The ultraviolet spectral region is generally considered to include from 190 nm to 380 nm (non-vacuum UV region). There are several available standards used for initial alignment, or for verifying alignment, when using ultraviolet spectrophotometers. Ultraviolet (UV) Wavelength Measurement Standards
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The typical standards used for spectrometer alignment or testing will be illustrated within this article (1–3). Multiple standards are available for each spectroscopic region. Thus, the alignment of the x-axis requires a known standard material that may be measured to either align the axis, or to verify whether the axis is aligned. Without such a condition, no spectroscopic methods are valid. The primary assumption of all quantitative regression and qualitative comparison methods is that the data channels, as wavelength or frequency, are precisely aligned for comparison.
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The alignment of the x-axis (also known as the wavelength or wavenumber axis) for spectroscopic data is essential to the basic use of these spectroscopic techniques.
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This article provides a discussion and set of spectra to illustrate the use of reference materials to align the x-axis for the major types of optical spectroscopy, to include the ultraviolet, visible, near-infrared, infrared, and Raman spectroscopic methods. Note that the assumption for regression modeling, as well as spectral comparison algorithms, is that the data channels, or x-axis scales of the spectroscopic data, are precisely aligned, and that only amplitude in the y-axis changes with respect to analyte concentration in a pre-defined mathematical relationship. Alignment of the x-axis (also known as the wavelength or wavenumber axis) is assumed for all spectra used for the purposes of quantitative and qualitative work.