Microdetermination of zinc by means of reagent crayons and the ring-oven technique

A sensitive and highly selective method for the rapid microdetermination of zinc by the ring-oven technique is presented. Very few cations when present in l00-fold excess interfere while anions do not interfere. The optimal range is 0.1–1.0 /smg zinc, which suggests its special applicability in air pollution investigations.     

Microdetermination of calcium, strontium and barium using the ring-oven method

Summary The ring-oven technique is recommended for the identification and determination of Ca, Sr and Ba in the micro scale. The elements are first converted into their nitrates and Ca is washed out by a mixture of absolute alcohol and ether. Sr is then separated from Ba as soluble diethyldithiocarbamidate in alcohol-ether. The rings obtained are developed by rhodizonate (Sr, Ba) and pyrogallol (Ca). Quantitative determinations are possible by comparison with standard rings. 0.60 g of Ca, 1.31 g of Sr and 8.24 g of Ba can be determined with an error lower than 6%.

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Zusammenfassung Zur Trennung und Bestimmung von Ca, Sr und Ba im Mikromaßstab wird die Ringofen-Technik empfohlen. Die drei Elemente werden dabei zunächst in die Nitrate übergeführt und Ca mit Äther-Alkohol ausgewaschen. Sr und Ba werden anschließend mit Diäthyldithiocarbamidat behandelt und Sr mit Äther-Alkohol abgetrennt. Die Identifizierung erfolgt mit Pyrogallol (Ca) bzw. Rhodizonat (Sr, Ba). Durch Vergleich mit Standardproben ist eine quantitative Bestimmung möglich. Hierbei können noch 0,60 g Ca, 1,31 g Sr und 8,24 g Ba mit einem Fehler < 6% erfaßt werden.

     

Microdetermination of caffeine using the ring oven technique

A rapid and highly selective method for the microdetermination of caffeine of special interest for air pollution studies is presented. With the ring oven technique and with solutions of acetylacetone in sodium hydroxide and p-dimethylaminobenzaldehyde in hydrochloric acid, as little as 0.5 μg caffeine on the ring can be determined with an average error of 3%. Compounds containing purine bases which would be likely to give the same color reaction as caffeine do not interfere. Of the organic air pollutants which might be collected from the atmosphere during thesampling for caffeine, benzo(α)pyrene and formic acid do not interfere. Interferences from formaldehyde and urea are easily eliminated.     

Microdetermination of secondary aliphatic amines using a copper ion-selective electrode

A simple, accurate, and selective method is described for the microdetermination of aliphatic secondary amines. The method is based on their reaction with carbon disulfide and ammoniacal copper sulfate at 40 °C for 30 min to yield copper dialkyldithiocarbamate. The excess copper is then measured by titration with EDTA or NaDDC using a copper ion-selective electrode. A mean recovery of 98.2% with a standard deviation of 0.8% is obtained for aliphatic secondary amines and their salts having a wide range of pK_a.     

An improved washing-in technique for use with the ring-oven

Summary The washing-in technique ofvan Nieuwenburg andvan Ligten has been modified to overcome its practical limitations and developed into a useful aid to analytical chemistry with possible new applications. It has been used to estimate phosphorus in the atmosphere of laboratories where transistors are made.

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Zusammenfassung Das vonvan Nieuwenburg undvan Ligten angegebene Washing-in-Verfahren wurde modifiziert, um seine praktische Anwendbarkeit als wertvolles Hilfsmittel der analytischen Chemie auf neue Gebiete auszudehnen. Es wurde zur Bestimmung von Phosphor in der Atmosphäre von Transistor-Herstellungsräumen verwendet.

     

Recent applications of the ring-oven technique : A brief review

The ring-oven technique is a special type of spot analysis. In this review, papers published since 1976 are discussed. The aspects dealt with include developments in the technique and its use, the identification and determination of inorganic ions, organic substances, enzymatic analysis, applications to air and water samples, and combinations with other techniques.     

The determination of nitrite and nitrate by the ring-oven technique

Determinations of nanogram amounts of nitrite and nitrate individually and together, based on a variation of the ring-oven technique, are described. In the “segment technique” used, a stable standard scale is not necessary. Interferences have been studied. Nitrite in sausages can be determined.     

Microdetermination of o-aminophenol and some substituted o-aminophenols using a copper ion-selective electrode

The compound o-aminophenol and some substituted o-aminophenols were determined on the microscale by potentiometric titration with standard cupric sulfate or nitrate in aqueous or partially methanolic medium. Emf's were monitored with a copper ion-selective electrode and a single-junction reference electrode. The o-aminophenols reacted on a 2:1 amine:Cu basis. The m- and p-isomers cannot be determined with cupric ion.     

Semiquantitative determination of ajmaline by the weisz ring-oven technique

Ajmaline has been determined semiquantitatively with p-dimethylaminobenzaldehyde as reagent, with an error of +/-2%.     

The ring-air technique: An alternative to the ring-oven technique in circular thin-layer chromatography

A technique is described in which a ring of air is used to produce sample concentration by solvent evaporation on high-performance thin-layer chromatography plates. The technique is compared to the ring-oven technique and both are evaluated by using a dye mixture. Both techniques are employed to reduce the size of relatively large spots on the plates in an attempt to match the resolution obtained from small spots in circular chromatography.     

Qualitative analysis of some alloys and determination of copper and iron by the ring-oven method

Methods for the qualitative analysis of various copper alloys, including ancient Egyptian coins, aluminium alloys and zinc alloys by the ring-oven method, are described. Procedures for the colorimetric determination of copper and iron after separation on the ring oven are given.