Over the past few years more and more studies have been carried out in an attempt to utilize chemical profiles

of soil using a wide variety of analytical methods. The value of soil as evidence rests with its prevalence at

crime scenes and its transferability between the scene and the criminal. This can be of value for comparison if

the scene of crime is known, but could also be so in the identification of a scene. The main basis for the

comparison of sites to determine provenance is that soils vary from one place to another. The aim of this work

is to find simple methods to identify soil provenance based on FTIR and multivariate analysi

Atherton, Thomas

Baron, Mark

Croxton, Ruth

Gonzalez Cano, Rafael

Gonzalez-Rodriguez, Jose

Jimenez Perez, Rebeca

English

University of Lincoln Institutional Repository

             THE FORENSIC ANALYSIS OF SOIL BY                                FTIR WITH  MULTIVARIATE ANALYSIS                         Thomas Atherton(1), Mark Baron(1), Ruth Croxton(1), Jose Gonzalez-Rodriguez(1),                                                            Rafael Gonzalez(2), Rebeca Jimenez(1)                               (1) School of Natural and Applied Sciences, University of Lincoln, Lincoln (UK)                              (2) Departmento de Quimica Fisica y Termodinamica Aplicada, Universidad de Cordoba, EspanaOver the past few years more and more studies have been carried out in an attempt to utilize chemical profiles of soil using a wide variety of analytical methods. The value of soil as evidence rests with its prevalence at crime scenes and its transferability between the scene and the criminal. This can be of value for comparison if the scene of crime is known, but could also be so in the identification of a scene. The main basis for the comparison of sites to determine provenance is that soils vary from one place to another. The aim of this work is to find simple methods to identify soil provenance based on FTIR and multivariate analysisMATERIALS AND METHODSSoil samples were taken from a flowerbed site and a woodland site in Lincoln (UK).  At each site samples were taken to a depth of 10 cm using a soil corer along the transect at 50 cm intervals (Fig.1) . Five samples were taken from each site. The samples were air dried followed by sieving (2 mm), grinding and sieved again (125 μm). Samples were measured directly on a Golden Gate Attenuated Total-internal Reflection (ATR) accessory (Specac) housed in a Perkin-Elmer Spectrum 100 Fourier Transform Infrared Spectrometer (FTIR). Fig.1. Sampling at the woodland siteRESULTSFig.2. Normalised spectra for samples taken at different locations at the same flowerbed site. Fig.3. PC1(57 %)/PC2(29%) score plot for different locations at the same flowerbed siteFig.4. PC1(62%)/PC2(25%) score plot for combined flowerbed and woodland site data (averages)The most interesting region of the spectrum is the fingerprint region and so multivariate analysis of the data was carried out on the spectral region 1800-400 cm-1. PCA of the flowerbed site spectra show good separation of locations a-e in the PC1/2 score plot (figure 3). Site a and b are strongly correlated with positive values of PC1 whereas site d is correlated with negative values of PC1 and is negatively correlated with sites a and bTo investigate variation between different types of site, the data from the flowerbed site were combined with a similar data set from a woodland site. The data from the woodland set also demonstrated that a PC model could be used to discriminate between sampling locations at the same site showing separation of replicates from sampling locations a-e in the PC1/2 score plot. PCA of the combined data give separation of the two sites on the PC1/2 score plot (figure 4). The individual examples used are average sampling location spectra and it shows that the flowerbed locations show a good grouping. Woodland locations are much more widely spread. This seems largely due to site b which is closest to the flowerbed examples on PC1 and is also individually discriminated from the other examples (flowerbed and woodland) along PC2CONCLUSIONSIt has been shown that a simple procedure using ATR-FTIR appears to be sufficiently sensitive to detect spectral differences between samples taken from a site that seem to relate to the sampling location within the site. Analysis of the spectra from different sites shows that better separation is achieved between sites although the examples used here show that care needs to be taken with possible outliers. This is only a small data set but shows that it may be possible to discriminate between soil types for forensic investigations. Further work will concentrate on increasing the number of sample sites and locations to create a representative model for the soil types found in the Lincoln region. A classification model will be created with this data.INTRODUCTION

The forensic analysis of soil by FTIR with multivariate analysis

Soil has been utilised in criminal investigations for some time because of its prevalence and transferability. It is usually the physical characteristics that are studied, however the research carried out here aims to make use of the chemical profile of soil samples.

It is thought that the land type a soil sample comes from can lead to a particular chemical profile being present, which may make it possible to identify which land type a sample of evidential soil may have come from such as woodland or river sites. This would limit the possibilities significantly and so narrow down the scope for comparison. It could also be used to limit the areas required to be searched in certain cases. The ideal scenario would be that there was a general profile found for each land type and a characteristic profile for each land type location that could be used to identify each specific type of soil and its location specifically.

The research we are presenting in this work used sieved (2mm) soil samples taken from the top soil layer (about 10cm) that were then analysed using Fourier Transform Infrared (FTIR) spectroscopy. The spectra obtained were used as raw data in Principal Component Analysis (PCA). Results showed that it was possible to discriminate between soil samples with different soil type and different origins and, with some degree of error, between samples with similar soil type and different origins

Gonzalez, Rafael

Jimenez, Rebeca

Portuguese

The forensic analysis of soil by FTIR with multivariate analysis

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