Determination of trace inorganic antimony in PET-bottled soy sauce by ion chromatography-inductively coupled plasma mass spectrometry

Abstract

In this work, a method for the determination of trace inorganic antimony in polyethylene terephthalate (PET)-bottled soy sauce by ion chromatography-inductively coupled plasma mass spectrometry (IC-ICP-MS) was developed. Trace inorganic Sb(III) has been discovered in PET-bottled soy sauce but has been difficult to directly quantify by using IC-ICP-MS. To determine trace inorganic Sb(III) in soy sauce, the sample was first filtered through a weak cation exchange solid-phase extraction (SPE) column and then subsequently washed with 3.0 mL of 0.02% l-ascorbic acid and 3.0 mL of methanol. Finally, the SPE column was eluted with 1.0 mL of 0.1% NaOH +2% H2O2. Under such conditions, the enriched inorganic Sb(III) in the SPE column converted into inorganic Sb(V) and was successfully eluted. Finally, the amount of inorganic Sb(V) in the eluate, equal to the amount of inorganic Sb(III) in the sample, was quantitatively analyzed by IC-ICP-MS. Thus, inorganic Sb(III) in soy sauce was detected. In the above method, the limit of detection (LOD) of inorganic Sb(III) was 0.1 μg L−1, and the linear correlation coefficient r was 0.995 when the calibration curve ranged from 0.5 μg L−1 to 5.0 μg L−1.The RSD (n = 6) was 8.8%, and the recoveries (n = 6) were 91%~97%. Comparing the amount of inorganic Sb(III) (0.8 μg L−1–2.3 μg L−1) with the total antimony (1.7 μg L−1–6.6 μg L−1), we found that 25.6% to 50.0% of the total antimony in soy sauce was inorganic Sb(III). In addition, spiked inorganic Sb(III) slowly converted into other forms of antimony in soy sauce over time, but that conversion was negligible within 10 min after spiking and did not affect the recovery experiment.