Screening tests for fumonisins are based either on thin-layer chromatography (TLC) separation after appropriate clean-up of maize extracts or on commercially available enzyme-linked immunosorbent assays (ELISAs). Other immunologically based methods, such as dipstick (Schneider et al., 1995) and biosensor methods (Thompson & Maragos, 1996; Maragos, 1997; Mullett et al., 1998), have been described but have not found general use. Immunoaffinity columns have been designed to purify extracts before high-performance liquid chromatography (HPLC) separation and quantification of fumonisins B1, B2, and B3 analogues, and have also been used in a direct fluorimetric method for rapid determination of ‘total fumonisin’ (Duncan et al., 1998).
The TLC and other chromatographic methods for fumonisins have been reviewed (Shephard, 1998). The reversed-phase technique developed by Rottinghaus et al. (1992) has been used in surveys of contamination of maize with fumonisins (Shelby et al., 1994a). When combined with an efficient extract clean-up procedure based on use of immunoaffinity columns and detection by densitometry, TLC can be considered quantitative (Preis & Vargas, 2000).
The performance characteristics of screening tests for fumonisins in maize, based on interlaboratory collaborative studies, have not been reported in the literature. However, in-house comparisons between HPLC methods and the various screening tests have been described. The TLC method of Rottinghaus et al. (1992) has been compared with HPLC over a contamination range of fumonisin B1 of 1–250 mg/kg (correlation coefficient, r = 0.953; p < 0.0005; Schaafsma et al., 1998). The results obtained with a fibre-optic immunosensor in a direct competitive monoclonal antibody format with a fumonisin B1–fluorescein isothiocyanate conjugate compare favourably with those obtained with HPLC (Maragos, 1997).
The commercial availability of ELISA methods has made them popular for screening for fumonisin contamination. Although the antibodies used in ELISAs are raised against fumonisin B1, they generally have significant (but lower) cross-reactivity with fumonisins B2 and B3. The performance of ELISAs is generally assessed by comparison with HPLC determination of fumonisins and has been found to depend on the antibody used (Pestka et al., 1994; Usleber et al., 1994; Sydenham et al., 1996a,b; Kulisek & Hazebroek, 2000). The correlation between the results of HPLC and ELISA for naturally contaminated samples has been reported to vary from 0.51 (p < 0.05; Pestka et al., 1994) to 0.97 (p < 0.001; Sydenham et al., 1996a). However, such comparisons have generally shown an overall trend for the concentrations of ‘total fumonisins’ with ELISA to be greater than those determined in the same samples by HPLC

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