Exeter Analytical has developed a sensitive and precise protocol for direct determination of total Carbon (C), Hydrogen (H) and Nitrogen (N) in air and water filter samples.
Filtering air and water samples and determining the chemical composition of the filtrate is of widespread interest to environmental laboratories. Using an Exeter Analytical Model 440 CHN elemental analyser to determine percentage C, H and N of filtered samples is a technique favoured by many labs because the method requires a minimum of sample preparation and may be used for single samples or automated for higher throughput environments.
Developed in conjunction with several leading environmental testing labs the protocol for determining CHN composition of filter samples is described in Exeter Analytical application note 210.
Direct determination of total CHN retained on a filter is more sensitive, precise and cost-effective than making measurements on pre- and post- filtered samples and calculating the difference1. Direct determination is preferred over the traditional "by difference" method because of the reduced sources of error, rapidity of analysis and increased sample representativeness due to the greater volume filtered.
The Exeter Analytical Model 440 employs a static combustion system, with a unique horizontal furnace design, which enables easy removal of filter and sample ash between each analysis. Consequently one combustion tube will analyse in excess of 1000 samples without the need for removal and cleaning. In addition the Model 440 provides the capacity to process filters up to 50 mm in diameter in one analytical cycle. By comparison other elemental analysers, employing vertical furnace designs, need cleaning after as little as 20 samples and larger filters have to be sub sampled several times and then corrective calculations made to enable analysis.
Effectively eliminating troublesome residue build-up the gas flow characteristics of the Model 440 analyser are superior to other elemental analysers thereby providing longer-term calibration stability as well as enhanced accuracy and precision for measured sample data. The Model 440 also provides complete control over combustion parameters enabling the analysis of filters without the need for expensive tin capsules.