Mars 6

The concentrations of nine elements—Ca, Na, Mg, Al, K, Fe, Mn, Cu, Zn—in each Baijiu sample were detected using an X-Series 2 ICP-MS (Thermo Fisher, Waltham, MA, USA) after being aged for 12, 16, and 20 months. The reagents used were 9 single-element standard solutions of Ca, Na, Mg, Al, K, Fe, Mn, Cu, and Zn with a concentration of 1000 mg/L, as well as Rh and Tl single-element standard solutions (Guobiao Testing & Certification, Beijing, China). The Thermo Fisher standard tune solution (Tune A) was utilized. 65% volume fraction nitric acid (Sigma-Aldrich, St. Louis, MO, USA). All experimental water was ultrapure water. First, each Baijiu sample was pretreated by microwave digestion (MARS6, CEM Corporation, Matthews, NC, USA). To do this, a 10 mL sample of Baijiu was placed in the microwave digestion tank, the solutions were concentrated to 4 mL in the acid extractor at 65 °C, and then add 6 mL of nitric acid. Cover the flask and let it stand for 1 h. Subsequently, the tank covered was tightened, and digestion was allowed to proceed according to the standard operation of the microwave digestion instrument. After cooling, the tank cover was slowly opened to release any pressure, and the inner cover was rinsed with a small amount of water. Then, the digestion tank was placed in an ultrasonic water bath to degasify it for 5 min. The volume of each solution was adjusted to 25 mL with water, and the resulting solutions were mixed well and set aside. A blank test was conducted simultaneously. The instrument parameters were optimized for the tuning solution. Internal standards of Rh and Tl (5 µg/L) were used to quantitatively analyze the mixed standard solutions of different elements in CCT mode. Among them, Na, Mg, Al, K, Ca, and Fe were combined together as a mixed standard solution, with series concentrations of 0 μg/L, 20 μg/L, 50 μg/L, 100 μg/L, 200 μg/L, 300 μg/L, 400 μg/L, and 500 μg/L. Mn, Cu, and Zn were grouped together as another mixed standard solution, with concentrations of 0 μg/L, 0.1 μg/L, 0.5 μg/L, 1 μg/L, 4 μg/L, 7 μg/L, and 10 μg/L.

The response surface methodology (RSM) was employed to optimize the extraction of quinine from bark using microwave-assisted extraction (MAE) and ultrasound-assisted extraction (UAE). Solvent concentration, extraction time, and temperature were evaluated as independent variables, with the tested conditions detailed in Table 1 (a and b). Additionally, Soxhlet extraction was performed as a reference method following the conditions described by Gatti et al. [39 (link)]. To prevent the sample-to-solvent ratio from influencing the results, the same ratio was consistently applied across all three methods.
MAE was conducted using a laboratory microwave oven (Mars 6, CEM Corporation, Matthews, NC, USA) operating at 1000 W, with an initial ramp time of 15 min. Samples of 1 g were weighed into microwave extraction tubes, followed by the addition of 40 mL of EtOH. For UAE, a bath sonicator (FS30D, Fisher Scientific, Waltham, MA, USA) with a frequency of 42 kHz and a power output of 100 W was used. In this method, 25 mg of the sample was weighed into 2 mL microtubes, and 1 mL of the solvent was added. The internal standard, caffeine, was added along with the solvent before starting the extraction process.
The optimal conditions determined were as follows: for MAE, 65% EtOH, a temperature of 130 °C, and an extraction time of 34 min; for UAE, 61% EtOH, a temperature of 25 °C, and an extraction time of 15 min. After extraction, the solid phase was separated from the liquid extract by centrifugation at 8000 rpm for 15 min (Sorvall ST8, Thermo Scientific, Waltham, MA, USA). The liquid extracts were filtered using 0.2 μm hydrophilic PTFE syringe filters (Titan 3, Thermo Scientific, Shanghai, China). The filtered extracts were then transferred to vials for chromatographic analysis.

About 0.05–0.1 g of the powder was weighed, and 10 mL of HNO₃ was added and digested using a microwave digestor (Mars 6; CEM Corporation, Matthews, NC, USA). A blank method was used during the digestion of each batch to eliminate the interference of reagents and solvents. For quality control, standard shrimp material (GBW10050a; Institute of Geophysical and Geochemical Exploration, Chinese Academy of Geological Sciences) was digested under the same conditions to ensure that the recoveries of tissues were controlled at 95–105%. Cadmium concentrations were determined for each tissue using ICP-MS, and Cd concentrations were expressed as μg-g⁻¹ dry weight (w/w).

The details about digestion process and quantification of metals in leaves have been fully explained elsewhere^{36 (link),37 (link)}. In brief, 7 mL of HNO₃, 2 mL of H₂O₂ and 1 mL of H₂O were added to 0.5 g of fresh leaves and heated at 200 °C during 45 min in a microwave digester (MARS 6 – CEM Corporation). The extraction for each point was performed in triplicate. The samples were filtered followed by adjusting the volume to 25 mL with Milli-Q water, and the concentrations of metals were measured using an Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES, Thermo Scientific iCAP 7000 Series). The metals included in the composition of tires, with given certified values and recoveries in the range of 43.41–91.14%, were analyzed (i.e., Al, Fe, Zn, Pb, Cu, Mg, Co, Ba and Cr). K (% Recovery 78.89) was also quantified, since it is a metal commonly detected during biomass burning. Moreover, more natural metals, such as Ca and Mn (%Recovery 88.02 and 111.01, respectively), were also measured. For the recovery percentage, the certified reference material NIST SRM 1575a—Trace elements in Pine Needles was used. The limits of detection (LOD) were calculated as 3 times the standard deviation of 10 blanks measurements divided by the slope of the analytical curve, while the limits of quantification (LOQ) were calculated similarly by multiplying the standard deviation by 10. The range values for LOD and LOQ were 2.58 × 10⁻⁷–0.0088 μg g⁻¹ and 8.59 × 10⁻⁷–0.029 μg g⁻¹, respectively.
In order to have an idea if the concentrations of metals found in this area were high—since there was no data from before the protest events – an extra sample of Araucaria heterophylla needles was collected at point E4 for the same chemical analysis. The Araucaria heterophylla concentrations of metals in the urban park were then compared with those found in the streets of Quito with a range in vehicular traffic intensity^{49 (link)}. It is important to compare the concentrations using the same plant species since it has been widely reported in literature that the accumulation capacity of plants for pollutants is species dependent^{62 (link),63 (link)}.

For the determination of Na, K, Mg and Ca contents, the protocol by D’Imperio et al. [40 (link)], with some modification of mineralization process, was used. Briefly, 0.3 g of OFI was accurately weighed in microwave digestion vessels, followed by the addition of 10 mL of 65% HNO₃ and digestion in a closed-vessel microwave assisted digestion system (MARS 6, CEM Corporation, Matthews, NC, USA). The two step digestion procedure was performed as follows: 15 min to reach 200 °C and 10 min at 200 °C (constant T; power set at 900–1050 W; 800 psi). Blanks, HNO₃ without the sample, were also prepared and digested using the same conditions, before the digested solutions were cooled and quantitatively transferred to 50 mL volumetric flasks, diluted to volume (50 mL) with ultrapure H₂O (Milli-Q Millipore 18 M Ω cm⁻¹, Burlington, Massachusetts, USA) and filtered using a 0.45 μm filter. The resulting solution was analysed by ion chromatography (Dionex DX120, Dionex Corporation, Sunnyvale, CA, USA) with a conductivity detector, using an IonPac CG12A guard column and an IonPac CS12A analytical column (Dionex Corporation, Sunnyvale, CA, USA) at 35 °C, flow 1 mL/min. The content of cations was calculated on the basis of the calibration curves previously obtained. Standard used: Multi Element IC Standard solution Fluka TraceCERT^®, Supelco^® (Merck KGaA, Darmstadt, Germany), contains cation element. The limits of detection (LOD) and quantification (LOQ) were defined as the minimum amounts at which the analyte can be reliably detected and quantified. As follows, the values of LOD and LOQ of cations in µg/L were Na (0.239, 0.717), K (1.732, 5.196), Mg (1.371, 4.113) and Ca (0.806, 2.418). The accuracy and precision of the cation measurement procedures were verified by testing the certified reference standard 1573a-Tomato Leaf powder of the National Institute for Standards and Technology (NIST), with an element recovery average of 102 ± 5.5%.