Ultraviolet / Visible Absorption Spectroscopy

Analytical Services: Ultraviolet / Visible Absorption Spectroscopy

G. Dana Brabson, Department of Chemistry, University of New Mexico

General Use
- Quantitative analysis
- Qualitative analysis, especially of organic compounds
- Fundamental studies of the electronic structure of atomic and molecular species
Examples of Applications
- Quantitative determination of the principal and trace constituents in metals and alloys
- Quantitative determination of trace constituents in environmental (air and water) samples. These determinations are often conducted on-site
- Measurement of the rates of chemical reactions
- Identification of the functional groups in organic molecules
- Detection of species in the effluent of liquid chromatographs
- On-line monitoring of species in process streams
- Quantitative analysis of electroplating and chemical treatment baths
- Analysis of wastewater streams before and after treatment
Samples
- Form: Gas, liquid, or solid. Analyses are most commonly performed on liquid solutions
- Size: For solutions, typical sample volumes range from approximately 0.1 to 30 mL
- Preparation: Often quite complex. Complexity increases with the difficulty of placing the analyte in solution and the number of interferences
Advantages
- For quantitative analysis of inorganic ions, spectroscopic samples may contain as little as 0.01 mg/L in the case of species that form highly absorbing complexes
- For qualitative analysis of organic compounds, concentrations of spectroscopic samples may be as small as 100 nanomolar
- The initial capital outlay for ultraviolet/visible spectrophotometric techniques is usually far less than that for related techniques
Limitations
- The analyte must absorb radiation from 200 to 800 nm, or be capable of being converted into a species that can absorb radiation in this region
- Additional steps are often necessary to eliminate or account for interferences by species (other than the analyte) that also absorb radiation near the analytical wavelength
Estimated Analysis Time
- The actual time required to analyze each sample is a matter of minutes. However, it may take several hours to prepare the sample, make the standards, and create a calibration curve
Capabilities of Related Techniques
- Molecular fluorescence spectroscopy: For molecules that fluoresce strongly, this technique offers significantly greater sensitivities and freedom from interferences
- Atomic absorption spectroscopy, optical emission spectroscopy: For quantitative analysis of metals and some nonmetals, these techniques usually offer better sensitivity and almost complete freedom from interferences