Practical Forensic Microscopy (eBook)

A Laboratory Manual

Barbara P. Wheeler (Autor)

eBook Download: EPUB

2021 | 2. Auflage
John Wiley & Sons (Verlag)
9781119154518 (ISBN)

Infos

An applied approach to teaching forensic microscopy in educational settings, featuring new experiments and an up-to-date overview of the field

Practical Forensic Microscopy: A Laboratory Manual, 2nd Edition, is a unique resource that brings the microscopic procedures used by real-world forensic investigators to the college laboratory, providing hands-on knowledge of the microscopes and microscopic techniques used in the field. Presenting a balanced, skills-based approach to the subject, this student-friendly lab manual contains dozens of experiments designed to cover the various microscopic evidence disciplines, including examinations of fingerprints, firearm, toolmark, shoeprint and tire impressions, gunshots, fibers, soil, glass breakage, drugs, semen, and human hair.

The second edition includes revised and updated experiments that reflect current technologies and techniques used in forensic science, including new experiments examining plastic film, food condiments, feathers, building materials, explosive residue, cigarette butts and more. Each chapter includes a list of simple objectives for the experiment, a general overview of the topic, further readings, and selected references. The manual contains worksheets and templates for students to use when compiling analytical results. The concluding chapter features an innovative case scenario that requires students to analyze items of evidence, complete a laboratory report, reach a conclusion, and present their findings. This popular lab manual:

• Teaches practical forensic microscopy skills through hands-on experiments and engaging practical activities
• Covers a wide range of microscopes and forensic tools, including stereomicroscopes, ocular micrometers, and fluorescence, polarized light, and phase contrast microscopes
• Explains simple stereomicroscopic techniques for analyzing various types of common forensic evidence
• Includes more complex procedures for examining biological, drug, and trace evidence Discusses laboratory safety, microscope maintenance, and the Micro Kit

Written by an author with years of academic and professional experience, Practical Forensic Microscopy: A Laboratory Manual, 2nd Edition, is a must-have companion for any college-level forensic science course with a laboratory component, and is a useful supplement for related courses that cover microscopy and the principles of forensic lab procedures.

Barbara P. Wheeler? worked with the Kentucky State Police Forensic Laboratory for many years, providing forensic work and analytical examinations to the law enforcement community. As Adjunct Professor in the Forensic Science Program at Eastern Kentucky University, she taught in various forensic courses and with placing students in laboratory internships. Wheeler has worked thousands of criminal cases and has testified in district, state, and federal courts as an expert witness in forensics.

Inhalt

Preface ix

Acknowledgments xi

Laboratory Safety xiii

Microscope Maintenance xv

The Micro Kit xvii

About the Companion Website xix

Experiments 1

1 Stereomicroscope 3

Experiment 1A: Familiarization with the Stereomicroscope 5

2 Compound Light Microscope 13

Experiment 2A: Familiarization with the Compound Light Microscope 15

Experiment 2B: Measurements Using the Ocular Micrometer 23

Experiment 2C: Microscopic Mounting Techniques 29

Experiment 2D: Determining Refractive Index 35

3 Polarized Light Microscope 47

Experiment 3A: Familiarization with the Polarized Light Microscope 49

Experiment 3B: Determining Refractive Index of Anisotropic Materials 57

Experiment 3C: Determining Sign of Elongation and Birefringence 63

4 Fluorescence Microscope 69

Experiment 4A: Familiarization with the Fluorescence Microscope 71

5 Phase Contrast Microscope 77

Experiment 5A: Familiarization with the Phase Contrast Microscope 79

Application Experiments 85

6 Experiment 6: Physical Match Examinations 87

7 Experiment 7: Construction Examinations of Evidence 93

8 Experiment 8: Lamp Filament Examinations 103

9 Experiment 9: Fingerprint Examination and Comparison 113

10 Experiment 10: Tool Mark Examinations 121

11 Experiment 11: Firearms Examinations 127

Experiment 11A: Gunshot Residue Examinations 135

12 Experiment 12: Shoe and Tire Impression Examinations 145

13 Experiment 13: Botanical Examinations 151

14 Experiment 14: Paint Examinations 159

15 Experiment 15: Cigarette Butt Examinations 165

16 Experiment 16: Document Examinations 173

17 Experiment 17: Hair Examinations 183

Experiment 17A: Animal Hair Examinations 195

Experiment 17B: Determination of Racial and Somatic Origin Characteristics of Human Hair 205

Experiment 17C: Human Hair Examinations and Comparisons 213

Experiment 17D: Evaluation of Human Hair for DNA 223

18 Experiment 18: Feather Examinations 231

19 Experiment 19: Glass Breakage Determinations 239

Experiment 19A: Glass Examinations 247

20 Experiment 20: Fiber Examinations 257

Experiment 20A: Natural Fiber Examinations 265

Experiment 20B: Man-made Fiber Examinations 279

Experiment 20C: Fiber Comparisons 289

21 Experiment 21: Soil Examinations 295

Experiment 21A: Identification of Minerals in Soil 303

22 Experiment 22: Microchemical Testing - Inorganic Ions 317

23 Experiment 23: Building Material Examinations 329

24 Experiment 24: Explosive Residue Examinations 337

25 Experiment 25: Food Condiment Examinations 345

26 Experiment 26: Plastic Film Examinations 355

27 Experiment 27: Microscopic Examination of Controlled Substances 363

28 Experiment 28: Semen Examinations 377

Application Experiments, Instrumental Microscopy 383

29 Experiment 29: Fourier Transform Infrared Microspectrometry Examinations 385

30 Experiment 30: UV-Visible-NIR Microspectrophotometry Examinations 395

31 Experiment 31: Thermal Microscopy Examinations 405

32 Experiment 32: Scanning Electron Microscopy Examinations 413

33 Experiment 33: Case Study Scenario 423

Appendices 429

A Optical Properties of Natural Fibers 431

B Optical Properties of Man-made Fibers 433

C Michel-Lévy Chart 437

D Dispersion Staining Graph 439

E Circle Template 441

Glossary of Microscopy Terms 443

Index 453

Textauszug

Chapter 1
Experiment 1A: Familiarization with the Stereomicroscope

Recommended pre‐lab reading assignment:

Schlueter GE, Gumpertz WE. The Stereomicroscope, Instrumentation and Techniques. American Laboratory. 1976; 8(4): 61–71.

Recommended website:

Flynn BO, Davidson MW. SMZ‐1500 Stereoscopic Microscope [Java Interactive Tutorial; cited 2019]. Available from: http://www.microscopyu.com.

Objective

Upon completion of this practical exercise, the student will have developed a basic understanding of:

1. components of the stereomicroscope
2. magnification
3. field of view
4. depth of field
5. working distance

Introduction

A microscope is defined as an optical instrument that uses a combination of lenses to produce a magnified image of small objects. To accomplish this, a stereomicroscope utilizes several components, which gather light and redirect the light path so that a magnified image of the viewed object can be focused within a short distance.

A stereoscopic microscope contains five basic components: light source, sample stage, objective(s), focusing knob, and oculars. This is somewhat different in construction than standard compound light microscopes, in the fact that there is no condenser.

There are two choices of illumination with the stereomicroscope. Reflected light, light that bounces off a surface, is used for objects that are opaque (objects impervious to light). If the sample is transparent it can be observed with transmitted light, light that is able to transfer through a material. Some samples are best observed with both reflected and transmitted light and can be viewed under both settings using a stereomicroscope.

Some stereomicroscopes use a simple platform for a sample stage (see Figure 1A-1), while others utilize the tabletop. The body of the stereomicroscope is the area that holds or contains the other components of the microscope: focusing knobs, objectives, and oculars. Knobs are used to raise and lower the body of the microscope so that various size samples can be viewed in focus. The objective lenses are typically built into the body of the stereomicroscope with a mechanism for changing magnifications from the outside. Older model stereomicroscopes and the less expensive newer stereomicroscopes employ a series of fixed objective lenses, which step up the magnification in discrete increments. The newer and typically better stereomicroscopes utilize a continuous zoom lens system, which allows any magnification within the range of the microscope. The objective collects the light from the sample and magnifies the focused image to the oculars, which further magnifies and refocuses the image to the viewer’s eye.

Figure 1A-1 The Leica EZ4TM microscope is capable of providing both reflected and transmitted light while utilizing continuous zoom magnification.

There are two general designs of a stereomicroscope: Greenough and the Common Main Objective (CMO). The optical path for both stereoscope designs is shown in Figure 1A-2.

Figure 1A-2 Optical path for a stereomicroscope: (a) Greenough design, and (b) CMO design.

The Greenough design (Figure 1A-2a) utilizes two identical optical systems within twin body tubes. The CMO (Figure 1A-2b) utilizes a single objective that is shared between a pair of ocular tubes and lens assemblies. With a Greenough design stereomicroscope, the light initially interacts with the sample. Once it leaves the sample, it is collected by two identical optical systems. These systems are made up of an objective and a pair of image‐inverting prisms, which de‐rotate and invert the magnified sample image received from the back focal plane of the objectives to the oculars. The oculars re‐focus the sample image to the viewer’s eye. With a CMO stereomicroscope, the light interacts with the sample and is then collected by the common main objective. Light entering the objective is divergent light but once it leaves the objective it is parallel light, which is then split by a series of prisms redirecting the light to each of the oculars. The objective produces a sample image on its back focal plane. The oculars receive this sample image and re‐focus it onto the viewer’s eye. Most stereomicroscopes are CMO.

Magnification is the process by which lenses are used to make objects appear larger. A simple lens increases the refraction and in turn produces a virtual image that appears larger. Magnification of a simple lens is described by the equation:

(1A-1)

where f is the focal length (the distance from a lens to its point of focus in centimeters), and 25 is the normal reading distance in centimeters.

Magnification of an image of a sample produced by a lens can be determined by the relationship:

(1A-2)

The portions of a microscope (oculars, objectives, etc.) that increase magnification usually have visible labeling noting the magnification power. To determine the combined magnification of a microscope, all magnification components must be taken into account. Total magnification is determined by multiplying all factors as shown in Equation 1A-3.

(1A-3)

When using any microscope, the examiner must select the best magnification for viewing each sample. There are several factors that should be considered when determining magnification power. To start, it is important that sufficient detail can be viewed for the sample. In addition, when examining samples, a good microscopist always fills the viewing area to enhance detail but also to minimize white space. This often requires that the sample be viewed under a higher magnification. However, it is equally important to remember that when using high magnifications, a smaller portion of an overall sample is viewed. Field of view relates to that portion of the object that one is able to see when using the microscope. Field of view varies with magnification. A low power of magnification will provide the greatest field of view. Likewise, higher magnification restricts the field of view.

Depth of field is another factor to consider when choosing magnification. In photography if a lens focuses on a subject at a distance, all subjects at that distance are sharply focused. Subjects that are not at the same distance are out of focus and theoretically are not sharp. However, since human eyes cannot distinguish a very small degree of “unsharpness,” some subjects that are in front of and behind the sharply focused subjects can still appear sharp. The zone of acceptable sharpness is referred to as the depth of field. Thus, increasing the depth of field increases the sharpness of an image. Just as in classical photography, depth of field is determined by the distance from the nearest object plane in focus to the farthest plane also simultaneously in focus. In microscopy, depth of field is very short and usually measured in units of microns. The term depth of field, which refers to object space, is often used interchangeably with depth of focus, which refers to image space. Once a focus has been obtained on a sample, areas lying slightly above and below will be blurred. The area or thickness of sample that remains in focus is the depth of field. Depth of field also varies with magnification.

The working distance of a stereomicroscope is another factor to bear in mind. The working distance is the distance between the objective lens and the sample. Stereomicroscopes generally have a large working distance and may also be placed on an adjustable stand, allowing for even more flexibility. The distance between the objective and the sample is determined by the focal length of the objective. To focus the sample, the distance is changed using the coarse focus for large increments and the fine focus for small changes in distance.

The stereomicroscope is a valuable tool in a forensic laboratory. The stereomicroscope combines low magnification, good depth of field, and a large working distance so that samples can be viewed three‐dimensionally. These properties make it the “first instrument” used in many examinations.

Equipment and Supplies

Stereomicroscope

Micro kit

Samples:

Artificial Sweetener

Beard Hair

Black Pepper

Cigarette Ash

Cigarette Tobacco

Coffee

Glass

Graphite

Nutmeg

Oregano

Pencil Dust

Pencil Eraser Dust

Rosemary

Rust

Salt

Sand

Soap Powder

Soil

Tea

Petri dish unknowns (various combinations of eight [8] samples from the Samples list)

Safety

Use standard laboratory safety procedures as described in guidelines set by your instructor.

Part I: Parts of a Stereomicroscope

1. Obtain a photograph of the stereomicroscope used in the...

Produkt-Details

• Erscheint lt. Verlag: 31.3.2021
• Sprache: englisch
• Themenwelt: Naturwissenschaften ► Biologie
• Themenwelt: Naturwissenschaften ► Chemie ► Analytische Chemie
• Schlagworte: Analytische Chemie / Forensik • Chemie • Chemistry • college forensic science • forensic examinations • forensic instrumentation • forensic microscopes • forensic microscopy • forensic microscopy exercises • forensic microscopy experiments • forensic microscopy lab manual • forensic microscopy techniques • Forensics • Forensische Wissenschaft • Microscopy • Mikroskopie
• ISBN-13: 9781119154518 / 9781119154518