Exeter Analytical develops protocol for determination of carbon, nitrogen and hydrogen
Filtering air and water samples and determining the chemical composition of the filtrate is of widespread interest to environmental laboratories.
The company claims that using an Exeter Analytical Model 440 CHN elemental analyser to determine percentage C, H and N of filtered samples is ideal because the method requires a minimum of sample preparation and may be used for single samples or automated for higher throughput environments.
According to the company, 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 difference.
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 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 of up to 50 mm in diameter in one analytical cycle.
By comparison the company claims that 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.