adulterant See cutting agent.
aerogel A low-density porous transparent material that consists of more
than 90% air. Usually based on metal
oxides or silica, aerogels are used as
drying agents and insulators.
aerosol A colloidal dispersion of a
solid or liquid in a gas. The commonly used aerosol sprays contain an
inert propellant liqueÜed under pressure. *ChloroÛuorocarbons, such as
dichlorodiÛuoromethane, are commonly used in aerosol cans. This use
has been criticized on the grounds
that these compounds persist in the
atmosphere and may lead to depletion of the *ozone layer.
AES See atomic emission spectroscopy.
A-factor See arrhenius equation.
afÜnity chromatography A biochemical technique for purifying natural polymers, especially proteins. It
functions by attaching a speciÜc ligand by covalent bonding to an insoluble inert support. The ligand has to
have a speciÜc afÜnity for the polymer, so that when a solution containing the ligand is passed down a
column of the material it is speciÜcally retarded and thus separated
from any contaminating molecules.
An example of a suitable ligand is
the substrate of an enzyme, provided
that it does not change irreversibly
during the chromatography.
aÛatoxin A poisonous compound,
C 15 H 12 O 6 , produced by the fungus Aspergillus Ûavus. It is extremely toxic to
farm animals and can cause liver cancer in humans. It may occur as a contaminant of stored cereal crops,
cotton seed, and, especially, peanuts.
There are four isomeric forms.
AFM See atomic force microscope.
agar An extract of certain species of
red seaweeds that is used as a gelling
agent in microbiological culture
media, foodstuffs, medicines, and
cosmetic creams and jellies. Nutrient
agar consists of a broth made from
beef extract or blood that is gelled
with agar and used for the cultivation of bacteria, fungi, and some
algae.
agarose A carbohydrate polymer
that is a component of agar. It is used
in chromatography and electrophoresis.
agate A variety of *chalcedony that
forms in rock cavities and has a pattern of concentrically arranged bands
or layers that lie parallel to the cavity
walls. These layers are frequently alternating tones of brownish-red.
Moss agate does not show the same
banding and is a milky chalcedony
containing mosslike or dendritic patterns formed by inclusions of manganese and iron oxides. Agates are
used in jewellery and for ornamental
purposes.
agitator A bladelike instrument
used in fermenters and *bioreactors
to mix the medium continuously in
order to maintain the rate of oxygen
transfer and to help keep the cells in
suspension.
air See earth’s atmosphere.
15
air
a
N
O
N
N
OH
OH
N
NH 2
O
H
Aflatoxin
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aerogel A low-density porous transparent material that consists of more
than 90% air. Usually based on metal
oxides or silica, aerogels are used as
drying agents and insulators.
aerosol A colloidal dispersion of a
solid or liquid in a gas. The commonly used aerosol sprays contain an
inert propellant liqueÜed under pressure. *ChloroÛuorocarbons, such as
dichlorodiÛuoromethane, are commonly used in aerosol cans. This use
has been criticized on the grounds
that these compounds persist in the
atmosphere and may lead to depletion of the *ozone layer.
AES See atomic emission spectroscopy.
A-factor See arrhenius equation.
afÜnity chromatography A biochemical technique for purifying natural polymers, especially proteins. It
functions by attaching a speciÜc ligand by covalent bonding to an insoluble inert support. The ligand has to
have a speciÜc afÜnity for the polymer, so that when a solution containing the ligand is passed down a
column of the material it is speciÜcally retarded and thus separated
from any contaminating molecules.
An example of a suitable ligand is
the substrate of an enzyme, provided
that it does not change irreversibly
during the chromatography.
aÛatoxin A poisonous compound,
C 15 H 12 O 6 , produced by the fungus Aspergillus Ûavus. It is extremely toxic to
farm animals and can cause liver cancer in humans. It may occur as a contaminant of stored cereal crops,
cotton seed, and, especially, peanuts.
There are four isomeric forms.
AFM See atomic force microscope.
agar An extract of certain species of
red seaweeds that is used as a gelling
agent in microbiological culture
media, foodstuffs, medicines, and
cosmetic creams and jellies. Nutrient
agar consists of a broth made from
beef extract or blood that is gelled
with agar and used for the cultivation of bacteria, fungi, and some
algae.
agarose A carbohydrate polymer
that is a component of agar. It is used
in chromatography and electrophoresis.
agate A variety of *chalcedony that
forms in rock cavities and has a pattern of concentrically arranged bands
or layers that lie parallel to the cavity
walls. These layers are frequently alternating tones of brownish-red.
Moss agate does not show the same
banding and is a milky chalcedony
containing mosslike or dendritic patterns formed by inclusions of manganese and iron oxides. Agates are
used in jewellery and for ornamental
purposes.
agitator A bladelike instrument
used in fermenters and *bioreactors
to mix the medium continuously in
order to maintain the rate of oxygen
transfer and to help keep the cells in
suspension.
air See earth’s atmosphere.
15
air
a
N
O
N
N
OH
OH
N
NH 2
O
H
Aflatoxin
www.AzShimi.ir www.AzShimi.com