Nitrogen cycle analytical methods

There is also a great need to measure DON with accuracy. DON is the primary form of nitrogen in much of the surface ocean and may limit phytoplankton production in many areas. The difficulty in measuring DON is largely analytical, and accurate values for deep water will only be obtained after new direct DON methods are developed. Measurement of certain forms of DON is probably more important for understanding the global carbon cycle than is knowledge of concentrations for most trace metals. 

With the aid of the carrier gas flow the trace zone was transferred into the analytical column. Under such conditions carbon dioxide is completely retained by diethanolamine. The concentration and analysis were performed at room temperature. The separated trace components were sensed by a flame-ionization detector. The carrier gas (nitrogen) flow-rate was 60 ml/min. For regeneration the concentration column was heated in the carrier gas flow at 100—105°C for 5—7 min. For heating and cooling a special device forming part of a KhT-2M chromatograph manufactured in the U.S.S.R. was used. The duration of the total analytical cycle was 25 min. This method permits the determination of hydrocarbon gases in carbon dioxide at concentrations down to 10" %. 

PFE procedures for the soil were carried out in an Accelerated Solvent Extractor (ASE, Dionex Corporation, Salt Lake City, Utah). The extraction method was optimized by varying extraction temperature and number of extraction cycles. The extraction solvent was acetonitrilermethanol (1 1, v v) and the pressure was kept constant at 1500 psi, which in previous studies pressure did not show a big influence on the extraction efficiency (13), The soil used for optimization was of the Helemano series (14), spiked in the laboratory by the organic solvent slurry method (15) at approximately 3 pg/g for each of the analytes. After extraction, the sanq)les were filtered through sodium sulfate and 0.2 pm nylon filter and concentrated with a gentle flow of nitrogen gas before GC-MS analysis. 

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