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- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Sprache: Englisch
This book is essential for anyone seeking to understand and apply the latest analytical techniques in forensic investigation, saving time, materials, energy, and manpower by providing guidance on the most appropriate techniques for different types of investigations.
Advances in Analytical Techniques for Forensic Investigation is aimed to describe the applicability of different types of analytical techniques used for the forensic investigation, including FT-IR, chromatography, mass spectroscopy, NMR spectroscopy, atomic absorption spectroscopy, UV- vis spectroscopy, etc. This book will focus on current and emerging developments in the latest analytical techniques and methods used in the forensic investigation and sample analysis of various physical, chemical, and biological samples in order to facilitate the smooth conduction of justice.
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Table of Contents
Cover
Table of Contents
Series Page
Title Page
Copyright Page
Preface
1 Introduction to Analytical Techniques for Forensic Analysis
1.1 Introduction
1.2 Analytical Techniques for Evidence Analysis
1.3 Conclusion
References
2 Forensic Sample Collection and Preparation
2.1 Introduction
2.2 Collection and Preservation of Evidence at the Crime Scene
2.3 Legal Considerations
2.4 Chain of Custody
2.5 Admissibility in Court
2.6 Forensic Laboratory Analysis
2.7 DNA Analysis
2.8 Fingerprint Analysis
2.9 Ballistic Analysis
2.10 Toxicology Analysis
2.11 Quality Control Measures
2.12 Challenges and Emerging Technologies
2.13 Handling Digital Evidence
2.14 Emerging Technologies
2.15 Advances in DNA Analysis
2.16 AI and Machine Learning in Forensic Analysis
2.17 Cyber Forensics Techniques
2.18 Conclusion
References
3 Vibrational Spectroscopy in Forensic Sample Analysis
3.1 Fundamentals of Vibrational Spectroscopy (VS)
3.2 General Forms of Vibrational Spectroscopy
3.3 The Deployment of Vibrational Spectroscopy in Forensics and Criminal Investigations
3.4 Conclusions and Future Prospects
References
4 UV-Vis Spectroscopy in Forensic Sample Investigation
4.1 Introduction
4.2 Forensic Science
4.3 UV-Vis Spectroscopy
4.4 Applications of UV/Visible Spectroscopy in Forensic Science
4.5 Future Perspective
4.6 Conclusion
Consent for Publication
Conflict of Interest
Acknowledgement
References
5 Nuclear Magnetic Resonance Spectroscopy: A Versatile Tool for Forensic Sample Analysis
5.1 Introduction to NMR in Forensic Science
5.2 NMR Instrumentation and Sample Preparation
5.3 NMR Spectroscopy Techniques
5.4 Forensic Applications of NMR Spectroscopy
5.5 Data Processing and Interpretation
5.6 Conclusion
References
6 Forensic Aspects of Mass Spectroscopy and Isotope Ratio Mass Spectroscopy
6.1 Introduction
6.2 Mass Spectroscopy Principle Instrumentation
6.3 Ion Source
6.4 Mass Analyzer
6.5 Detector
6.6 Applications of Mass Spectrometry in Forensics
6.7 Isotope Ratio Mass Spectrometry Principle and Instrumentation
6.8 Applications of Isotope Ratio Mass Spectroscopy in Forensics
6.9 Case Study
6.10 Challenges and Limitations of Mass Spectrometry in Forensics
6.11 Conclusion
References
7 Application of Plasma and Atomic Absorption Spectroscopy in Sample Analysis
7.1 Introduction
7.2 Absorption Spectroscopy
7.3 Atomic Absorption Spectroscopy (AAS)
7.4 Plasma Absorption Spectroscopy (PAS)
7.5 Analysis of Forensic Samples Using AAS and PAS
Consent for Publication
Conflict of Interest
Acknowledgement
References
8 Application of Gas Chromatography in Criminalistics
8.1 Introduction
8.2 Gas Chromatography
8.3 Principle of Gas Chromatography
8.4 Instrumentation of Gas Chromatography
8.5 Advancement in Gas Chromatography Technique
8.6 Miniaturization and Automation in GC
8.7 Application of Gas Chromatography in Criminalistics
8.8 Conclusion
References
9 HPLC and HP-TLC
9.1 Introduction
9.2 Principle
9.3 Applications of HPLC and HP-TLC in Forensic Sciences
9.4 Conclusion
Consent for Publication
Conflict of Interest
Acknowledgement
References
10 Forensic Aspects of Hyphenated Techniques
10.1 Introduction to Hyphenated Techniques in Forensic Science
10.2 Hyphenated Techniques Used in Forensic Science
10.3 Conclusion
References
11 Microscopic Techniques and Their Application in Forensic Science
11.1 Introduction to Microscopy
11.2 Types of Microscopes
11.3 Forensic Application of Microscopy
Conclusion
References
12 EDX and X-Ray Technique in Forensic Science
12.1 Introduction and Overview
12.2 Importance of XRD and EDX Technique in Forensic Science
12.3 Instrumentation for XRD and EDX Techniques
12.4 Applications of EDX and X-Ray Technique in Forensic Science
12.5 Future Aspects and Conclusion
References
13 Nanotechnology in Forensic Science
13.1 Introduction
13.3 Techniques for the Synthesis of Nanomaterials
13.4 Role of Nanotechnology in Forensic Investigation
13.5 Conclusion
References
Index
Also of Interest
End User License Agreement
List of Tables
Chapter 4
Table 4.1 Absorption Maxima of some abusive drugs.
Table 4.2 UV-Vis spectroscopy of some important metals.
Chapter 6
Table 6.1 Stable isotopes of light elements [1].
Chapter 9
Table 9.1 Advantages of HPLC over other chromatographic techniques.
Table 9.2 Advantages of HPTLC over other chromatographic techniques [8].
Chapter 11
Table 11.1 Advantages and disadvantages of stereomicroscope.
Table 11.2 Advantages and disadvantages of bright field microscope.
Table 11.3 Advantages and disadvantages of confocal microscope.
Table 11.4 Advantages and disadvantages of fluorescence microscope.
Table 11.5 Advantages and disadvantages of polarizing microscope.
Table 11.6 Advantages and disadvantages of TEM.
Table 11.7 Advantages and disadvantages of SEM.
Table 11.8 Advantages and disadvantages of atomic force microscope.
List of Illustrations
Chapter 1
Figure 1.1 Types of evidence analyzed with various instrumental analysis.
Figure 1.2 Electromagnetic spectrum.
Figure 1.3 Diagrammatic representation of NMR.
Figure 1.4 Flow chart representing the functioning of mass spectrometer.
Figure 1.5 Schematic diagram of atomic absorption spectrometer.
Figure 1.6 Schematic diagram of atomic emission spectrometer.
Figure 1.7 Diagrammatic representation of GC-MS.
Figure 1.8 Compound microscope.
Figure 1.9 An image through SEM showing pollen grains.
Figure 1.10 Images taken from stereo microscope.
Chapter 3
Figure 3.1 General comparison between Raman and IR spectroscopy.
Figure 3.2 Graphical representation of the principal of Raman Spectroscopy. (I...
Figure 3.3 (a) Comparative Raman spectra of all 11 species (b) Standard deviat...
Figure 3.4 Graphical representation of differentiation of colored textile fibe...
Figure 3.5 Tabular representation of most discriminatory methods for the ident...
Chapter 4
Figure 4.1 The process of crime scene investigation.
Figure 4.2 UV-Vis spectroscopy for analysis of forensic samples.
Figure 4.3 Normalized absorbance spectra of different types of hemoglobin: Ohb...
Figure 4.4 UV-VIS spectrum of yellow fibers mounted in glycerin using quartz s...
Chapter 5
Figure 5.1 Illustration explaining the forensic applications of NMR spectrosco...
Figure 5.2 Illustrates the NMR spectrum for identifying different type of drug...
Figure 5.3 Illustration explaining about
1
H NMR of (A) saliva (B) seminal flui...
Figure 5.4 Showing
1
H NMR of PETN explosive (a) standard sample of PETN (b) sa...
Figure 5.5 Illustrates about the
1
H NMR spectra of PVC electrical tape with st...
Chapter 6
Figure 6.1 Mass spectrometer [2].
Figure 6.2 Stable isotope ratio analysis of forensic samples [1].
Figure 6.3 Mechanism of working of mass spectroscopy [3].
Figure 6.4 Isotope ratio mass spectrometry: Instrumentation.
Credit: Adobe Sto
...
Figure 6.5 Isotope ratio mass spectrometry: Instrumentations [4].
Chapter 7
Figure 7.1 Diagram of electromagnetic radiation.
Figure 7.2 Electromagnetic radiation converting into Black line of electromagn...
Figure 7.3 Basic instrumentation of atomic absorption spectroscopy.
Figure 7.4 Process of atomization.
Figure 7.5 Diagram of monochromator.
Figure 7.6 Instrumentation of plasma absorption spectroscopy (PAS).
Figure 7.7 Diagram of ICP.
Chapter 8
Figure 8.1 A simple diagrammatic representation of gas chromatography [53].
Figure 8.2 Column oven [54].
Figure 8.3 Applications of multidimensional GC [56].
Figure 8.4 Use of GC in various fields of criminology [28].
Figure 8.5 Analysis of fire debris [56].
Figure 8.6 The analysis of explosives mixture with the GC-MS [58].
Figure 8.7 Determination of phenobarbital in hair matrix by GC-MS [57].
Chapter 9
Figure 9.1 Classifications of HPLC.
Figure 9.2 The HPLC instrument.
Figure 9.3 Various protocols for method validation for an analytical instrumen...
Figure 9.4 General workflow for HPLC process.
Figure 9.5 General workflow for HPTLC process.
Chapter 10
Figure 10.1 Gas chromatography–mass spectrometry: Instrumentation [1].
Figure 10.2 Phases of the headspace in the vial are shown schematically [2].
Figure 10.3 Gas chromatography–headspace: instrumentation [3].
Figure 10.4 Gas chromatography–infrared spectrophotometry: instrumentation [4]...
Figure 10.5 Liquid chromatography–mass spectrometry: instrumentation [5].
Figure 10.6 Instrumentation of FTIR-MS [6].
Figure 10.7 Liquid chromatography-tandem mass spectrometry (LC-MS/MS): instrum...
Figure 10.8 Capillary electrophoresis mass spectrometry (CE MS): Instrumentati...
Chapter 11
Figure 11.1 Created
“Working mechanism of Stereomicroscope”
, by ...
Figure 11.2 Created
“Working mechanism of Bright-field microscope”
...
Figure 11.3 Created
“Working mechanism of confocal microscope”
b...
Figure 11.4 Created
“Working mechanism of fluorescence microscope”
...
Figure 11.5 Created
“Working mechanism of Polarizing microscope”
Figure 11.6 Created
“Working mechanism of TEM”
by Biorender.com ...
Figure 11.7 Created
“Working mechanism of Scanning Electron Microscope (SEM)”
...
Chapter 12
Figure 12.1 Constructive interference shown by diffracted x-rays when distance...
Figure 12.2 X-ray diffraction technique with diffraction pattern [13].
Figure 12.3 An x-ray diffractometer [12].
Figure 12.4 Schematic representation of energy levels.
Figure 12.5 Energy dispersive x-ray spectrometer.
Figure 12.6 Setup of EDX microanalysis with SEM.
Figure 12.7 Steps for sample preparation in the x-ray diffraction (XRD) proces...
Chapter 13
Figure 13.1 Classification of nanomaterials.
Figure 13.2 Principle of dynamic light scattering (DLS) technique.
Figure 13.3 Diagram showing the light path in a dark field microscope.
Guide
Cover Page
Table of Contents
Series Page
Title Page
Copyright Page
Preface
Begin Reading
Index
Also of Interest
WILEY END USER LICENSE AGREEMENT
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Scrivener Publishing100 Cummings Center, Suite 541JBeverly, MA 01915-6106
Publishers at ScrivenerMartin Scrivener ([email protected])Phillip Carmical ([email protected])
Advances in Analytical Techniques for Forensic Investigation
Edited by
Priyanka Chhabra
Divya Bajpai Tripathy
Anjali Gupta
Rajeev Kumar
Kajol Bhati
and
Shruti Shukla
This edition first published 2024 by John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USA and Scrivener Publishing LLC, 100 Cummings Center, Suite 541J, Beverly, MA 01915, USA© 2024 Scrivener Publishing LLCFor more information about Scrivener publications please visit www.scrivenerpublishing.com.
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Library of Congress Cataloging-in-Publication Data
ISBN 978-1-394-16631-2
Front cover images supplied by Adobe FireflyCover design by Russell Richardson
Preface
Forensic science is a multidisciplinary field that employs various scientific disciplines, such as chemistry, biology, and physics, to gather, examine, and interpret physical evidence associated with criminal activities. It serves as a crucial bridge between criminal actions and the legal system, guiding investigations through various stages, from scrutinizing crime scenes to preparing evidence for courtroom presentation. Analytical methods like spectroscopy, chromatography, and microscopy are essential tools in uncovering valuable information from physical evidence, ensuring precise analysis. Emerging technologies, such as nanotechnology and hybrid methods, also contribute to evidence examination. The importance of this field becomes apparent in its capacity to identify and decipher a wide range of evidence, including biological, chemical, and physical traces. Biological samples encompass materials like hair, blood, semen, and insects, while chemical evidence involves substances like poisons and explosives. Physical evidence includes items such as fingerprints, glass, fibers, and paints. Each type of evidence requires specific analytical techniques for accurate analysis. Forensic evidence analysed through these methods plays a pivotal role in criminal investigations. This comprehensive handbook addresses the use and applications of these techniques, catering to a diverse audience, including students, researchers, forensic scientists, medical professionals, educators, and law enforcement personnel.
The chapters presented within this book offer an in-depth description, theory, principal, sample preparation and analysis of various forensic evidence ranging from biological, chemical, and physical evidence through various conventional and advanced analytical techniques. Each chapter delves into specific applications of analytical instruments, highlighting their use in identification and analyzing forensic evidence.
Chapter 1 “Introduction to Analytical Techniques for Forensic Analysis” This chapter provides a comprehensive discussion regarding various analytical techniques and their application in the forensic analysis of diverse samples encountered at crime scenes. These samples encompass blood, semen, saliva, DNA, explosives, paints, glass, inks, urine, drugs, poisons, and questioned documents.
Chapter 2: “Forensic Sample Collection and Preparation” In this chapter, cutting-edge techniques employed in the collection, sampling, and preparation of forensic samples for subsequent analysis using different analytical methods are explored.
Chapter 3 “Vibrational Spectroscopy in Forensic Sample Analysis” delves into the realm of vibrational spectroscopy, including FT-IR, Raman spectroscopy, and vibrational circular dichroism, elucidating their application in the analysis of a broad spectrum of biological, chemical, and toxicological samples.
Chapter 4 “UV-Vis Spectroscopy in Forensic Sample Investigation” investigates the extensive utility of UV-visible spectroscopy across various domains of forensic science. Encompassing drug identification, chemical analysis, and quantification, this section provides insights into the principles, theories, and applications of UV-Vis spectroscopy.
Chapter 5 “Forensic Application of Nuclear Magnetic Resonance (NMR) Spectroscopy” sheds light on the forensic applications of Nuclear Magnetic Resonance (NMR) spectroscopy. The focus is on its role in elucidating the molecular structure of diverse body fluids, drug analysis, and identification of counterfeit samples, enhancing the accuracy of forensic investigations.
Chapter 6 “Forensic Aspects of Mass Spectrometry and Isotope Ratio Mass Spectrometry” underscores the significance of Mass Spectrometry and Isotope Ratio Mass Spectrometry in forensic science. Notably effective in identifying and analyzing chemicals, especially in drug analysis, this section explores their widespread applications.
Chapter 7 “Application of Plasma and Atomic Absorption Spectroscopy in Sample Analysis” concentrates on elemental analysis at minute concentrations, pivotal in forensic science for confirming the elemental composition of forensic evidence. The discussion revolves around the forensic use of plasma and atomic absorption spectroscopy.
Chapter 8 “Application of Gas Chromatography in Criminalistics” takes on the challenge of analysing trace evidence that can be easily volatized without decomposition through gas chromatography coupled with techniques like mass spectrometry. This section covers the analysis of various forensic evidence, including alcohol, organic compounds, drugs, explosives, ignitable materials, fingerprints, inks, paints, and toxins.
Chapter 9 “HPLC and HP-TLC” focuses on the crucial task of separating components in mixed crime scene samples. HPLC and HP-TLC are explored for their effectiveness in investigating poisoning cases and cases requiring component separation and trace impurity detection.
Chapter 10 “Forensic Aspects of Various Hyphenated Techniques” unveils the application of hyphenated analytical techniques, combining chromatographic and spectroscopic methods for analysing questioned samples such as paint, blood, saliva, explosives, and drugs.
Chapter 11 “Microscopic Techniques and Their Application in Forensics” delves into microscopic techniques like SEM, TEM, and AFM, enabling the scrutiny of minute morphological and structural details in trace samples.
Chapter 12 “EDX and X-Ray for Forensic Samples” reconnoitre the quantitative examination of elements in gunshot residue (GSR), paint, soil, and toxins are explored using EDX and X-ray techniques in forensic science in this chapter.
Chapter 13 “Nanotechnology in Forensic Science” The final chapter provides a comprehensive overview of nanotechnology’s applications in forensic science and crime detection. It highlights nanotechnology’s role in enhancing accuracy, precision, speed, and suitability in inquiries.
Collectively, these chapters strive to offer a comprehensive perspective on the diverse terrain of progress in analytical techniques for forensic sample analysis. They commemorate the achievements accomplished thus far, all the while recognizing the obstacles that await. As we embark on this expedition into the domain of enhanced analytical techniques, we extend an invitation to readers to uncover the potential of these advanced analytical techniques to bring about substantial transformations in how we tackle and overcome intricate identification hurdles.
Dr. Priyanka Chhabra
Prof. (Dr.) Divya Bajpai Tripathy
1Introduction to Analytical Techniques for Forensic Analysis
Megha Walia1*, Bhoopesh Kumar Sharma1 and Faray Jamal2
1Department of Forensic Science, SGT University Gurugram, Haryana, India
2Central Forensic Science Laboratory, Bhopal, Madhya Pradesh, India
Abstract
Forensic analysis is the application of scientific techniques to investigate and solve crimes or other legal issues. Analytical techniques play a crucial role in forensic analysis as they provide valuable information that can be used as evidence in court. Globally, the forensic sciences are utilized to settle disputes of the civil court, employ criminal laws, govern the created rules fairly, and safeguard public health. Forensic Science or Criminalistics is the application of science to law enforcement. Forensic scientists rely on instrumental examination of trace quantities of substances such as pharmaceuticals, toxicological specimens, fibers, glass, GSR, and soil etc. Individualization of evidence is facilitated by variances in manufacturing chemical composition, allowing for a high degree of differentiation even with minute pieces. The purpose of this chapter is to emphasize the qualitative and quantitative analytical techniques, such as IR Spectroscopy, UV-Visible Spectroscopy, AAS, NMR, Chromatography, Microscopic techniques, EDX, XRD, and nanotechnology, employed in criminalistics for the examination of vital and soupcon evidences that are procured from various scene regions.
Keywords: Analytical techniques, instrumentation, spectroscopy, NMR, chromatography, microscopic techniques, EDX, XRD
1.1 Introduction
The evolution and development of Forensic Science is not something that has occurred in the recent past but has its root situated back to ancient Roman and Greek societies. As most of the English words are adopted and utilized in English, the term “forensic” is no exception and thus has its roots to the Latin language, wherein it refers to ‘of the forum’ where in ancient time law courts with discussion were held [1]. An area of study known as “forensic science” is one in which scientific principles are utilized in the course of a criminal investigation for the purpose of conducting an evaluation of the evidence that has been gathered over the course of the inquiry [2]. Forensic sciences use several disciplines, including the basic sciences-physics, chemistry, mathematics, and biology, along with law (both civil and criminal), engineering, dentistry, geology, microbiology, biotechnology to name a few and incorporate them to analyze the physical evidence [1]. In other words, forensic science applies scientific knowledge to the definition and execution of the law [3]. In fact, Forensic Discipline is acknowledged in and of itself as a science that draws from a variety of other fields. The amalgamation of all the sciences with the sole responsibility to assist the criminal justice system is the appropriate definition of Forensic Science. Forensic science is a realm that has indefinite possibilities [1].
The team that consists of people participating in the examination and investigation of crime scenes incorporate medics, police, and forensic professionals who are accountable for the collection of evidence. Laboratory-based forensic scientists/experts are more familiar with the many analytical procedures utilized for their analysis [2].
As a three-part structure, Forensic Science consists of
Collection: Associated with Inquiry of Facts (Science);
Examination: Associated with Generation of Results;
Presentation: Associated with the Court of Law [
3
]
1.1.1 Forensic Analysis
Analysis of any crime scene requires the person to be competent in the domain of physical and biological sciences, including other sectors of technology and law enforcement. Forensic experts examine and analyze fingerprint ridges, fabrics, glass, and residues from gunshot, assess medications and poisons, investigate possibilities of forgeries, and inspect residues for any possible incendiary and explosive crimes [4]. Human body fluids such as blood, urine, seminal fluid, and saliva play a major role in the investigation of crimes like murder and rape [5]. Since forensics is primarily a scientific discipline, an extensive array of analytical methods is employed to examine evidence collected at the site of the crime. There is a plethora of information stored in this evidence; it just needs the right eye for identification. This motivation has fueled the development of forensic science, where information is gained via the analysis of numerous types of evidence to help the legal system in piecing together the past [2].
According to forensic community-recognized criteria, the result that is generated after thorough examination should be statistically correct and should always have high probability in reaching a fair and just decision. No categorical judgements are permitted unless the samples being compared have entirely distinct physicochemical profiles that are regarded as having a confidence level of one hundred percent [6–8].
Therefore, interpreting data as categorical while ignoring the “fuzziness of limits” may result in forensic malpractice.
Most known to occur during an investigation are biological, physical, and chemical evidence. Typically, these samples are prepared prior to examination utilizing analytical procedures to guarantee optimal analysis [2].
Application of analytical chemistry in forensic is one of the most helpful and initiating fields of research, with widespread usage in areas such as the examination of illicit and illegal narcotics in diverse matrices, the analysis of food adulteration, the analysis of adulteration of fuels and car chassis, and the analysis of frauds in works of arson [1].
They are two types of forensic analytical methods:
Destructive methods: This entails the destruction of the evidence and the loss of evidence integrity. Chromatographic procedures are examples.
Non-Destructive methods: This procedure preserves the integrity of the evidence because it does not entail the destruction of the evidence. Examples include microscopy and spectroscopy [
9
].
1.1.2 Introduction to Instrumentation in Forensic Science
In criminal and civil investigations, forensic science involves the use of sophisticated scientific methods. This right eye with the correct instrumental technique can not only just recognize, but detect and even segregate the articles found at the crime scene to forensically relevant material.
Figure 1.1 Types of evidence analyzed with various instrumental analysis.
This relevant material has stored incriminating stories regarding the event, the identity of the origin (who, what, with) and of the incident (how, when, why, where) that generated it [10]. The likelihood ratio method was given special study by Biosa et al., who provided clarity on the interpretation of analytical data in the forensic context. The data has been classified into two categories using penalized logistic regression and the computation of likelihood ratios. Using data on alcohol biomarkers, the approach was utilized to categorize individuals who often consume alcoholic beverages [11]. Figure 1.1 depicts the physical, chemical, and biological evidence that can be analyzed by various instrumental techniques.
The numerous approaches to evidence analysis are going to be broken down into their essential components and outlined in this chapter [6–8].
1.1.2.1 Validation of Instrument
As never before, the legitimacy and credibility of forensic expert testimony, as well as its capacity to distinguish between defense and prosecution positions, are being challenged as well as questioned [12, 13].
Therefore, it is inevitable that the scientific basis of forensics would be questioned; thus, it is essential to shift the attention to the integrity of the investigation procedure. Thus prior to the deployment of any new forensic procedure, certain efforts must be performed to confirm the efficiency of the suggested method for its planned use i.e., every new procedure must be verified/validated. Analytical procedures have evolved greatly with time, from extremely subjective evaluations of data with limited information to objective evaluation using chromatographic and spectroscopic signals with detailed information [8]. To completely comprehend the efficiency of an instrument, experts must be conversant with the general features of investigative assays. This includes the limit of detection (LOD), the signal-to-noise ratio (S/N), the limit of quantification (LOQ), accuracy, precision, interference, and resilience. Due to the significance of such factors for defining evaluates, they are crucial mechanisms of validation of method. Numerous investigative equipment alter a specific characteristic of an analyte into an electrical indicator. Numerous factors, including arbitrary electrical transmissions, varying chemical concentrations innate to the sensor, which leads to undesired signals which might hinder the response of the target. Such irregular impulses are referred to as noise. The finest machinery enhances S/N by enhancing analyte signal, reducing noise, or both. A high S/N ratio reduces LOQ and LOD. These limits are often derived by gauging successive dilutions of an evidence in the matrix of interest and selecting the lowest concentration where readings fulfil S/N and other requirements in forensic toxicology [14].
1.1.2.2 Instrumentation for Organic Evidence
For the purpose of determining the presence of organic compounds like alcohols, alkenes, amino acids, carboxylic acids, aldehydes, ketones, esters, and phenols, among other things, organic analytical methods are utilized. The investigation reveals both the kind (the qualitative outcome) and the degree of something (quantitative result). Chromatography, UV-visible Spectrophotometry, GCMS, LCMS, Infrared Spectrophotometry, & Mass Spectrometry are some of the several analytical methods that are utilized in the process of analyzing organic substances [3].
1.1.2.3 Instrumentation for Inorganic Evidence
For the purpose of determining the presence of inorganic elements like C, B, P, K, Ca, Zn, S, Ba, Pb, V, Mo etc. in the unknown substances, inorganic analytical methods are utilized. The investigation reveals both the kind (the qualitative outcome) and the degree of something (quantitative result).
XRD, AES, AAS and NAA are few techniques that come under the category of the analytical methods that are utilized in the process of analyzing inorganic substances [3].
1.1.2.4 Instrumentation for Biological Evidence
Illicit and illegal substances, such as ethanol, benzodiazepines, MDMA, cocaine, LSD, barbiturates etc., used to be investigated evidences for a very long time, particularly in biological samples (blood, urine, viscera, and hair) derived from living and deceased humans. Research on legal or illegal substances in biological specimens, in vivo and post mortem, is in high demand because of the widespread drug usage that contributes to major public health problems across the world and disproportionately affects young people. During the Middle Ages, Europe saw an increase in the number of cases of poisoning caused by opium, arsenic, and hydrocyanic acid. At the same time period, Paracelsus, saw that the dose at which a drug is consumed determines whether it is a poison or not [1].
Arsenic was initially recovered from a variety of post-mortem biological samples in 1814 by Mathieu Joseph Bonaventure Orfila, who is also known as the Father of Toxicology. This study was the first to be systematized & classify poisons. He was the first person to propose that a poison must first be absorbed into the body or enter the bloodstream to have its harmful effects.
Jean Servais Stas came up with the first successful investigative method for removing alkaloids present in biological materials in the year 1851. Friedrich Julius Otto, segregated pure alkaloids, substantially changed the extraction method years later. This type of analysis is now often referred to as the StasOtto Method, and it continues to be one of the essential methods used in the drug extraction process [15].
When operating with biological samples, especially urine, having a full understanding of the metabolism of chemicals is essential for building diagnostic techniques. Wagmann et al. conducted research on in vitro methods to study the metabolites of several new psychoactive substances (NPS). Their findings highlighted the feasibility of zebrafish larvae for explaining the toxicokinetic of NPS, particularly in situations where studies on humans are impractical due to ethical considerations [16]. Putz et al. then carried out an extensive in vivo metabolic investigation centered on trenbolone; a drug commonly abused for the purpose of enhancing athletic performance [17]. The authors discovered new possible metabolites using Hydrogen Isotope Ratio Mass Spectrometry in conjunction with Liquid Chromatography. For the purpose of determining whether the detected trenbolone metabolites truly contribute anything of use to the standard doping control procedures, more research will be conducted. Since the credibility of forensic science has taken a significant hit in recent years as a result of a number of inefficient forensic pathologies (Trager, 2018), thus it is vital to guarantee the examination of evidence by means of trustworthy analytical techniques [18]. After a procedure involving the creation of sodium hydroxide and hydride, the examination of hair is carried out using atomic absorption spectroscopy. This approach would make it possible to detect the inelastic light dispersion that occurs as a result of molecular vibration modes when the sample in question is exposed to a source of monochromatic light e.g., laser. In conjunction with the diameter of the hair shaft, the synchrotron radiation beam had a size of either 1 or 4 mm. It is still not quite clear the number of times hair shafts were counted in addition to the number of particles discovered. In accordance with the research arsenic has been discovered on just 1–2/100 hair shafts [19, 20].
This chapter discusses the philosophy behind contemporary technology as well as its most recent advancements in relation to the investigation of harmful substances found in biological fluids and tissues.
1.1.2.5 Instrumentation for Chemical Evidences
Recently, synthetic cannabinoids, compounds derived from fentanyl and cathinone, and other novel psychoactive drugs have been thrust into the mainstream of forensic analytical chemistry [1]. These chemicals are more commonly referred to by their acronym, NPS. The class of substances known as NPS, that are intended to simulate the effects of illegal recreational drugs that are already on the market, are the subject of a significant amount of research attention. The ever-increasing prevalence of NPS presents forensic laboratories with several difficult analytical hurdles [8]. In this context, it is of the utmost importance to do research, create new analytical methods, and conduct validation tests on those methods in order to meet the substantial demand posed by contemporary society for the clarification of forensic cases [1]. For instance, Cal et al. devised a bioanalytical procedure for the analysis of oral fluid and validated by using HPLC-MS that requires nominal evidence treatment prior to analysis [21]. On the other hand, Salerno et al. analyzed real “street” samples seized by GC-FTIR. Both approaches were successful in unequivocally determining the NPS that were being studied [22]. A collaborative research effort aimed at the synthesis and characterization of various NPS was presented by Bulska et al. with the intention of making the job of law enforcement authorities easier. The non-routine analytical methodology that was proposed to couple chromatography with combined XRD, and then mass spectrometry was used to identify the produced compounds. Also, NMR investigation was carried out in order to verify the compounds hypothesized chemical structures [23].
1.1.2.6 Instrumentation for Physical Evidences
Few qualified experts worldwide begin the task of documenting the type of bullets used and identifying the qualitative variations in GSR’s chemical composition. Niewoehner [24] and Broiek Mucha et al. [25, 26] attempted a separate procedure for examination of GSR using SEM-EDX and interpreted results based upon chemical methods. It aids to identify the group of bullets that were utilized based on the GSR research. Analytical techniques are developed such as Inductively Coupled Plasma Mass Spectrometry (ICPMS) that offer more discriminating results than SEM EDX and are all being used to investigate the composition of primary residues [27]. Nevertheless, given that knowledge of both their morphology and the major important elements continues to be a useful tool for GSR examination. SEM-EDX is the GSR analytical approach that is more accurate [28].
1.2 Analytical Techniques for Evidence Analysis
These analytical techniques, along with others, are used to analyze different types of evidence, such as drugs, fibers, gunshot residues, and biological fluids, among others. The results of these analyses can provide important information that can be used in legal proceedings [10]. The subsequent section will encompass spectroscopy, chromatography, microscopy, and other emerging techniques that are frequently utilized in Forensic Science.
1.2.1 Spectroscopy
Spectroscopy is a technique that involves the measurement of the interaction between light and matter. It provides valuable information about the structure, composition, and dynamics of materials. There are many types of spectroscopy techniques, each of which uses a different region of the electromagnetic spectrum, from radio waves to gamma rays. The electromagnetic radiation (EMR) as represented in Figure 1.2 is the assorted scale of energy in the form of waves; they are arranged in the increasing and decreasing manner of their wavelengths and photon energies. The green color of leaves is result of the absorption and reflection of radiation from the electromagnetic spectrum.
When light strikes the surface of the leaf, it absorbs all the light except green color, thus only reflecting green light. The entire domain of spectroscopy is based on this interaction of light with the sample of our choice to understand nature. EMR is composed of packets and bundles of energy called photons. The presence of photons imparts dual nature to the EMR; it behaves and propagates in the form of waves or particles. The waves move along in a perpendicular manner to each other. Thus, spectroscopy is the study of the electromagnetic spectrum and how dispersion of light occurs into various constituents and finally how matter behaves on interaction with light. Analytically speaking, every element or compound has a specific way it behaves when varying intensities of light are bombarded on it [10]. The output of the analysis is an electromagnetic spectrograph that quantifies the wavelength of the light that is emitted by the substance, in the form of graphs. The graph comprises lines that are unique to the specific element that emitted it, thus aiding the scientist in reaching a positive conclusion. Additionally, spectroscopy measures the amount of light absorbed by the substance, thereby deciphering the concentration of the element.
Figure 1.2 Electromagnetic spectrum.
When heat is applied to a substance, it diffuses out light at a particular wavelength. Spectroscopy utilizes this chemical attribute for determining the characteristic element that is there in the sample. Spectroscopy is and can be utilized to identify numerous types of evidence that are recovered from the location of crime. Drugs, Fibers, Ink, Glass, Paint, Explosives, Trace elements and can additionally be used to identify contaminants that are found in the diverse material that is at our disposal for analysis [3].
The following section will shed some light on various classical and contemporary approaches in spectroscopy, namely; IR Spectroscopy, UV-Visible Spectroscopy, MS, AAS, AES and NMR.
1.2.1.1 Infrared Spectroscopy
There are two principal regions that aid in characterization of unknown substances; namely Ultraviolet-Visible and Infrared Region. Infrared (IR) region in comparison to the Ultraviolet (UV) region has lower energy-lower frequency but a higher wavelength. In case of UV-Visible spectroscopy, the analyte absorbs the energy of radiation and transition to the higher orbital takes place whereas in case of IR Spectroscopy there is not enough energy to be absorbed, thus the bonds between atoms vibrate. Thus, the output is achieved by identifying and quantifying the vibrational frequencies of the atoms upon IR irradiation. The IR radiation has a range from 700 nm to 1 mm. When the energy is absorbed by the bonds, they vibrate in a manner that is like that of a spring, they can rock, twist, stretch and bending in the direction of choice. The frequency, direction and manner of vibration are specific to each compound and thus aid in identification. To impart sensitivity to the technique it is ideally coupled with Fourier Transform which develops the final spectrogram post analysis, where Michelson Interferometers are used for the purpose of calibration. This is based on the principle of interference (constructive & destructive) radiation that is emitted by the evidence under evaluation. The technique is preferred as it is non-destructive in nature and is compatible for biological sample, counterfeited products, gun-shot residue, and explosives. Near-IR Spectroscopy has the same principle as of IR but it utilizes the near IR radiation that ranges between 0.7 mm and 1.4 mm for the analysis of evidence. The technique is quite popular for its ease and non-destructive approach. The energy in the radiation is less thus when the compound absorbs, the spectra achieved has a series of overlapping bonds; which aids in identifying elements that have high light scattering tendencies and strong absorption [10].
IR spectroscopy is commonly used in the analysis of organic molecules, such as polymers and biomolecules. It is also used in the analysis of inorganic materials, such as minerals and ceramics. However, IR spectroscopy has limitations, such as its inability to detect elements lighter than carbon and its sensitivity to sample preparation [29–31].
1.2.1.2 UV-Visible Spectroscopy
Ultraviolet Spectroscopy (UV) quantifies the wavelength of a beam and determines the proportion of various components that are present in an analyte [3]. It is a technique that uses the absorption or reflection of ultraviolet and visible light by a sample to determine its composition. The absorption of light causes electrons in the sample to transition from the ground state to an excited state, and the energy of the absorbed light is equal to the energy difference between the two states. The absorption spectrum of a sample is a plot of the amount of light absorbed versus the wavelength of the light [10].
The technique that quantifies the absorption that occurs in the UV-Vis range; with the UV section being 190 nm to 350nm on the contrary to the visible region that extends from 350 nm to 800 nm. The primary postulate behind the working of UV Visible spectroscopy are the electronic transitions that take place in bonding and antibonding orbitals. These transitions occur in unsaturated compounds. The amount of light they absorb is measured through Beer-Lambert law, depending upon the concentration of sample and path length of light traveling within the sample. It is also suitable for analyzing myriad compounds. The governing principle of the technique is the excitation of electrons from ground level to a higher energy level after absorbing the desired intensity of transmitted light. The sample when bombarded with a light that has a high energy source, the electrons absorb energy and transition to a higher energy level. Conversely, over time the absorbed energy is lost and comes back to the previous state by releasing light of specific wavelength. Each element emits a light that is highly specific and unique thus aiding in elemental analysis and identification [10]. The output that is achieved through UV Spectroscopy is compared with the graphs in the database as part of the quantitative analysis to yield fruitful outputs. The technique is suitable for detecting drugs in blood, saliva and urine samples analyze the components of food additives, paint, dyes, petroleum products and can also be used to monitor air and water quality [3, 9, 31]. Such products are qualitatively and quantitatively analyzed through Spectroscopy making it the most ubiquitous tool. However, UV-Vis spectroscopy has limitations, such as its inability to distinguish between compounds with similar absorption spectra and its sensitivity to sample concentration [32, 33].
1.2.1.3 Nuclear Magnetic Resonance Spectroscopy (NMR)
NMR is an intriguing investigating tool that ascertains the structure of any chemical substance or molecule. The analysis through NMR takes into account nuclei spin and its magnetic moment under the influence of the peripheral magnetic field. The nucleus of an atom contains protons and neutrons that account for the arbitrary orientation spin. Thus, nuclei are considered as tiny magnets having random orientation that cancel out by each other. Under the influence of an external magnetic field, spin of all nuclei tends to be in or opposite direction of external magnetic field. Under the influence of radio frequency from an external source, the nuclei absorb specific energy and will move to a higher energy level from the ground energy level (also switches its orientation in opposite direction in respect to the orientation present under the influence of external magnetic field only). The wavelength and frequency at which this occurs is characteristic and unique to every compound. Upon removing the external source of radio frequency, the absorbed energy (specific to the compound) is released that is detected by the detector and nuclei come back to the ground state along with previous orientation. The detected energy is encoded in the form of peaks (as represented in Figure 1.3) that are characteristic to the compound.
Hydrogen is used in NMR as hydrogen has a single proton in the nucleus resulting in a better spectrum, Phosphorus is also an alternative for analysis of evidence. NMR is used for the examination of body fluids, toxins, drugs as well as for examining the post-mortem changes. Being extremely sensitive, NMR is used not only to elucidate the structure of compounds but can also be used to identify impurities thereby determining the quality making it an essential tool in the field of forensic.
NMR spectroscopy is commonly used in the analysis of organic molecules, such as proteins and carbohydrates. It is also used in the analysis of inorganic materials, such as minerals and catalysts. However, NMR spectroscopy has limitations, such as its sensitivity to sample purity and its inability to detect elements with low natural abundance [34, 35].
Figure 1.3 Diagrammatic representation of NMR.
1.2.1.4 Mass Spectrometer (MS)
Mass Spectroscopy when coupled with Gas Chromatography deciphers the m/z ratio of the molecule/s that is present in the evidence. The sample is loaded into the mass spectrometer; that will be turned into vapor and into ions (charged particles). These charged particles are then transferred through an electric and magnetic field. The distance it covers/travels will be directly proportional to the m/z ratio. The final output will be decoded by a detector. Each element has an extremely exclusive field; thus, MS is an indispensable tool for the precise examination of exhibits procured from various crime scenes [3, 9, 31]. MS analyses organic compounds by vaporizing them into gaseous form followed by segregating the ion as their mass/ charge ratio (m/z).
Mass Spectrometer as represented in Figure 1.4 is made up of the following parts:
An
ion source
where ionization takes place through electron impact, plasma desorption, fast atom bombardment, thermospray ionization, chemical ionization or through laser desorption;
a
mass analyzer
where the ions get segregated through ion trap, magnetic sector, time of flight (TOF), or through a quadruple according to their mass to charge ratio; and
a
detector
which can be faraday cups, photomultiplier tubes or scintillators that identifies the separated ions.
The mass spectrum is plotted wherein mass to charge ratio is plotted against their relative intensity. The highest intensity peak in the spectrum is the point where the substance fragmented and ionized as per the molecular weight of the parent ion of the analyte. In order to increase efficiency; mass-spectroscopy is coupled with thin layer chromatography, gas or liquid chromatography to obtain more accurate analysis of forensic evidence.
Figure 1.4 Flow chart representing the functioning of mass spectrometer.
The two properties of mass spectroscopy make it a suitable tool in analytical chemistry and is an ideal choice for Forensic Chemistry. Firstly, while transferring energy, if the source is monitored and is stable, the fragmentation of ions for the substance under evaluation can be reproducible. Lastly, the spectrum achieved post analysis is extremely specific to the substance and thus can be used for the purpose of identification.
The technique estimates the substance under examination both quantitatively and structurally. Both form of sample i.e., Solid and liquid can be examined through this technique [36]. 2.1.5 Atomic Absorption Spectroscopy (AAS) and Atomic Emission Spectroscopy (AES) Atomic Absorption Spectroscopy (AAS) quantifies the specific wavelength that is absorbed by atoms of substance under examination [3, 9, 31].
This type of spectroscopy considers the light absorbed and light emitted by atoms of analyte. These methods are quite effective when it comes to carrying out the elemental profiling of the analyte. AAS: As depicted in Figure 1.5, a typical atomic absorption spectrometer has four major components: the light source, the atomization system, the monochromator, and the detecting system. Liquid or solid samples are nebulized and subsequently atomized in either a flame or a graphite furnace. The unbound atoms are then illuminated by light, which is commonly emitted by a lamp with a hollow cathode, and experience electronic transitions from the ground state to excited electronic states by absorbing a light of certain wavelength that is characteristic to the atom [10].
Figure 1.5 Schematic diagram of atomic absorption spectrometer.
As stated above, AAS depends on the element being sampled to absorb the radiation which is emanated by the source; it adheres to the Beer Lambert law. This law establishes a correlation between the quantity of radiation that is absorbed and the concentration of the element in the sample [37].
Between the sample and the detector, a monochromator is inserted to decrease background interference. The detector then translates the measured intensity of the light beam into absorption data. Therefore, it may be utilized for the purpose of carrying out the quantitative analysis of the element in the sample. Solid samples can be utilized for AAS analysis, although typically only in graphite furnaces with controlled electrical heating as opposed to a direct flame. Moreover, AAS is often exclusively employed to examine metal atoms. The primary reason is that these metals have single emission and absorption lines that are narrow, brilliant, and distinct [37]. The technique is suitable for deciphering various heavy-metal contaminants that are present in air, water, and soil samples. Paint and soil samples when analyzed using AAS can aid in identifying the location at which the crime took place [3, 9, 31].
Figure 1.6 Schematic diagram of atomic emission spectrometer.
AES: This method relies on the excitation of electrons to higher energy levels by the absorption of a certain wavelength at high temperatures. When excited species depart the high-temperature zone, they return to their ground states by emitting discrete wavelength packets of radiation. As depicted in Figure 1.6, these emissions travel via a monochromator or filter before being detected.
The excited levels have an extremely brief lifespan (10-8 s). This emission is specific to the element that can be found in the sample. As a result of the fact that the amount of radiation emitted is related to its concentration, quantitative analysis may also be done. This method can perform analyses on a wide variety of samples, including fibers, GSR, and combustible substances [10, 38, 39].
1.2.2 Chromatographic Techniques
Mikhail Tsvett, a Russian scientist, is credited with being the one who originally established chromatography in the year 1900. In the beginning, it was utilized for the purpose of separating the plant pigments found in a leaf. Chromatography is a technique that separates components of a mixture depending on the physical characteristics of those components. The basic principle of chromatography is based upon the fact that different components in a mixture have different physical and chemical properties, which can be exploited to separate them from each other. In its most fundamental form, it is a method for separating substances that makes use of a stationary phase and a mobile phase. The ability of the analytes to have an affinity for either the stationary phase or the mobile phase determines which direction the separation will proceed. In most cases, the analytes will become adsorbed on the stationary phase if they have a greater affinity towards it. This is because the analytes will move through the system at a slower speed. They have a greater tendency to move at a faster speed if they have a stronger affinity towards the mobile phase. Based on this fundamental concept, it is possible to readily isolate and identify the analytes contained inside any substance. The retention time of substances that move at a slow rate is greater than that of substances that move at a quicker rate, which has a shorter retention time [10]. In the chromatography technique known as paper chromatography, a trace quantity of a liquid combination is positioned close to the base of a sheet of paper. In the process of paper chromatography, the RF value is determined as the distance travelled by the substance divided by the distance travelled by the solvent. Chromatography is utilized in the arena of forensic science for the purpose of analyzing pigments found in fibers, testing for the presence of explosives or accelerants, and determining whether narcotics are present in bodily fluids or not. Paper chromatography has been superseded by more technologically advanced kinds of chromatography. The components of a mixture can be identified with the assistance of gas chromatography, which maps each spike to a distinct component of the mixture. The relative heights provide information about the proportional abundance of each component. In forensic laboratories, the chromatographic techniques of thin layer chromatography (TLC), gas chromatography (GC), and high-performance liquid chromatography (HPLC) are frequently utilized. In contrast to GC, the HPLC method may be carried out at ambient temperature. Therefore, HPLC can be utilized in the process of detecting the presence of combustible substances, such as explosives or accelerants [3, 9, 31].
1.2.2.1 Gas Chromatography (GC)
Gas chromatography is used to separate volatile compounds, which are compounds that can be easily vaporized. The sample is injected and vaporized by heating the column that is filled with a stationary phase. The mobile phase is an inert or noble gas like argon or helium which act as a carrier for a sample. Thus, this method involves transporting the analyte through the column in conjunction with the mobile phase (also known as carrier gas). At this point, the sample will be separated at various retention times depending on whether it has a stronger affinity for the stationary phase or the mobile phase. Even though this method offers a great deal of adaptability, it does have a few limitations. Because the sample must first be brought to the vapor state before it can be analyzed, this method cannot be used on substances that are thermally unstable. This is because such substances are more likely to undergo pyrolysis. It is feasible, however, to precisely segregate the components present in an analyte by making use of the required sample preparation processes and the use of protectants to maintain the authenticity of the sample. Some of the forensic samples that are extensively examined include illegal substances and the amount of alcohol in the blood. This method is also capable of detecting explosives and other flammable compounds, accelerants, and even pesticides and toxins. It is yet one of the fascinating types of chromatography that is frequently used in the arena of forensic all around the world [40, 41].
1.2.2.2 High Performance Liquid Chromatography (HPLC)
Liquid chromatography is used to separate non-volatile compounds, which are compounds that cannot be easily vaporized. The sample is dissolved in a liquid and passed through a column that is packed with a stationary phase and the mobile phase (in liquid state) in conjugation with prepared the sample is forced through the column at high pressure. In HPLC, the whole procedure is automated, and at the present time, several equipment come packaged along with autosamplers. The stationary phase (generally silica gel) can come in a variety of forms, such as normal phase, reverse phase, ion exchange, and size exclusion. The mobile phase of normal phase HPLC columns is less polar than the stationary phase. In columns that use the reverse phase separation technique, the stationary phase is nonpolar, while the mobile phase that is utilized is polar. Size exclusion columns employ acidic or basic columns and porous stationary phases. Ion exchange chromatography is used to separate charged compounds. The stationary phase is made up of charged groups, and the mobile phase is a solution of ions of opposite charge. The examination of each sample calls for the development of a unique protocol, which considers a variety of criteria, including the kind of column that will be utilized, the mobile phase, the pH of the mobile phase, the flow rate, the retention duration, and the pressure.
In HPLC, the detectors that are employed might also change depending on the type of material that is being examined. The ultraviolet/visible light detector, the fluorescence detector, the electrochemical detector, the conductivity detector, the evaporative light scattering detector, and the chiral detector are examples of commonly used detectors.
The HPLC technique is used to investigate illegal substances including opioids, pesticides, cannabis, alkaloids, plant toxins, and poisons [34, 42, 43].
1.2.2.3 High Performance Thin Layer Chromatography (HPTLC)
When it comes to the examination of forensic evidence, HPTLC is likely one of the chromatographic methods that is capable of the greatest degree of flexibility. In this method, an adsorbent or stationary phase-coated thin-layer chromatography or TLC plate is employed, and it is then incubated in a chamber that is saturated with the mobile phase. Before beginning the chromatographic development process, the material is also put very carefully onto the TLC plate. In this scenario, the length of time that the analytes contained in the sample have been traveling is considered when determining the retention period of the samples. This method is exceptionally helpful in the field of forensic science since it generates photographic evidence of the facts that can be effortlessly produced in court. In addition to this, every stage in this method is independent of the one that comes before it, which helps to keep any cumulative mistakes to a minimum. This method is typically used to evaluate samples such as illegal narcotics and poisons; however, it may also be used to identify samples of adulterants in food, counterfeit ink, and fabric, and even explosives. In addition, this method is widely used to examine materials. This method also provides outstanding automation, optimization, and detection capabilities while requiring only a little amount of sample preparation [34, 44].
1.2.3 Hyphenated Techniques
Hyphenated techniques refer to the combination of two or more analytical techniques in order to provide more comprehensive and accurate results than each individual technique could provide alone. These techniques have become increasingly popular in recent years, as they allow for a more complete understanding of complex systems and materials. Even if methods of chromatography are helpful for segregating the analytes and their detection is discovered through their retention time, it is not always feasible to estimate the chemical structure with complete accuracy. Because of this, these approaches are frequently combined with others that can shed light on the molecular structure. The most common hyphenated techniques involve coupling chromatography with spectroscopy, which can provide both separation and identification of analytes in a sample. GC, HPLC, and HPTLC are frequently combined or linked with other analytical instruments such as mass spectrometers (MS), FTIR, and nuclear magnetic resonance [45].
Figure 1.7 Diagrammatic representation of GC-MS.
In the GC-MS method, the material is first separated, as it would be in a standard GC analysis as represented in Figure 1.7.
