Handbook of Solvents - George Wypych - ChemTech - Ventech!

1064 George Wypych
used. A thermal conductivity or flame ionization detector is used. A stainless steel column
with 80-100 mesh Chromosorb G-HP is used with 9.05% Dow Corning QF-1 and 0.45%
Igepal CO-990. The concentration of the main component and the amount of free alcohol
are measured by the method.
Traces of benzene in hydrocarbon solvents are measured by capillary gas chromatography.
80 Because of the hazardous nature of benzene, the method was introduced to ensure
compliance with the stringent regulations. A flame ionization detector is used with 0.53 mm
fused silica capillary columns with bound methyl silicone or polyethylene glycol. Similar
method is used to determine benzene content in cyclic products (cyclohexane, toluene,
cumene, styrene, etc.). 81 This method does not specify any particular column but the column
used should be able to resolve benzene from other components. The method can determine
benzene in concentrations of 5 to 300 mg/kg. Traces of thiophene in refined benzene are determined
by a flame photometric detector. 82 Several column types given in standard are
found satisfactory to overcome potential problem of quenching effects of hydrocarbons on
the light emissions from thiophene. High purity benzene for cyclohexane feedstock is tested
for several known impurities by capillary gas chromatography. 83 The gas chromatograph is
equipped with a flame ionization detector and a splitter injector suitable for fused silica capillary
column internally coated with crosslinked methyl silicone. The concentration of benzene
and the concentrations of impurities can be adequately determined.
The purity of halogenated solvents is determined using a thermal conductivity or
flame ionization detector, a column made from 3.2 mm stainless tubing packed with 30 wt%
silicone fluid on 80-100 mesh diatomaceous earth or using capillary column. 84 Admixtures
in 1,1,1-trichloroethane are determined using a thermal conductivity or hydrogen flame detector.
Column from copper or stainless steel is packed with Chromosorb W HP with 20%
polydimethylsiloxane. 85
Various impurities, such as hydrocarbons, acetone, alcohols and other can be determined
using a thermal conductivity or a flame detector. 86 Several columns are specified in
the standard mostly using polyethylene glycol on diatomaceous earth. For determination of
purity of methyl isobutyl ketone different method is used. 87 In both cases the amounts of determined
impurities are subtracted from total mass to give purity of specimen.
The determination of aromatics in mineral spirits is another method that has been developed
to ensure compliance with regulations restricting aromatic content. 88 Three methods
are given, each capable to determine ethylbenzene and total aromatic content. The
methods differ in column type and packing.
A spectrophotometric method 89 for determining thiophene in benzene is available as
alternative to gas chromatography. 82 The spectrometer used is capable of detecting
absorbance in the range from 400 to 700 nm with a repeatability of 0.005 absorbance units.
Thiophene is reacted with isatin to form a colored compound. The quantitative determination
is based on reading concentrations from master curve.
The presence of reducing substances in pyridine can be detected by a simple visual observation.
90 The sample of pyridine is mixed with 0.32% potassium permanganate solution
and color is observed after 30 min. If color of the potassium permanganate is retained, the
sample is free of reducing agents.
Oxidative microcoulometry is used to determine trace quantities of sulphur in aromatic
hydrocarbons. 91 An oxidative pyrolysis converts sulfur to sulfur dioxide which is titrated
in titration cell with the triiodide ion present in the electrolyte.
The total chloride (organic and inorganic) in aromatic hydrocarbons and cyclohexane
can be determined by titration. 92 Bromides and iodides present are recorded as chlorides.
The sample is mixed with toluene in a proportion which depends on the expected concentration
of chloride. The reagent sodium biphenyl is added to convert organic halogens into in-