Elemental analysis of trace evidence by laser induced breakdown spectroscopy – LIBS
El papel de oficina es un tipo de evidencia que los especialistas en documentoscopia se encuentran con frecuencia. Los métodos de análisis tradicional como fluorescencia por UV inducida son subjetivos y pueden verse afectados por factores como la antigüedad del papel y la variación de resma.
Uno de los tipos de evidencias que suponen un mayor reto para los especialistas en documentoscopia son lo lápices con mina de grafito. La naturaleza inorgánica del material supone que las técnicas tradicionales en el análisis documental como la Comparación Video Espectral, no son aplicables. Las diferencias en la composición elemental del grafito entre las distintas marcas significa que la espectroscopía de sublimación inducida por laser es un método analítico para la discriminación de lápices de grafito.
Los residuos de disparos consistentes en partículas con contenido de Bario (Ba), Plomo (Pb) y Antimonio (Sb) se encuentran frecuentemente en los brazos y ropas de la persona que ha utilizado un arma de fuego.
La producción y uso de las metanfetaminas se ha convertido en un azote para muchos países del mundo. Esto en parte se debe a la disponibilidad de los productos químicos necesarios para su fabricación, que hace posible llevar a cabo una producción a pequeña escala en laboratorios clandestinos.
Los incendios intencionados son un delito mayor del que se reportan más de 2.200 casos cada año en el Reino Unido. Las cabezas de cerillas quemadas, usadas para iniciar la combustión son una de las evidencias más frecuentes en la escena del incendio.
Methamphetamine production and use has become a scourge of many countries worldwide. This in part is due to the ready availability of the pre-cursor chemicals for its manufacture. This makes it possible for small scale production in Clandestine Laboratories to be carried out.
Using the Foster + Freeman ECCO Elemental Composition Comparator it is possible to detect and identify each of the ingredients associated with the production of methamphetamine, lithium, phosphorous and iodine. Lithium with atomic number 3 is particularly difficult to detect by other analytical methods.
One of the most widely applied techniques for the forensic analysis of glass involves the measurement of its refractive index (RI) using the oil immersion method. The Foster + Freeman GRIM system is a compact and convenient instrument intended for this purpose and has been used by all major forensic science laboratories for over twenty years. Improvements in glass manufacturing processes, however, have caused the variation in RI to be significantly reduced and it is now often necessary to subject glass evidence to additional examination by elemental analysis.
In this Application Note, we demonstrate the potential of the ECCO to differentiate between glass samples which cannot be distinguished by the measurement of RI alone.
It is generally useful to be able to identify the type of glass in the fragments recovered from a scene of crime. Whilst the measurement of RI is an extremely discriminatory technique, this alone cannot always conclusively determine the glass type: float and container glass, for example, exhibit distributions of RI which overlap in value even though the elemental compositions of these glass types are often quite different. Similarly, whilst a borosilicate glass, such as Pyrex, can be distinguished from float or container glasses by its refractive index, in practice, the difference in RI is so significant that the GRIM system must be laboriously recalibrated each time the type of glass is changed. Other elemental analysis techniques such as SEM-EDX and XRF are also blind to low atomic number elements, such as boron, the detection of which would confirm a glass as of the borosilicate type.
The most commonly applied method for the forensic examination of paper involves close visual inspection, possibly aided by the wide spectral range of the UV, IR and visible light sources in instruments such as the Foster + Freeman Video Spectral Comparator.
Recent studies have been reported, however, in which paper has been examined using elemental analysis techniques. These studies have measured trace elements such as barium and strontium, which occur as impurities in the calcium carbonate and other fillers used in the papers manufacture. Security papers, however, tend to have a quite different composition to normal types of paper and are often devoid of optical brighteners. Instead, uncommon elements, such as manganese or titanium, may be present, either having been added intentionally or occurring incidentally as a constituent of colourants.
This Application Note shows the different elemental profiles of three different types of security paper.
The number of counterfeit £1 coins in circulation in the UK has risen steadily over the last few years, probably because of the ease with which coins can now be counterfeited compared with paper banknotes. Whilst close visual inspection (inconsistencies in the date and design, poor quality of less prominent features, incorrect dimensional tolerances) can often be used to identify counterfeit coins, such methods are not entirely reliable.
Recent studies have been reported, however, in which counterfeit coins can be detected by elemental analysis. The presence or absence of specific trace elements can often distinguish genuine coins from counterfeit.
Using Laser Induced Breakdown Spectroscopy (LIBS) the ECCO has been used to rapidly screen swabs from suspects’ hands for elements consistent with GSR, such as the detection of Barium (Ba) and Lead (Pb). Once a screened sample has tested positive for GSR it may then undergo lengthier and more detailed analysis if required.
Office paper is one of the evidence types frequently encountered by forensic document examiners. Traditional analysis methods such as UV induced fluorescence, are subjective and can be affected by factors such as the age of the paper and ream variation. Here we present a study utilising the ECCO-DE laser induced breakdown spectrometer, to analyse and discriminate A4 office paper based on its elemental composition.
Pencil lead is one of the more challenging evidence types encountered by the forensic document examiner. The inorganic nature of the material means that traditional documents examination techniques such as the Video Spectral Comparison are not applicable. The differences in elemental composition of the lead between different brands means that Laser Induced Breakdown Spectroscopy is an applicable analytical method for discrimination of pencil lead.