Chris Lennard

Classification and Identification of Photocopying Toners by Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS): I. Preliminary Results

A diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) technique has been employed to record the IR spectra of 152 different black and color toners used in photocopiers and laser printers. Based on characteristic absorption bands in the infrared (IR) spectra, 149 of these toners were classified into 36 distinct groups. A small sample of toner was removed from the surface of a questioned document (produced on a photocopier or laser printer), the IR spectrum was recorded using the diffuse reflectance technique, and the class of toner was determined by comparison with a collection of standard spectra. A knowledge of the compatibility of each type of toner can then be employed to provide a list of photocopying machines (or laser printers) that could have produced the questioned document. The technique does not appear to be affected by the age of the photocopy, the batch or toner, or the prior treatment of the questioned document with a fingerprint development reagent such as ninhydrin.

A simple combined technique for the analysis of toners and adhesives

A simple but efficient procedure has been developed for the extraction and analysis of adhesives and toners on questioned documents. From the single extraction of a sample of document equivalent to approximately 1 cm of a printed line, it is possible to record both the infrared spectrum and the pyrogram of the compound of interest. Good sensitivity and reproducibility has been observed for the analysis of toner and adhesive samples and the technique has proved effective in actual casework. The application of the technique to the analysis of adhesive tapes, inks and correction fluids is under investigation.

Soot as an Indicator in Fire Investigations: Physical and Chemical Analyses

The possibility of determining the combustion products (or accelerants) at the seat of a fire by the analysis of corresponding soot samples was investigated. Twenty liquid fuels (principally petroleum derivatives) and twelve plastic materials (from seven different polymer groups) were individually burned over one hour under controlled laboratory conditions. The soot produced was collected on glass plates and subsequently submitted to a sequence of physical and chemical analyses. Twelve casework samples (soot deposits on glass fragments collected at the fire scene) and five control samples (blind trials prepared in the laboratory) were submitted to the same analytical procedure. A total of 49 soot samples were considered. Macroscopic (35× magnification) and microscopic (TEM) studies were conducted on each soot sample. Digitized micrographs were processed in order to obtain certain physical parameters serving to characterize the size and form of the soot aggregates: perimeter, surface area, circularity and principal surface moments ratio. These data were transformed and used as variables for a discriminant analysis carried out with an SPSS program. Furthermore, the soot aggregates were characterized by their fractal dimension. The chemical composition of the soot samples was explored using three chromatographic methods: GC-FID, GC-MS, and pyrolysis-GC. Two studies were conducted: a comparison of the total chromatographic profiles obtained by GC-FID and pyrolysis-GC, and a comparison based upon qualitative and semi-quantitative analyses of 11 polycyclic aromatic hydrocarbons (PAHs) in order to determine the value of these compounds as potential markers for accelerants used at the start of a fire. The combination of physical and chemical parameters permitted the differentiation of most of the laboratory-prepared soot samples. The discriminating power was higher for the chemical analyses, with soot samples resulting from the combustion of plastic materials being the easiest to identify. Microscopy nevertheless provided interesting information concerning specific soot forms or elements. The combined results obtained by the analytical methods employed permitted the construction of a dichotomic table that can be used for the classification of soot samples taken from the scene of a fire. Additional research is required before such techniques can be routinely applied in casework.

Use of a gaseous electrical discharge to induce luminescence in latent fingerprints

Abstract A novel technique has been developed for the induction of luminescence in latent fingerprints. A gaseous electrical discharge (20 000 V) followed by treatment with the vapours formed by heating ammonium hydrogen carbonate induces UV excited luminescence in latent prints. Good results have been achieved on a number of surfaces and the technique is effective on fresh prints as well as prints up to several weeks of age. Developed prints have remained luminescent over a year after initial treatment and the method does not prohibit the subsequent application of conventional fingerprint development techniques. It can also be used to induce luminescence in prints developed with cyanoacrylate.

Collection of Fiber Evidence Using Water-Soluble Cellophane Tape

The collection and preservation of microtraces, such as fibers, using cellophane tape is generally accepted as being very practical and efficient. At the scene of a crime, for example, this means of sample collection is both easy and rapid, which explains in part its popularity. However, in addition to a very low specificity (high background), this technique suffers from one major disadvantage: the microtraces must undergo a long and tedious pretreatment before any detailed analysis is possible. This pretreatment involves the isolation and separation of the microtrace from the tape, followed by a solvent wash (usually with xylene) to remove all trace of the adhesive. A recently commercialized product alleviates some of the problems associated with sample collection by this means: “Mask Plus II” (No. 5414, Scotch™, St-Paul, MN) is a new cellophane tape that is completely soluble in water. Microtrace collection can be performed with this tape by the conventional lifting procedure. In the laboratory, the microtraces may then be conveniently released from the tape by immersion in warm water (60°C) with continual agitation. After solubilization of the cellophane tape, the microtraces are isolated by membrane filtration then allowed to air dry. The described technique has been thoroughly evaluated for fiber collection with comparison of the results with those obtained using conventional cellophane tape. Particular attention has been paid to operating conditions (temperature, humidity, conservation, etc.), collection efficiency, as well as possible alterations to the fibers themselves.

Use of a Silicon Carbide Sampling Accessory for the Diffuse Reflectance Infrared Fourier Transform Analysis of Samples of Interest to Forensic Science

An infrared spectroscopy method is described which requires little sample preparation and may be used for analysis of a wide range of samples of interest to forensic science. A small quantity of a sample is rubbed onto an abrasive silicon carbide disk, which is then measured by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The technique has been successfully applied to the infrared analysis of paint, synthetic rubber, cosmetics, corrector fluid, and adhesives.