Nitrogen ammonia reagent set

Peat samples were homogenized and topped with distilled water in a 10:1 (H₂O: sample) v/w ratio. Samples were mixed with water and endured for 12 h. The suspension was filtered, and the filtrate was used for further chemical analysis. рН was measured by pH-meter HI 2550 (HANNA instruments, Italy). Concentrations of mineral nitrogen (NH₄⁺, NO₂⁺, NO₃⁺) and soluble phosphates in the filtrate were measured by spectrophotometer Hach Lange DR3900 (Hach, USA) in 1 inch square glass cuvettes according to the standard manufacturers’ instructions that correspond to the following methods of water analysis certified by EPA Environmental Protection Agency (USA) (Rice and Bridgewater, 2012 ). In brief, the concentration of NO₂⁻ was measured by the diazotization method (reagent set NitriVer 3, Hach), the concentration of NO₃− was measured by the cadmium reduction method (reagent set NitraVer 6, Hach), the salicylate method was used to measure NH₄⁺ (Nitrogen-Ammonia Reagent Set, Hach), and ascorbic acid method was used to measure concentration of PO₄³⁻ (reagent set PhosVer 3). Nitrate Standard Solution (100 mg/L), Nitrite Standard Solution (250 mg/L NO₂⁻-N), Ammonium Standard Solution (50 mg/L), Phosphate Standard Solution (50 mg/L as PO₄³⁻, NIST) provided by Hach (USA) were used to build the calibration curves. All measurements were performed in triplicates at 18°C.

Standard ammonia (5 mg/L) and multi-cation III solutions were purchased from Wako Pure Chemical Industries (Osaka, Japan). Ultrapure water was produced by a Milli-Q Integral3 System (Merck Millipore, Tokyo, Japan). A Nitrogen-Ammonia Reagent Set, which includes two regents (ammonia cyanurate and ammonia salicylate), was purchased from HACH (Germany).