Module No.15: UV/visible spectroscopy-forensic application. PAPER No. 4: Instrumental Methods and Analysis

Transcription

1 SUBJECT Paper No. and Title Module No. and Title Module Tag Paper No. 4: Instrumental Methods and Analysis Module No.15: UV/visible spectroscopy-forensic FSC_P4_M15

2 TABLE OF CONTENTS 1. Learning Outcomes 2. Applications of UV/visible spectroscopy in forensic science Analysis of narcotics and drug testing Determination of alcohol in blood Ink analysis Drug overdose study Analysis of carboxyhemoglobin in forensic blood samples Forensic determination of metals by UV/visible spectroscopy Examination of blood stains by UV/Visible spectroscopy Forensic discrimination of dyed textile fibers using UV/Visible spectroscopy 2.9. Quantitative determination of hemoglobin in tooth and bone sample using UV/visible spectroscopy 3. Summary

3 1. Learning Outcomes After studying this module, you shall be able to Understand the s of UV/visible spectroscopy in forensic science. 2. Applications of UV/visible spectroscopy in forensic science Forensic drug analysis deals with the identification and quantification of illegal drugs. The testing of drugs is generally carried out in two steps, namely, screening and confirmation. UV/visible spectroscopy is widely used as a very significant tool for both qualitative and quantitative drug analysis. Some of the s of UV/visible spectroscopy in forensic science as discussed below Analysis of narcotics and drug testing Analysis of narcotics and related drugs is an important part of forensic science. UV/Vis molecular absorption is routinely used for the analysis of narcotics and for drug testing. The presence of these drugs can be confirmed from their absorption maxima i.e. λ max or by comparing the UV/visible spectra of these drugs with spectra of authentic sample. The value of λ max (nm) for various abusive drugs is given in Table 1.

4 Table 1. Absorption maxima for various abusive drugs S. No. Drug Absorption maxima (λ max in nm) 1 Cocaine in 0.2 N H 2 SO Codeine in water Ecstasy or MDMA in ethanol Morphine in acidic solution Phencyclidine or PCP in 0.1 M HCl Amphetamine in methanol Nicotine in 0.2 N H 2 SO Caffeine in 0.2 N H 2 SO Metamphetamine in methanol Tetrahydrocannabinol in methanol Determination of alcohol in blood UV/visible spectroscopy can be used for quantitative estimation of blood alcohol using the breathalyzer test. In this test, sample of breath of the person is passed through an acidic solution of potassium dichromate which is orange in colour. Potassium dichromate in acidic medium is an oxidizing agent and oxidizes ethanol to acetic acid while dichromate ions get reduced to green colored Cr 3+ ions. The concentration of ethanol in the breath sample is determined by the decrease in absorbance at 440 nm around which the dichromate ion absorb. Using this value, by using Lambert-Beers s law, the concentration of alcohol can be then measured Ink analysis Ink analysis is one of the areas in forensic questioned document aims at comparing, identifying, characterizing and discriminating ink obtained from writing instrument used to write on a document. Ink becomes important forensic evidence when it is written on a document suspected to be associated with criminal activities such as threatening letters, insurance frauds and will frauds.

5 The examination of different inks and their classification can be easily done with UV-Vis spectra of pen inks. This is much simple and quick to perform as compared to other methods of ink analysis such as chromatographic and spectroscopic techniques Drug overdose study The drug overdose may lead to death. The cases of drug overdose can be studied by UV/visible spectroscopy. For example overdose of aspirin can be studied by studying the UV/visible spectra of blood plasma of a person with overdose of aspirin. Aspirin is prepared by the acetylation of salicylic acid using acetic anhydride. It is usedas a drug for many purposes like as an analgesic to reduce pain, anti-inflammatory to reduce inflammation, antipyretic to reduce temperature, and platelet aggregation inhibitor to thin the blood and stop clotting. Therapeutic levels taken after a heart attack are typically mg/l and for post by-pass operations 75 mg/l. The levels of salicylate present in blood plasma can be analysed using UV-visible spectroscopy to indicate if the subject has taken a therapeutic dose or an overdose. This method involves measuring the absorbance of the red-violet complex of ferric and salicylate ions at about 530 nm using a UV/Visible spectrometer Analysis of carboxyhemoglobin in forensic blood samples Carbon monoxide (CO) is colorless, tasteless, odorless, and nonirritating and hence its exposure and intake in human beings is impossible to detect. When inhaled, CO is instantly absorbed from the lungs into the bloodstream and has highly toxic effect. In the blood stream, the carbon monoxide slowly forms a reversible complex with hemoglobin (Hb) known as carboxyhemoglobin (COHb). The presence of COHb in the blood decreases its oxygen carrying capacity, and hence reduces the availability of oxygen to body tissues, resulting in tissue hypoxia. It may even lead to death, which can be explained as follows. The increase in the level of COHb reduces the oxygen delivery. It is worsened by impaired perfusion resulting from hypoxic cardiac dysfunction. This further potentially damages the cellular oxidative metabolism and hence lead to death. The binding of carbon monoxide with heme chromophore effects its absorption in UV/visible region. That is why, the levels of COHb can be determined by UV/visible spectra of the blood sample of a person with suspected carbon monoxide poisoning.

6 Total hemoglobin can be measured by performing a reaction of the hemoglobin present with potassium cyanide to form a hemoglobin cyanide complex. In this method, hemoglobin is reacted with potassium cyanide to form a hemoglobin cyanide complex. This complex has a peak around 546 nm, which can be measured and quantitated Forensic determination of metals by UV/visible spectroscopy Iron, aluminium, and copper are three metals, which are most widely used for fabricating various articles of daily need. These elements are found as a part of almost every weapon, tools, and metal shards in crime scenes. Thus, the forensic investigation of these metal ions is an important area of study. Weapons often used in robberies to cut metals or in murders. The investigation of crime scenes often revealed the presence of these metal ions usually on clothing of suspect. Other metals such as lead, arsenic are sometimes encountered at industrial work places and many time used as poisons. Arsenic salts are commonly used as insecticides in houses. In addition to these metal ions are also found in paints, dyes, explosives such as gunpowder and in glass. The presence and concentration of these metal ions can be easily measured by UV/visible spectroscopy using various methods as summarized in Table 2.

7 Table 2: UV/visible analysis of various metals Metal Method λ in nm Aluminum React with Eriochrome cyanide R dye at ph6 to forms 535 red to pink complex Arsenic On reaction with Zn arsenic reduces to AsH 3 which react 535 with silver to form red color complex diethyldithiocarbamate Cadmium On reaction with chloroform solution of dithizone in 518 presence of NaOH gave pink to red complex Chromium Cr(VI) react with diphenylcarbazide to give red-violet 540 complex Lead On reaction with chloroform solution of dithizone in 510 presence of with NH 3 gave cherry red complex Mercury On reaction with chloroform solution of dithizone under 492 acidic conditions gave orange complex Copper React with neocuprine in neutral to slightly acid solution and extract into CHCl 3 /CH 3 OH; forms yellow complex Examination of blood stains by UV/Visible spectroscopy At crime scenes, especially related to murder, the most significant of evidence for forensic investigators are blood stains. The sample of blood stain collected from the crime scene can be used for DNA-profiling for verifying the suspect s identity as well as for pattern analysis in order to reconstruct the crime. UV/visible spectroscopy method can be used to study blood stains by detecting the presence of enzyme activity in stain. There is higher activity of enzymes lactate dehydrogenase (LDH), glutamic oxaloacetic transaminase (GOT) and glutamic pyruvic transaminase (GPT) in bloodstains than in serum; also there is a comparable activity in completely hemolyzed blood. This forms the basis for the use of UV/visible spectroscopy method for analysis of blood stains. Using a combination of LDH/GOT and GOT/GPT ratios, the age estimation up to 12 weeks after formation of the bloodstain has been estabilished.

8 In this method, removal of the bloodstain, followed by extraction with saline is done. The sample so prepared is then subjected to labeling of the enzymes and is detected at a wavelength of 340 nm. It is important to note that the GOT/GPT ratio remains stable over the first weeks, while the LDH/GOT ratio is initially high (>10), and decreases to a ratio of 5 after eight weeks Forensic discrimination of dyed textile fibers using UV/VIS spectroscopy In incidents involving personal contact, such as homicide, assault, and sexual offenses, as well as hit-and-run accidents and other crimes, fibers are often encountered as trace evidence. Objects peripherally associated with crimes, such as weapons or cars involved in armed robberies, etc also most often have fibers associated with them as trace evidence. From forensic point of view, the knowledge of chemistry of fibres and fibre dyes is very important for both i.e., as the basis of fiber identification and for the forensic relevance of various fiber/dye combinations. The UV/visible spectroscopy offers a significant contribution to differentiate between various type of fibers and dyes. The UV/visible spectra of the trace evidence as fibre collected from crime scene can be easily matched with reference spectra of known fibre materials and dyes. For example Figure 1 shows the UV/visible spectrum of various fibers.

9 Figure 1. UV-VIS spectrum of yellow fibers mounted in glycerin using quartz slides and cover slips: (A) cotton; (B) acrylic, (C) nylon; (D) polyester Quantitative Determination of Hemoglobin in Tooth and Bone sample by UV/visible spectroscopy In the forensic investigation, the detection and quantification of hemoglobin in the skeletal or dried remains can be very significant. This can be achieved with the help of UV/visible spectroscopy using leuco crystal violet dye. E.g., Extractions of hemoglobin from a femur bone by can be done using 0.5 M hydrochloric acid and from a tooth it can be done by using 6.0 M urea. A violet product is obtained when these extractions are treated with leuco crystal violet. Using the measured absorbance at 590 nm of each extraction, the corresponding amount of hemoglobin in each sample can be determined. UV/visible spectrum of extract containing hemoglobin is shown in Figure 2. Figure 2. The UV/Vis absorbance spectrum of the leuco crystal violet dye reaction with 1.0 µm Hb.

10 3. Summary UV/visible spectroscopy provide an important method for both qualitative and quantitative analysis in forensic investigations. UV/visible spectroscopy is most widely used for detection and analysis of drugs of abuse based upon their absorption maxima. It also found for determination of alcohol in blood. Ink analysis which is important part of forensic study can also done with UV/visible spectroscopy. UV/visible spectroscopy is also used for drug overdose study in body. UV/visible spectroscopy can also used for study of carbon monoxide poising by analysis of carboxyhemoglobin in forensic Blood Samples. Determination of metals in forensic samples can also done with UV/visible spectroscopy. UV/visible spectroscopy can also used to find the age and for analysis of blood stains commonly present at crime scenes. UV/visible spectroscopy can be used for forensic discrimination of dyed textile fibers. UV/visible spectroscopy can be used for quantitative determination of hemoglobin in tooth and bone samples.