FAKULTÄT FÜR CHEMIE
Mikroanalytisches Laboratorium
Universitaet Wienhttp://www.univie.ac.at

 
Elemental Oxygen Analysis

In this web pages you can find a short description of the method used, a characterization of the working range, and a list of known interferences limiting the use of the method.


By January 2004 we have cancelled offering Elemental Oxygen Analysis.

This analysis is rarely required and numerous interferences with hetero elements, especially metals, make results useless. As we plan to implement an appropriate method probably on a new instrument if required we keep this information available.

Introduction

Determination of the oxygen content in an organic sample is not ordered frequently. Althouigh our laboratory is equipped with a method to perform this analysis.

Since 1990 oxygen determination has been performed using the "EA 1108 CHNS-O" (originally developed by Carlo Erba Instruments, then supplied by Fisons Instruments who became "ThermoQuest" in 1996).

Now (since November 1996) we have equipped our old "240 CHN Elemental Analyzer" (Perkin Elmer) to be always available in oxygen determination mode

Method

Oxygen determination using the EA 1108 CHNS-O:

The solid sample is weighed in using a silver capsule. 2 to 5 mg of material are required. After closing and folding the capsule it is placed in the autosampler.

The silver capsule is released and falls down into an oven held at 1.070 °C where it is degraded in pure helium atmosphere. The volatile products react at a nickel carbon phase where oxygen is set free in the form of carbon monoxide.

In addition to CO the only important product gas observed is N2. These products are sparated by gas chromatography and detected and quantified at a TCD (thermal conductivity detector).

A blank value is determined at an empty capsule

Calibration is performed using acetanilide and benzoic acid as standard materials.

Oxygen determination using the "240 CHN Elemental Analyzer"

Working range

Analysis returns the total amount of oxygen from ordinary organic samples. There are some severe interferences at compounds containing hetero elements which are listed below.

Problems and Interferences

It is not possible to investigate liquid samples.

Fluoron reacts to form HF which attacks the fused silica tubes which are the essential parts of the system. Oxygen is set free from the SiO2 and is detected.

SiO2 + 4 HF --> SiF4 + 2 H2O
2 H2O + 3 C --> 2 CO + CH4

The mineralization of metallic or metal organic compounds can also be limited by interferences. Reduction of nickel- and ironcompounds should theoretically be possible ander the conditions of the process. Alkaline and earth alkaline elements, lanthanides and actinides, silicon and other elements that form oxygen compounds which cannot be reduced by carbon are able to form stable oxides under the chemical conditions which leads to systematic errors which can even be stoichiometric loss compared to the expected oxygen content.

Using the "EA 1108 CHNS-O" no residue can be identified.

Oxygen determination on the "240 CHN" elemental analyzer makes the redual material accessible if no additives are necessary.

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