Rapid analysis of tetracycline in honey by microwave plasma torch mass spectrometry with ablation samples†
To ensure honey foodstuff safety, a rapid and sensitive mass spectrometric analysis method with minimal or no prior sample pretreatment was developed for the direct detection of trace amounts of tetracycline (TC) in honey products by using a microwave plasma torch combined with mass spectrometry (MPT-MS). In the study, reagent ions observed in the MPT background spectrum were commonly formed from the MPT source-generated plasma reacting with discharge gas (Ar), H2O and O2 in air. Moreover, the ionization process of the MPT for target molecules (M) was summarized in the positive ion mode, including proton transfer, charge transfer, penning ionization, high energy electron–molecule reaction and so on. For semi-quantitative detection of tetracycline in honey by MPT-MS, considerations for each approach including adjustment of the microwave power and optimization of the discharge gas flow rate are discussed. The present research mainly focused on the most abundant precursor ion [M + H]+ (m/z 445) and its fragment ion (m/z 427) in collision-induced dissociated (CID) experiments. In addition, the semi-quantitative data by monitoring m/z 427 vs. the amounts of samples illustrated that the limit of detection (LOD) for tetracycline is 19.27 μg L−1, the linear dynamics range is from 0.05 mg L−1 to 10 mg L−1, and the correlation coefficient (R2) is 0.98812. Moreover, the direct detection of four kinds of honey samples was conducted, and the recoveries of samples were shown to be in the range of 84.35–112.86%, and relative standard deviations (RSD, n = 11) of the method were in the range of 0.35–3.59%. With advantages of rapidity and high sensitivity, this research showed that MPT-MS is promising to be applied in on-site analysis of samples which are a little glutinous involving several fields, such as drug quality control, food safety and criminal investigation.