Particle size analysis by laser diffraction

Abstract

Particle size distribution is a fundamental property of any sediment or soil, and particle size determination can provide important clues to sediment provenance. For forensic work, the particle size distribution of sometimes very small samples requires precise determination using a rapid and reliable method with a high resolution. A protocol has been developed using a Coulter™ LS230 laser granulometer, which can analyse particles in the size range 0.04 μm–2000μm. The technique is essentially non-destructive, permitting the recovery of critical samples, and has been demonstrated to have high precision for a range of soils, sediments and powders of interest in forensic investigations.

The role of forensic geoscience in wildlife crime detection

“…By their very nature soils and sediment vary not only within a spatially restricted site, but they may also contain similar characteristics to soils and sediments from other sites. This does not stop some practitioners from attempting to find matches between samples [5] [6], or at least to strive to find similarities [7]. The four samples were analysed by binocular microscopy to obtain a broad indication of the presence of detrital minerals and other debris.…”

The use of grain size distribution analysis of sediments andsoils in forensic enquiry

“…This example contrasts with another hit and run case documented in the forensic science literature ( [7] [8]). In this case sediment samples taken from the nearside and offside of a vehicle were compared to soil samples taken from two grassy verges (nearside and offside) at the scene of the crime.…”

“…All sample preparation techniques employed conformed to standard procedures [7]. Of the twenty samples taken from both spade 1 and 2, twelve of the samples from spade 1 and eleven of the samples from spade 2 were of a sufficient quantity for grain size distribution analysis.…”

“…Whilst a variety of different techniques have been employed during geological analyses to present these distributions ( [5] [6]), the ultimate aim of the researcher has been to describe the sediment and provide some environmental or palaeoenvironmental information as to the mechanisms by which the deposit has been transported and deposited to its final resting place ( [1]). Grain size distribution analysis is now being employed routinely during forensic casework analysis ( [7] [8]) although it will be shown in this paper that there are problems in using this well-established geological technique in forensic investigation in any way other than as a descriptive mechanism.…”

“…More recently still, there have been a number of papers published on the application of particle size distribution analysis to the analysis of soil and sediment samples in forensic investigations ( [7] [8] [13] and [14]). These papers have generally all provided the results of experimental studies (using both laser granulometry and sieving techniques) and have demonstrated, in the first instance, that it is possible to distinguish between soil and sediment samples taken from distinct geological areas.…”