Total nitrogen (TN) measurements were performed on an N/Protein Analyzer (Flash EA 1112 Series, Thermo Electron S.p.A., Rodano, Italy), equipped with a carbon trap (soda lime), water trap (silica gel), catalysts of CuO and Pt/Al2O3, a separation column of Teflon and activated carbon, and a thermal conductivity detector (TCD). Dried samples were used per established TS protocols. In the analytical equipment, on dynamic flash combustion (Dumas method) of the samples, nitrogen compounds are released and reduced to nitrogen gas [25 ]. The analysis was performed at 900 °C, with helium as the carrier gas and oxygen gas was used for the combustion. Aspartic acid was used as the calibration standard.
The nitrogen salts that were analyzed included ammonia, nitrite, and nitrate. Spectrophotometry-based cuvette tests LCK 303, LCK 342 and LCK 340 (Hach Lange GmbH, Düsseldorf, Germany) were used to measure ammonia, nitrite, and nitrate, respectively. All cuvettes were analyzed on a DR2800 spectrophotometer (Hach Lange GmbH, Düsseldorf, Germany).
The nitrogen salts that were analyzed included ammonia, nitrite, and nitrate. Spectrophotometry-based cuvette tests LCK 303, LCK 342 and LCK 340 (Hach Lange GmbH, Düsseldorf, Germany) were used to measure ammonia, nitrite, and nitrate, respectively. All cuvettes were analyzed on a DR2800 spectrophotometer (Hach Lange GmbH, Düsseldorf, Germany).