Destructive Soil Analysis Methods

Destructive methods, often called pyrolysis, are also used to determine components in soil. This commonly involves heating soil to a high temperature and analyzing the components given off. Often, analysis is by GC, mass spectrometry, or a combination of the two, although spectroscopic analysis is also possible [16]. 

Hyphenated methods can be divided into two types those that do and those that do not destroy the sample in the process of analysis. Spectrophotometric methods, thermal conductivity, and refractive index methods of detection do not destroy the sample. Chromatographic methods using flame ionization and similar detection methods destroy the sample as it is detected. Any hyphenated method that involves MS or thermal analysis (TA) will also destroy the sample. In most cases, the identification of the components in soil is most important, so the destruction of the analyte is of less importance. 

Comparative studies were performed to evaluate microwave digestion with conventional sample destruction procedures. These included the analysis of shellfish, meats, rocks, and soils. Generally, comparable accuracy at much shorter digestion time was found for the MAE vs the classical digestion method (39). 

It is well known that botanical materials may contain various soil and/or mineral fractions, and may therefore be difficult to dissolve [15,16]. Since the white clover material contains silicates, it was necessary to treat the material with HF to ensure complete digestion and recovery of the total metal content. Results obtained with destructive methods without using HF were therefore withdrawn, unless the laboratory could prove that the residue of the digest did not contain the elements determined. Neutron activation analysis was an important method for identifying the losses due to incomplete digestion. 

The CS variable, chemical concentration in soil, is a site-specific value measured by performing U.S. Environmental Protection Agency (USEPA) SW-846 Method 3050 (10) on site soil samples for metal analysis. This is a destructive method involving a hot acid digestion with nitric acid (HNO3) and water, and results in a total metals analysis rather than a determination of a specific species or soil fraction of metal. The underlying assumption, in quantifying metal intake by the above formula, is that all of the As measured by the total metal analysis is quantified as the absorbed dose. 

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