تسجيل الدخول

تسجيل

CHEMICAL PROPERTIES

المؤلف:  Max M. Houck، Jay A. Siegel

المصدر:  Fundamentals of Forensic Science

الجزء والصفحة:  p434-436

2026-08-18

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CHEMICAL PROPERTIES

Chemical analysis of soil is performed less frequently than physical analysis. This is because there is no type of forensic classification for soils and because there is so much variation in chemical content of soils from similar locations. In spite of this, valuable information about the association of known and unknown soil samples can be gained by careful chemical analysis. One method receiving increased attention is high performance liquid chromatography (HPLC). A soil sample is extracted with an organic solvent such as acetonitrile and then analyzed by HPLC. The resulting chromatogram gives a profile of many of the organic substances found in the soil. This provides excellent comparative data for known and unknown samples. A liquid chromatogram of a soil sample is shown in Figure 1. The pseudo-three-dimensional appearance is due to simultaneous measurements of time, absorbance wavelengths, and intensity of absorption. Infrared spectrophotometry of soils is also a useful technique. It is possible, for example, to obtain the infrared spectrum of a bulk soil sample, then extract the organic fraction and obtain its infrared spectrum, and then by spectral subtraction, obtain the infrared spectrum of the rest of the mostly inorganic fraction. Other tests are sometimes done on organic fractions of soil. These include oxygen bioavailability and DNA analysis on bacteria or other microbes in the soil. The latter is a relatively new technique and is quite complex and expensive.

FIGURE 1 Liquid chromatogram of a soil sample extracted with acetonitrile. This is a pseudo three-dimensional plot. Many chromatograms are collected, each one at a different wavelength of the UV detector. The plot of wavelength versus time versus absorbance has a three-dimensional appearance. This presents much more data for comparison than can be gained from a single chromatogram.

There have been a number of other celebrated cases where soil analysis has had a major effect. In South Dakota v. Eugene Moeller in 1990, Becky O’Connell was kidnapped and murdered near a small town in South Dakota. The accused claimed that he had been elsewhere when the crime occurred. Soil taken from the wheel wells of his truck was similar chemically and physically to soil from the rural area where the victim was found. The soil from the area where the accused claimed to have been at the time of the crime had different chemical and physical characteristics. He was convicted of the crime in part because the soil analysis called his alibi into question. Enrico Camerena was a United States Drug Enforcement Administration agent working in Mexico when he was kidnapped and murdered in February 1985 after leaving the United States Consulate in Guadalajara. His body was subsequently recovered from the grave where he had been buried. An FBI forensic geologist saw the body on television and noted that soil that was adhering to the body was different from soils in the location where authorities had indicated the body had been recovered. Subsequent investigation of the soil led investigators to the exact location where the body had been buried. This information indicated that a cover up of the murder was taking place.