Adsorption on Teflon

B igure 3. Cohn I human fibrinogen, 3 mg/dl, adsorption on Teflon gold decoration TEM technique. (a) air dried (b) critical-point dried with bar equal to 0.1 ym. (Reproduced with permission from Ref. 5. Copyright 1982 American Chemical Society.)... 

Figure 4. Cohn I human fibrinogen, 30 mg/dl, adsorption on Teflon partial gold decoration TEM technique. Bar equal to 1000 A.

Batch adsorption experiments were conducted to verify the assumption that polymer adsorption on Teflon powder was negligible. Seven separate determinations were made with equilibrium polymer concentrations ranging from 91 to 471 ppm. In each test, about 155 gm of Teflon powder were shaken intermittently with a known volume of polymer solution in a 250-ml Pyrex bottle. Samples of the supernatant liquid were analyzed for polymer concentration after 50 hours of contact. A material-balance calculation was made to determine the amount of polymer adsorbed. 

A zero or near-zero contact angle is necessary otherwise results will be low. This was found to be the case with surfactant solutions where adsorption on the ring changed its wetting characteristics, and where liquid-liquid interfacial tensions were measured. In such cases a Teflon or polyethylene ring may be used [47]. When used to study monolayers, it may be necessary to know the increase in area at detachment, and some calculations of this are available [48]. Finally, an alternative method obtains y from the slope of the plot of W versus z, the elevation of the ring above the liquid surface [49]. 

The influence of adsorption on the structure of a -chymotrypsin is shown in Fig. 10, where the circular dichroism (CD) spectrum of the protein in solution is compared with that of the protein adsorbed on Teflon and silica. Because of absorbance in the far UV by the aromatic styrene, it is impossible to obtain reliable CD spectra of proteins adsorbed on PS and PS- (EO)8. The CD spectrum of a protein reflects its composition of secondary structural elements (a -helices, / -sheets). The spectrum of dissolved a-chymotrypsin is indicative of a low content of or-helices and a high content of //-sheets. After adsorption at the silica surface, the CD spectrum is shifted, but the shift is much more pronounced when the protein was adsorbed at the Teflon surface. The shifts are in opposite directions for the hydrophobic and hydrophilic surfaces, respectively. The spectrum of the protein on the hydrophilic surface of silica indicates a decrease in ordered secondary structure, i.e., the polypeptide chain in the protein has an increased random structure and, hence, a larger conformational entropy. Adsorption on the hydrophobic Teflon surface induces the formation of ordered structural elements, notably an increase in the content of O -helices (cfi, the discussion in Sect. 3.1.4). 

The enzymatic activities of O -chymotrypsin in solution and adsorbed at the different surfaces are presented in Fig. 11, where the specific enzymatic activity (defined as activity per unit mass of protein) is plotted as a function of temperature. The enzyme loses activity due to adsorption. On the hydrophobic Teflon and PS surfaces, the activity is completely gone, whereas on the hydrophilic silica surface, or-chymotrypsin has retained most of its biological function. These differences are in agreement with the adsorption isotherms and the circular dichroism spectra. The influence of the hydrophobicity of the sorbent surface on the affinity of the protein for the sorbent surface, as judged from the rising parts of the adsorption isotherms (Fig. 8), suggests that the proteins are more perturbed and, hence, less biologically active when adsorbed at hydrophobic surfaces. Also, the CD spectra indicate that adsorption-induced structural perturbations are more severe at hydrophobic surfaces. 

Photolysis half-lives on different atmospheric particulate substrates (approx. 25 (xg/g on substrate) t,2 = 7.0 h on silica gel, t,/2 = 22 h on alumina and t,/2 = 29 h on fly ash (Behymer Hites 1985) first order daytime photodegradation rate constants for adsorption on wood soot particles in an outdoor Teflon chamber k = 0.0077 min-1 with 1000-2000 ng/mg loading and k = 0.0116 min-1 with 30-350 ng/mg loading (Kamens et al. 1988) ... 

Air t,/2 = 0.321-3.21 h, based on estimated photooxidation half-life in air (Atkinson 1987 quoted, Howard et al. 1991) t,/2 = 0.6 h for adsorption on wood soot particles in an outdoor Teflon chamber with an estimated first order rate constant k = 0.0179 min-1 at 1 cal cm-2 mhr1, 10 g/m3 H20 and 20°C (Kamens et al. 1988). Surface water t,/2 = 14160-15600 h, based on aerobic soil die-away test data at 10-30°C (Coover Sims 1987 quoted, Howard et al. 1991). 

The adsorption of trace silver ion (2 x 10-6 M) has been studied by use of a silver ion-selective electrode the results are shown in Figure 6.6. For periods of up to a day, silver losses on Teflon were less than 2% at the end of 30 days the losses (28%) were least for Vycor glass. The study indicates that none of the materials is suitable for long-term storage of solutions containing low levels of silver unless a complexing ligand such as thiosulfate is present. 

Figure 7. Adsorption of a-chymotrypsin on Teflon (o), polystyrene (x) and (EO -tethered polystyrene ( ). For details refer to the text.

Thus, for example, the deviations from the expected behavior for the higher homologs in the determination of the diffusion coefficients of the m-alkoxyphenol and alkyl p-hydroxybenzoate homologous series, in alkaline aqueous ethanol solution, was attributed in part to solute adsorption on the walls of the Teflon dispersion tube. ... 

Flow-Through Column Measurements. All apparatus in contact with the wastewater solution was made of plastic (either Teflon or polypropylene) to avoid adsorption on glass walls. A Teflon cylinder with bed dimensions of 56 mm long x 25... 

Figure 8. Summary of fluid shear dependence of protein adsorption on Fluorofilm Teflon, using critical-point dry technique for sample preparation...

In principle, liquid partition chromatography (LPC) is a liquid-liquid extraction where one of the liquid phases is stationary and attached to a supporting material, and the other liquid phase is mobile. It can be carried out with either the aqueous or die organic phase stationary in the latter case the technique is referred to as reversed phase LPC. The aqueous phase can be made stationary by adsorption on silica gel, cellulose powder, etc. In order to make the organic phase stationary, beads (usually 50 - 200 pta) of PVC, teflon, Kel-F, etc., are being used. 

Remark 7 The membrane used should preferably be a silicon rubber/Teflon to avoid compound adsorption on the liner. The finer (membrane) should be used only once, as the hole in the Teflon after piercing with the SPME needle remains opened, and there is a probability of the analyte adsorption on the silicon rubber. 

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