Feature Gas detection & measurement


HN microanalysis provides a fast and inexpensive method for determining the purity of a compound. Used in conjunction with techniques such as NMR and Mass Spectrometry, it can also be used to fully characterise compounds. Typically, 1-2mg of a sample is introduced into a high temperature furnace at c. 1000˚C and combusted in high purity oxygen. The resulting combustion products pass through oxidation reagents to produce carbon


C


dioxide (CO2), water (H2O), nitrogen (N2) and nitrogen oxides. The gases are passed over copper to remove excess


oxygen and reduce the oxides of nitro- gen to elemental nitrogen.


Accurate detection of these combus- tion products is achieved using thermal


A CHN microanalysis system


Environmental analysis


conductivity detectors. Sample weights are entered into the analyser software in µg, and CHN microanalysis software is then used to automati- cally calculate the sample results as % carbon, hydrogen and nitrogen.


Microanalysis for environmental monitoring CHN microanalysis is proving extremely useful to a growing number of organisations around the world for environmental monitoring. Driven by increasing governmental legislation, monitoring of contamination of air, land and water samples now needs to be undertaken by any organisation producing emissions. These monitoring processes are important for assessing the risk that human activities pose to the natural environment. The analysis of material retained on filters used in water filtration and air monitoring applications can be easily achieved using a CHN micro- analysis system. The analysis of water filters is frequently used for the analysis of river water particulates and oceanographic monitoring. Furthermore, the determination of carbon and nitrogen in sea water can also be used to monitor the oceanographic food chain. Air applications that have benefited from CHN microanalysis include the monitoring of filters taken from workplace environments and also flue stack emissions monitoring.


Sample Sample A Sample B Sample C


%C


31.10 34.09 35.44


%H 4.75 5.19 5.38


%N 7.44 8.35 8.68


Typical water monitoring filter results


Using CHN microanalysis, these water and air analyses can be carried out with minimal sample preparation and without the need for weigh- ing. Here, a known amount of air can be passed through a filter sample, and the filter can then be run through the CHN microanalysis system from which the levels of carbon, hydrogen and nitrogen in the filtered sample will be expressed as µg. If the amount of air passed over the sample was known, these results can be expressed as µg per litre of air. A similar process can be used for the analysis of oceanographic monitoring filter samples. A known amount of water can be passed through the filter samples prior to analysis, with the results following analysis being expressed as µg per litre of water. Using an Exeter Analytical Model 440 CHN microanalysis system, whole filters up to 50mm in size can be analysed, eliminating the need for sub-sampling which can introduce errors and diminish data quality.


Analysis technology


Determining the carbon, hydrogen and nitrogen content of soils is vitally Instrumentation NOVEMBER 2013


important to environmental and agrochemical laboratories around the globe. With environmental ‘solids’, CHN microanalysis is able to analyse carbon in both its organic and inorganic forms fol- lowing a pre-treatment with acid. Not only does determining the levels of organic carbon provide valuable information relating to the biological, chemical and physical properties of a soil sample, but it also has a bearing on the produc- tive capacity of soils. The determi- nation of nitrogen content in soils using an elemental analyser is more time and cost effective than the traditional Kjeldahl method and avoids the use of highly corro- sive and toxic chemicals.


In a world where environmental responsibility is becoming increasingly important, companies are looking to techniques such as CHN microanalysis to quantify organic matter. Tracie Hart, laboratory manager for Warwick Analytical Service, a division of Exeter Analytical, looks into the demands faced and the applications in which microanalysis can help


Detailed below in the table are percentage carbon, hydrogen and nitrogen results obtained from soil samples using an Exeter Analytical Model 440 CHN microanalysis system. Three samples were run in duplicate, all taken at the same depth and within a one metre square area, to ensure representative sampling. Provided that representative samples are taken, CHN microanalysis can provide extremely accurate and reproducible results.


Sample


Ref: 1456.5 Ref: 1456.6 Ref: 1456.7


Weight 10-20mg 10-20mg 10-20mg


%C 2.55 2.57 2.52 2.54 2.55 2.57


Responsible waste disposal


The disposal of waste materials is a key environmental issue in many developed countries as designated landfill sites becoming increasingly full to capacity. So, not only is there the drive to recycle more, but there is increasing pressure on organisations to dispose of waste responsibly and efficiently. To help, CHN microanalysis systems can directly determine the carbon, hydrogen and nitrogen content in waste materials, and these results can be directly related to the energy content of the waste materi- als analysed. Applications for this analysis include testing of recovered secondary fuel samples and performance testing for material recovery facilities producing solid recovered fuels. Due to the non-homogeneous nature of most waste materials, the samples are dried, shredded and then ground to increase homogeneity. These samples are typically analysed three times and an average of the results taken. Hydrogen results are useful when determining the calorific value of fuels.


Sample Sample 1 Sample 1 Sample 1


%C


37.90 38.48 38.13


A fast and precise technique


CHN microanalysis is an analytical technique that lends itself to fast, precise and reproducible analysis of a wide range of environmental sample types. The technique is proven in labs worldwide to provide an inexpensive and reliable method of quantifying organic matter.


Exeter Analytical www.exeteranalytical.co.uk/environmental_monitoring.htm 13 Enter 656


%H 4.95 5.04 4.96


%N 1.09 1.14 1.03


Typical waste material CHN results


%H 1.05 1.07 1.03 1.06 1.05 1.06


%N 0.21 0.21 0.20 0.22 0.22 0.23


Results from soil samples using the CHN system


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