Optima 8000 icp oes

To draw the standard curve of Cd content, the Cd standard solution (1 mg mL^-1) was diluted with 5% HNO₃ to 10 mg L^-1 stock solution. The stock solution was then prepared into 0, 0.1, 0.2, 0.4, and 1 mg L^-1 standard solutions and mixed for detection. The solutions were detected by an Inductively Coupled Plasma Spectrometer (ICP-OES optima 8000, Perkin Elmer, US) using the wavelength of 214.44 nm. The standard curve was drawn only when the linear correlation coefficient was greater than 0.99.
Approximately 0.2–1.0 g dried samples were added to polytetrafluoroethylene digestion tanks, then, 5 mL HNO₃ was injected and the tanks were left to stand. When the reactions finished, the tanks were sealed with caps and put into a microwave digestion instrument (WX-8000) using the following digestion procedure: 100°C, 3 min; 140°C, 3 min; 160°C, 3 min; 180°C, 3 min; 190°C, 15 min. When the temperature cooled below 50°C, the digestion tanks were taken to the fume hood. The digestion solutions were transferred to 50 mL volumetric flasks and fixed volume to 50 mL by rinsing three or four times using ultrapure water. The blank control was treated using the same method. The sample solutions were detected under the same wavelength and the Cd contents were calculated according to the standard curve.

Clean agricultural wastes were oven-dried at 40 °C to constant weight, milled and screened through a 60-mesh sieve, and then analyzed by Van Soest’s method [22 (link)] to quantify cellulose, hemicellulose and lignin content. Total carbon (TC) and TN of agricultural wastes were determined by an elemental analyzer (Thermo Flash 2000 CHNS/O, Thermo Fisher Scientific, Waltham, Massachusetts, USA), and TP of agricultural wastes was analyzed by an Inductively Coupled Plasma Optical Emission Spectrograph (ICP-OES optima 8000, Perkin Elmer, Waltham, MA, USA).

The BET (Brunauer, Emmett and Teller technique) surface area, pore size distribution and total pore volume of adsorbent were characterized with a surface area and porosimetry analyzer (Micromeritics ASAP 2460, Norcross, GA, USA). Scanning electron microscope (Hitachi Ultra High-Resolution Analytical FE-SEM SU-70, Tokyo, Japan) was used for surface morphology, and Fourier transform infrared spectrometer (Thermo Scientific™ Nicolet™ iN10, Waltham, MA, USA) was used to describe the type and content of functional groups of biochar. Physical phase analysis was conducted on an X-ray diffractometer (X’Pert Pro MPD, Heracles Almelo, The Netherlands) with a conventional angular (5 to 100°) physical phase scan at room temperature. A laser confocal Raman spectrometer (Horiba Jobin-Yvon, LabRAM HR800, Paris, France) was used to determine the molecular vibration spectra. The concentration of Cd(II) was analyzed using an inductively coupled plasma emission spectrometer (ICP-OES Optima 8000, PerkinElmer, Waltham, MA, USA) while the concentration of MO was measured with an ultraviolet spectrophotometer (Lambda750, PerkinElmer, Waltham, MA, USA) at the wavelength of 463 nm.

Calcium (Ca), potassium (K), magnesium (Mg), and phosphorus (P) contents were determined in accordance with the method described by Li et al. (2016 (link)) by using an inductively-coupled plasma spectrometer (ICP-OES Optima 8000, Perkin Elmer, USA). The contents of Se, copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn) were determined in accordance with the method of Li et al. (2017 (link)) by using an inductively-coupled plasma mass spectrometer (ICP-MS, Thermo Fisher Scientific, USA). The daily intake of Se for adults was calculated on the basis of the Se concentrations as follows: daily intake of Se = Se concentrations in plants (μg kg⁻¹ DW) × conversion factor × daily intake of vegetables. The conversion factors 0.120, 0.116, 0.104, and 0.093 were used to convert the fresh weight to DW of the samples Se0, Se50, Se100, and Se200 in this study, respectively. The average daily vegetable intake for adults is 0.345 kg person⁻¹ day⁻¹ (Parveen et al., 2015 (link)).

The samples (cellular pellet or homogenate) were digested overnight with 200 µL of Nitric Acid 65%, Suprapur^® for trace analysis (Carlo Erba). After digestion, ultra-pure water (Merck) was added to the samples up to a volume of 2 mL and iron (Fe) was quantified with an Inductively Coupled Plasma‒Optical Emission Spectrometer (ICP-OES Optima 8000, Perkin Elmer, USA). Standards for the instrument calibration were prepared on the basis of mono-element certified reference solution ICP Standard (Merck) in the same acid matrix of the samples as well as the calibration blank. The method detection limits (MDL) estimated with 10 blanks was 5.4 µg/L, calculated according to the following equation: MDL= One-tailed student’s t-test (p = 0.99%; df = n − 1) × Sr. A laboratory-fortified matrix (LFM) was determined as quality control and a recovery rate of 111% was obtained.