A simplified version of the total kjeldahl nitrogen method using an ammonia extraction ultrasound-assisted purge-and-trap system and ion chromatography for analyses of geological samples
| Autor: | Lílian Irene Dias da Silva, Arnaldo Alcover Neto, Manuel Castro Carneiro, Genilda Pressato da Rocha, Delmo Santiago Vaitsman, Fernanda Veronesi Marinho Pontes, Maria Inês Couto Monteiro |
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| Rok vydání: | 2009 |
| Předmět: |
Geologic Sediments
Time Factors Nitrogen Ion chromatography Analytical chemistry chemistry.chemical_element Biochemistry Analytical Chemistry law.invention Steam distillation Soil Ammonia chemistry.chemical_compound law Environmental Chemistry Ultrasonics Indophenol Kjeldahl method Spectroscopy Chromatography Extraction (chemistry) Certified reference materials chemistry |
| Zdroj: | Analytica Chimica Acta. 632:284-288 |
| ISSN: | 0003-2670 |
| DOI: | 10.1016/j.aca.2008.11.011 |
| Popis: | The total Kjeldahl nitrogen (TKN) method was simplified by using a manifold connected to a purge-and-trap system immersed into an ultrasonic (US) bath for simultaneous ammonia (NH 3 ) extraction from many previously digested samples. Then, ammonia was collected in an acidic solution, converted to ammonium (NH 4 + ), and finally determined by ion chromatography method. Some variables were optimized, such as ultrasonic irradiation power and frequency, ultrasound-assisted NH 3 extraction time, NH 4 + mass and sulfuric acid concentration added to the NH 3 collector flask. Recovery tests revealed no changes in the pH values and no conversion of NH 4 + into other nitrogen species during the irradiation of NH 4 Cl solutions with 25 or 40 kHz ultrasonic waves for up to 20 min. Sediment and oil free sandstone samples and soil certified reference materials (NCS DC 73319, NCS DC 73321 and NCS DC 73326) with different total nitrogen concentrations were analysed. The proposed method is faster, simpler and more sensitive than the classical Kjeldahl steam distillation method. The time for NH 3 extraction by the US-assisted purge-and-trap system (20 min) was half of that by the Kjeldahl steam distillation (40 min) for 10 previously digested samples. The detection limit was 9 μg g −1 N, while for the Kjeldahl classical/indophenol method was 58 μg g −1 N. Precision was always better than 13%. In the proposed method, carcinogenic reagents are not used, contrarily to the indophenol method. Furthermore, the proposed method can be adapted for fixed-NH 4 + determination. |
| Databáze: | OpenAIRE |
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