Determination of trace amount of oxalic acid with zirconium(IV)-(DBS-arsenazo) by spectrophotometry

Article abstract of DOI:10.1016/j.saa.2007.12.026

A novel method is proposed for the determination of trace amount of oxalic acid in the present article. In 1.0 M hydrochloric acid medium, oxalic acid can react with the zirconium(IV) in Zr(IV)-(DBS-arsenazo) complex and replaces the DBS-arsenazo to produce a hyperchromic effect at 520 nm. The hyperchromic degree is proportional to the concentration of the oxalic acid added over a defined range. Based on this property, a new method for the spectrophotometric determination of trace oxalic acid was developed. Beer's law is held over the concentration range of 9.0 × 10^-6 to 5.0 × 10^-4 M for oxalic acid with a correlation coefficient of 0.9995. The apparent molar absorptivity of the method is ε_{520 nm} = 1.16 × 10³ L mol^-1 cm^-1 and the detection limit for oxalic acid is 0.815 μg/mL. The developed method was directly applied to the determination of oxalic acid in tomato samples with satisfactory results.

Full text of DOI:10.1016/j.saa.2007.12.026

Available online at www.sciencedirect.com
Spectrochimica Acta Part A 71 (2008) 332–335
Determination of trace amount of oxalic acid with
zirconium(IV)–(DBS-arsenazo) by spectrophotometry
Qing-Zhou Zhai∗
Research Center for Nanotechnology, South Campus, Changchun University of Science and Technology,
7186 Weixing Road, Changchun 130022, Jilin Province, PR China
Received 28 March 2007; received in revised form 23 December 2007; accepted 27 December 2007
Abstract
A novel method is proposed for the determination of trace amount of oxalic acid in the present article. In 1.0 M hydrochloric acid medium,
oxalic acid can react with the zirconium(IV) in Zr(IV)–(DBS-arsenazo) complex and replaces the DBS-arsenazo to produce a hyperchromic
effect at 520 nm. The hyperchromic degree is proportional to the concentration of the oxalic acid added over a defined range. Based on this
property, a new method for the spectrophotometric determination of trace oxalic acid was developed. Beer’s law is held over the concentration
range of 9.0 × 10−6 to 5.0 × 10−4 M for oxalic acid with a correlation coefficient of 0.9995. The apparent molar absorptivity of the method
is ε520 nm = 1.16 × 103 L mol−1 cm−1 and the detection limit for oxalic acid is 0.815 ␮g/mL. The developed method was directly applied to the
determination of oxalic acid in tomato samples with satisfactory results.
© 2008 Elsevier B.V. All rights reserved.
Keywords: Oxalic acid; Zirconium(IV); DBS-arsenazo; Spectrophotometry
Oxalic acid is a common material in some food samples.
It can form stable and precipitated calcium oxalate complex
with calcium in the body. This not only hinders the absorption
of calcium in human body, but also easily initiates urinary
calculus. The excessive oxalic acid can influence the people’s
health [1]. Thus, the determination of the amount of oxalic acid
in some samples such as fruits, etc., has very important practical
significance. Although spectrophotometry [2,3], extraction-
spectrophotometry [4], catalytic kinetic spectrophotometry
[5–7], fluorimetry [8], catalytic fluorimetry [9] have been
used for the determination of trace oxalic acid, the proposed
methods have their own defects such as poor selectivity
[2–9], time-consuming operation [4–7,9], expensive analytical
instrument [8,9]. A few spectrophotometric, extraction- or
catalytic-spectrophotometric methods for the determination
of oxalic acid have been reported, but their selectivity is still
poor [2–7]. Thus, there is a demand for an inexpensive, simple
and selective procedure in order to obtain more accurate
information about oxalate levels in some samples. It is of
very interest to develop a simple and selective method for
the determination of oxalic acid. DBS-arsenazo (DBS-ASA),
3-(2,6-dibromo-4-sulfophenylazo)-6-(2-arsenophenylazo)-4,5-
dihydroxynaphthalene-2,7-disulfonic acid, is an azo dye reagent
that has been used for the spectrophotometric determination of
rare earths [10]. It is found in the present study that oxalic acid
can replace the DBS-ASA in Zr(IV)–(DBS-ASA) complex,
while the oxalic acid coordinates with the Zr(IV) to form
a stable complex. The replaced DBS-arsenazo produces a
hyperchromic effect at 520 nm. The hyperchromic degree is
proportional to the concentration of the oxalic acid added over
a defined range. Based on this property, a new, simple and
selective method was developed for the determination of trace
oxalic acid. Compared with other methods [2–9], the present
method has the advantages of operation simplicity, rapidity and
good selectivity. The method was directly used to determine
trace oxalic acid in tomato samples with satisfactory results.
1. Experimental
1.1. Reagent and apparatus
Oxalic acid standard solution: 1.0 × 10−3 M working solu-
tion was prepared by dissolving 0.0315 g of oxalic acid (Beijing
Chemical Plant) with water in a beaker. The solution was
∗
Fax: +86 431 85383815.
E-mail addresses: zhaiqingzhou@hotmail.com, zhaiqingzhou@sohu.com.
1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2007.12.026

Q.-Z. Zhai / Spectrochimica Acta Part A 71 (2008) 332–335
333
placed in a 250-mL calibrated flask, diluted up to the mark
with distilled water, and mixed well. Another 1.0 × 10−4 M
oxalic acid working solution was obtained by appropriate
dilution of 1.0 × 10−3 M oxalic acid solution. Zr(IV) solu-
tion: 5.0 × 10−4 M Zr(IV) solution was prepared by dissolving
0.0403 g of ZrOCl2·8H2O (Shanghai Chemical Reagent Com-
pany) with 10 mL of 1 M nitric acid in a beaker, the solution
was placed in a 250-mL calibrated flask, diluted up to the
mark with distilled water and mixed well. DBS-Arsenazo
(DBS-ASA, C22H15AsBr2N4O14S3) solution: 5.0 × 10−4 M
working solution was prepared by dissolving 0.1073 g of DBS-
ASA (Shanghai Changke Research Institute for Reagent) with
distilled water in a beaker, placed in a 250-mL calibrated
flask and diluted up to the mark with distilled water, and
mixed well. A 10.0-M hydrochloric acid solution was pre-
pared by appropriate dilution of its concentrated solution. All
reagents were of analytical grade and the water was distilled
water.
A 722S spectrophotometer (Shanghai Lingguang Tech-
nique Co., Ltd., China) with 1 cm cells was used in the
experiment.
Fig. 1. Absorption spectra: (a) DBS-ASA (against H2O); (b) (DBS-
ASA)–Zr(IV) (against H2O); (c) H2C2O4–(DBS-ASA)–Zr(IV) (against
H2O); (d) H2C2O4–(DBS-ASA)–Zr(IV) (against corresponding reagent
blank). [H2C2O4] = 1.05 × 10−4 M; [DBS-ASA] = 5.0 × 10−5 M; [Zr(IV)]
= 2.5 × 10−5 M; [HCl] = 1.0 M.
1.2. Procedure
A 1.0-mL of 10.0 M hydrochloric acid solution, 0.50 mL of
5.0 × 10−4 M Zr(IV) solution, 1.0 mL of 5.0 × 10−4 M DBS-
arsenazo solution and an appropriate amount of oxalic acid
standard solution were successively added into a 10-mL cal-
ibrated flask, respectively. The solution was diluted up to the
mark with water and mixed well. After 25 min, the absorbance
was measured in 1 cm cells at 500 nm against a corresponding
reagent blank.
imum and constant over the concentration of 0.80–1.5 M
hydrochloric acid. Outside this range, the sensitivity of the deter-
mination of oxalic acid is lower. Thus, 1.0 M hydrochloric acid
solution was recommended as the acidity of color medium in
experiments. A 1.0-mL of 10.0 M hydrochloric acid was added
to control the acidity.
2. Results and discussions
2.3. Effect of the amount of DBS-arsenazo
2.1. Absorption spectra
The experiments showed that over the range of 0–0.90 mL
of 5.0 × 10−4 M DBS-arsenazo the absorbance gradually raised
with increasing the amount of DBS-ASA. When the amount of
DBS-ASA solution was 0.90–1.2 mL and the concentration of
DBS-ASA was 4.5 × 10−5 to 6.0 × 10−5 M, the absorbance was
a maximum and constant. In the present experiment 1.0 mL of
5.0 × 10−4 M DBS-ASA solution was selected. The concentra-
tion of DBS-ASA was 5.0 × 10−5 M.
The absorption spectra of the colored systems were drawn by
using the general procedure and are shown in Fig. 1. The results
showed that the maximum absorption peak of DBS-ASA is at
500 nm. The maximum absorption peaks of Zr(IV)–(DBS-ASA)
complex and H2C2O4 + Zr(IV) + (DBS-ASA) system against
water are both at 520 nm. After oxalic acid was added to the
Zr(IV)–(DBS-ASA) system, the absorbance of colored solu-
tion against water at 520 nm was increased. Because oxalic
acid can coordinate with the Zr(IV) in the Zr(IV)–(DBS-ASA)
complex, the DBS-ASA that is not complexed turns up in
solution. The change of absorbance takes place. The maxi-
mum absorption peak of the H2C2O4 + Zr(IV) + (DBS-ASA)
colored system against the corresponding reagent blank is at
520 nm. Therefore, 520 nm was selected as measurement wave-
length.
2.4. Effect of the amount of zirconium(IV) solution
The effect of the amount of zirconium(IV) was tested. The
results showed that the absorbance gradually increased with
increasing the concentration of zirconium(IV) over the con-
centration range of (0–2.0) × 10−5 M. When the zirconium(IV)
concentration was 2.0 × 10−5 to 1.0 × 10−4 M, the absorbance
was maximum and constant. In the experiments, the con-
centration of zirconium(IV) was selected to be 2.5 × 10−5 M
and a 0.50-mL of 5.0 × 10−4 M zirconium(IV) solution was
employed.
2.2. Effect of acidity
The experimental results showed when the amount of
hydrochloric acid was 0.80–1.5 mL, the absorbance was max-

334
Q.-Z. Zhai / Spectrochimica Acta Part A 71 (2008) 332–335
Table 1
Analytical results of samples
Sample
Found
(mg/g)
Average
(mg/g)
R.S.D.
(%)
Added
(10−5 M)
Recovered
(10−5 M)
Recovery
(%)
Contrast method
[5] (mg/g)
No. 1
No. 2
1.22, 1.25, 1.20, 1.20, 1.21, 1.26
1.62, 1.64, 1.60, 1.65, 1.62, 1.60
1.22
1.62
2.14
1.27
5.00
5.00
4.96
4.98
99.2
99.6
1.23
1.62
2.5. Effect of temperature
2.7. Composition of the complex and mechanism of the
reaction
For the H2C2O4 + Zr(IV) + (DBS-ASA) system, the
absorbance attained maximum and constant at room tem-
perature (20 5 ◦C). Outside this range of temperature, the
sensitivity decreased.
The complex ratio of Zr(IV)–(DBS-ASA), determined by
using molar ratio and the equimolar continuous variation meth-
ods, was 1:1.
The chemical reactions, which can be expected to take place
in the corresponding systems, can be expressed as follows:
2.6. Stability of the chromogenic system
ZrOCl2 + C22H15AsBr2N4O14S3 →
Zr(C22H11AsBr2N4O14S3) + 2HCl + H2O
After all reagents were mixed, the absorbance of system
reached a maximum in 25 min and the colored system reached
equilibrium. The variation of absorbance of the system was less
than 5% in 12 h and the system kept stable at room temperature
(20 5 ◦C).
(1)
(2)
Zr(C22H11AsBr2N4O14S3) + 2H2C2O4 →
Zr(C2O4)2 + C22H15AsBr2N4O14S3
Table 2
Comparison of the present method with other reported methods
Analytical
method
System
Linear
range
Detection
limit
Remark
Analytical
application
References
(␮g/mL)
(␮g/mL)
Spectrophotometry
Spectrophotometry
Oxalic acid-zinc-
phenylhydrazine
hydrochloride
Oxalate-zirconium(IV)-
quercetin
Oxalate-vanadium(V)-
mandelohydroxamic acid
(extraction solvent is
toluene solution of
trioctylmethylammonium
chloride/adogen 446)
Oxalic acid-rhodamine
B-potassium dichromate
0–20
0.1
Poor selectivity
Poor selectivity
Water
[2]
0–5.0
2–8
0.25
0.5
–
[3]
[4]
Extraction-
spectrophotometry
Extraction is needed and
operation is
time-consuming
Urine, blood serum
Catalytic kinetic
spectrophotometry
0.40–6.0
0.252
3.86
Metal ions, i.e. Cr3+
,
Spinach, tea, urine
Water
[5]
[6]
Bi3+, La3+, Eu3+, Y3+
interfere and selectivity is
poor. Heating is needed
Heating time is 1 h and
operation is
Catalytic kinetic
spectrophotometry
Oxalic acid-
chromium(III)-alizarin
red S
0–140.8
time-consuming. Poor
sensitivity and selectivity
present
Catalytic kinetic
spectrophotometry
Fluorimetry
Oxalic acid-iron(II)-
iodide-bromate
0.10–7.0
0.080
0.074
Poor selectivity
Tap water, river water,
spinach, mushroom
Spinach, urine
[7]
[8]
2,2,7,7,12,12,17,17-
Octamethyl-21,22,23,
24-tetraoxaqyaterene-Mg
Oxalic acid-rhodamine
6G-potassium dichromate
0.55–73.9
Poor selectivity
Catalytic fluorimetry
Present method
0.80–14.0
0.81–45.0
–
Sensitive but less
selective. Heating is
needed
Simple and highly
sensitive, free from
interference of common
ions. No heating is needed
Spinach, urine
Tomato
[9]
Oxalic acid-
Zr(IV)–(DBS-arsenazo)
0.815
Present paper

Q.-Z. Zhai / Spectrochimica Acta Part A 71 (2008) 332–335
335
Here, Zr(IV) first reacts with DBS-ASA to produce
Zr(C22H11AsBr2N4O14S3) product. Then, H2C2O4 replaces the
C22H11AsBr2N4O14S3 intheZr(C22H11AsBr2N4O14S3)topro-
duce Zr(C2O4)2. The reason, why the replacement reaction takes
place, was that the stability constant of Zr(C2O4)2 is expected
to be larger than the one of Zr(C22H11AsBr2N4O14S3).
the general procedure. The analytical results are listed in Table 1.
From the table it can be seen that the analytical results of the
present method were in excellent agreement with those by oxalic
acid-rhodamine B-potassium dichromate catalytic kinetic spec-
trophotometry [5]. The relative standard deviation of six parallel
determinations for the samples and recovery were 1.27–2.14%
and 99.2–99.6%, respectively. The mean relative standard devi-
ation and mean recovery were 1.71% and 99.45%, respectively.
The analytical results obtained were quite satisfactory.
2.8. Calibration curve
Under the optimum experimental conditions, a linear rela-
tionship was shown over the concentration range of 9.0 × 10−6
to 5.0 × 10−4 M for oxalic acid. The regression equation for
calibration graph was: A = 3.30 × 102 C + 0.0884 (C:M), with a
correlation coefficient 0.9995, and the apparent molar absorp-
tivity is ε520 nm = 1.16 × 103 L mol−1 cm−1. The precision of the
present method was evaluated by determining 2.0 × 10−4 M
oxalic acid standard solution 11 times with a relative stan-
dard deviation of 0.98%. The limit of detection as defined by
IUPAC [11] and the limit of quantification [12] were found to
be 0.815 ␮g/mL and 2.39 ␮g/mL, respectively.
4. Comparison with other methods
A comparison of the present procedure with other methods
is listed in Table 2. From the table it can be seen that the present
method has the advantages of operation simplicity, rapidity and
low analytical cost. The method possesses distinct advantages
over existing methods with respect to sensitivity, selectivity,
speed, accuracy, precision and ease of operation. It has much
more practical value for the determination of trace oxalic acid.
5. Conclusions
2.9. Interference study
A new spectrophotometric method for the determina-
tion of trace amount of oxalic acid was proposed with
Zr(IV)–(DBS-arsenazo) complex in this paper. The linear range
of determination of oxalic acid is 9.0 × 10−6 M to 5.0 × 10−4 M.
The detection limit of the present method for oxalic acid is
0.815 ␮g/mL. The proposed method has been applied to the
determination of oxalic acid in tomato samples with satisfactory
results. The present procedure has the advantages of the oper-
ation simplicity, rapidity and low analytical cost. It is simple,
highly sensitive, free from interference of common ions and has
much more practical value for the determination of trace oxalic
acid compared with other methods [2–9].
The effect of a series of 54 diverse inorganic and organic
substances on the determination of 2.0 × 10−4 M oxalic acid
was checked. The tolerance limits (mass multiple, m/m) of the
common ions tested (causing < 5% relative error) are summa-
rized as follows: K+ (700); Na+ (500); Li+ (400); NH4 (100);
+
Ag+ (0.03); Mn2+ (400); Fe2+ (40); Cu2+ (4); Cd2+, Sn2+ (1);
Ba2+, Ni2+ (0.3); Zn2+, Co2+ (0.2); Ca2+, Mg2+ (0.05); Pb2+
(0.007); Al3+ (400); Fe3+ (5); Cr3+ (0.8); Bi3+ (0.2); Y3+ (0.07);
La3+ (0.05); Th4+ (0.005); Br−, I−, NO3− (100); F−, NO2− (5);
−
−
−
−
VO3 (0.4); WO4 (0.1); BrO3 (0.007); MnO4 (0.0005);
SO4 (100); S2O7 (4); Cr2O72−, SiO3 (2); PO4 (8);
Mo7O246− (0.07); EDTA (ethylene diamine tetraacetic acid) (8);
citric acid, urea (500); glucose (400); ascorbic acid (70); lysine,
alanine (7); acetic acid, leucine, serum albumin (5); glycocoll,
bovine red albumin (4); tartaric acid, malic acid (2); salicylic
acid (1).
2−
2−
2−
3−
References
[1] M.Y. Leng, General Chemistry, Press of Wuhan University of Technology,
Wuhan, 1993, p. 268.
[2] G.J. Wang, Y. Lv, J.F. Wang, Environ. Monit. China 17 (2001) 36.
[3] A.L. Allan, B.S.F. Band, E. Rubio, Microchem. J. 34 (1986) 51.
[4] F. Salinas, J.L. Martinez, V. Gonzalez, Analyst 114 (1989) 1685.
[5] Q.Z. Zhai, X.X. Zhang, Q.Z. Liu, Spectrochim. Acta Part A 65 (2006) 1.
[6] Q.F. Zhou, Y. Wu, Q. Wang, Phys. Test. Chem. Anal. Part B 33 (1997)
352.
[7] M.A. Chamjangal, V. Keley, G. Bagherian, Anal. Sci. 22 (2006) 333.
[8] L.P. Long, Chin. J. Anal. Lab. 21 (2002) 80.
[9] S.L. Feng, B. Li, J. Fan, Chin. J. Anal. Chem. 25 (1997) 1274.
[10] Q.Y. Luo, Z.H. Lei, X.M. Yu, Chin. J. Anal. Chem. 12 (1984) 985.
[11] G.L. Long, J.D. Winefordner, Anal. Chem. 55 (1983) 712A.
[12] G.L. Long, J.D. Winefordner, Anal. Chem. 52 (1980) 2242.
3. Applications
The applicability of the proposed method has been checked in
two tomato samples. A 50.0000 g of tomato sample was soaked
for 30 min with 250 mL of boiling water at 100 ◦C in a beaker.
After the solution was cooled, it was filtered three times and
transferred into a 250-mL calibrated flask. An aliquot of the
above testing solution was placed into a 10-mL calibrated flask
and then the content of oxalic acid was determined according to