Abstract
This paper describes a method for determining the density of contact trace objects with magnetic levitation (MagLev). MagLev measurements accurately determine the density (± 0.0002 g/cm(3) ) of a diamagnetic object and are compatible with objects that are nonuniform in shape and size. The MagLev device (composed of two permanent magnets with like poles facing) and the method described provide a means of accurately determining the density of trace objects. This method is inexpensive, rapid, and verifiable and provides numerical values--independent of the specific apparatus or analyst--that correspond to the absolute density of the sample that may be entered into a searchable database. We discuss the feasibility of MagLev as a possible means of characterizing forensic-related evidence and demonstrate the ability of MagLev to (i) determine the density of samples of glitter and gunpowder, (ii) separate glitter particles of different densities, and (iii) determine the density of a glitter sample that was removed from a complex sample matrix.
Highlights
The objects commonly encountered in crime scenes are diamagnetic, and interact weakly with an applied magnetic field
In a magnetic field gradient, suspended in a paramagnetic fluid medium, diamagnetic samples appear to be repelled from regions of high magnetic field; in actuality, the diamagnetic object displaces an equal volume of paramagnetic solution, and it is the attractive interaction between this paramagnetic volume and the regions of high magnetic field and this paramagnetic volume that results in MagLev
We and others have shown that a variety of aqueous solutions of paramagnetic salts (e.g., MnCl2, MnSO4, GdCl3, FeCl3, CuSO4, etc.) and chelated paramagnetic ions (e.g., Gd(DTPA) and Mn(EDTA); both in aqueous and non-aqueous solutions) are suitable for MagLev.[3,4,5,6]
Summary
Iii) The heterogeneity of a glitter sample may be determined from MagLev measurements, based on the range of observed levitation heights. We determined the average height of the glitter (or gunpowder) samples, as well as their deviation from the mean, for each MagLev measurement.
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