Singlet and Triplet States
Photoluminescence is divided into two categories: fluorescence and phosphorescence. A pair of electrons occupying the same electronic ground state have opposite spins and are said to be in a singlet spin state; […]
Illustration
Graphite Furnace
A typical electrothermal atomizer, also known as a graphite furnace, consists of a cylindrical graphite tube approximately 1–3 cm in length and 3–8 mm in diameter. As shown here, the graphite tube […]
Cross-Sectional Profile of Flame in FAAS
The illustration below shows a cross-section through a typical flame looking down the burner’s slot along the source radiation’s optical path. The primary combustion zone is usually rich in gas combustion products that […]
Absorbance vs. Height Profiles in FAAS
Where within the flame one measures absorbance is critical as two competing processes affect the concentration of free atoms in the flame. The more time the analyte spends in the flame the […]
Methods for Improving Precision in Absorbance Measurements
As shown here, the relative uncertainty in determining absorbance (and thus in determining concentration) is greater at very high and very low absorbances (that is, when very little or almost all of […]
Uncertainty in Measurement of Absorbance
In absorption spectroscopy, precision is limited by indeterminate errors—primarily instrumental noise—introduced when measuring absorbance. Precision is generally worse for low absorbances where P0≈ PT, and for high absorbances when PT approaches 0. […]
Mole-Ratio Method for Determining Metal-Ligand Stoichiometry
An alternative to the method of continuous variations for determining the stoichiometry of metal-ligand complexes is the mole-ratio method in which the amount of one reactant, usually the moles of metal, is held […]
Method of Continuous Variations
The method of continuous variations, also called Job’s method, is used to determine the stoichiometry of a metal-ligand complex. In this method we prepare a series of solutions such that the total […]
Spectral Searching and Spectral Subtraction
With the availability of computerized data acquisition and storage it is possible to build digital libraries of standard reference spectra. The identity of an a unknown compound can often be determined by […]
Determining Absorbance in IR Spectroscopy
A quantitative analysis based on the absorption of infrared radiation, although important, is less frequently encountered than those for UV/Vis absorption. One reason is the difficulty in establishing a 100% T (A […]
FT-IR Spectrometer
The illustration below shows an FT-IR spectrometer equipped with a diamond ATR sample cell. The inserts show a close-up photo of the sample platform, a sketch of the ATR’s sample slot, and […]
Effect of Signal Averaging on Signal-to-Noise Ratio
Examples showing the effect of signal averaging on a spectrum’s signal-to-noise ratio. From top to bottom: spectrum for a single scan; average spectrum after four scans; and average spectrum after adding 16 […]