Criminalistics - Chapter06.doc

<CHAP NUM="6" ID="CH.00.006">chapter 6

<FM><TTL>Inorganic Analysis</TTL>

<KTSET><TTL>Key Terms</TTL>

<KT>alpha ray</KT>

<KT>atomic mass</KT>

<KT>atomic number</KT>

<KT>beta ray</KT>

<KT>continuous spectrum</KT>

<KT>electron</KT>

<KT>electron orbital</KT>

<KT>emission spectrum</KT>

<KT>excited state</KT>

<KT>gamma ray</KT>

<KT>isotope</KT>

<KT>line spectrum</KT>

<KT>neutron</KT>

<KT>nucleus</KT>

<KT>proton</KT>

<KT>radioactivity</KT>

<KT>X-ray diffraction</KT></KTSET>

<OBJSET><TTL>Learning Objectives</TTL>

<P>After studying this chapter you should be able to:

<OBJ><P><INST><              </INST>Describe the usefulness of trace elements for forensic comparison of various types of physical evidence</P></OBJ>

<OBJ><P><INST><              </INST>Distinguish continuous and line emission spectra</P></OBJ>

<OBJ><P><INST><              </INST>Understand the parts of a simple emission spectrograph</P></OBJ>

<OBJ><P><INST><              </INST>List the parts of a simple atomic absorption spectrophotometer</P></OBJ>

<OBJ><P><INST><              </INST>Define and distinguish protons, neutrons, and electrons</P></OBJ>

<OBJ><P><INST><              </INST>Define and distinguish atomic number and atomic mass number</P></OBJ>

<OBJ><P><INST><              </INST>Appreciate the phenomenon of how an atom absorbs and releases energy in the form of light</P></OBJ>

<OBJ><P><INST><              </INST>Explain the concept of an isotope</P></OBJ>

<OBJ><P><INST><              </INST>Understand how elements can be made radioactive</P></OBJ>

<OBJ><P><INST><              </INST>Describe why an X-ray diffraction pattern is useful for chemical identification</P></OBJ></P></OBJSET></FM>

<CASE NUM="1" TY="CS"><TTL>What Killed Napoleon?</TTL>

<P>Napoleon I, emperor of France, was sent into exile on the remote island of St. Helena by the British after his defeat at the Battle of Waterloo. St. Helena was hot, unsanitary, and rampant with disease. There, in 1815, Napoleon was confined to a large reconstructed agricultural building known as Longwood House. Boredom and unhealthy living conditions gradually took their toll on Napoleon’s mental and physical state. He began suffering from severe abdominal pains and experienced swelling of the ankles and general weakness of his limbs. From the fall of 1820, Napoleon’s health began to deteriorate at a rapid rate until death arrived on May 5, 1821. An autopsy concluded the cause of death to be stomach cancer.</P>

<P>It was inevitable that dying under British control, as Napoleon did, would bring with it numerous conspiratorial theories to account for his death. One of the more fascinating inquiries was conducted by a Swedish dentist, Sven Forshufvud, who systematically correlated the clinical symptoms of Napoleon’s last days to those of arsenic poisoning. For Forshufvud, the key to unlocking the cause of Napoleon’s death rested with Napoleon’s hair. Forshufvud arranged to have Napoleon’s hair measured for arsenic content by neutron activation analysis and found it consistent with arsenic poisoning over a lengthy period of time. Nevertheless, the cause of Napoleon’s demise is still a matter for debate and speculation. Other Napoleon hairs have been examined and found to be low in arsenic content. Some question whether Napoleon even had clinical symptoms associated with arsenic poisoning. In truth, forensic science may never be able to answer the question—what killed Napoleon?</P></CASE>

<BM><P>In the previous chapter, analytical techniques were described for characterizing a class of matter known as organics. Generally, these materials contain carbon. Although organic substances constitute a substantial portion of the physical evidence submitted to crime laboratories, carbon does not appear among the earth’s most abundant elements. Surprisingly about three-quarters of the weight of the earth’s crust is composed of only two elements—oxygen and silicon. In fact, only ten elements make up approximately 99 percent of the earth’s crust (see <LINK LINKEND="TB.06.001">Table <TBLIND NUM="1" ID="TB.06.001"/>6–1</LINK>). The remaining elements may almost be considered impurities, although exceedingly important ones. Carbon, the element that is a constituent of most chemical compounds, constitutes less than 0.1 percent of the earth’s crust.</P>

<P>Considering these facts, it is certainly reasonable that non-carbon-containing substances—that is, inorganics—are encountered as physical evidence at crime scenes. One only has to consider the prevalence of metallic materials, such as iron, steel, copper, and aluminum, in our society to understand the possibilities of finding tools, coins, weapons, and metal scrapings at crime scenes.</P>

<TBL NUM="1" ID="TB.06.001"><TTL><P><INST>Table 6–1  </INST>Elemental Abundances as Percentages in the Earth’s Crust</P></TTL>

<P>Less well known, but perhaps almost as significant to the criminalist, is the use of inorganic chemicals as pigments in paints and dyes, the incorporation of inorganics into explosive formulations, and the prevalence of inorganic poisons such as mercury, lead, and arsenic.</P>

<P>To appreciate fully the role of inorganic analysis in forensic science, we must first examine its application to the basic objectives of the crime laboratory—identification and comparison of physical evidence. Identification of inorganic evidence is exemplified by a typical request to examine an explosive formulation suspected of containing potassium chlorate, or perhaps to examine a poisonous powder thought to be arsenic. In each case, the forensic scientist must perform tests that will ultimately determine the specific chemical identity of the suspect materials to the exclusion of all others. Only after completing the tests and finding their results identical to previously recorded tests for a known potassium chlorate or a known arsenic can the forensic scientist draw a valid conclusion about the chemical identity of the evidence.</P>

<P>However, comparing two or more objects in order to ascertain their common origin presents a different problem. For example, a criminalist may be asked to determine whether a piece of brass pipe found in the possession of a suspect compares to a broken pipe found at the crime scene. The condition of the two pipes might not allow for comparison by physically fitting together any broken edges. Under these circumstances, the only alternative will be to attempt a comparison through chemical analysis. It is not enough for the analyst to conclude that the pipes are alike because they are brass (an alloy of copper and zinc). After all, hundreds of thousands of brass pipes exist, a situation that is hardly conducive to proving that these two particular pipes were at one time a single unit. The examiner must go a step further to try to distinguish these pipes from all others. Although this may not be possible, a comparison of the pipes’ trace elements—that is, elements present in small quantities—will provide a meaningful criterion for at least increasing the probability that the two pipes originated from the same source.</P>

<P>Considering that most of our raw materials originate from the earth’s crust, it is not surprising that they are rarely obtained in pure form; instead, they include numerous elemental impurities that usually have to be eliminated through industrial processing. However, in most cases it is not economically feasible to completely exclude all such minor impurities, especially when their presence will have no effect on the appearance or performance of the final product. For this reason, many manufactured products, and even most natural materials, contain small quantities of elements present in concentrations of less than 1 percent. For the criminalist, the presence of <ITAL>trace </ITAL><ITAL>elements</ITAL> is particularly useful because they provide “invisible” markers that may establish the source of a material or at least provide additional points for comparison. <LINK LINKEND="TB.06.002">Table <TBLIND NUM="2" ID="TB.06.002"/>6–2</LINK> illustrates how two types of brass alloys can readily be distinguished by their elemental composition. Similarly, the comparison of trace elements present in paint or other types of metallic specimens may provide particularly meaningful data with respect to source or origin. Forensic investigators have examined the evidential value of trace elements present in soil, fibers, and glass, as well as in all types of metallic objects. One example of this application occurred with the examination of the bullet and bullet fragments recovered after the assassination of President Kennedy.</P>

<TBL NUM="2" ID="TB.06.002"><TTL><P><INST>Table 6–2  </INST>Elemental Analysis of Brass Alloys</P></TTL>