HPLC determination of fumonisin mycotoxins in maize: a comparative study of naphthalene-2,3-dicarboxaldehyde and o-phthaldialdehyde derivatization reagents for fluorescence and diode array detection.

Fumonisins are mycotoxins produced by various species of Fusarium and occur naturally in contaminated maize and maize-based foods. Ingestion of fumonisins has considerable health implications for humans and animals. Since fumonisins lack a useful chromophore or fluorophore, their determination in maize is routinely achieved via HPLC with fluorescence detection (FLD) after precolumn derivatization. This study optimized naphthalene-2,3-dicarboxaldehyde (NDA) derivatization of fumonisins in naturally contaminated maize following strong anion exchange (SAX) solid phase extraction (SPE) clean-up and utilizing diode array detection (DAD) as a practical alternative simultaneously to FLD. The limit of detection (LOD) for fumonisin B(1) (FB(1)), fumonisin B(2) (FB(2)) and fumonisin B(3) (FB(3)) with FLD was 0.11 ng, 0.50 ng and 0.27 ng, respectively, and with DAD it was 13.8 ng, 12.5 ng and 6.6 ng, respectively injected on column. The coefficient of variation (CV, n = 6) for FB(1), FB(2) and FB(3) in a naturally contaminated samples obtained with FLD was 2.6%, 1.8% and 5.3%, respectively, compared to 6.0%, 3.4% and 9.5%, respectively, obtained with DAD. Subsequently the optimized NDA derivatization was compared to the widely used o-phthaldialdehyde (OPA) derivatization agent as well as alternative sample clean-up with immunoaffinity column (IAC) by analyzing naturally contaminated maize samples (n = 15) ranging in total fumonisin (TFB = FB(1)+FB(2)+FB(3)) levels from 106 to 6000 µg/kg. After immunoaffinity column clean-up of extracted samples, the recoveries of spiked maize samples for NDA-FLD of FB(1), FB(2) and FB(3) were 62%, 94% and 64%, respectively. NDA proved to be an effective derivatization reagent of fumonisin in naturally contaminated maize samples following IAC clean-up, except for DAD at TFB levels below 1000 µg/kg. In contrast NDA derivatization following SAX clean-up produced results comparable to OPA only for levels below 1000 µg/kg. Aside from the difference in detection limits, FLD and DAD produced comparable results irrespective of the clean-up method or the derivatization agent.

Determination of fumonisins in maize by HPLC with ultraviolet detection of o-phthaldialdehyde derivatives.

Fumonisins are mycotoxins that are produced by various Fusarium species and occur naturally in maize and maize-based foods. Fumonisins are carcinogenic, causing liver cancer in rats, and are associated with oesophageal cancer and neural tube defects in humans. Analytical methods for individual fumonisin analogues in maize rely on reversed-phase high-performance liquid chromatographic (HPLC) separation after suitable extraction and clean-up. As fumonisins lack a useful chromophore or fluorophore, HPLC detection is achieved by suitable derivatization and sensitive, specific fluorescence detection. A widely used and validated method involves extract clean-up on strong anion exchange solid phase extraction cartridges and pre-column derivatization with o-phthaldialdehyde (OPA). However, many laboratories requiring infrequent fumonisin analysis are only equipped with HPLC with ultraviolet (UV) detection. A HPLC system equipped with both UV and fluorescence detectors connected in series was used to determine the extent to which UV offers an alternative to fluorescence detection in the above analytical method. Comparison of the detection systems using fumonisin standards indicated that fluorescence is about 20-times more sensitive than UV. Analysis of maize samples with differing fumonisin contamination levels indicated that, at fumonisin B1 levels above 1,000 µg/kg, the two detection systems were comparable and gave repeatabilities equal or less than 10% on six replicate analyses. Although a sensitive fumonisin analysis requires fluorescence detection, UV may offer an alternative in certain circumstances.