Membrane analytical examination

The results obtained with NaCl at 25°C and with KCl at 25°, 35° and 45°C in Eastman Kodak 398-3 cellulose acetate are listed in Table I. When examining the data it should be remembered that the fixed charge capacity measured here is that effective in electro-kinetic properties of the membrane it is not a quantity of analytical chemistry. Nevertheless, because NaCl and KCl are very similar in their electrochemical properties, one would expect the apparent number of moles of fixed charges per unit mass of dry... 

Introduction of a suppression device between the column and the detector can be expected to cause some degree of peak broadening due to diffusional effects. The shape of the analyte band will also be influenced by hydrophobic adsorption effects, especially when the adsorption and desorption processes are slow. Examination of peak shapes and analyte losses can therefore provide important insight into the use of suppressors with organic analytes which are weakly acidic or weakly basic. It can be expected that peak area recovery rates after suppression are governed by a combination of hydrophobic interactions with the suppressor and permeation through the membranes with the balance between these mechanisms being determined by eluent composition, suppression conditions and analyte properties. 

Affinity of MIP towards the target analyte should be examined prior to fabrication of the chemosensor. Batch binding assays are used to test selectivity of suitable MIPs. Especially, affinity of MIP to compounds, which are structurally related to the target analyte, should be tested. If MIP binds similarly with these compounds as the template, then cross-reactivity is manifested [156], This effect was exploited for determination of adenine and its derivatives with the use of MIP templated with 9-ethyladenine. Nevertheless, the cross-reactivity, if undesired, can be avoided by suitable sample pretreatment, e.g. by interferant extraction with a supported liquid membrane (SLM) coupled to the MIP-PZ chemosensor. The Fluoropore membrane filter of submicrometre porosity can serve that purpose. That way, this membrane holds interferants, thus eliminating the matrix effect. The SLM-involving determination procedure is cheaper than traditional laborious sample pretreatment used to remove the interfering substances. For instance, caffeine [143] and vanillin [157] in food samples have been determined using this procedure. 

To examine the ability of membranes to prepare samples with known contaminants, we contaminated the above peptide and protein solution with 5% glycerol and 500 mM NaCl. In addition to preventing effective crystallization of analyte samples with matrix on conventional stainless steel surfaces, glycerol and sodium contaminants are frequently present in biological samples. Doped samples were prepared for MALDI-TOF analysis by saturating the membrane with MeOH, immediately followed by the addition of 1 ul of the sample. The membrane was washed 3 times with 3-6 ml 70% methanol in water and allowed to dry after each wash. Once dry, lul saturated matrix solution was added to the sample spot. 

Wandrey, C. Bartkowiak, A. Membrane formation at interfaces examined by analytical ultracentrifugation techniques. Colloids Surf. A Physicochem. Eng. Asp. 2001, 180, 141-153. 

The application of membrane extraction of analytes prior to spectrophotometric determination has been examined [19-22]. 

In the present chapter, the relationship between the electrode potential and the activity of the solution components in the cell is examined in detail. The connection between the Galvani potential difference at the electrode solution interface and the electrode potential on the standard redox scale is discussed. This leads to an examination of the extrathermodynamic assumption which allows one to define an absolute electrode potential. Ion transfer processes at the membrane solution interface are then examined. Diffusion potentials within the membrane and the Donnan potentials at the interface are illustrated for both liquid and solid state membranes. Specific ion electrodes are described, and their various modes of sensing ion activities in an analyte solution discussed. The structure and type of membrane used are considered with respect to its selectivity to a particular ion over other ions. At the end of the chapter, emphasis is placed on the definition of pH and its measurement using the glass electrode. 

In contrast to equilibrium-based sensing such as described above, it is also possible to use the zeolite film as a membrane controlling molecular access to an appropriate transduction mechanism. In this case, Pd-doped semiconductor gas sensors were used as a fairly non-selective sensor platform. After coating these sensors with a thin film of MFI-type or LTA-type zeolites, they were examined with respect to gas phase sensing of different analytes such as methane, propane and ethanol, at different humidity levels (Fig. 14).[121] The response of a zeolite-coated sensor towards the paraffins was strongly reduced compared to the non-coatcd sensor device, thus resulting in an increase of the sensor selectivity towards ethanol. 

Unfortunately, at this point, interpreting results for the electrode measurement of salicylate in blood samples is complicated by the fact that a large fraction of the total salicylate is bound to proteins (22, 23). The Sn(TPP)Cl2 based membrane electrode detects "free" salicylate while the conventional colorimetric procedure (i.e. the Trinder method (21) or variations thereof) measures total salicylate concentration (free plus bound). The former is the physiologically active form of the compound (24). Thus, the salicylate selective electrode could provide a new analytical tool for scientists who are examining the pharmacological effects of aspirin and other... 

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