Solvents UV cutoffs

Solvent UV cutoff B.P., °C Density, g/cc Refractive index Viscosity, cP... 

Solvent UV cutoff (nm) Viscosity (cP) Boiling point (°C) Polarity P ... 

Solvent Boiling point, °C Solvent strength parameter Viscosity, mN s m (20°C) Refractive index (20°C) UV cutoff, nm... 

Some common solvents and their UV cutoff wavelengths... 

For HPLC, some fairly broad generalizations can be made about the selection of certain preferred solvents from the large number available. A suitable solvent will preferably have low viscosity, be compatible with the detection system, be readily available in pure form, and if possible have low flammability and toxicity. In selecting organic solvents for use in mobile phases, several physical and chemical properties of the solvent should be considered. From the standpoint of detection, the refractive index or UV cutoff values are also important. 

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

This method is used to detect impurities that show UV absorption. The UV cutoff points for various solvents are listed in Table 10.1. Usually it is not easy to identify the impurities that cause UV absorption. However, if the impurities are removed by purification, better results can be obtained in electrochemical mea-... 

These detectors obviously require a careful selection of solvents utilized as mobile phases. Tables of UV cutoffs are readily available. UV-VIS detectors can be used with gradients. An interesting feature is the use of derivatives of the spectra. 

Solvent s° 5 Viscosity, m Pa-sec (20°C) uv Cutoff, nm Refractive Index (20° C) Normal Boiling Point, °C Dielectric Constant (20° C)... 

One major obstacle to effective use of UV monitoring of HPLC effluent in the range of 200-220 nm was solvent incompatibility. Two types of incompatibilities were noted 1) impurities in the solvent 2) solvent functional group absorbance, i.e. UV cutoff. The former incompatibility was easily overcome by using high quality solvents from the same lot. Solvent functional group absorbance proved to be the more difficult of the two incompatibilities. 

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. 

The second solvent or modifier is then chosen from one of the remaining solvent groups. In reversed phase HPLC, this is most often one of three solvents methanol (Group II), acetonitrile (Group VI) or THF (Group III). All three of these solvents have low viscosity, a reasonably low toxicity level and a low UV cutoff and most separations can be achieved with a mixture of one or more of them with water. 

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. 

Neutral Solutes. In the reversed-phase mode, water is used as the weak solvent and acetonitrile, methanol, or THF (where applicable) is used as the strong solvent. (It is notable that the addition of acid or base to the mobile phase used for neutral molecules does not preclude separation, and, as such, the approach outlined later for ionizable components is equally viable.) In normal-phase HPLC, hexane is used as the weak solvent and isopropanol is used as the strong solvent. To change selectivity based on the strong solvent, isopropanol may be replaced (in part) with methylene chloride, methyl t-butyl ether, or ethyl acetate. However, note should be made of the relatively high UV cutoffs of these solvents when UV detection is to be used and precautions should be taken to ensure solvent miscibility across the range of the gradient. 

UV cutoff This is the wavelength at which the absorbance of the pure solvent is 1.0, measured in a 1 cm cell with air as the reference (10% transmittance). The values listed here are only valid for highly pure solvents. Less pure solvents have higher UV cutoffs. 

Solvent Strength s° Viscosity T7(mPa s) Refractive index 20 D UV cutoff (nm) Boiling point ( C) Dipole 71 Acidity a Basicity 13... 

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