## 1 Introduction  
Zeralenone (ZEN), mainly produced by _F. gramineum_ and other _Fusarium_ species, is one of the most important mycotoxins frequently found in maize, barley, wheat, and compound feeds (poultry, pig, dairy, cattle, and pet feeds) [1; 2; 3; 4]. A number of toxicities were revealed to be associated with ZEN, including teratogenicity, mutagenicity, nephrotoxicity, immunotoxicity, genotoxicity, and carcinogenicity [5]. It is also an estrogen analogue, which can affect the reproductive system and lead to abnormal reproductive functions [6; 7; 8; 9]. Due to its widespread occurrence and high toxicity, the maximum regulation level of 100-3000 ug/kg has been set for ZEN in feeds and feed materials by the European Union (EU) [10]. The European Food Safety Authority (EFSA) set a tolerable daily intake (TDI) for ZEN of 0.25 ug/kg body weight (BW) per day [11]. In recent years, masked mycotoxins generated by plants during detoxification have aroused more and more attention due to their potential toxicities and the difficulties in their detection [12; 13; 14]. As a masked form of ZEN, zeralenone-14-glucoside (ZEN-14G) was discovered to occur in grains such as maize (16.7%), barley (17.6%), and rice bran (60%), with the levels ranging from 1.3 \(\upmu\)g/kg to 274 \(\upmu\)g/kg [15; 16; 17]. Common foods such as fiber-enriched bread (29%), oatmeal (38%), and breakfast cereals (40%) were also contaminated with ZEN-14G [18]. ZEN-14G frequently co-occurs with ZEN in wheat (42%) and various feed products (formula feed, concentrated feed, and premixed feed) (35%) at concentration ranges of 17-104 \(\upmu\)g/kg and 0.89-15.31 \(\upmu\)g/kg, respectively [19; 20]. Although it has low toxicity, ZEN-14G could be converted to ZEN within the digestive tract of mammals, posing potential health risks to humans and/or animals [21; 22; 23]. Therefore, the European Commission declared that it is essential to assess the exposure of ZEN-14G apart from ZEN [24]. In recent years, comprehensive investigations on the absorption, distribution, metabolism, and excretion of ZEN have been extensively conducted in different animal species [25; 26; 27]. Among them, pigs were reported by [PERSON] et al. to have absorption ratios of approximately 80-85%, and [PERSON] et al. revealed that the absolute oral bioavailability was about 51.5% [25; 28]. In comparison, fewer studies could be found on ZEN-14G. An in vitro study carried out by [PERSON] et al. clearly indicated that ZEN-14G could pass through the cell barrier to be absorbed by a human colorectal cancer cell line (Caco-2) and further converted into ZEN [29]. [PERSON] et al. revealed that ZEN-14G could be absorbed into a human breast cancer cell line (MCF-7) and cleaved to ZEN by an estrogen-sensitive cell culture [30]. Additionally, as reported, more than 97% of ZEN-14G could be rapidly and efficiently hydrolyzed to ZEN by the colonic microbiota, and even completely cleaved after 24 h of fecal fermentation [12; 31]. The investigations of [PERSON] et al. indicated that ZEN-14G could be deglucosylated into ZEN in the liver microsomes of several animals (swine, rats, goats, cows, and chickens) and humans [32]. However, knowledge of the in vivo kinetics and transformations of ZEN-14G are still insufficient, hindering the assessment of the exposure risks to humans and animals related to this masked mycotoxin. The development of reliable and sensitive analytical technologies is the primary requirements for investigations into the in vivo kinetics and distributions of ZEN-14G and its metabolite, ZEN. Various analytical methods have been developed to detect ZEN, including the enzyme-linked immunosorbent assay (ELISA), thin-layer chromatography (TLC), gas chromatography-mass spectrometry (GC-MS), and high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) [25; 33; 34]. ELISA provides high sensitivity, but it only serves as a supplementary method due to its erratic accuracy and the possibility of cross-reactivity [35; 36].