Forensic Analytics

The concepts of trace and microtrace were introduced into criminalistics to define material that had been found at the scene of a crime and then subjected to examination. The concept of a criminalistic trace was defined by Jan Sehn, who stated that traces in the criminalistic sense are changes in objective reality (.. . ) 

Jan Sehn Institute of Forensic Research, Krakow, Poland e-mail jzieba ies.krakow.pl mkala ies.krakow.pl 

The importance of traces hes mainly in their reconstructive potential on the basis of traces it is possible to recreate the course of a particular incident and determine which persons took part in it, as well as their behaviour at the time of the event. Furthermore, traces can be useful aids in enabling direct apprehension of the perpetrator of an incident. Examination of traces can also indicate whether and how defined persons were linked to an event that is of interest to a judicial body. Traces can also play a significant role in the identification of places, persons and things. 

Microtraces are characterised not only by their microscopic size, but also by their prevalence, the fact that perpetrators are unable to avoid leaving them (irrespective of perpetrators efforts) and the difficulty in removing them. Microtraces arise as a result of the interactions of the perpetrator (his/her clothes, tools/instruments used) with the surroundings. Most frequently, microtraces are small particles of an originally larger object that have separated from it, such as microfibres, particles 

Because of the (tiny) size of microtraces, they are often unconsciously destroyed for example, they can be accidentally lost or transferred to another substrate, evaporate at elevated temperatures, or destroyed by the action of fire. Their properties might also change. The time elapsed between leaving a trace and its disclosure and securing for examination, as well as atmospheric conditions, are sometimes the cause of chemical and biological breakdown of the trace, or the substrate on which it occurs, making it difficult to carry out analyses. 

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Comprehensive two-dimensional GC has also been employed for the analysis of pesticides from serum, which, although not strictly a forensic analytical problem , provides an example of the promise of this technique to forensic applications, such as the analysis of drugs of abuse (40). Two-dimensional gas chromatograms of a 17-pesticide standard and an extract from human serum are shown in Figure 15.13. The total analysis time of about 5 min, high peak capacity and the separation of all... 

Mass spectrometry is an indispensable analytical tool in chemistry, biochemistry, pharmacy, and medicine. No student, researcher or practitioner in these disciplines can really get along without a substantial knowledge of mass spectrometry. Mass spectrometry is employed to analyze combinatorial libraries [1,2] sequence biomolecules, [3] and help explore single cells [4,5] or other planets. [6] Structure elucidation of unknowns, environmental and forensic analytics, quality control of drugs, flavors and polymers they all rely to a great extent on mass spectrometry. [7-11]... 

United States of America Edgewood Chemical and Biological Forensic Analytical Center 17-Nov-1998 Designated... 

Regarding tissues and body fluids to be analyzed, blood and urine serve most frequently as source material, although the interest of forensic analytical chemists can be easily extended to other specimens (e.g., saliva, bile, or vitreous humor). A tissue that has attracted a lot of inter-... 

The development of instrumental methods in analytical chemistry made possible fast, precise, and accurate analyses of a wide variety of important substances. Instrumental methods changed forever the metals industries, medical diagnosis, oil analysis, and forensic analytical chemistry, to mention a few highlights. In a very real sense, these developments in analytical chemistry made contemporary science and technology possible by opening up vast new continents of information about the world, which could be gained relatively easily and applied toward technological and/or scientific ends. 

Dr. Thornton, could you tell us what you do at your lab, Forensic Analytical Specialties ... 

DNA analysis is now a basic tool in the establishment of links between biological evidence and comparison samples. It has reached such a widespread use and its power is so impressive that it is probably the best-known forensic analytical method in the general public. Because of the need of high-tech instruments and sophisticated analysis kits, standardization has been surprisingly quick to come, favored by the almost monopoly of a couple of providers in this field. As a consequence, forensic DNA analysis is being practiced worldwide using almost identical tools and protocols. 

Cruces-Bianco C, Gamiz-Gracia L, Garcia-Campana AM (2007) An overview of capillary electrophoresis applications in forensic analytical chemistry gunshot residues, inks and dyes. Trac Trends Anal Chem 26 215-226... 

Forensic analytical science conducts analyses, identification, and interpretation of physical criminal evidence. Experts in forensic science can provide their services to a criminal court as they can interpret and consult on the results of their analytical techniques. There are many techniques forensic scientists use, and the type of analytical method used depends on the type of sample and the type of results needed. 

Isotope dilution This relatively new calibration method is occasionally used in specialized forensic applications. The method affords exceptional accuracy and precision, but is limited by the availability of suitable standards. Although the use of deuterated internal standards is sometimes equated with isotope dilution, the techniques are not the same. Isotope-dilution calibration is based on the addition of standards that contained enriched levels of stable isotopes of common elements such as C. The enriched standard, referred to as the spike, is added to the sample and allowed to reach equilibrium. The sample is then analyzed via mass spectrometry. Because the spike is chemically identical to the target analyte, the matrix correction is as good as that achieved with standard-addition calibration. However, until enriched stable isotope analogs of forensic analytes are available and affordable, isotope dilution will not be widely applied in forensic chemistry. 

Because TLC screening tests follow presumptive tests in the forensic analytical scheme, standards of suspected analytes are easily incorporated. 

There is one broad class of instrumental methods yet to make mroads into forensic analytical chemistry the electrochemical methods, such as ion-selective electrodes, coulom-etry, amperometry, and potentiometry. The relative inattention paid to these techniques is due to the nature of the analyses required and the kinds of matrices and target analytes with which forensic chemistry deals. Electrochemical techniques excel in applications such cis the evaluation of reactions, kinetics, mechanisms, and other areas that are not usually of forensic interest. Ion-selective electrodes are generally good qualitative and quantitative tools, but Ih target ions and gases that are rarely involved in forensic work. 

Hyphenated Instruments have come to play a central role in forensic analytical chemistry, taking their place alongside of microscopy and spectroscopy as the primary instruments of the modern laboratory. As mentioned at the beginning of the chapter, the microscope and the spectrometer were the pillars of the first forensic laboratory add to that a GC-MS, and a modem forensic chemistry laboratory takes shape. The most important advancement in recent years has been the development of reliable and affordable IR microspectrophotometers, hyphenated instruments, and capillary electrophoresis. 

Review articles allow even the busiest forensic chemist the opportunity to find summaries of current research. The journal Analytical Chemistry publishes a semiarmual review of forensic science that emphasizes forensic analytical chem-istry. This publication contains extensive and current research in drug analysis, as well as in many other aspects of forensic chemistry. For drug analysis, the DEA has published a recent extensive review of articles covering 1992-2002. As part of the Microgram Journal, this review is available online. 

The above summarizes what the textbook is now a few notes about what it is not. It is not meant to be a textbook in forensic toxicology, an enormous subject in which there are many fine books to choose from. Rather, the intent is to introduce this topic eis a major aspect of forensic analytical chemistry. Nor is the book meant to cover advanced aspects of all the many forensic chemistry areas, each of which (glass, soils, fibers, paints, inks, drugs, and so on) have been addressed in specialized volumes. Having read this text, you will have the back-groimd to tackle these more advanced treatments. 

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