Polarographie analyzers

Finally, the techniques of nmr, infrared spectroscopy, and thin-layer chromatography also can be used to assay maleic anhydride (172). The individual anhydrides may be analyzed by gas chromatography (173,174). The isomeric acids can be determined by polarography (175), thermal analysis (176), paper and thin-layer chromatographies (177), and nonaqueous titrations with an alkaU (178). Maleic and fumaric acids may be separated by both gel filtration (179) and ion-exchange techniques (180). 

Zinc smelters use x-ray fluorescence spectrometry to analyze for zinc and many other metals in concentrates, calcines, residues, and trace elements precipitated from solution, such as arsenic, antimony, selenium, tellurium, and tin. X-ray analysis is also used for quaUtative and semiquantitative analysis. Electrolytic smelters rely heavily on AAS and polarography for solutions, residues, and environmental samples. 

Raki, a Turkish alcoholic drink was also analyzed by differential pulse polarography and copper, iron and zinc could be determined. For the arsenic content in beer a more sensitive method had to be applied. For this method a new catalytic method is established and the arsenic content was determined by using this new method. 

In conclusion, synthetic dyes can be determined in solid foods and in nonalcoholic beverages and from their concentrated formulas by spectrometric methods or by several separation techniques such as TEC, HPLC, HPLC coupled with diode array or UV-Vis spectrometry, MECK, MEECK, voltammetry, and CE. ° Many analytical approaches have been used for simultaneous determinations of synthetic food additives thin layer chromatography, " " derivative spectrophotometry, adsorptive voltammetry, differential pulse polarography, and flow-through sensors for the specific determination of Sunset Yellow and its Sudan 1 subsidiary in food, " but they are generally suitable only for analyzing few-component mixtures. 

Hydrazine may be analyzed by various methods including GC-FID, GC-NPD, HPLC, GC/MS, polarography, colorimetry, and iodometric titrations. The iodometric method is simple and apphcable to measure hydrazine quantitatively in water at aU concentrations. 

Midget bubblers were used as a last resort where sorbent methods had failed. Bubblers were generally charged with a derivatiz-ing agent that would stabilize the analyte. Aldehydes were collected as Girard "T" or hydroxylamine derivatives that could be analyzed by polarography or HPLC with uv detection. 

Polarographic methods have been extremely useful for the determination of the urinary excretion of the 1,4-benzodiazepines. An assay that employs selective solvent extraction and acid hydrolysis of diazepam and its major metabolites, iV-desmethyldiazepam and oxazepam, to their respective benzophe-nones has been employed to measure the urinary excretion of diazepam [183]. A pulse polarographic assay has been reported that will measure the urinary excretion of bromazepam following a single 12-mg dose [184]. The assay employs selective extraction of bromazepam and the 2-amino-5-bromobenzoyl-pyridine metabolite from the deconjugated metabolites, 3-hydroxybromazepam and 2-amino-3-hydroxy-5-bromobenzoylpyridine, into separate diethyl ether fractions. The residues of the respective extracts are dissolved in phosphate buffer (pH 5.4) and analyzed by pulse polarography, which yields two distinct... 

Confirmation of the identity of the gas chromatographic components has been accomplished by thin layer chromatography, relative retention times on different gas chromatographic columns, "p" values, and most recently by mass spectrometry. Dicofol can be separated from its phenone by using a Florisil column (17) or TLC. Dehydrochlorination of dicofol to DBP can be used as a confirmatory test for the parent compound. Gajan and Lisk (23) used cathode ray polarography to analyze vegetables for dicofol residues. 

Simple aldehydes, such as formaldehyde or acrolein may be analyzed by derivatizing into a suitable derivative for GC-FID or -NPD determination (Methods 2502, 2501, NIOSH 1984). The derivatizing agents for these compounds are 2-(benzylamino)ethanol and 2-(hydroxymethyl)piperidine, respectively, coated on a support. Formaldehyde may also be determined using colorimetry and polarography (Methods 3500 and 3501, NIOSH 1984). See Part 3 of this book. 

Formaldehyde may be analyzed by several techniques involving GC, colorimetry, polarography, HPLC, and GC/MS. 

Electrolysis at controlled potential can also serve as an elegant method of removing interfering metals from samples to be analyzed by other methods such as spectrophotometry or polarography. The electrogravimetric and coulometric procedures mentioned above represent such separations. The electrolysis can, however, be carried out primarily as a selective separation, with the actual determination being... 

Originally, polarography was defined as a method making use of current-voltage curves obtained in the electrolysis at a dropping mercury electrode of the solutions to be analyzed. Later, the application of solid electrodes [8] which may be stationary, rotated or vibrated was introduced. Polarography with solid electrodes is often called voltammetry. 

In order to obtain information about the polarographic properties of the individual protein components in blood sera, the polarography was combined with paper electrophoresis. After electrophoretic separation, the cut strips of paper with separated fractions of albumins and globulins are eluted in physiological sodium chloride solution and each sample is analyzed polarographically. These combined methods were applied for study of various pathological cases [147]. 

In principle, any measurable property of a reacting system that is proportional to the extent of reaction may be used to monitor the progress of the reaction. The most common techniques are spectrophotometric (UV-visible, fluorescence, IR, polarimetry and NMR) or electrochemical (pH, ion-selective electrodes, conductivity and polarography). Either a "batch" method can be used, in which samples are withdrawn from the reaction mixture and analyzed, or the reaction may be monitored in situ. By far the most widely used technique involves UV-visible spectrophotometry. 

Sensitization Via Electron Transfer. Pappas and Jilek analyzed the energetics of energy and electron transfer sensitization.(5j ) Their evidence indicated that inmost cases, sensitization could be explained by an electron transfer mechanism (see Figure 5). Sensitization is believed to involve the transfer of an electron from an excited photosensitizer (S ) to an onium molecule, which may involve the formation of an excited state complex. Product analysis and irreversible polarography previously determined from electrochemical studies, indicate that the reduced iodonium salt undergoes homolytic bond cleavage to form a phenyl radical and iodobenzene. ( ) The reduced sulfonium salt produces phenyl sulfide and a phenyl radical.(10)... 

Low-temperature treatment of Cr(VI) /silica by ethylene can also produce Cr(II) as was shown in 1968 by Baker and Carrick [239], who reported the valence of a catalyst containing 0.5 wt% chromium, initially hexavalent, after it reacted with ethylene at 135 °C. Afterward, the catalyst was treated with deoxygenated dilute HC1 to dissolve the chromium. The solution was then analyzed by polarography to determine the chromium oxidation state. The authors measured 85-96% conversion to Cr(II) within a few minutes of exposure to ethylene. Formaldehyde was released as the major (probably only) by-product. More recently, formaldehyde was again confirmed as the by-product of Cr(VI) reduction by ethylene [232],... 

Most applications of polarography involve metal ion analysis, where only one valence state is present in solution, such as Tl+, Cd2+, Pb2+, or Zn2+. However, that is not always the case one can analyze Fe2+and Fe3+simulta-neously by polarography, in a complexing solution such as made with oxalate, in which case the polarogram shows (at E< i/2) a limiting reduction current i due to the reduction of Fe3+to Fe2+, and (at E> EV2) a limiting oxidation current i for the oxidation of Fe2+to Fe3+. We simulate this in Fig. 6.10-2. 

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