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 mineral contents, including zinc (Zn), calcium (Ca), potassium (K), magnesium (Mg), sodium (Na), iron (Fe), were determined using the AOAC method. For the analysis of all the minerals, a microwave digestion method was used for the sample preparation. We used 70% nitric acid (Chemitop Co., Ltd., Jincheon, Republic of Korea) as the digestion reagent, and ultrapure water (18.2 MΩ·cm or higher) was produced using an ultrapure water system (ELGA, High Wycombe, UK). For the sample preparation, 0.1 g of each sample was placed in a microwave vessel, and 10 mL of nitric acid solution was added. The sample was then subjected to microwave digestion using a microwave digestion system (MARS 6, CEM Corporation, Matthews, NC, USA) for 1 h. After digestion, the sample was allowed to cool, and deionized water (ddH₂O) was added to bring the final volume to 25 mL. The solution was filtered using a 0.45 μm syringe filter (for laboratory use) and used as the final sample. The five minerals (Ca, K, Mg, Na, Fe) were analyzed using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES, Agilent, Santa Clara, CA, USA), while the zinc (Zn) was analyzed using Inductively Coupled Plasma Mass Spectrometry (ICP-MS, Agilent, Santa Clara, CA, USA).

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).

Flour (0.25 g) was mixed with 5 mL 69% nitric acid (HNO₃) in teflon vessels then digested in a microwave reaction unit (CEM-Mars 6, USA) in “vegetable” mode with a four step heating program (step 1 ramp to 180 °C; step 2 hold 180 °C for 10 min; step 3 ramp to 205 °C for 20 min; step 4 cooling down). After digestion, samples were allowed to cool to room temperature and then were filtered through blue ribbon quantitative filter paper (Whatman Grade 589/3), the filtrates were mixed with distilled water and diluted with ultrapure water in 50 mL flasks. Digested solutions were stored in Sterilin tubes at 4 °C until analysis.

The analytical procedure for metals in seawater follows the guidelines outlined by USEPA [2 ] and Yüksel et al. [23 –25 (link)]. An atomic absorption spectrophotometer (AAS) (Shimadzu, AA-7000, Tokyo, Japan) was used in order to determine the levels of the metals (Cd, Cr, Pb, and Fe) that were present in the filtered water sample. The units of measurement were mg/L. The metal detection limits for Cr, Cd, Pb, and Fe were 0.005 mg/L, 0.001 mg/L, 0.008 mg/L, and 0.05 mg/L, respectively. With the use of the seawater-certified reference material (NASS-7), which was supplied by the National Research Council of Canada (NRCC), the analytical performance was assessed in terms of its precision as well as accuracy. Analysis of NASS-7 produced the metal recoveries that are presented in Table 2.
The analytical methodology used in the determination of metals in sediment follows the standards provided by USEPA [26 (link)] and Yüksel et al. [23 –25 (link)]. Samples of sediment were permitted to dry at ambient temperature before being sieved via a 2 mm mesh. A grinder was then used to pulverize the sediment samples. One gram of the crushed sediment sample was carefully placed into a digesting jar. The sample was then digested using a mixture of HCl and H₂NO₃ (Suprapur, Merck, Darmstadt, Germany) in a specific ratio (1 : 3). This digestion process took place in a microwave digester (MARS 6, CEM Corporation, USA) for a duration of four hours, maintaining a temperature of 90°C. Following the sample's cooling to the ambient temperature, it underwent filtration via filter paper (Whatman, with a pore size of 0.45 μm). To achieve a final volume of 50 mL, deionized water was added. The AAS was used to analyze the concentrations of Cd, Cr, Pb, and Fe. Two separate measurements were taken of each sample, and then an average value was determined. The units of measurement were mg/kg. The metal detection limits were as follows: 0.01 mg/kg for Cr, 0.02 mg/kg for Cd, 0.01 mg/kg for Pb, and 0.03 mg/kg for Fe.
An analytical blank was analyzed using the same procedure that was used to analyze the sample. The standard solutions were similarly formulated using the acid matrix that was used to determine the sample concentrations. The precision and accuracy of the analytical performance were evaluated by measuring the certified sediment reference material (PACS-3), which was provided by the National Research Council of Canada (NRCC). The analysis of this reference material was conducted using the identical techniques that were used to analyze the samples. Analysis of PACS-3 produced the metal recoveries that are presented in Table 3. All of the metal standard solutions (Certipur, Merck, Darmstadt, Germany) possessed a high standard of analytical quality.