Joint International Conference on Long-term Experiments ...

that spot intensity could be regenerated by reheating the plate. This fading was unlike fading
shown by aflatoxins, in that aflatoxin fading is minimized when plates are protected from
light and, in some cases, from atmospheric contaminants such as ozone. With
sterigmatocystin, I surmised that the activity of the silica gel was causing the observed
behaviour. I concluded that the problem would be solved if the silica was held in an
activated state, which could be accomplished by sealing the plate with paraffin or silicone.
Various mixtures of silicone-anhydrous ether were applied by spraying before arriving at the
mixture described here.
In addition to sealing the plate, the silicone also enhanced the fluorescence of the
sterigmatocystin spots approximately 10-fold. This type of fluorescent spot enhancement
had been noted earlier by other researchers (17), who used viscous organic solvents such as
mixtures of liquid paraffin and n-hexane as a spray.
No significant loss in fluorescent intensity of sterigmatocystin was observed in plates
that were stored unprotected from light and moisture for 2 weeks.
A sterigmatocystin standard curve gave a linear response in the range from 3 to 106 ng, with
a correlation coefficient (r) of 0.9994. One ng sterigmatocyctin standard is easily detected,
while 3 ng represents the lowest amount quantitated at a signal-to-noise ratio of 3:1.
The proposed method is simple, practical, rapid, economical, and precise. Incorporation
of calcium chloride solution into the sample extract before hexane defatting and methylene
chloride partitioning solved emulsion problems previously encountered when using other
methods. The elimination of emulsion formation during separatory funnel cleaup and
partitioning has possibly provided the breakthrough necessary to improve analytical
methods used for the determination of other mycotoxins. The concentration of calcium
chloride used may vary among commodities. The minimum concentration required to be
effective in this method has not been thoroughly investigated. Remaining TLC interferences
are eliminated by passing the methylene chloride extract through the cupric carbonate
column. Further work is in progress on the use of the method to determine other
mycotoxins.
REFERENCES
1. 1.Purchase, I., F., H., & van der Watt, J. J. (1970), Food Cosmet, Toxicol. 8, 289-296.
2. 2.van der Watt, J.J. (1974) Mycotoxins, Elsevier Scientific Publishing Co., Amsterdam,
The Netherlands, pp. 369-382
3. 3.Bartos, J. & Matyas, Z. (1983) Vet. Med. (Prague) 28, 189-192
4. 4.Nowotny, P., Baltes, W., Kroenert, W., & Weber, R. (1983) Lebensmittelchem.
Gerichtl. Chem 37, 71-72
5. 5.Official Methods of Analysis (1984) 14 th Ed., AOAC, Arlington, VA
565