Calibration wavelength scale

The spectra were recorded by a Cary-14 recording spectrophotometer with a wavelength scale calibrated with reference to mercury lines. Cells with 7=10 mm were used (20 mm cell for Yb, and 50 mm cell for Tb). All solutions contained 20 mg of oxide in 1 ml of 1 M HCIO4 (except in the case of Er, 10 mg/ml, the figures in bold type refer to the coefficients at the wavelengths used (or recommended) for determining the respective element. 

Calcium cations 144,145, 311, 312 Calibration of the wavelength scale 21 Campesterol 213 Cannabinoids 288,291 Canrenone 411 Capsaicinoids 65 Carbadrine 76... 

The wavelength (or wave number) scale calibration of infrared spectrophotometers is usually carried out with the aid of a strip of polystyrene film fixed on a frame. It consists of several sharp absorption bands, the wavelengths of which are known accurately and precisely. Basically, all IR-spectrophotometers need to be calibrated periodically as per the specific instructions so as to ascertain their accuracy and precision. 

The calibration of a method involves comparison of the value or values of a particular parameter measured by the system under strictly defined conditions with pre-set standard values. Examples include calibration of the wavelength and absorbance scales of a UV/visible spectrophotometer (Ch. 4), calibration of the wavelength scale of an IR spectrometer (Ch. 5) and construction of chromatographic calibration curves (Ch. 12). 

The wavelength scale may also be calibrated according to the spectral lines of deuterium or mercury discharge lamps and such tests may be built into some instruments. 

Despite the advantages of employing wave numbers, intensity vs. A plots will probably continue to be common, both because of habit and because of the design of commercial, visible and ultraviolet spectrometers many of which employ scales calibrated in wavelength. 

The position of an absorption band is measured on a wavelength scale which may be calibrated in angstroms (A), nanometre (nm) or micron (pm) units. Angstrom units were most commonly used in early mineral spectroscopy literature, including the first edition of this book. However, in current spectral mineralogy research, absorption spectra are often plotted on nanometre scales, whereas micron units are commonly employed in reflectance spectra and remote-sensing applications (chapter 10). The relationship between these wavelength units is... 

Calibration and standardization are often confused and used interchangeably. Calibration refers to the process of adjusting an instrument or instrument s scale to a known physical standard [22], Wavelength scales are calibrated by comparing the instrument s wavelength scale to a spectral line whose value is known from first... 

Standardization in infrared spectroscopy is diflicult (FIO). As with all spectrophotometers, there may be nonlinearity of the detector and recorder and errors in cuvette calibration. Wavelength scales are usually... 

The continuum produced by both of these lamps is accompanied by emission lines in the visible spectral region at A = 486.12 nm (H2) and A = 485.99 nm (D2) these can be employed for adjustment and calibration of the wavelength scale. 

Figure 9.11 Emission spectra of the different types of sources in UV/Vis. A logarithmic scale accounts for the big differences of light intensity according to the wavelengths, notably for filamentless lamps. Below left and middle, general view of a lamp and that seen from above (reproduced courtesy of Oriel). Schematic presenting the circuit details for the lamp. The lamp is booted with a voltage of between 3 to 400 V. The anode is a molybdenum plate while the cathode is a filament of metallic oxide able of emitting electrons and connected to an electrical supply. The emission peaks of deuterium at 486 and 656.1 nm are often used to calibrate the spectrometer wavelength scale.

For most routine purposes, a solution of holmium oxide in perchloric acid will provide a convenient method for routinely checking the calibration of the wavelength scale. Figure 11 shows a typical spectrum. The values are known to within 0.2 nm and are adequate for most solution work. If wavelengths in the region below 241 nm are needed, then either atomic line sources such as a vapour discharge lamp or other rare earth solutions may be used. 

As in the case of dispersive Raman spectrometers (cf Section 4.4.1), it is necessary to calibrate the wavelength scale of dispersive UV/VIS spectrometers. The most accurate standards for checking the UV/VIS wavelengths are lasers of various types. The inexpensive helium-neon laser can be used to check at 632.8 nm. For spectrometers with a deuterium source, spectral lines at 486.6 and 656.1 nm can be used for calibration. A common method for wavelength calibration is the use of optical filters. A filter of didymium glass has many sharp absorption peaks, which can be used as a second wavelength standard (precision within 0.5 nm). 

Samarium perchlorate (Sm(llt)oxide in perchloric acid) is a particularly suitable calibration material for checking the wavelength scale of a spectrophotometer over the most commonly used range of 200-500 nm, as it has peaks throughout this region (Optiglass 2015). 

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