# A Review: Sample Preparation and Chromatographic Technologies for Detection of Aflatoxins in Foods
## 3 Chromatography
### Thin Layer Chromatography
The method could detect aflat in wine as low as 0.02 \(\upmu\)g/L, 8\(\times\) more sensitive than TLC [206]. The procedure has been extended and modified for different food matrices [207; 208]. For example, using the same derivatization procedures, [PERSON] [209] developed an LC-FLD method for aflat analysis in green coffee and peanut butter. Recoveries of aflat spiked at 1-15 ppb ranged from 72 to 104%; [PERSON] and [PERSON] [210] replaced TFA with hydrochloric acid for derivatization and achieved the detection of aflat at subpicogram levels in corn using a laser fluorescence detector; [PERSON] and [PERSON] [211] derivatized aflatoxin M\({}_{1}\) extracts from milk and dairy products using TFA, followed by an LC-FLD analysis. Aflatoxin M\({}_{1}\) could be detected at as low as 0.3 ppb and recoveries were 93-125% at 1 ppb in spiked matrices. An AOAC official method was also developed for aflatoxin analysis in corn and peanut butter using TFA precolumn derivatization, a C18 analytical column and water-methanol-acetonitrile as the mobile phase [212]. TFA derivatization was companied by considerable disadvantages. These included peak broadening caused by residual TFA and instability of the derivatization products, aflatoxin B\({}_{2}\)a and G\({}_{2}\)a in methanol [205; 208; 213]. Additionally, TFA derivatization had to be conducted offline prior to LC separation, making it less desirable compared to post-column derivatization, which could be integrated with LC-FLD as an online operation. Similar to precolumn derivatization, post-column derivatization started with the finding that iodination of aflatoxin B1 and G1 exhibit strong fluorescence [214]. [PERSON] and [PERSON] [215] developed a prototype post-column derivatization device, in which an iodine solution was pumped from a reservoir and mixed with eluted aflat in a reaction coil (3000 mm \(\times\) 0.5 mm, 60 \({}^{\circ}\)C) inserted between the LC column and FLD. This led to a 50\(\times\) increase in sensitivity of aflat. Encouraged by the promising results, researchers conducted a series of studies to optimize this post-column derivatization method, focusing on compositions of the mobile phase, iodine reagent flowrates, reaction temperatures, iodine concentrations, confirmation of derivatization products using MS, etc. [216; 217; 218; 219; 220; 221; 222; 223]. Despite the wide acceptance of iodine-based post column derivatization, [PERSON] and his colleagues [224; 225; 226] developed another online post-column derivatization based on bromination of aflat to simplify derivatization steps and lower instrument cost. In their approach, bromine is generated from bromide (e.g., potassium bromide) added into the mobile phase and reacted with eluted aflat in a post-column electrochemical cell, namely KOBRA-cell, prior to FLD analysis. The bromine concentration can be carefully controlled by the generating current, maximizing fluorescence intensity. Using this approach, aflat could be detected at an on-column mass at 20-40 pg. Other valuable signal-enhancement techniques were also developed [227; 228; 229; 230]. [PERSON] et al. [227] developed a more cost effective bromination method using pyridinium bromide perbromide as the derivatization agent. To further increase sensitivity, [PERSON] et al. [228] and [PERSON] et al. [229] evaluated the addition of cyclodext as a fluorescence enhancer. [PERSON] [230] reported the first photochemical derivatization method of aflat. Compared to chemical derivatization, this approach does not need the addition of any chemical reagents. Aflatoxins were derivatized using UV generated by a photochemical reactor and could be detected in corn below 1 ppb. In recent years, there have been notable efforts to evaluate and compare photochemical derivatization to chemical derivatization. Studies by [PERSON] et al. [231] and [PERSON] et al. [232] demonstrate photochemical derivatization is as efficient as chemical derivatization using bromine or iodine.