Spectroscopy Grade chemicals

What the grade means

A spectroscopy grade solvent is tested for what it does to the light path. The key figures are transmittance or absorbance at defined wavelengths against a reference, measured in a 1 cm cell. There are grades for UV-visible, infrared and fluorescence work, and for salts such as potassium bromide used to press IR discs.

Typical specification points

For ethanol in UV spectroscopy you might see GC assay of 99.8 percent or more, transmittance of at least 50 percent at 210 nm, 75 percent at 220 nm and 95 to 98 percent above 240 nm, with water at 0.1 to 0.2 percent. Fluorescence grades add a limit expressed against quinine sulfate.

UV cutoff

Each solvent has a UV cutoff, the wavelength where absorbance reaches about 1 AU in a 1 cm cell. Approximate values are 190 nm for acetonitrile and water, 205 nm for methanol and ethanol and 245 nm for chloroform. Measure well above the cutoff for reliable results. See the UV cutoff entry for more.

When to choose it and documentation

Choose it for quantitative UV-vis, fluorescence and IR measurements. Each lot ships with a COA and GHS SDS. See Solvents (HPLC and GC).