Solvents wavelength cutoff

The following table lists some useful solvents for ultraviolet spectrophotometry, along with their wavelength cutoffs and dielectric constants.16... 

The common solvents used in UV/VIS spectroscopy are listed in Table 5.5, along with their low wavelength cutoff. At wavelengths shorter than the cutoff wavelength, the solvent absorbs too strongly to be used in a standard 1 cm sample cell. The cutoff is affected by the purity of the solvent. For spectroscopy, the solvents should be of spectral or spectro-chemical grade, conforming to purity requirements set by the American Chemical Society. 

Table 5.5 Common UV Solvents and their Lower Wavelength Cutoffs...

Prepare two aqueous solutions which contain approximately 1000 ppm each of 1-octanesulfonic acid or sodium dodecyl sulfate (use whichever is available) and p-toluenesulfonic acid dissolved in distilled, deionized water (DDI). Transfer a portion of this solution into a quartz, rectangular cuvette and record the UV absorption spectrum for both organic compounds. Prepare a 100-ppm solution that contains methyl methacrylate and a 100-ppm solution that contains ethyl glycolate. You will need to use the wavelength cutoff guide to choose a suitable solvent because these organic compounds do not dissolve to any great extent in water. Record the UV absorption spectrum between 200 and 350 nm. Compare the spectra when a solvent is placed in the reference beam of the dual-beam instrument. 

The wavelength cutoff for the solvent may be important if the sample absorbs below about 250 nm. 

Table 7.9 Electronic Absorption Bands for Representative Chromophores Table 7.10 Ultraviolet Cutoffs of Spectrograde Solvents Table 7.11 Absorption Wavelength of Dienes Table 7.12 Absorption Wavelength of Enones and Dienones Table 7.13 Solvent Correction for Ultraviolet-Visible Spectroscopy Table 7.14 Primary Bands of Substituted Benzene and Heteroaromatics Table 7.15 Wavelength Calculation of the Principal Band of Substituted Benzene Derivatives...

The solvent chosen must dissolve the sample, yet be relatively transparent in the spectral region of interest. In order to avoid poor resolution and difficulties in spectrum interpretation, a solvent should not be employed for measurements that are near the wavelength of or are shorter than the wavelength of its ultraviolet cutoff, that is, the wavelength at which absorbance for the solvent alone approaches one absorbance unit. Ultraviolet cutoffs for solvents commonly used are given in Table 7.10. 

Some common solvents and their UV cutoff wavelengths... 

Typical UV Cutoff Wavelengths for Some Commonly Used HPLC Solvents and Buffer Components, Taken Primarily from Manufacturer Product Specifications... 

Table 25-2 Eluotropic series and ultraviolet cutoff wavelengths of solvents for adsorption chromatography on silica...

Solvents for spectroscopic use need to be transparent in the wavelength or wavenumber ranges where the desired spectral information is to be obtained. All liquids have an ultraviolet cutoff, meaning that at and below some wavelength in the ultraviolet they absorb so much of the UV light that they cannot be used as solvents for spectroscopic purposes in this range. 

Our earlier work with a polar silica gel column had demonstrated the need for a solvent of higher dielectric constant, i.e. methylene chloride, to effectively elute the cannabinoids. Methylene chloride could not be used at 209 nm due to its UV cutoff at 230 nm. The other partner in the earlier used gradient program, heptane, was compatible with use for lower wavelength monitoring because of its 200 nm cutoff. 

Solvents used for visible-ultraviolet spectroscopy may be used only for wavelengths greater than some ultraviolet cutoff wavelength Xc, below which the solvent absorbs strongly. These cutoff wavelengths /,c are listed with some other useful data in Tables 11.3 and 11.4. 

Table 11.3 Ultraviolet Cutoff Wavelength Ac (at which the Solvent in a Cell of Path Length L = 1 cm has an Absorbance of 1 unit). Dielectric Constant e, Scalar Refractive Index nD (Measured at 589 nm, the Na D-line), Dipole Moment ft (Debyes30), and Reichardt s31 Solvent Polarity Index ET...

Approximate lower cutoff wavelengths for commonly used solvents in UV-visible spectroscopy of organic substances... 

Solvent Cutoff wavelength, nm Solvent Cutoff wavelength, nm... 

Table 6.2 Approximate UV cutoff wavelength and RI of commonly used solvents...

Highly UV absorbing mobile phase. Change detection wavelength taking into account the UV cutoff of mobile phase solvents. 

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