Adsorption on porous glass

The determination of the adsorption entropy from the isotherms 38) has unexpectedly established that benzene adsorption on porous glass is of a mobile type, with the properties of a two-dimensional ideal gas. Only at low coverages (less than 1 X 10 mole-gm ) the freedom of motion is decreased, and the molecules may be held on definite sites, which is also reflected by an increase in the adsorption energy. 

It is known from infrared spectra that benzene adsorption on porous glass decreases the 0—H frequency of the surface silanol groups more than that of cyclohexane. This is considered as an indication that benzene molecules form H-bonds with the strongly acidic (protonic) Si—OH sites, their 7r-electron system acting as a base 17). 

In the case of horse radish peroxidase, peroxidase shows the weakest adsorption on porous glass. It did not adsorb in saline or Tris-buffer but only in distilled water. Therefore, peroxidase was adsorbed on a porous glass column and stored in distilled water. 

Fig. 3.2 Adsorption isotherms for argon and nitrogen at 78 K and for n-butane at 273 K on porous glass No. 3. Open symbols, adsorption solid symbols, desorption (courtesy Emmett and Cines). The uptake at saturation (calculate as volume of liquid) was as follows argon at 78 K, 00452 nitrogen at 78 K, 00455 butane at 273 K, 00434cm g .

Fig. 4.25 Adsorption isotherms showing low-pressure hysteresis, (a) Carbon tetrachloride at 20°C on unactivated polyacrylonitrile carbon Curves A and B are the desorption branches of the isotherms of the sample after heat treatment at 900°C and 2700°C respectively Curve C is the common adsorption branch (b) water at 22°C on stannic oxide gel heated to SOO C (c) krypton at 77-4 K on exfoliated graphite (d) ethyl chloride at 6°C on porous glass. (Redrawn from the diagrams in the original papers, with omission of experimental points.)...

Changes in relative peak intensity and marginal line shifts have been observed for benzene adsorbed on porous glass (26). More significantly, infrared spectroscopic evidence had been found in the appearance of inactive fundamentals for the lowering of molecular symmetry of benzene on adsorption on zeolites (47). 

Various methods ofachieving preconcentration have been applied, including Hquid -hquid extraction, precipitation, immobihzation and electrodeposition. Most of these have been adapted to a flow-injection format for which retention on an immobihzed reagent appears attractive. Sohd, sihca-based preconcentration media are easily handled [30-37], whereas resin-based materials tend to swell and may break up. Resins can be modified [38] by adsorption of a chelating agent to prevent this. Sohds are easily incorporated into flow-injection manifolds as small columns [33, 34, 36, 39, 40] 8-quinolinol immobilized on porous glass has often been used [33, 34, 36]. The flow-injection technique provides reproducible and easy sample handhng, and the manifolds are easily interfaced with flame atomic absorption spectrometers. 

A methyl-rich spectrum from propene adsorption had been earlier observed after hydrogenation during work on Pt supported on porous glass (250). The marked contrast between this spectrum and that from a n-propyl group chemisorbed on a Ni catalyst had led to the hypothesis that the former arose from chemisorbed 2-propyl species. It was subsequently shown to be caused instead by physically adsorbed propane that was present because of the greater propensity for complete hydrogenation of the initial surface species on Pt. 

The isosteric heat of adsorption at low coverage on porous glass is definitely higher (17 kcal-mole- ) for the untreated surface in comparison to the methylated or sintered one (10-12 kcal mole- ) (3S). These values are approximately the same as found for CgHg on silica gel (39). 

Fio. 8. Adsorption isotherms for argon, nitrogen, and butane on porous glass No. 3. Open symbols, adsorption closed symbols, desorption (45b). 

Adsorption and Chromatography of Proteins on Porous Glass Activity Changes of Thrombin and Plasmin Adsorbed on Glass Surfaces... 

Adsorption of proteins on porous glass varied with the protein, the buffer and the pH of the buffer. Based on these differences, porous glass can be used as an adsorbent for the separation of proteins by adsorption chromatography (, ). The amounts of basic amino acids, -icleosides, cations, and proteins adsorbed were about 4-5pmol/100 m (22-23). These results indicate that these materials adsorb on the surface as monolayers. 

MIZUTANI Adsorption and Chromatography of Proteins on Porous Glass... 

Firstly this phenomenon was noticed in [97,98] when the adsorption was examined of H2O on porous glass pretreated at 400°C. Analogous results were obtained also for methanol adsorption, what served as a base for the assumption on the presence of another sites (along with hydroxyl groups) on the surface that were called by the authors second kind sites. When the studies were... 

The use of a pair of thermodynamically good solvents (adsorli/desorli) results in the perfect solubility of a selected polymer. One solvent should support adsorption of the polymer onto the column packing, the second one desorption. Such mixtures can enable critical behavior up to very high molar masses, as shown in Table 5. At present only a the small number of solvent/solvent systems is known (Table 1 PMMA (6 systems), PtBMA (at least 1 system), PS (1 system)). A screening of solvents, for example, using silica and polymer of interest, could enable to identify suitable solvents, where the polymer is adsorbed. Specifically, it is known that PS is adsorbed on porous glass from carbon tetrachloride [7], PMMA is adsorbed on silica gel from DCM [45] and from chloroform [155] or toluene [57] and PtBMA from DCM [45]. PS, PBMA, PMMA, PTHF are adsorbed on silica... 

Patents [102, 103] describe the preparation of open tubular columns with an inside thickness-fixed porous layer by etching. First, the authors prepared a capillary column from a two-layer workpiece composed of two concentric tubes, one of them (external) being made of sodium borosilicate glass. To obtain an adsorption layer of defined thickness, the inner layer of the two-layer capillary was entirely leached. The method relies on porous glasses as the adsorbents. Porous glasses have been successfully used in gas capillary (see, for example, [104]). 

---