Development of a Solid-phase microextraction (SPME) Fiber protector and its application in flammable liquid residues analysis.

Solid-phase microextraction (SPME) has been established as a very powerful alternative to traditional extraction methods since its introduction in the early 1990s. The heart of the SPME device is an expensive thin and very delicate fused-silica fiber, coated with a thin polymer film. When extracted, the fiber may bend and break. Due to the fragility of the SPME fiber, a fiber protector device is proposed. The protector is easily assembled on the SPME device and can easily be removed by unscrewing for sampling to the injector. The SPME with the fiber protector was tested by headspace-SPME (HS-SPME) gasoline and diesel fuel vapor analyses. The results of the extractions with the SPME protector were compared with the results of the extractions by SPME without the protector. An enhancement to the lighter hydrocarbons was observed in the results with the protector but the method sensitivity was not altered. The SPME protector was easily cleaned from contaminant residues by ethyl acetate washings. The protector can be used for years and the fibers remain intact for hundreds of samplings.

An analytical method to identify traces of white phosphorus on burned victim clothes.

We report for the first time, the chemical identification of phosphorus on the remains of burned clothes taken from an injured woman. The woman was accidentally burned as a result of spontaneous combustion of a "stone" pebble-like material her daughter picked up innocently on a beach. The remains of the woman's clothes were analyzed by gas chromatograph mass spectrometer (GCMS) after headspace adsorption using solid phase microextraction (SPME). The results of this test showed that the injuries were due to phosphorus, leading to the understanding that the "stone" was actually white phosphorus. This method can help both forensic investigators in a crime scene investigation and physicians that need this information in order to give the correct treatment to their patient.

A new method for casting three-dimensional shoeprints and tire marks with dental stone.

Dental stone is used as the major material for recovering three-dimensional shoeprints and tire tracks from crime scenes. The procedure for using dental stone sparsely changed over the years. There are two common methods for mixing dental stone: (i) a premeasured amount of dental stone is put in a zip-lock bag to which water is added, and (ii) the water and dental stone are mixed in a bucket. We suggest a novel rapid and efficient method of mixing dental stone and water in a bottle. These methods were compared at equal conditions. The parameters measured were the number of air bubbles, the strength of the cast, the ease of use, and the sharpness and quality of the accidental characteristics present in the cast. The proposed bottle method has the advantages of both the bucket and the zip-lock methods hence it combines strength, sharpness, high quality, and ease of use.

Authentication of forensic DNA samples.

Over the past twenty years, DNA analysis has revolutionized forensic science, and has become a dominant tool in law enforcement. Today, DNA evidence is key to the conviction or exoneration of suspects of various types of crime, from theft to rape and murder. However, the disturbing possibility that DNA evidence can be faked has been overlooked. It turns out that standard molecular biology techniques such as PCR, molecular cloning, and recently developed whole genome amplification (WGA), enable anyone with basic equipment and know-how to produce practically unlimited amounts of in vitro synthesized (artificial) DNA with any desired genetic profile. This artificial DNA can then be applied to surfaces of objects or incorporated into genuine human tissues and planted in crime scenes. Here we show that the current forensic procedure fails to distinguish between such samples of blood, saliva, and touched surfaces with artificial DNA, and corresponding samples with in vivo generated (natural) DNA. Furthermore, genotyping of both artificial and natural samples with Profiler Plus((R)) yielded full profiles with no anomalies. In order to effectively deal with this problem, we developed an authentication assay, which distinguishes between natural and artificial DNA based on methylation analysis of a set of genomic loci: in natural DNA, some loci are methylated and others are unmethylated, while in artificial DNA all loci are unmethylated. The assay was tested on natural and artificial samples of blood, saliva, and touched surfaces, with complete success. Adopting an authentication assay for casework samples as part of the forensic procedure is necessary for maintaining the high credibility of DNA evidence in the judiciary system.