5
Spectroscopy of the Solid State
Spectroscopy - Interaction between radiation and matter. NIR – offers possibility of study of interaction of solids with radiation since sample preparation is not required.
Ultraviolet
v i s i b l e
NIR
MIR
FIR
ESR
NMR
Region
Infrared
Microwave
Radio, TV Waves
Interaction
Nuclear Transitions
Inner Shell Electronic Transitions
Valance Electron Transitions
Molecular Vibrations
Molecular Rotations
Spin Orientation in Magnetic Field
Wavelength (m) 10-10 10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 1 101
Courtesy Bruker Optics
2
Infrared Spectroscopy Regions of Infrared Spectrum: • A vibration occurs when the dipole moment of the molecule changes, and the Far Infrared: 650 – 25 cm-1 molecule interacts with Mid Infrared: 4000 – 650 radiation equal to the cm-1 frequency of vibration. Near Infrared: 12800 – 4000 cm-1(0.8 - 2.5 m, or 8002500 nm)
NIR Fundamentals: Electromagnetic Spectrum
12,500 cm-1 (800 nm)
4,000 cm -1 (2500 nm)
108 Frequency (cm-1)
107
106
105
104
103
102
101
1
10-1y
X – Ray
STRUCTURED ORGANIC PARTICULATE SYSTEMS
RUTGERS UNIVERSITY PURDUE UNIVERSITY NEW JERSEY INSTITUTE OF TECHNOLOGY UNIVERSITY OF PUERTO RICO AT MAYAGÜ EZ
10/11/2005 1
6
Disadvantages of NIRS
• • • • • Calibration requires careful experimental design. Depends on accuracy of reference methods. Overlapping bands, not easy to interpret. Differences in spectra are often very subtle. Usually not for trace level analysis.
4
Advantages of NIR
Process Applications: Excellent analytical method for the study of solids. Spectra may be obtained in non-invasive manner. Remote sampling is possible (good for hazardous materials). Possibility of using it in a wide range of applications (physical and chemical), and viewing relationships difficult to observe by other means. Laboratory Applications: Sample preparation is not required leading to significant reductions in analysis time. Waste and reagents are minimized.
Vibrational Spectroscopy for Pharmaceutical Analysis
Part IX. Introduction and Origin of NIR Bands Rodolfo J. Romañ ach, Ph.D.
ENGINEERING RESEARCH CENTER FOR
3
Infrared Spectroscopy (mid-IR) and Near Infrared Spectroscopy
Infrared Spectroscopy (mid-IR), studied in organic chemistry courses; principal identification method in pharmaceutical industry. Mid-IR sharp bands that provide structural information on compounds; better than fingerprint. (region of 4000 cm-1 to 400 cm-1, wavelengths from 2.5 m to 25 m). Near IR weak overlapping bands; difficult to interpret (region of 12500 to 4000 cm-1, wavelengths from 0.8 to 2.5 m.)