Analysis of Forensic Soil Samples Via High‐Performance Liquid Chromatography and Ion Chromatography

Abstract

Traditional forensic soil comparisons are performed via physical and/or chemical examinations of color, texture, and mineral content, leaving any organic- or water-soluble fractions unexamined. This study uses high-performance liquid chromatography (HPLC) and ion chromatography (IC) to assess the qualitative and quantitative variation in these fractions of soil. Soil samples (n=120) were collected over the course of 3 weeks from urban, suburban, and rural locations in and around Lansing, MI. Additional samples from six of these locations (two urban, two suburban, and two rural) were collected once a week for 10 weeks for temporal analysis. Nine additional samples, equally spaced over a 1 m(2) grid, from these same six locations were collected for spatial analyses. Qualitative and quantitative analysis of the resultant chromatograms separated the 120 samples into 10 groups by HPLC and 23 groups by IC. This study shows that using HPLC and IC to analyze the organic- and water-soluble fractions of soil can successfully discriminate samples. Quantitative analysis of the results eliminates some false inclusions by providing further differentiation of samples. The results of this study indicate that adding HPLC and IC analyses to traditional forensic soil analysis schemes can improve overall sample differentiation. The methods used in this study were also able to detect both qualitative and quantitative variations in soil over a relatively small geographic area. This demonstration of soil heterogeneity underscores the importance of the collection of a representative known sample population when assessing a forensic soil comparison. Significant temporal variation was also demonstrated over the course of 10 weeks of sampling; however, samples were found to be consistent over shorter periods of time. Baseline levels of inorganic anions were determined via IC; these levels may be useful in assessing the significance of anions detected in soil from cases involving low explosives.

High Performance Liquid Chromatography as a valuable tool for geoforensic soil analysis

“…Bommarito et al 20 presented good chromatography results, with well resolved peaks and good signal-to-noise ratios, enabling unambiguous assignment of distinctive peaks, however the method had an unusually long run time (100 min). In light of the reduced budgets of police forces internationally, it is more important than ever to bear in mind the importance of developing analytical techniques that are cost effective and practical for implementation in a commercially oriented laboratory.…”

“…Longer run times reduce productivity and increase both the hard and soft costs to the laboratory, thereby reducing the likelihood of a technique being implemented by commercial end users and diminishing the ultimate impact of research beyond academia which is a key concern in the forensic science sector. Initial chromatographic conditions were therefore based on the research of Bommarito et al 20 with the aim of optimising the conditions to reduce the analysis time whilst maintaining the ability to retain and resolve a sufficient number of peaks to allow useful and accurate comparisons to be made.…”

“…These techniques are well established within forensic science since organic compounds are found in a fibres 32 , explosives 33−34 , accelerants 35 , alcohol 36−37 , drugs and poisons 37−39 . High Performance Liquid Chromatography (HPLC) is a widely used analytical technique, which has been reported to be potentially useful in the analysis of forensic soil samples [20][21][22]40 , however these studies used larger sample sizes than are typically available in forensic analysis and relatively long sample preparation and analysis times, which could be problematic in a casework scenario. The purpose of this study was to develop the sample collection, preparation, analysis and interpretative approaches used in order to assess the feasibility of the use of HPLC for soil analysis in a more forensically relevant context.…”

“…In addition to the weathered rock fragments, which currently attract the greatest scrutiny in geoforensic analyses, soil is comprised of biological material, liquid and gaseous components 28 . There is therefore a need for more techniques capable of the analysis of soil components other than the inorganic minerals 12,20 . The uppermost layers of soils are rich in organic matter 29−30 , which comprises living organisms, their intact remains and the organic compounds (molecules which, with very few exceptions, contains carbon-carbon bonds) produced by their decomposition plus any synthetic organic compounds added to the soil, such as agrochemicals or pollutants 31 .…”

“…This offers potential for false positive or false negative results since components acquired before, during and after a forensic event can become mixed 16−18,24−26 . Furthermore, many existing techniques require sample quantities in excess of the materials recovered from items of forensic interest, such as shoes, clothing or vehicles 5,[20][21][22]24,26 . It is, therefore, valuable to develop analytical methods that take into account these specific requirements of forensic casework 27 .…”