June 2011
Regular Article
Chem. Pharm. Bull. 59(6) 721—724 (2011)
721
Spectrophotometric Determination of Cobalt(II) and Cyanocobalamin
with Vanillilfluorone and Its Applications
Mitsuru HOSHINO,* Momoka MATSUSHITA, Megumi SAMMA, Mamiko ASANO, Takako YAMAGUCHI, and
Yoshikazu FUJITA
Osaka University of Pharmaceutical Sciences; Nasahara, Takatsuki, Osaka 569–1094, Japan.
Received February 7, 2011; accepted March 30, 2011; published online April 4, 2011
Spectrophotometric determination of cobalt(II) was accomplished with vanillilfluorone (VF) in the presence
of dimethylbenzyltetradecylammonium chloride (Zephiramine, Zep). In the determination of cobalt(II), Beer’s
law was obeyed in the range of 24—470 ng/ml, with an effective molar absorption coefficient (at 575 nm) and rel-
5
ꢁ1
ꢁ1
ative standard deviation of 1.35ꢀ10 l mol cm and 0.66% (nꢂ5), respectively. The composition ratio of the
colored complex was determined by the mole ratio and continuous variation methods, and it was found to be
Co(II) : VF : Zepꢂ1 : 2 : 4. Analysis of cyanocobalamin by the same procedure showed that cyanocobalamin could
be determined in the concentration range of 0.5—0.11 mg/ml using the proposed method.
Key words spectrophotometry; cobalt(II); vanillilfluorone; cyanocobalamin
ꢁ
3
9)
Cobalt, having a Clarke number of 4ꢀ10 , is produced scribed in literature, 1,4-benzoquinone was dissolved in 20 ml of acetic an-
hydride and 1 ml of sulfuric acid and maintained at 30—40 °C for 30—
0 min. The reaction mixture was poured into 500 ml of water to afford a
white precipitate that was filtered and washed with water. 1,2,4-Benzenetriol
triacetate was obtained after drying the precipitate under reduced pressure
for 2 h. In the synthesis of VF, 3 g of vanillin and 10 g of 1,2,4,-benzenetriol
along with nickel, and a small amount of cobalt is also con-
6
tained in copper zinc ore. Cobalt is present in steel as an im-
purity and is used as an additive in alloy steel in the refinery
process. Additionally, cobalt is one of the essential trace ele-
ments. Cobalt is contained in blood at a concentration of triacetate were dissolved in 100 ml of 20% ethanol and 1 ml of concentrated
sulfuric acid. The color of the solution changed to deep red upon heating in
0
.2—2 mg/l, and it also forms a part of the structure of the
a steam bath for 3 h. This solution was subsequently allowed to stand in a
cool, dark place for 3 weeks. The obtained crude VF was then collected and
dissolved in methanol saturated with sodium bicarbonate, on a steam bath.
vitamin B . Therefore, the microanalysis of cobalt is very
important.
1
2
Numerous studies have attempted to quantify cobalt(II) The solution was then filtered hot into 10% acetic acid and allowed to stand
using atomic absorption spectrochemical analysis, flame in a cool, dark place for several days. The precipitate was filtered and
washed with pure water to yield pure VF that was dried under reduced pres-
photometry, inductively-coupled plasma optical emission
spectrometry, fluorescent X-ray analysis, neutron activation
1
sure. [ H-NMR d: 7.04 (d, 1H, Jꢂ8.05 Hz), 7.03 (sd, 1H, Jꢂ0.55 Hz), 6.86
(
dd, 1H, Jꢂ8.05, 1.65 Hz), 6.83 (s, 2H), 6.68 (s, 2H), 3.80 (s, 3H)]. [High
analysis, calorimetry, and spectrophotometry. In addition, or-
ganic reagents including nitroso-R, 1-nitroso-2-naphthol, 2- C H O : 367.0818). The synthetic scheme is shown in Fig. 1.
resolution-mass spectra (HR-MS) FAB-MS m/z: 367.082 (Calcd for
2
0
15
7
ꢁ
3
ꢁ3
nitroso-1-naphthol, nitrosocresol, 2-nitroso-1-naphthol-4-sul-
fonic acid, salts of thiocyanic acid, 1-(2-pyridylazo)-2-naph-
thol, and diethyldithiocarbamic acid have been used in the
Reagents and Apparatus A stock (1.0ꢀ10 M, 1 Mꢂ1 mol dm )
Co(II) standard solution (Wako Pure Chem. Co., Ltd., Japan) was prepared
in water. Working solutions were prepared by suitable dilution of this stock
solution as required. A solution of VF, which had been synthesized accord-
1—8)
spectrophotometric determination of cobalt(II).
However,
9)
ꢁ3
ing to a method described in the literature, was prepared in a 1.0ꢀ10
M
most of these methods are organic solvent extraction meth- methanol solution. A 1.0% aqueous solution of dimethylbenzyltetradecyl-
ammonium chloride (Zephiramine, Zep, Dojindo Laboratories Co., Ltd.,
Japan) was prepared by dissolving Zep in water and was filtered using a
ods, and they suffer from the disadvantages that the use of
organic solvents is not eco-friendly and the procedures are
difficult and complicated. This report describes a simple and
highly sensitive method for the determination of cobalt(II)
0
.65-mm membrane filter. A buffer solution of pH 9.2 was prepared by dis-
solving borax (Nacalai Tesque Co., Ltd., Japan) in water and filtered using a
.65-mm membrane filter. Reagent-grade chemicals were used throughout.
0
and the application of this method to the determination of Pure water was prepared by purifying deionized water using a Milli-Q Labo
system just before use. A Shimadzu spectrophotometer (Model UV-160)
cyanocobalamin using vanillilfluorone (VF), which has a rel-
with 1.0-cm matched silica cell was used for absorbance measurements. The
atively facile synthetic procedure relative to other xanthene
pH measurements were made using a Horiba (F-11) pH meter in combina-
dyes.
tion with a calomel glass electrode.
Standard Procedure for Determination of Cobalt(II) The following
Experimental
components were mixed in a 10-ml volumetric flask: a stock solution con-
taining cobalt ions, 1.0 ml of 1.0% Zep solution, 2.0 ml of 0.05 M borax solu-
Synthetic procedure: vanillilfluorone According to a method de-
Fig. 1. Synthesis of VF
∗
© 2011 Pharmaceutical Society of Japan