# A Review: Sample Preparation and Chromatographic Technologies for Detection of Aflatoxins in Foods
## 2 Sample Preparation
### Extraction
#### 2.2.2 Solid Phase Extraction
Samples were first mixed with the PD-MNPs and then placed on a magnet to precipitate PD-MNPs. Absorbed aflat were eluted from the PD-MNPs with acetonitrile-methanol (1:1, _v/v_). Under the optimized MSPE conditions, recoveries of aflat ranged from 59% for aflatoxin G\({}_{2}\) to 89% for aflatoxin B\({}_{1}\). Best suited for extracting aflat from liquid matrices, MSPE applications have additionally been investigated for the determination of aflatoxin M\({}_{1}\) in milk ([PERSON] et al., 2018). For solid food matrices, samples need to be extracted, filtered and mixed with buffers, making the extracts compatible to the MSPE step because physicochemical properties of synthesized magnetic nanoparticles are sensitive to temperature, polarity and pH of the extracts. [PERSON] et al. (2019) applied MSPE for the determination of aflat B\({}_{1}\) and B\({}_{2}\) in cereal products. In this study, magnetic nanoparticles coated with 3-(trimethoxysilyl)-1-propanthiol (TMSPT) and modified with 2-amino-5-mercapto-1,3,4-thiadiazole (AMT) were used as the adsorbent. Prior to the MSPE step, rice samples were extracted with a mixture of methanol: PBS solution (pH 7.4) and the resulting extracts were filtered prior to dilution with PBS solution. Corn samples were similarly extracted with an additional partitioning step using hexane. Such pretreatment steps, however, reduce the simplicity and efficiency of MSPE clean-up. Furthermore, magnetic nanoparticles with high selectivity and absorption efficiency are rarely commercially available. The cost, time and expertise required to synthesize and characterize magnetic nanoparticles contribute to the low attention to MSPE among mycotoxin labs. The application of solid phase micro extraction (SPME) for aflatoxin analysis is another area of development worth noting. Originally, SPME was mainly coupled with gas chromatography to analyze volatile compounds but has been extended to LC analysis for semi- and non-volatile compounds ([PERSON] et al., 2018; [PERSON] et al., 2019). [PERSON] et al. (2019) developed an online SPME procedure by placing an in-house SPME device (a porous capillary column with divinylbenzene polymer as the stationary phase, film thickness of 17 \(\upmu\)m) between the injection loop and needle of the autosampler promoting selective elution of aflat from sample extracts for LC-MS analysis. The SPME procedure showed a significant increase in sensitivity compared to the direct injection of the same sample extract. The within-day and between-day precision of aflat at 1.0 ng/mL were below 3.3% and 7.7%. However, the whole process was highly customized and needed to use in-house software and hardware to operate the SPME device. In another study, [PERSON] et al. (2018) used commercially available SPME devices coupled with LC-FLD for the determination of aflat in cereal flows. Flour extracts were prepared using a methanol:phosphate buffer, followed by a SPME extraction using a fiber coated with polydimethylsiloxane/divinylbenzene (PDMS/DVB). Key parameters such as fiber polarity, temperature, pH, ionic strength, adsorption and desorption time, mobile phase, were evaluated. Under optimized conditions, the recoveries of aflatoxin B\({}_{1}\) at 10 and 1 ng/g were 60% \(\pm\) 7% and 67% \(\pm\) 7% (14 h of extraction) and 52% \(\pm\) 4% and 56% \(\pm\) 2% (30 min of extraction), respectively, suggesting limited adsorption capacity of the fiber and the need of using an internal standard to compensate insufficient extraction efficiency. Currently, SPME is not widely used for aflatoxin analysis, though it has the potential to be automated. To make SPME more practical and applicable for aflatoxin analysis, one should address the high cost and limited selection of stationary phases of SPME in future studies.