This is a draft cheat sheet. It is a work in progress and is not finished yet.
Definitions
Spectroscopy |
Interaction of radiation, traditionally electromagnetic radiation, with matter |
Spectrometry |
Measurement of the intensity of radiation |
Spectrophotometry |
Quantitative measurement of light absorption and transmission as function of the wavelength |
Absorbance |
Log measure of the amt of light that is absorbed when passing though a substance |
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Beer's Law: A=logIo/It |
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Components of spectroscopic instruments
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Figures of Merit
Sensitivity |
High, steep curve so that for every small change in conc, there is a large change in signal |
Signal to noise ratio (S/N) |
Compares level of desired signal to level of background noise. Mean of signal/standard deviation of noise. Large S/N >3 times that SD of noise |
Specificity |
High responsiveness to target analyte |
Detection limit |
Lowest analyte conc. that can be measured at a certain confidence level. 1) Run solvent/blank multiple times 2) Signal for LOD=mean of blank +3SD of blank. In conc. below detection limit, cannot measure sample because don;t know if signal is from analyte or solvent |
Dynamic range |
Wide, linear concentration range that can be determined using the calibration curve ie. calibration curve to be proportional |
Accuracy |
Closeness of a measured value to a standard value (reference sample) |
Precision |
Closeness of 2 or > measurements to each other .. |
Speed |
Ease and convenience |
Skill required of operator |
As conc. decrease, we are limited by prep error and intrumental error (signal fluctuates) ie. % error will increase |
Cost and availability of equipment |
Per-sample cost |
Relative standard deviation (RSD) ...% = standard deviation/mean |
We are reaching LOD of instrument thus decrease in concentration, RSD increases |
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