5.4 Notes5.4 Notes

Objectives 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

BeerBeer’’s Laws Law

The relationship exists between absorption The relationship exists between absorption and concentrationand concentration

A = kcA = kc Where Where AA is the absorption or quantity of light, is the absorption or quantity of light,

cc is the concentration of the absorbing is the concentration of the absorbing material and material and kk is a proportionality constant is a proportionality constant

FT-IRFT-IR

Fourier transport infrared spectrometer Fourier transport infrared spectrometer using a Michelson interferometerusing a Michelson interferometer The current laboratory approach. The current laboratory approach.

It uses a prism and two mirrors to direct It uses a prism and two mirrors to direct light to a samplelight to a sample As light passes through the sample it is As light passes through the sample it is

detected by an instrument that measures all detected by an instrument that measures all wavelengths simultaneouslywavelengths simultaneously

Then uses a mathematical operation (FT) to Then uses a mathematical operation (FT) to decode the signals and record the wavelength. decode the signals and record the wavelength.

FT-IRFT-IR

It is calculated by a computer and It is calculated by a computer and prepares a printout. prepares a printout.

Samples have been dissolved in a Samples have been dissolved in a solvent.solvent. Glass cells used to measure the visible Glass cells used to measure the visible

regionregion Quartz to measure the UV regionQuartz to measure the UV region Sodium chloride or potassium bromide Sodium chloride or potassium bromide

used to measure the restused to measure the rest

UV & Visible UV & Visible SpectrophotometrySpectrophotometry

measures the absorbance of UV and measures the absorbance of UV and visible light based on wavelength or visible light based on wavelength or frequency. frequency. Heroin has a wavelength of 278 nm. Heroin has a wavelength of 278 nm. Sugar and starch are often the dilutants for Sugar and starch are often the dilutants for

heroin and do not absorb UV light.heroin and do not absorb UV light.

Absorption in IR RegionAbsorption in IR Region

is more specific and can be the equivalent is more specific and can be the equivalent of a fingerprint based on the spectra. of a fingerprint based on the spectra. Thousands of organic compounds have been Thousands of organic compounds have been

indexed and catalogued.indexed and catalogued.

GC-Mass SpecGC-Mass Spec

Use of gas chromatography and mass Use of gas chromatography and mass spectrometry can now be used identify spectrometry can now be used identify specificallyspecifically

Substance is passed through a GC then Substance is passed through a GC then flows into a Mass Specflows into a Mass Spec Material is ionized and decomposesMaterial is ionized and decomposes Smaller fragments are separated by their massesSmaller fragments are separated by their masses NO TWO SUBSTANCES PRODUCE THE NO TWO SUBSTANCES PRODUCE THE

SAME FRAGMENTED PATTERN.SAME FRAGMENTED PATTERN.

In-Class Assignment/HomeworkIn-Class Assignment/Homework