Chemistry Reference
In-Depth Information
TABLE 1
Some Physicochemical Properties of Cobalt Compounds
CAS No.
Formulae
MW
Melting
Density
Water
point (°C)
solubility (g/L)
Cobalt(II,III)
1308-06-1
Co
3
O
4
240.80
895
6.07
Insoluble
oxide
(0.00084)
Cobalt(II)
1307-96-6
Co
74.93
1795, 1935
6.45
Insoluble
oxide
(0.000313)
Cobalt(II) acetate
71-48-7
Co(CH
3
CO
2
)
2
177.03
—
—
Readily soluble
(tetrahydrate)
(6147-53-1)
Cobalt(II)
513-79-1
CoCO
3
118.94
Decomposes
4.13
Practically
carbonate
insoluble
Cobalt(II)
7646-79-9
CoCl
2
129.84
Decomposes
3.36
Soluble (529 @
chloride
(7791-13-1)
20°C)
(hexahydrate)
Cobalt(II)
21041-93-0
Co(OH)
2
92.95
Decomposes
3.60
Very slightly
hydroxide
soluble (0.0032)
Cobalt(II) nitrate
10141-05-6
Co(NO
3
)
2
182.96
Decomposes
2.49
Soluble
(hexahydrate)
(10026-22-9)
(100)
Cobalt(II) sulfate
10124-43-3 ()
Co(SO
4
)
2
154.99
Decomposes
3.71
Soluble (362 @
(heptahydrate)
(735)
20°C)
Cobalt(II) sulfi de
1317-426
CoS
90.99
>1100
5.45
Insoluble
(0.0038 @ 18°C)
α
- and ß-forms
2 ANALYTICAL METHODS
carbide (WC) particles (i.e., in hard metal powders), the
reduction of oxygen in ROS by cobalt metal is catalyzed
at the surface of WC particles (Keane
et al.,
2002; Lison
et
al.,
1995), and soluble cobalt cations are produced in larger
amounts. In this system, cobalt (II) ions are produced
during the critical reaction but they do not drive it. This
mechanism is illustrated in Figure 1.
In the presence of H
2
O
2
, Co(II) ions are able to pro-
duce hydroxyl radicals through a Fenton-like mecha-
nism (Kadiiska
et al.,
1989), and the oxidation potential
of Co(II) ions can be modulated by chelating agents
(e.g., 1,10-phenanthroline) to facilitate the generation of
these radicals (Kadiiska
et al
., 1989; Mao
et al.,
1996).
In vivo
, the bioavailability of Co(II) ions is relatively
limited, because these cations precipitate in the pres-
ence of physiological concentrations of phosphates
(K
sp
: 2. 5× 10
−35
at 25°C) and nonspecifi cally bind to
proteins such as albumin.
Colorimetric methods were introduced during
the 1940s for analyzing cobalt in biological materials.
Detection limits of approximately 0.1
g Co in a 20-mL
sample of blood have been reported with these meth-
ods (Hubbard
et al.,
1966; Stone, 1965). During the
1960s, emission spectrographs, polarography, X-ray
fl uorescence, and atomic absorption spectrophotome-
try (AAS) were introduced. By use of fl ame AAS, detec-
tion limits of 0.05 and 0.03 mg/L were reported in water
(Fishman and Midgett, 1967; Sachdev
et al
., 1967). Saari
and Paaso (1980) used a fl ameless AAS method for the
measurement of cobalt in various foodstuffs after diges-
tion of the samples in acid and extraction into methyl
isobutylketone (MIBK). The authors were able to detect
cobalt in foodstuffs down to concentrations in the order
of 1 to 10
µ
g/kg. Lidums (1979) also used fl ameless AAS,
but by use of an ion-exchange technique to concentrate
cobalt, was able to detect cobalt in urine and in blood at
concentrations of approximately 0.15
µ
WC
g/L. A neutron
activation method described by Cornelis
et al
. (1975)
detected cobalt in urine at concentrations <0.5
µ
Co
O
2
g/L.
Since then, a variety of modern techniques have
been developed, and lower detection limits have been
achieved.
Baruthio and Pierre (1993) have reported a method
for the determination of cobalt in blood and urine by
use of electrothermal atomic absorption spectrom-
etry after mineralization and extraction with MIBK.
The detection limit of this method was 1.90 nmol/L
(approximately 0.12
µ
e
−
ROS
Co
++
FIGURE 1
Physicochemical mechanism of interaction between
cobalt metal (Co) and tungsten carbide particles (WC) producing
amounts of reactive oxygen species (ROS) in aqueous solution and
leading to the ionisation of cobalt (Co
++
). Adapted with permission
from Lison
et al
. (1995). Copyright (1995) American Chemical Society.
µ
g/L) in serum and urine.
