Aflatoxin Standards

A large source of error in the analysis is due to incorrectly prepared aflatoxin standards. In a check sample series, standards were found that contained more or less than the stated amount of aflatoxins when compared with a correctly prepared standard sent out with the study. It is very important to work with pure and accurate standards if accurate quantitative and qualitative results are to be obtained. Aflatoxin standards may be purchased from chemical distributors but need to be checked by means of TLC or liquid chromatography (LC) to ensure that they are pure. Small quantities of aflatoxin standards are sometimes available from organizations such as the FDA without cost.

Crystalline aflatoxin standards should be handled in a glove box because of their carcinogenicity and the electrostatic nature of the crystals. Because of the difficulty in handling the crystalline material, the aflatoxins are often received as dry films deposited in a precise amount in the bottom of a glass vial. The contents of the vial should be dissolved in the solvent (benzene-acetonitrile, 98:2 v/v) and mixed on a vor tex mixer for 1 min since the standards do not dissolve rapidly. After mixing, the solution is transferred to a screw-cap vial and the ultraviolet spectra measured between 370 and 330 nm. The concentration can then be calculated using the values listed in the AOAC International Official Method 971.22. The standards are applied to a TLC plate to verify the purity. The solutions must be stored in a closed and sealed vial in a refrigerator at 4-8°C. Mixtures of the four major aflatoxins can be prepared by diluting the concentrated stock solutions. The mixture most often used contains aflatoxins B1 and G1 at 1.0 |gmL_1 and B2 and G2 at 0.2 |g mL_1. This ratio between the four aflatoxins approximates to the ratio found in some sample extracts. The aflatoxins in benzene-acetonitrile (98:2 v/v) are stable when stored in a closed and sealed vial in a refrigerator at 4-8°C. Evaporation or decomposition of the aflatoxins can be detected using TLC or LC, shown by additional spots or additional peaks or an increase or decrease in the fluorescent intensity, as evidenced by unusual area integration values from the LC detector or TLC den-sitometer.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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