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Metals Analysis of Plant Tissue Extracts by Flame Atomic Absorption Spectrophotometry

Last revised July 22, 1997

Page contents (click to skip down):

* [Available analytes]
* [Overview of technique]
* [Considerations for plant material]
* [Sample requirements]

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Available analytes

- plant Calcium:
* [dry ash/double-acid extraction]
* [Flame-AA assay for Ca]
- plant Magnesium:
* [dry ash/double-acid extraction]
* [Flame-AA assay for Mg]
- plant Potassium:
* [dry ash/double-acid extraction]
* [Flame-AA assay for K]

Overview of technique

In flame atomic absorption spectroscopy a liquid sample is aspirated and mixed as an aerosol with combustible gasses (acetylene and air or acetylene and nitrous oxide.) The mixture is ignited in a flame of temperature ranging from 2100 to 2800 degrees C (depending on the fuel gas used.) During combustion, atoms of the element of interest in the sample are reduced to the atomic state. A light beam from a lamp whose cathode is made of the element being determined is passed through the flame into a monochronometer and detector. Free, unexcited ground state atoms of the element absorb light at characteristic wavelengths; this reduction of the light energy at the analytical wavelength is a measure of the amount of the element in the sample.

Considerations for plant tissue analysis

Samples must be in liquid form to be aspirated by the instrument. Therefore, solid material must be liquified by means of some form of extract or digest protocol. Procedures have been devised that make the total amount of an element in the sample available for assay or that use some particular property to extract that portion of the element which exists in some chemical forms but not in others.

The dry ash/double acid extraction method determines the total element content of the sample.

Sample requirements
The [dry ash/double-acid extraction] procedure calls for an amount of material that yields 0.5 gm. after drying and grinding.

Allen, S. E., et al. 1974.
Chemical Analysis of Ecological Materials. John Wiley and Sons, New York.

Jones, J. B. Jr., B. Wolf and H. A. Mills. 1990.
Organic matter destruction procedures. pp.195-6. In Plant Analysis Handbook. Micro-Macro Publishing, Inc., Athens, GA.

U. S. Environmental Protection Agency. 1983.
Metals (atomic absorption methods). pp. 55-72. In Methods for Chemical Analysis of Water and Wastes, EPA-600/4-79-020. U.S.E.P.A., Cincinnati, Ohio, USA.

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