Determination of 9,10-anthraquinone in tea consumed in Shandong Province of China
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ORIGINAL PAPER
Determination of 9,10‑anthraquinone in tea consumed in Shandong Province of China Lijun Shao1 · Guoling Wang1 · Mingcai Guo1 · Luping Yang1 · Dafeng Jiang1 · Renpeng Li1 · Jing Zhu2 Received: 7 November 2019 / Accepted: 15 June 2020 © Institute of Chemistry, Slovak Academy of Sciences 2020
Abstract In this study, 170 tea samples were investigated for the occurrence of 9,10-anthraquinone (AQ), which was collected from Shandong Province of China in 2018. The contamination levels of AQ were detected by a combination of QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) procedure with gas chromatography tandem mass spectrometry. Under the optimal conditions, the linear range for AQ was from 10 to 200 ng/mL. The recoveries ranged from 95.6% to 101%, with the coefficient of variation less than 3.99%. The limits of detection and quantification for AQ were 0.001 and 0.003 mg/kg, respectively. Owing to the good accuracy, precision, and high sensitivity, the proposed method is suitable for the determination of trace AQ in tea. The results demonstrated that AQ was detected in 67.1% of tea samples, with the average concentration of 0.0160 mg/kg. The contamination levels varied from tea types and sale locations. The individual average values of AQ in green tea, black tea, oolong tea, and pu-erh tea products were 0.0161 mg/kg, 0.0140 mg/kg, 180 was higher than that of m/z 208 > 152, so m/z 208 > 180 was chosen as the quantitative ion pair and m/z 208 > 152 as the qualitative ion pair. Table 2 shows parameters and collision energies of parent and daughter ions for AQ and d8-AQ.
Solvent
Added (ng/mL)
Determined Recovery (%) (ng/mL)
RSD (%)
Acetonitrile Acetone Ethyl acetate n-Hexane
50 50 50 50
49.3 46.0 40.1 54.1
5.30 7.94 10.55 17.76
98.6 92.0 80.2 108.2
Selection of purification method In this experiment, several commonly used adsorbents in QuEChERS method were studied and compared. As a purifying agent, florid silica can remove some polar compounds, but cannot remove pigments. Graphitized black carbon (GCB) is an efficient adsorbent for removing pigments, but it can retain planar compounds (Chamkasem et al. 2013). PSA can remove not only fatty acids and organic acids but also some pigments and sugar impurities. Moreover, PSA has less adsorption on pesticides. So PSA was chosen as the main adsorbent. In addition, C18 and anhydrous N a2SO4 were used to remove lipophilic, fat residue, and excess water from the extract, respectively.
Selection of solvent for extraction
GC–MS/MS method validation
Tea is a dry sample, which needs to be immersed in deionized water for 30 min before extraction with organic solvents to facilitate the full extraction of the target compound. Acetonitrile, acetone, ethyl acetate, and n-hexane were used as solvents for extraction. It was found that the recoveries of ethyl acetate and n-hexane were not stable, while the recoveries of acetone and acetonitrile could meet the requirements. However, acetone extracted more impurities and the extract was dark in color. Whe
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