Page 59 - Illustrated Pocket Dictionary of Chromatography

54 DICHLOROMETHANE (METHYLENE CHLORIDE)

Cl
Cl

1,2-Dichlorobenzene

dichloromethane (methylene chloride) Molecular weight:
84.9; boiling point: 39.8°C; refractive index (20°C): 1.4241; density
(20°C): 1.3391g/mL; viscosity (25°C): 0.44cP; UV cutoff: 233nm; elu-
o
otropic strength (e ): on alumina—0.42, on silica—0.30; polarity index
(P¢): 3.1; Hildebrand solubility parameter (d): 9.7; solubility in water
(20°C): 1.6%; water solubility in dichloromethane (20°C): 0.24%.
Dichloromethane is extensively used as a sample solvent in GC work.
For environmental samples this is typically due to the fact the
dichloromethane is used to extract organics from water in a liquid-
liquid extraction step. Dichloromethane is also used at low levels in
normalphase LC and TLC work. In all cases it is preserved with an
alkene such as amylene or cyclohexene because it is prone to free
radical degradation.

CH 2 Cl 2
Dichloromethane

diethylaminoethyl (DEAE) A common substituent used as a
weak anion-exchange functional group.

diethyl ether See ethyl ether.

diffusion The process by which molecules are driven away from
areas of high concentration to lower concentration (via chemical
potential differences). See Fick’s first law of diffusion; Fick’s second
law of diffusion.

diffusion coefficient, D A quantitative measure of how rapidly
a molecule moves through a defined matrix. The value for D is
dependent on analyte, temperature, pressure, matrix, etc. The units
for D are square centimeters/second. Common gas in a gas diffusion
2
coefficients range from 0.01 to 3cm /s, whereas solute in a liquid
-5
2
-7
diffusion coefficients range from 10 to 10 cm /s.