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scientific Principles, Instrumentation, and Equipment

The tools of the modern analytical chemist began to emerge in the 1600s as simple, even primitive, tests that relied on little more than a color change as a positive result. Later developments were tests that integrated the separation of compounds with detection, similar to the Marsh test, which separated arsenic from tissues. Simple separations and detection were the mainstays of forensic chemists from Orfila's time to the middle of the 20th century. It is only within the last 60 years that instrumentation has become the core of forensic testing and only within the last 20 years that computer-enabled automation has become common. Still, many modern forensic tests begin with simple color tests and end with sophisticated instruments. In a sense this approach is a replay of the history of the tools and techniques used by forensic chemists.

EARLY ANALYTICAL TECHNIQuEs: WET CHEMisTRY

Chemistry was born from the study of drugs and medicine, but analytical chemistry sprang from the study of metals. Once ancient

The "flow" of a forensic analysis. The goal is to narrow down the possibilities to the smallest size possible or to one single compound.

peoples recognized the value of precious metals such as gold and silver, they required methods for detecting and validating purity. Chemists learned to use heat to extract gold and silver from raw ores and materials, a technique that is still part of modern metallurgy. Those skilled in these arts were the first analytical chemists, and their techniques are now referred to as dry chemical techniques since no solutions were used to separate the metals. In fact, all that was required was a very hot fire.

The first wet methods for the analysis of metals and gold were published in the early 1500s. The wet method was so named because the sample of metal was dissolved in a water-based solution such as a strong acid. By making and weighing a compound with a known percentage of the metal, it was relatively easy to calculate the amount of the metal in the original sample. The only instrument needed was a reliable balance to weigh the initial sample and final product. Since the resulting product falls out of solution to form a solid, this type of wet chemical method is called a gravimetric method. Gravimetric analyses are still used today and most students who take chemistry in college still perform gravimetric laboratory experiments to learn laboratory fundamentals. From the forensic perspective these methods are important because they represent the first separation techniques.

Gravimetric methods were among the first that were both quantitative and qualitative, meaning that it was possible to determine both

All possible com/,

All possible com/,

Definitive identification

Screening tests

Presumptive tests

Definitive identification

Screening tests

Quantitative analysis

O Infobase Publishing what was present in a sample (qualitative) and how much (quantitative). Both capabilities are still crucial in forensic chemistry. The early dry heating methods used to separate metals were crude, and quantitative results were not reliable. However, once chemists learned

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