Coatings, analysis

Promising new analytical tools are further enzymatic analysis, coated wire electrodes, high-pressure liquid chromotography, sulfide electrode use, and use of computers for data storage and retrieval and for monitoring laboratory instrumentation. 

The realized experiments have shown the large possibilities of analysis by the eddy currents method. They allow, besides the verification of the coating and the determination of its thickness, to give an overview on the percentage of the main chemical components of the controlled samples coating by a deepened processing. 

This is used extensively for qualitative analysis, for it is a rapid process and requires simple apparatus. The adsorbent is usually a layer, about 0 23 mni. thick, of silica gel or alumina, with an inactive binder, e.g. calcium sulphate, to increase the strength of the layer.. A. i i slurry of the absorbent and methanol is commonly coated on glass plates (5 20 cm. or 20 x 20 cm.), but microscope... 

Solid-phase microextractions also have been developed. In one approach, a fused silica fiber is placed inside a syringe needle. The fiber, which is coated with a thin organic film, such as poly(dimethyl siloxane), is lowered into the sample by depressing a plunger and exposed to the sample for a predetermined time. The fiber is then withdrawn into the needle and transferred to a gas chromatograph for analysis. 

Mifflin and associates described a membrane electrode for the quantitative analysis of penicillin in which the enzyme penicillinase is immobilized in a polyacrylamide gel that is coated on a glass pH electrode. The following data were collected for a series of penicillin standards. 

Capillary Electrochromatography Another approach to separating neutral species is capillary electrochromatography (CEC). In this technique the capillary tubing is packed with 1.5-3-pm silica particles coated with a bonded, nonpolar stationary phase. Neutral species separate based on their ability to partition between the stationary phase and the buffer solution (which, due to electroosmotic flow, is the mobile phase). Separations are similar to the analogous HPLC separation, but without the need for high-pressure pumps, furthermore, efficiency in CEC is better than in HPLC, with shorter analysis times. 

The second form consists of Pt metal but the iridium is present as iridium dioxide. Iridium metal may or may not be present, depending on the baking temperature (14). Titanium dioxide is present in amounts of only a few weight percent. The analysis of these coatings suggests that the platinum metal acts as a binder for the iridium oxide, which in turn acts as the electrocatalyst for chlorine discharge (14). In the case of thermally deposited platinum—iridium metal coatings, these may actually form an intermetallic. Both the electrocatalytic properties and wear rates are expected to differ for these two forms of platinum—iridium-coated anodes. 

Analysis of coatings is simplified if the coating can be removed from the paper in a water bath by ultrasonic cleaning. If fibers are not present, a carbohydrate deterrnination can be used to identify gums and other carbohydrate polymers in the coating. 

Applications. The capabiHties of a gc/k/ms in separating and identifying components in complex mixtures is very high for a broad spectmm of analytical problems. One area where k information particularly complements ms data is in the differentiation of isomeric compounds. An example is in the analysis of tricresyl phosphates (TCPs) used as additives in a variety of products because of thek lubricating and antiwear characteristics (see Lubrication and lubricants). One important use of TCPs is in hydrauHc fluid where they tenaciously coat metal surfaces thereby reducing friction and wear. Tricresyl phosphate [1330-78-5] (7.2 21 exists in a variety of isomeric forms and the commercial product is a complex mixture of these isomers. 

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