Adsorbed mass determination

Adsorbent mass determined under dry ambient pressure (alternatively, this mass determined at Step 2, after outgassing, taking into account initial mass of air). 

Interparticle volume could be measured using GPC as the total exclusion volume of high-molecular-weight polymers, and the void volume could be accurately measured as the elution volume of deuterated acetonitrile eluted with neat acetonitrile. The example of these measurements and comparison with the adsorbent mass determined by unpacking the column and weighing the dried adsorbent are shown in Table 3-5. 

The specific metal surface area of our nickel samples was established by means of deuterium chemisorption, the amount of deuterium adsorbed being determined by exchange with a known quantity of hydrogen followed by mass speetrometric analysis. It was assumed in the calculation that 1 cm3 (NTP) of deuterium corresponds to 3.64 m2 of nickel surface area. 

The detectable amount of adsorbed species can be extremely low. A retention time shift of Atr=0.310 at a modest G (103 g) with w=250 pm results in only -10 17gof adsorbed mass (density 1.4 g/cm3). This mass corresponds to a very small layer, only 0.6 A thick on a 0.2 pm sphere [186]. The above approach has been used to measure protein adsorbed on latex surfaces [186-188], which is relevant to immunodiagnostic assays and biomedical implants. Complete adsorption isotherms can be measured [186] and antigen-antibody binding ratios determined [187]. 

In summary, the QCM-D technique has successfully demonstrated the adsorption of pectin on the BSA surface as well as determined the viscoelastic properties of the pectin layer. As pectin concentrations increase, the adsorbed mass of pectin estimated from the Voigt model show higher values than those estimated from the Sau-erbrey equation because the former takes into account the hydrated layer. But the similar increase of thickness of pectin suggests that the pectin chains form a multilayer structure. In agreement with our previous rheology results, the main elastic character of the pectin layer in terms of Q-tool software tells us the network structure of the pectin layer on the BSA surface. In summary, QCM-D cannot only help to better understand the polysaccharide/protein interactions at the interface, but also to gain information of the nanoscale structure of polysaccharide multilayers on protein surface. 

The column void volume, Vo, is dehned as the total volume of the liquid phase in the column and could be measured independently [18]. Total adsorbent surface area in the column, S, is determined as the product of the adsorbent mass and specific surface area. 

The estimation of the amount of adsorbent in the column is based on the comparison of the total pore volume (Vptot [niL]) of the adsorbent in the column with the specific pore volume (Vp [mL/g]) of the same adsorbent determined from the full nitrogen adsorption isotherm. The ratio of these two values will give the adsorbent mass. Total pore volume in the column is determined as the difference of the column void volume (Vo) and the interparticle volume (Vip). 

Recently, Keller published a method allowing for the absolute determination of the adsorbed mass m of porous materials [5]. It consists of a combination of calorimetric and impedance spectroscopic measurements. Unfortunately, that method is experimentally difficult and needs improvements for practical applications [6]. 

A wastewater treatment technique has been investigated, for reactive dye removal, in batch kinetic systems. Results indicate that charred dolomite has the potential to act as an adsorbent for the removal of reactive dye from aqueous solution. The effect of initial dye concentration, adsorbent mass liquid volume ratio, and agitation speed on removal have been determined with the experimental data mathematically described using empirical external mass transfer and intra-particle diffosion models. The experimental data show conformity with an adsorption process, with the removal rate heavily dependent on both external mass transfix and intra-particle diffosion. 

The extent of adsorption of gases onto solid surfaces can be determined experimentally using a wide variety of apparatus and techniques, and the literature on this subject is extensive. In general, measurements fall into one of two categories either the volume of the gas adsorbed is determined manometrically, or gravimetric methods are used, where the mass adsorbed on the solid is determined directly. 

The value of % ZnO are reflective of the relative amounts of zinc present in given mass of samples. The sample Zi (%ZnO = 72.8) is indicative of high porosity and the difference 27.2% could be largely attributed to the presence of adsorbed water. Determination of approximate pore volume by adsorption of water, has confirmed the highest porosity for Zj. 

Thermodynamically it is the total charge balance of the adsorbed ion and co-adsorption of counter ions. The value can be obtained by independent measurements of adsorbed charge and adsorbed mass. The charge is usually determined by chronoamperometry and integration of potential scans either in the negative direction (adsorption) or the positive one (desorption and anodic stripping method). The latter method is usually preferred because the adsorption film reaches a stable condition. The mass can be determined by several methods. The experimental techniques and examples will be described in Section 4.2. 

Several methods are available for the determination of the adsorbed mass. One is the radio-tracer method pioneered by Horanyi and Kazarinov and Andreev. Experimental details are found in the literature. 

The electrosorption valency for lead adsorbed on silver is determined by plotting the adsorbed charge versus the adsorbed mass. This is shown for Pb on Ag(l 11) in Figure 4.31. 

Figure 4.30 Determination of the adsorbed mass of lead with the twin electrode thin-layer method descrihed in Figure 4.15. Pb UPD on (a) Ag(lll) and (b) Ag(lOO). Concentrations as given in Figures 4.27 and 4.28. (Reproduced with permission from Ref. [60], 1978, Elsevier.)...

Gas adsorption is often applied to determine the specific surface area (= surface area per unit mass) of a porous material. From the known size of the gas molecules, the adsorbed mass in a complete monolayer and the mass of sorbent material, the specific surface area can be derived. Adsorption from solution of compounds, having well-defined dimensions, may also be used to determine the specific surface area. 

The present study aims to understand the influence of solvent quality on the molecular-level friction mechanism of tethered, brushlike polymers. It involves complementary adsorption studies of PLL-,g-PEG by means of optical waveguide lightmode spectroscopy (OWLS) and quartz crystal microbalance with dissipation (QCM-D) as well as friction studies performed on the nanoscale using colloidal-probe lateral force microscopy (LFM). The adsorbed mass measured by QGM-D includes a contribution from solvent molecules absorbed within the surface-bound polymer fllm. This is in contrast to optical techniques, such as OWLS, which are sensitive only to the dry mass of a polymer adsorbed onto the surface of the waveguide.By subtracting the dry mass , derived from OWLS measurements, from the wet mass , derived from QCM-D measurements, it is therefore possible to determine the mass of the solvent per unit substrate area absorbed in the brushlike structure of PLL- -PEG, expressed as areal solvation, P. Areal solvation was varied by choosing solvents (aqueous buffer solution, methanol, ethanol, and 2-propanol) of different quality with respect to the PEG brush. The solvents were characterized in terms of the three-component Hansen solubility parameters, and these values were compared with measured areal solvation of the PEG brush. 

While the two coating materials, Si02 and PDMS, have different thicknesses and refractive indexes, the change of the refractive index, which is the basis for tbe determination of adsorbed mass, was observed to be nearly identical by testing with polymer-free aqueous solutions with different bulk refractive indexes, which validates the comparison of the adsorbed mass of the polymers onto both surfaces. 

Areal adsorbed mass density data were calculated from the thickness and refractive index values derived Irom the mode equations according to Feijter s formula. A refiactive index increment (dn/dc) value of 0.182 cm /g was used for the protein-adsorption calculations, and a value of 0.202 cm /g, as determined in a Raleigh interferometer, was used for the PLI g-PEG adsorption calculations. All OWLS experiments were conducted in a BlOS-1 OWLS instrument (ASl AG, Zurich, Switzerland) using a Kalrez (Dupont, Wilmington, DE) flowthrough cell as described previously. The flow-though cell was used for studying both PLL-g-PEG adsorption and protein adsorption. The flow rate and wall shear rate were 1 mL/h and 0.83 s, respectively. 

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