title: Method Development for the Determination of Total Fluorine in Foods by Tandem Inductively Coupled Plasma Mass Spectrometry with a Mass-Shift Strategy.
abstract: A method for total F determination in food and tea samples based on a mass-shift strategy using tandem inductively coupled plasma quadrupole mass spectrometry (ICP-MS-MS) was developed. This method consists of four steps: (1) conversion of the hardly ionized F atoms to BaF+via ICP, (2) use of the first quadrupole (Q1, set at 157) to ensure only the m/z 157 ions (i.e.,138Ba19F+,157Gd+, and138Ba18OH+) enter the reaction cell (RC), (3) shifting138Ba19F+to a new mass138Ba19F(14NH3)3+by reacting with NH3in RC to avoid the interfering ions (i.e.,157Gd+and138Ba18OH+), and (4) passing interference-free138Ba19F(14NH3)3+to the second quadrupole (Q2, set at 208) for detection by the MS detector. The mass-shift process of the target F (in ICP and RC) expected to follow the path: F +138Ba+→157BaF++ 3NH3→208BaF(NH3)3+, while the reaction pathway of dominant157Gd+in RC proposed to157Gd++ NH3→157Gd14N1H++ nNH3→157Gd14N1H(14N1H3)n+(n = 0-5). Under the optimized setting of tandem MS (Q1 → Q2 = 157 → 208) and RC reaction gas flow rate (NH3/He = 10:90, 8.0 mL min-1), the background equivalent concentrations (BECs) and limits of detection (LODs) were 0.021 and 0.022 μg mL-1, respectively. The calibration curve was linear in the range between 0.1 and 10 μg mL-1, with a correlation coefficient of R2= 0.9999. The results obtained for 14 different food-related standard reference materials (SRMs) were in good agreement with the certified values on a 95% confidence level. The proposed method was then employed to evaluate the F contents of 13 branded tea samples. The total F concentrations ranged from 39.2 to 93.2 μg g-1. The tea infusions contained F between 23.5 and 85.4 μg g-1, with an extraction efficiency of 56.0-91.6%, and the water-soluble F contents of a Pu'er brick tea were 58.7, 21.4, 3.82, and 1.41 μg g-1for filtrates 1, 2, 3, and 4, respectively.
authors.affiliation: State Key Laboratory of Biogeology and Environmental Geology, School of Earth Sciences, China University of Geosciences , Wuhan, Hubei 430074, People's Republic of China.
authors.forename: Wei
authors.identifier: http://orcid.org/0000-0001-8799-1051
authors.initials: W
authors.lastname: Guo
authors.affiliation: State Key Laboratory of Biogeology and Environmental Geology, School of Earth Sciences, China University of Geosciences , Wuhan, Hubei 430074, People's Republic of China.
authors.forename: Lanlan
authors.initials: L
authors.lastname: Jin
authors.affiliation: State Key Laboratory of Biogeology and Environmental Geology, School of Earth Sciences, China University of Geosciences , Wuhan, Hubei 430074, People's Republic of China.
authors.forename: Shenghong
authors.initials: S
authors.lastname: Hu
authors.affiliation: State Key Laboratory of Biogeology and Environmental Geology, School of Earth Sciences, China University of Geosciences , Wuhan, Hubei 430074, People's Republic of China.
authors.forename: Qinghai
authors.initials: Q
authors.lastname: Guo
mesh_terms: D005461:Fluorine / Q000032:analysis*; D005506:Food Contamination / Q000032:analysis*; D053719:Tandem Mass Spectrometry / Q000295:instrumentation / Q000379:methods*; D013662:Tea / Q000737:chemistry*
chemical_list: D013662:Tea; D005461:Fluorine
keywords: atomic spectroscopic techniques; fluorine; food samples; food-related standard reference materials; mass-shift strategy; reaction cell; tandem inductively coupled plasma mass spectrometry; tea