Used in Forensic Laboratories

Because the scent of a flower may be due to hundreds of different compounds, it is difficult for perfume manufacturers to duplicate floral scents. Establishing the identities and relative amounts of the components of a fragrance was actually impossible until the development of chromatography. Related techniques are used in forensic laboratories to match samples of fluids, by food manufacturers to test product quality, and to search for evidence of life on other planets. All these techniques depend on subtle differences in intermolecular forces to separate compounds. 

Ion mobility spectrometry (IMS) is in worldwide, daily use in laboratories in many fields of chemistry, medicine, food science, and manufacturing and is perhaps the most commonly used technology for detection of explosives at the present time. Its use in forensic laboratories is well known. In fact, it is so well established that there is a journal specializing in IMS [1], A recent book... 

Titration is one of the universal techniques of chemistry and is commonly used to determine the concentration of a solute. Titrations may be either acid-base titrations, in which an acid reacts with a base, or redox titrations, in which the reaction is between a reducing agent and an oxidizing agent. Here we concentrate on acid-base titrations. The technique is used in research laboratories, hospitals, and industry to determine the amounts of acid and base in solutions. It is also used in forensic laboratories and for monitoring the environment. 

PGC can be classified into two distinct types, depending on the method in which heat is applied to the sample static-mode (furnace) reactors and dynamic (filament, pulse-mode) reactors. Furnace-type pyrolysis systems are seldom used in forensic laboratories. The most common pyrolysis systems used are the Curie... 

In forensic laboratories, chemical spot tests based on color reactions, have been replaced over the years by modem, more accurate instrumental methods. However, analytical techniques based on color formation are stiU commonly employed in field tests for explosives. Being inexpensive, simple, easy-to-operate and often quite sensitive (see above), they are most suitable for use outside the laboratory as presumptive field tests for the presence of explosives. 

Such results have been used to both convict and acquit suspects and, in other cases, to establish paternity with an extraordinary degree of certainty. The impact of these procedures on court cases will continue to grow as societies agree on the standards and as formal methods become widely established in forensic laboratories. Even decades-old murder mysteries... 

MICROSCOPY tChemical). Use of a microscope primarily for study of physical struclure and identification of materials. This is especially useful in forensic chemistry and police laboratories. Many types of microscopes are used in industry most important arc the optical, ultra-, polarizing, stereoscopic, electron, and X-ray microscopes, Organic- dyes of various types are used to stain samples for precise identification. 

In recent years, Raman spectroscopy has undergone a major transformation from a specialist laboratory technique to a practical analytical tool. This change was driven on several parallel fronts by dramatic advances in laser instrumentation, detectors, spectrometers, and optical filter technology. This resulted in the advent of a new generation of compact and robust Raman instruments with improved sensitivity and flexibility. These devices could be operated for the first time by non-specialists outside the laboratory environment. Indeed, Raman spectroscopy is now found in the chemical and pharmaceutical industries for process control and has very recently been introduced into hospitals. Handheld instruments are used in forensic and other security applications and battery-operated versions for field use are found in environmental and geological studies. 

Urine analysis for illegal drugs is increasingly performed in forensic laboratories (especially in Japan). Gas chromatography-mass spectrometry (GC-MS) is extensively used because of its versatility and reliability. By way of sample preparation for GC analysis, conventional liquid-liquid extraction has a widespread use, but it is not only laborious but also environmentally unfriendly due to the consumption of considerable amounts of organic solvents. Therefore, microintegration of the sample preparation procedure is required. 

A wide array of laboratory techniques and instrumentation is used in forensic studies. This includes ultraviolet, infrared, and visible spectrophotometry neutron activation analysis gas chromatography and mass spectrophotometry high pressure liquid chromatography and atomic absorption spectrophotometry. The techniques and instrumentation chosen depend on the type of sample or substance to be examined. 

Sensitivity, which is defined as a measure of the minimum amount of sample that can be detected, is often a major concern. Sometimes these problems can be resolved by employing a fluorescence or electrochemical detector and/or preparing a derivative of the analyte. True microbore (i.e. coliunn i.d. < 1.0 mm) HPLC systems can provide gains in sensitivity but these are not used extensively in forensic laboratories mainly because of practical problems associated with reproducibility and short column lifetimes. However, there is a trend towards using narrow-bore columns of 2-3 mm i.d. 

The analyst can improve the identification of solutes or discrimination between samples by studying the multi-wavelength plots or spectra of the eluted components. Transformation of spectral data to yield derivative spectra have been used to improve sample discrimination, whilst a plot of the ratio of absorbances for two selected wavelengths is an excellent method for confirming the homogeneity of chromatographic peaks. However, there is a trend in forensic laboratories to use and develop techniques whereby the spectral data are reduced to a smaller number of numerical values. Results in this format at easier to compare and present in court and furthermore can be evaluated statistically. 

The National Institute of Justice provided funding for the initial application of STRs in forensics. STRs were used in forensic casework during the first Persian Gulf War and were widely adopted for testing by forensic laboratories in the United Kingdom and the United States in the mid to late 1990s. 

Besides EDXRF spectrometers that are intended for use in the laboratory, a number of portable EDXRF instruments are also available. These devices are used in various fields for on-site analysis of works of art, environmental samples, forensic medicine, industrial products and waste materials etc. In their simplest form, the instraments consist of one or more radioisotope sources combined with a scintillation or gas proportional counter. However, combinations of radio-sources with ther-moelectronically cooled soHd-state detectors are also available in compact and lightweight packages (below 1 kg). In Fig. 11.21, schematics of various types of radiosource based EDXRF spectrometers are shown. In Fig. 11.21a, the X-ray source is present in the form of a ring radiation from the ring irradiates the sample from below while the fluorescent radiation is efficiently detected by a solid-state detector positioned at the central axis. Shielding prevents radiation from the source from entering the detector. In Fig. 11.21b and c, the X-ray source has another... 

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