5.4 Notes

Objectives Describe the utility of ultraviolet and infrared spectroscopy for the identification of organic compounds Describe the concept and utility of mass spectrometry for identification analysis

Beer’s Law The relationship exists between absorption and concentration A = kc Where A is the absorption or quantity of light, c is the concentration of the absorbing material and k is a proportionality constant

FT-IR Fourier transport infrared spectrometer using a Michelson interferometer The current laboratory approach. It uses a prism and two mirrors to direct light to a sample As light passes through the sample it is detected by an instrument that measures all wavelengths simultaneously Then uses a mathematical operation (FT) to decode the signals and record the wavelength.

FT-IR It is calculated by a computer and prepares a printout. Samples have been dissolved in a solvent. Glass cells used to measure the visible region Quartz to measure the UV region Sodium chloride or potassium bromide used to measure the rest

UV & Visible Spectrophotometry measures the absorbance of UV and visible light based on wavelength or frequency. Heroin has a wavelength of 278 nm. Sugar and starch are often the dilutants for heroin and do not absorb UV light.

Absorption in IR Region is more specific and can be the equivalent of a fingerprint based on the spectra. Thousands of organic compounds have been indexed and catalogued.

GC-Mass Spec Use of gas chromatography and mass spectrometry can now be used identify specifically Substance is passed through a GC then flows into a Mass Spec Material is ionized and decomposes Smaller fragments are separated by their masses NO TWO SUBSTANCES PRODUCE THE SAME FRAGMENTED PATTERN.

In-Class Assignment/Homework