Determination of Halogens and Sulphur in Complex Matrices

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This article presents a method that combines combustion digestion and ion chromatography into a single analysis (combustion ion chromatography [CIC]) making it possible to detect halogens and sulphur in complex matrices. The method is suitable for use in a wide range of application areas.

Table 1: A selection of international standards that recommend combustion ion chromatography as a means of determining the halogen and sulphur content in flammable samples.
There are a number of different methods available to determine fluorine, chlorine, bromine, iodine, and sulphur in flammable substances. The majority of these are based on independent analysis steps, beginning with sample digestion using high-temperature combustion followed by halogen and sulphur analysis. As an alternative, combustion digestion coupled with ion chromatography (CIC) combines sample digestion and analysis in one step. CIC can be performed on a wide range of sample types regardless of whether solid, liquid, or gas. The only condition is that the sample has to be flammable. In addition to the halogen and sulphur analysis processes discussed in this article, which are used in the plastics, power generation, petroleum, and fuel industries, CIC is also suitable for samples from the pharmaceutical, environmental, and food sector. It is for these advantages that many international standards refer to CIC when determining the presence of halogens and sulphur in complex matrices (Table 1).

CIC Method Principles

Figure 1: Effect of 90 mg/L hydrogen peroxide in the absorption solution. Red: once with in-line matrix elimination; Black: once without.
Combustion: Combustion takes place in the presence of steam, which ensures that the gaseous halogen and sulphur compounds (HX, X2, SOx) are quantitatively collected by the absorption solution. Adding hydrogen peroxide to the absorption solution (for example, 90 mg/L) ensures that all sulphur compounds are present in the form of sulphate, which is necessary for ion chromatographic detection. However, when hydrogen peroxide is added as an oxidizing agent it can result in various interference peaks that overlay the fluoride peak. With in-line matrix elimination, these interferences disappear and the fluoride peak can be evaluated again (Figure 1).

An optical sensor in the pyrolysis oven indicates the progression of the combustion and regulates the feed of the sample boat. This ensures complete combustion by similarly reducing the sample's oven dwell time.

Instrumentation: The combustion unit is from Analytica Jena, while the liquid handling and IC are from Metrohm. The software used was MagIC Net from Metrohm.