Multi-energy calibration: an easy strategy for fast and accurate determination of macro- and micro-nutrients in biomass waste samples by ICP OES

Abstract

Multi-energy calibration (MEC) was explored here for fast and accurate multi-element determination of Ca, Cu, Fe, K, Mg, Mn, Ni, and Zn in biomass waste samples by inductively coupled plasma optical emission spectrometry (ICP OES). For MEC, only two solutions (S₁ and S₂) per sample were prepared and used for the calibration procedure. 15 mL of solutions S₁ and S₂ were prepared for the determination of Cu, Fe, Mn, Ni, and Zn in order to contain 50% (v/v) sample + 50% (v/v) analyte standard solution, and 50% (v/v) sample + 50% (v/v) blank [1.0% (v/v) HNO₃], respectively. For Ca, K, and Mg diluted solutions were prepared by diluting 1.0 mL of S₂ with 1.0% (v/v) HNO₃ up to 50 mL. The calibration strategy was carried out by measuring S₁ and S₂ separately and the signal emission intensity of each analyte at different wavelengths by ICP OES is monitored. The obtained values are plotted on graphs that illustrate I(λ_i)^S₁ (x-axis) vs. I(λ_i)^S₂ (y-axis), and the slopes of the resulting curves provide the analyte concentrations. The accuracy of MEC was evaluated using SRM 1515 apple leaves and the results were in agreement at the 95% confidence level (t-test) with certified values and relative standard deviation < 4.7%. Recovery tests using cassava peel were carried out and the results obtained were in the ranges of 94–100%. The LOD was 0.6, 0.1, 0.07, 1.5, 0.6, 0.02, 0.04 and 0.03 μg g⁻¹ for Ca, Cu, Fe, K, Mg, Mn, Ni, and Zn, respectively. The calibration strategy was applied in cassava, green bean and banana peel, and the results were in the ranges of 1117 ± 22–4517 ± 32 (Ca), 4.00 ± 0.10–176.0 ± 2.0 (Cu), 29.5 ± 0.6–167.0 ± 2.0 (Fe), 11 250 ± 108–33 903 ± 780 (K), 1186 ± 21–4019 ± 77 (Mg), 43.0 ± 1.5–83.2 ± 2.2 (Mn), 2.4 ± 0.07–63.8 ± 0.6 (Ni), and 9.0 ± 0.4–241 ± 2.0 μg g⁻¹ (Zn). The proposed method applied here was compared to external standard calibration (ES) and the results were in agreement at the 95% confidence level (t-test).