Multi element calibration standard

Whole blood samples were analyzed using inductively coupled plasma mass spectrometry (ICP-MS; 7700x, Agilent, USA). The dilution solution consisted of 2% methanol, 0.05% Triton X-100 (Sigma Aldrich, USA), and 0.2% nitric acid (Kanto Chemical, Japan), and the calibration standard solution was 10 mg/L multi-element calibration standard (Perkin Elmer). Seven calibration standards of 0.05, 0.1, 0.5, 1, 2, 5, and 10 ppb were prepared and used for the blood addition experiments, and the samples were diluted 1:50 for analysis. The diluent contained 2% 1-butanol, 0.05% EDTA, 0.05% Triton X-100, and 1% NH₄OH (Sigma-Aldrich). A 10 mg/L multielement calibration standard (Agilent Technologies, USA) was used as the calibration standard solution. Serum and urine samples were analyzed with ICP-MS (Nexion 2000, Perkin Elmer, USA). To calibrate the nickel in serum and urine, seven calibration standards of 0.05, 0.1, 0.5, 1, 5, 10, and 20 ppb were used, and each sample was diluted 1:10 for analysis. Rhodium (10 mg/L; Agilent Technologies) was used as an internal standard for serum and urine analyses. The ICP-MS analysis conditions were as follows: radio frequency power was set to 1600 W; the sampler and skimmer cone were platinum; the nebulizer type was set to a concentric nebulizer to optimize the analysis; and the analysis mass was set to ⁶⁰Ni (Table S1).

The content of mineral elements was measured by ICP-MS (Agilent 7500 Series ICP-MS, Agilent Technologies, Santa Clara, CA, USA). The method of ICP-MS analysis for samples was carried out according to Mi’s method (Mi, Shang, Li et al., 2019). The analysis of each sample was performed in triplicate and quantified using external standards. The Environmental Calibration Standard (Part Number 5183-4688) and the Multi-Element Calibration Standard (Part Number 8500-6944), supplied by Agilent Technologies (Palo Alto, CA, USA), were used as the standard solution and the determination coefficient of the standard curve was higher than 0.99. Internal Standard Multi-Element Mix #4 (Part Number 5190-8593), containing ⁷²Ge, ¹¹⁵In, and ²⁰⁹Bi and supplied by Agilent Technologies (Palo Alto, CA, USA), was used to ensure the stability of the instrument. Samples were remeasured whenever the relative standard deviation (RSD) of internal standards was higher than 10%.

Ultrapure Type 2 water with a resistivity of 18.2 MΩ/cm, produced by a Merck Direct–Q UV water purification system (Merck KGaA, Darmstadt, Germany), was used for all applications. The trace metal grade HNO₃ was from Fisher Scientific, and the multi-element calibration standard and the ICP-MS internal standard mix were from Agilent Technologies.
Inductively coupled plasma mass spectrometry (ICP-MS) on Agilent 7800 series instrument was used to measure the metal content in wt Cu,Zn-SOD1 and G93A mutant samples. Metal concentrations were determined by the external calibration method by using multi-element calibration standard solutions in the range of 0.50–50 ppb in 2% trace metal grade HNO₃. The protein samples were diluted in 2% HNO₃ to a final concentration of 0.1 μM and 0.3 μM. The measurements were performed in He mode. For the ICP-MS instrument control Agilent MassHunter 4.4 software version C.01.04 was used under the following conditions: RF power 1550 W, nebulizer gas flow 1.03 L/min, auxiliary gas flow 0.90 L/min, plasma gas flow 15 L/min, nebulizer type: MicroMist, isotopes monitored: Cu-63 and Zn-66. The obtained results were analyzed by the program Origin 9 Pro.