3160
A.A. Ensafi, H. Movahedinia / Spectrochimica Acta Part A 59 (2003) 3159Á3164
/
A solution of methyl orange (100 mg lꢁ ) was
prepared by dissolving 0.0250 g methyl orange
(Merck) in water and diluting to 250 ml with
water. Hydrochloric acid was prepared by appro-
priate dilution of concentrated hydrochloric acid
(Merck).
1
methods are time consuming and suffer from lack
of selectivity or good sensitivity and/or have short
linear dynamic range or have higher limit of
detection and/or used reagents not commercially
available. Recently, Medien and Zahran [23] used
1,4-naphthoquinone as a spectrophotometric re-
agent for barbituric acid determination, but the
method is not sensitive and has high limit of
1
2.2. Apparatus
ꢁ
determination (2.7Á61.5 mg ml ) and has many
/
interfering substances for barbiturate determina-
tion. R. Bartzatt [24] used sodium nitrite as a
suitable reagent for colorimetric analysis of barbi-
A Spectronic 20 (Genesys) spectrophotometer
with two matched 1-cm quartz cells was used to get
absorbance graph at various wavelengths. A
Spectronic 20 (Genesys, Model 4001/4) spectro-
photometer with a 1-cm glass cell was used to get
ꢁ
1
turate, with linear range of 18.7Á225 mg ml . D.
/
Nematollahi et al. [22] used controlled potential
coulometric technique for barbituric acid analysis
absorptionÁtime graphs at a fixed wavelength. A
/
in the range of 1Á
/
200 mmol. The method is not
thermostat water bath (Memmert, Model KG
8540, Schwabachw, Germany) was used to keep
very sensitive and has several interferences. There-
fore, the need for a fast, low cost and sensitive
method is obvious, especially for routine quality
control analysis. According to our knowledge,
there is not any kinetic-spectrophotometric proce-
dure for determination of barbituric acid at trace
level.
Kinetic spectrophotometric method [25] is one
of the most attractive approaches for ultra trace
determination of some species. Its advantage is
that only a spectrophotometer is required as the
main instrument. In this present work, a sensitive,
facile, and relatively selective method was devel-
the temperature of solutions at 359
/
0.1 8C.
2.3. Recommended procedure
The inhibited reaction was followed spectro-
photometrically by monitoring the change in
absorbance of the mixed reagents solution at 510
nm. An aliquot of sample solution containing 1ꢀ
/
ꢁ
5
ꢁ3
10
Á
/
6.0ꢀ
/
10
mol barbituric acid was trans-
ferred into a 10-ml volumetric flask, and then 1.4
ml of 2.33 M hydrochloric acid was added,
1
ꢁ
followed by 1.0 ml 100 mg l
solution. The solution was diluted to ca. 8 ml with
methyl orange
oped for the determination of barbituric (1ꢀ
/
ꢁ
6
ꢁ4
ꢁ3
1
0
Á
/
6.0ꢀ/10
M) acid based on its inhibiting
water. Then 1.0 ml 1.44ꢀ
/
10
M bromate was
effect on the reaction of bromate with hydrochlo-
ric acid. The decolorization of methyl orange by
the reaction products was used to monitor the
reaction spectrophotometrically at 510 nm.
added to the solution and the result solution was
diluted to the mark with water. The solution mixed
and a portion of the solution was transferred to
the spectrophotometric cell. The change in absor-
bance with time was measured for a 10Á240 s from
/
initiation of the addition of last drop of bromate
solution. All the solutions were kept at the 35 8C.
2
. Experimental
2
.1. Reagents and chemicals
3. Results and discussion
Doubly distilled water and analytical-reagent
grade chemicals were used. Barbituric acid stock
solution 0.010 M was prepared by dissolving
barbituric acid (Fluka) in water.
Bromate can be reduced by hydrochloric acid as
the following:
ꢁ
ꢁ
3
ꢂ
1
0Cl ꢂ2BrO ꢂ12H X5Cl ꢂBr ꢂ6H O
2
2
2
A 0.010 M sodium bromate solution was pre-
pared by dissolving 1.510 g NaBrO (Merck) in
water and diluting to 100 ml in a volumetric flask.
The produced bromine and chlorine react with
methyl orange and this reaction cause decoloriza-
3
Ensafi, Ali A
