Meixner Test for Amatoxins

by Michael Kuo

The deadliest mushroom toxins are the "amatoxins," which are found in several species of Amanita (the Destroying Angel, for example), Galerina marginata (the "Galerina autumnalis" of field guides), and a few other mushrooms. This page discusses these toxins and how they affect the body. The presence of amatoxins can be revealed through the Meixner test (also known as the "Wieland Test"), if you have access to concentrated hydrochloric acid and experience with the safe use of this dangerous chemical. In other words: Don't try this at home!

Equipment

You will need concentrated hydrochloric acid, a newspaper, mortars and pestles, a pipette, rubber gloves, and a laboratory hood under which you will perform the test. If you are performing the test on dried mushrooms, you will need some 70% ethanol to rehydrate your mushrooms.

Control

Always perform the test with positive and negative controls, to be sure that your results are actually informative. In addition to the mushroom in question, test a mushroom known to contain the toxins, as well as a mushroom you are certain does not contain them--say, a Russula. With controls, you can be more sure that you have performed the test correctly and do not have a "false positive" or "false negative."

Method

Put a small portion of each mushroom in a mortar, and grind it to a paste with a pestle. Be sure to use separate mortars and pestles for each mushroom, in order to avoid contamination. You will probably want to label the mortars in order to avoid confusion about which paste corresponds to which mushroom, since they will all look more or less the same after grinding. Fresh mushrooms will turn into paste easily with grinding, but if you are working with dried mushrooms you will need to add a few drops of 70-percent ethanol to rehydrate the material. Use only 70-percent ethanol for rehydrating; scientists have determined that it produces the most accurate results for dried material.

Cut strips from the margins of newspaper pages, where no ink is present; you will need one strip for each mushroom. Clearly label each strip near one end, leaving plenty of room to perform the test without interference from ink or lead. Newspaper has high lignin content, and works much better for the Meixner test than other types of paper, which may produce bad results.

Using the pestles, your fingers, or any tools that seem appropriate, spread paste from each mushroom sample on its corresponding strip of newspaper. If you use your fingers, or use one tool for this process, be sure to avoid contamination by washing thoroughly in between samples. Scrape away excess material, so that the newspaper strips have been soaked with the paste, but are not coated with mushroom material.

Place the strips under the laboratory hood, turn on the fan, and wait until they are completely dry. There is some evidence that exposure to heat or wind stress (say, from a hair dryer) at this point can influence your results, so the best idea is to be patient and wait for the strips to dry.

Put on some rubber gloves, and some goggles. Using a pipette, place a tiny drop of concentrated hydrochloric acid on each newspaper strip, where it absorbed the mushroom paste. Be careful! Hydrochloric acid is very dangerous.

After a few minutes, color reactions should begin to appear on the strips. The positive reaction is bluish, and the negative reaction is, well, something else; it depends on what you used as your negative control. The Meixner test is known to produce reddish reactions for some mushrooms, though the significance of the reaction is apparently unclear. In the illustrations above, Russula crustosa is the negative control, and the color change with hydrochloric acid is sort of pinkish. Galerina marginata is the positive control in the illustrations. The mushroom under study is an un-named amanita I have called the Sand Dune Amanita.

The color changes may take a while to develop, and reactions that look faint at first may become more noticeable over the course of an hour or two; be sure to wait a while before giving up on color changes. Once the hydrochloric acid has dried, you can take the strips out of the hood, and away from the lab, fairly safely. Place them in separate envelopes, and be sure not to touch the spot of the acid droplet (wash your hands thoroughly if you do so by accident).

Within half a day or so the colors will begin to fade. I recommend taking photos in natural light within an hour, or scanning the strips of paper in a flat-bed scanner (wash the glass thoroughly when you're done).

Thanks to Rodham Tulloss and Heather Hallen for advice on the Meixner test, and thanks to Ken Osborne for patiently working with me.

Cite this page as:

Kuo, M. (2004, November). Meixner test for amatoxins. Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.com/meixner.html

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