Glossary of Terms

Absorbance – An expression for the relative amount of light absorbed by the sample, which is determined by using a logarithmic relationship to transmittance.

Beer’s Law – An optical law which states that the amount of light transmitted through a substance is logarithmically related to the concentration of the absorbing species and the distance that the light travels through the material.

Calibration file –A file that uses the analyzer to evaluate each spectra, which is developed by comparing lab results to spectra obtained from ProSpect.

Electromagnetic radiation – Electromagnetic radiation (EM radiation or EMR) is a form of energy emitted and absorbed by charged particles. EMR has both electric and magnetic field components, which stand in a fixed ratio of intensity to each other, and which oscillate in phase perpendicular to each other and perpendicular to the direction of energy and wave propagation. In a vacuum, electromagnetic radiation propagates at a characteristic speed, the speed of light.

Electromagnetic Spectrum – The range of all possible electromagnetic radiation, typically classified by wavelength, ranging from radio waves at one end of the spectrum to X-ray and gamma rays on the other.

Infrared Spectroscopy – The process of passing infrared radiation through a sample and detecting the characteristic absorbance of that sample.

Integration time – The interval over which measurements are taken and filtered together in order to improve the signal to noise ratio of the spectrometer.

M Distance – Mahalanobis Distance – Statistical method used to determine the similarity of an unknown sample to a known sample. It calculates the distance between the current sample point and the mean point of the remaining points in the calibration. It then assigns a probability rate to the sample in terms of standard deviation, and any point that lies outside of 3 standard deviations from this mean is considered to not fit with the data set.

In the picture shown, the oval represents 3 standard deviations from the mean point marked as X. Even though samples A and B are the same distance from the mean, sample A still fits in with the data set. Sample B on the other hand would have an MDistance greater than 3 since it lies outside the oval. This would indicate that sample B does not agree with the calibration, and that more samples similar to sample B should be added to the calibration.

Nanometer (nm) - 1x10-9 m - 0.000000001 m

Optical fiber – A strand of glass or plastic that carries light along its length.

Outlier – A data point that does not fit with the rest of the data set. In infrared calibration analysis this is typically because of error in gathering the sample or error in the laboratory measurement.

Path Length – The distance between the two optical probes where the radiation passes through the sample.

Spectrometer – an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify materials. The variable measured is most often the light's intensity. sThe independent variable is usually the wavelength of the light or a unit directly proportional to the photon energy, such as wavenumber or electron volts, which has a reciprocal relationship to wavelength. Spectrometer is a term that is applied to instruments that operate over a very wide range of wavelengths, from gamma rays and X-rays into the far infrared. The majority

Standard Deviation – How far a particular point in a data set is from the mean value of the data set.

Transmittance – The relative amount of light that passes though a sample, determined by taking the current intensity of light reaching the detector and dividing it by the amount of light generated at the source.

Tungsten lamp – A tungsten filament bulb used to generate the IR radiation that is passed through each sample.