Trace Spectrophotometric Determination of Dichlorvos using ...

Journal of the Chinese Chemical Society, 2007, 54, 345-350 345
Trace Spectrophotometric Determination of Dichlorvos using Diphenyl
Semicarbazide (DPC) in Environmental and Agricultural Samples
E. K. Janghel, a M. K. Rai, a * V. K. Gupta a and J. K. Rai b
a School of Studies in Chemistry, Pt. Ravishankar Shukla, University of Raipur. (Chhattisgarh), 492010, India
b Chhattisgarh Council of Science & Technology, Pt. Ravishankar Shukla University Campus,
Raipur, (Chhattisgarh), 492010, India
A new and highly sensitive spectrophotometric method is developed for the determination of sub ppm
levels of the widely used organophosphorus insecticide dichlorvos. The method is based on alkaline hydrolysis
of dichlorvos to dichloroacetaldehyde followed by coupling with diphenyl semicarbazide (DPC)
in alkaline medium. The absorption maxima of the wine red dye compound formed is measured at 490 nm.
Beer’s law is obeyed over the concentration range of 4.3 to 34 g in a final solution volume of 25 mL
(0.18-1.36 ppm). The molar absorptivity, Sandell’s sensitivity and correlation coefficient were found to be
2.9 10 5 l mole -1 cm -1 , 0.013 g cm -2 and 0.9999, respectively. The standard deviation and relative standard
deviation were found to be 0.007 and 1.90%, respectively. The lower limit of detection is 0.04 g.
The method is simple, sensitive and free from interferences of other pesticides and diverse ions. Other
organophosphorous pesticides do not interfere with the proposed method. The method has been satisfactorily
applied to the determination of dichlorvos in environmental and agricultural samples.
Keywords: Spectrophotometer; Dichlorvos; Diphenyl semicarbazide (DPC); Environmental;
Agricultural samples.
INTRODUCTION
Dichlorvos [DDVP, Apavap, Vapona, Benfos], an
organophosphorus insecticide, is a systemic insecticide and
acaricide, used to control sucking, chewing and boring insects
and spider mites on a very wide range of crops. Unfortunately,
its ready access has resulted in its increased misuse
in homicidal and suicidal poisoning cases. Hence the
need has therefore arisen for a rapid and reliable method for
the detection and determination of dichlorvos in enviromental
materials. Consequently characterization of this insecticide
is necessary in forensic toxicology. 1
Dichlorvos [2,2-dichlorovinyl dimethylphosphate] is
highly toxic to mammals, including human beings. It is
readily absorbed through the skin, because it is volatile. Inhalation
is the most common route of exposure. Dermal absorption
and ingestion also occur, causing acute toxicity. 2,3
The acute oral LD 50 for rats is 55-56 mg/kg body weight 4
and FDA for milk of 0.02 ppm. 5
Because of the wide applicability and high toxicity of
dichlorvos, numerous instrumental methods have been described
for the detection/determination of dichlorvos, such
as automated analyzer analysis, 6 pH-sensitive fluorescence
probe, 7 fluorimetry, 8 polarography, 9 tandem mass spectrometry,
10 thin-layer chromatography, 11 gas chromatography
electron capture detection, 12 high performance liquid
chromatography, 13 gas-liquid chromatography, 14 mass
spectrometric method, 15 gas chromatography flame photometric
detection, 16 gas chromatography flame thermionic
detection, 17 and some updated instrumental methods
such as biosensors methods i.e., amperometric enzymatic
biosensors, 18 flow injection analysis, 19 etc.
Several spectrophotometric methods have been reported
for the determination of dichlorvos. 20-24 The methods
described are generally based on alkaline hydrolysis of
dichlorvos to produce dichloacetaldehyde followed by reaction
with reagents like resorcinol, 20 2,4-dinitrophenylhydrazine,
21 J-acid 22 and phloroglucinol. 23 Some of these
methods have poor sensitivity and higher blank problems.
The cholinesterase 24 method is non selective as all organophosphorus
pesticides interfere with the method.
Here a simple and sensitive spectrophotometric method
* Corresponding author. E-mail: ek_j13@rediffmail.com (E. K. Janghel)

346 J. Chin. Chem. Soc., Vol. 54, No. 2, 2007 Janghel et al.
Scheme I Proposed reaction for formation of coloured species
The colour reaction involves the following steps.
1. Hydrolysis of dichlorvos to its corresponding aldehyde.
2. Coupling of aldehyde with DPC under alkaline conditions to form wine - reddish dye at 490 nm.
is described for the determination of dichlorvos, where
dichlorvos is hydrolysed to give dichloroacetaldehyde,
which is further reacted with diphenyl semicarbazide (DPC)
to produce a wine - reddish dye, with maximum absorbance
at 490 nm (Scheme I). The reagent is selective and sensitive
for dichlorvos, amongst the organophosphorus group. The
colour system obeys Beer’s law in the range of 0.18-1.36
ppm of dichlorvos. The method has been applied to the determination
of dichlorvos in various samples of polluted
water, vegetables, soil, foliage and environmental samples.
The technique can be applied as a useful method for
simple and rapid analysis. The features of the method are
its sensitivity and stability of the colour formed. The results
of trace of the target substance is not interfered with by the
presence of other pesticides, especially other phosphorous
pesticides.
EXPERIMENTAL
Apparatus
A Systronics UV-Vis spectrophotometer model - 104
with matched silica cells was used for all spectral measurements.
A Systronic pH meter model - 335 was used for pH
measurements. A Remi C-854/4 clinical centrifuge force of
1850 g with fixed swingout rotors was used for centrifuga-

Determination of Dichlorvos J. Chin. Chem. Soc., Vol. 54, No. 2, 2007 347
tion.
Reagents
All reagents used were of Anala R grade or of the best
available quality. Double distilled deionised water was
used throughout.
Dichlorvos (Hindustion Ciba-Geigy Bombay, India):
A stock solution of 1 mg mL -1 was prepared in ethanol.
Working standard solutions were prepared by appropriate
dilution of the stock standard solution with ethanol.
Sodium hydroxide: A 1.0 mol L -1 aqueous solution
was used.
Hydrochloric acid: A 0.001 mol L -1 aqueous solution
was used.
Diphenyl semicabazide (DPC) (E. Merck, Germany):
0.05% (m/v) solution of the reagent was prepared by dissolving
0.05 gm of diphenyl semicarbazide (DPC) in 100
mL ethanol.
Procedure
An aliquot of the test solution containing 4.3 to 34 g
of dichlorvos was taken in a 25 mL graduated tube and to it
1.0 mL of 1.0 mol l -1 sodium hydroxide was added. The solution
was kept for 30 min at room temperature for complete
hydrolysis. Then 1 mL, 0.05% (m/v) of diphenyl semicarbazide
(DPC) was added, shaken thoroughly, and the pH
was adjusted to 9.0-9.3 by adding 0.001 mol l -1 hydrochloric
acid. The solution was kept for 45 min for full colour
development. A wine - reddish monomethine dye is obtained.
25,26,27 The solution was then diluted to the mark with
water and absorbance was measured at 490 nm against a reagent
blank.
RESULTS AND DISCUSSION
Spectral characteristics
The wine - reddish dye formed in the proposed reaction
shows maximum absorption at 490 nm. All spectral
measurements carried out against deionised water as the reagent
blank showed negligible absorption at this wavelength.
The colour system obeys Beer’s law in the range of
4.3 to 34 g of dichlorvos in 25 mL of final solution at 490
nm. The molar absorptivity, Sandell’s sensitivity and correlation
coefficient were found to be 2.9 10 5 l mol -1 cm -1 ,
0.013 g and 0.9999 cm -2 , respectively.
Optimization of conditions
Hydrolysis of dichlorvos to dichloroacetaldehyde
was studied at different temperatures and alkalinity. It was
observed that alkaline conditions were required for the hydrolysis.
Maximum hydrolysis was observed with 1.0 mol
l -1 sodium hydroxide at a temperature of 20-25 C as it gave
maximum absorbance values, good stability and quantitative
results. It was observed that 1 mL of diphenyl semicarbazide
(DPC) was sufficient for complete colour reaction.
Effect of time and temperature
The effect of pH on the colour reaction was studied,
and it was found that constant absorbance values were obtained
at a pH range of ~ 9.0-9.3, and no buffer solution
was required to stabilize the colour. At pH lower and higher
than this, absorbance values decreased. It was found that 45
min was required for full colour development; the colour
was stable for several days. The maximum absorbance of
the dye was obtained at 25 C. At higher temperatures the
absorbance value decreased (Table 1).
Precision of the method was checked by the replicate
analysis of working standard solution containing 5 gmL -1
of dichlorvos in 25 mL final solution over a period of 7
days. The standard deviation and relative standard deviation
were found to be 0.007 and 1.90% respectively.
Effect of foreign species
The effect of common foreign species and pesticides
were studied to assess the validity of the method. Known
amounts of foreign species and pesticides were added to the
standard solution containing 5 g of dichlorvos prior to hydrolysis,
and the solution was analysed by the proposed
method. The method was found to be free from interfer-
Table 1. Effect of temperature on colour reaction (Concentration
of dichlorvos, 0.2 ppm)
Temperature C
Absorbance*, 490 nm
5 0.320
10 0.412
15 0.445
20 0.448
25 0.450
30 0.440
35 0.341
40 0.286
* Mean of three replicate values.

348 J. Chin. Chem. Soc., Vol. 54, No. 2, 2007 Janghel et al.
ences of most of the foreign species and pesticides (Table
2).
Determination of dichlorvos in water
River water samples, receiving run-off water from
agricultural fields sprayed with dichlovos, were collected.
These samples were extracted with 2 25 mL portions of
diethyl ether. The ether solution was evaporated to dryness,
and the residue was dissolved in 50 mL of ethanol. Aliquots
were then analysed as described above and in parallel by a
reported method (Table 3).
Determination of dichlorvos in soil and vegetables
Various samples such as soil, cauliflower and tomatoes
were collected from the fields were dichlorvos was
used as an insecticide. The samples where weighed (50 g),
crushed and extracted with 2 25 mL portions of diethyl
ether. Diethyl ether was then evaporated to dryness, and the
residue was dissolved in 50 mL of ethanol. Aliquots were
then analysed as described above and in parallel by a reported
method (Table 3).
Application
The proposed method has been applied satisfactorily
to the determination of dichlorvos in various samples of
water, vegetables, and soil. The results are in good agreement
with the reported method. To check the recoveries,
known amounts of dichlorvos were added to these samples
and then analysed by the proposed as well as the reported
method (Table 3). The recoveries were found to be 88 to
Table 2. Effect of various pecticides and pollutants (Concentration of dichlorvos, 0.2 ppm)
Foreign species
Tolerance limit*
ppm
Foreign species
BHC, DDT 600
--
SO 4
Benzene, Ether 500
--
CO 3
Malathion 400
-
NO 2
2:4-D, 2:4:5-T 350
--
NO 3
Tolerance limit*
ppm
450
300
150
100
Cyanide 200 Cu 2+ ,Pb 2+ 60
Kelthane, Fluoride, Sb 3+ , 50
100
Chloroform
Ca 2+ ,Mg 2+ ,Cd 2+ 40
Parathion 50 K + ,Cl - 30
* The amount causing an error of 2% in absorbance value.
Table 3. Determination of dichlorvos in various environmental and agricultural samples
Sample
Dichlorvos originally found*
Proposed
method
(g)
(a)
Agricultural 5.98
waste water a 4.63
Soil b 4.80
4.98
Cauliflower c 5.14
5.46
Tomatoes d 6.76
4.32
Reported
method 23
(g)
5.98
3.02
2.82
4.86
3.28
5.12
6.51
3.58
Dichlorvos added
(g )
(b)
10
20
10
20
10
20
10
20
Total dichlorvos
found by
proposed*
method
(c)
15.862
23.828
13.664
24.496
14.329
25.235
16.734
23.466
Difference
(c-a)
9.88
19.19
8.86
19.51
9.18
19.77
9.97
19.14
Recovery
%
(c-a)
b
98.8
95.9
88.6
97.6
91.8
98.9
99.7
95.7
* Mean of five replicate analysis.
a = Water sample 250 mL, after treatment 1 mL aliquot was analysed.
b, c and d = Sample 50 gm (taken from an agriculture field, 1 mL aliquot of sample was analysed after treatment as described
in the procedure section)
100

Determination of Dichlorvos J. Chin. Chem. Soc., Vol. 54, No. 2, 2007 349
Table 4. Comparison with other reported reagents
Reagent
max
(nm)
Beer’s law range
(ppm)
Remarks
Resorcinol 20 490 1-20 Dye unstable, high reagent blank
2,4-dinitrophenyl hydrazine 21 580 3.4-27.5 Less sensitive
Chlolinesterase 22 412 20 Interference of other organophosphorus pesticides
J-acid 23 470 1-10 Less sensitive
Phloroglucinol 24 475 0.4-4 Less sensitive
Diphenyl semicarbazide (DPC)
(present method)
490 0.18-1.36 High sensitivity
99%.
CONCLUSION
The proposed method has been compared with other
spectrophotometric methods and found to be more sensitive
and selective (Table 4). This method is a good alternative
to some of the reported costly instrument methods. 28
The advantage of the proposed method is mainly its sensitivity,
simplicity and selectivity and higher stability of the
coloured solution. The proposed method has been successfully
applied for the determination of dichlorvos in water,
soil and vegetables.
ACKNOWLEDGEMENTS
Authors are thankful to the Head School of Studies in
Chemistry, Pt. Ravishankar Shukla University, Raipur, and
the Director General, Chhattisgarh Council of Science &
Technology for providing laboratory and grant facilities.
One of them, V. K. Gupta is thankful to A.I.C.T.E, New
Delhi for the award of an Emeritus Fellowship.
Received March 10, 2006.
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