 2 h. The contents of the tube are cooled, and 2 ml of water, 0.7 g of sodium chloride and 5 ml of methylene chloride are added. The steroid derivative is extracted into the methylene chloride phase. An aliquot portion of this layer is used for TLC on plates of silica gel G with acetone-chloroform or ethyl acetate-chloroform as solvent. The composition of the solvent used is dependent on the nature of the primary alcohol. The developed plates are observed under UV light at 366 nm. The excitation and emission of the derivatives in alcohol solution occurs at 352 nm and 419 nm respectively. Amounts of less than 100 ng per spot can be detected. 

According to a simple model based on the assumption that the anions of oxide or salt form a close-packed monolayer on the surface of the support and the cations occupy the interstices left over by anions, one can figure out the close-packed monolayer capacity for oxide or salt on a unit area of the support. We estimate it at 0.10 g/100 m2 or higher for various active components (see later, Table II). The specific surface of the support is about 200 m2/g for y-Al203, 300 m2/g for silica gel, and 1000 m2/g for active carbon. Although each of the catalysts in Fig. 1 contains a considerable amount of active component, its content is still lower than that estimated on the basis of a close-packed monolayer. Therefore, the monolayer dispersion in many of these catalysts does not correspond to the full coverage of the support surface, and more precisely is known as submonolayer dispersion. 

Moderately polar crystalline molecular sieves with low aluminum and low cation contents, silica gel, activated alumina., activated carbons with highly oxidiz... 

In RP-TLC, silica gel plates impregnated with a strong hydrophobic agent (paraffin oil or silicone oil, usually 5%) have been extensively used in the past as nonpolar stationary phases. Nowadays, plates covered with octa-decyl-silanized (ODS) silica gel are available. In this material, the silanol groups are etherified with alkyls containing 8 (Cg) or 18 (Cig) carbon atoms. The low wettability of HPTLC plates coated with highly etherified silica gel poses limitations in the water content of the mobile phase. This problem is circumvented by the use of RP-Cig plates with 50% etherification. However, the presence of free silanol groups may lead to undesirable silanophilic interactions, especially with low water content in the mobile phase. 

The relatively high carbon content of Adsorbent X (2.46 %) does not cause any significant changes in the porous structure of the modified initial silica gel. Adsorbent H obtained through the pyrolysis of n-heptanol contains, in fact, the same amount (2.3 %) of carbon as Adsorbent X, but, in spite of this, as shown by Table 7, the adsorbents clearly differ in their surface characteristics. The n-heptanol carbonization products block more effectively the narrow pores of the modified silica than the carbon produced in the pyrolysis of dichloromethane. This is confirmed by the differences in the specific surface area of both adsorbents (Table 7). 

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