A liquid is classified in the M-number system by testing for miscibility with a
sequence of standard solvents. A correction term of 15 units is then either added or
subtracted from the cutoff point for miscibility.
B.2.2 Solvent stabilizers
Certain solvents degrade, or become unstable, over time. Highly unstable solvents
represent a potential explosion hazard. Solvent stabilizers are added to slow or stop
solvent degradation.
Do not leave solvents containing stabilizers, like THF with butylated hydroxytoluene
(BHT), to dry in the system’s flow path. A dry flow path, including the detector flow
cell, becomes contaminated with residual stabilizer, and a substantial cleaning effort
is needed to restore the flow path to its initial condition.
B.2.3 Solvent viscosity
Generally, viscosity is not a consideration when you use a single solvent or under low
pressure. In gradient chromatography, however, the viscosity changes that occur as
the solvents are mixed in varying proportion can effect pressure changes during the
run.
If you do not know the extent to which pressure changes affect the analysis, monitor
the pressure during the run.
B.2.4 Wavelength selection
The tables in this section provide UV cutoff values for these items:
• Common solvents
• Common mixed mobile phases
B.2.4.1 UV cutoffs for common solvents
The table below shows the UV cutoff (the wavelength at which the absorbance of the
solvent equals 1 AU) for some common chromatographic solvents. Operating at a
wavelength near or below the cutoff increases baseline noise because of solvent
absorbance.
Table B–3: UV cutoff wavelengths for common chromatographic solvents
Solvent
UV cutoff (nm)
Acetone
330
Acetonitrile
190
June 12, 2015, 715004747 Rev. A
Page 74