American Journal of Anal yt ical Chemistry, 2011, 2, 158-163
doi:10.4236/ajac.2011.22018 Published Online May 2011 (http://www.SciRP.org/journal/ajac)
Fourth Derivative Spectrophotometric Method for the
Determination of Fungicide Maneb Using Sodium
Molybdate
Manpreet Kaur, Ashok Kumar Malik, Baldev Singh
Department of Chemistry, Punjabi University, Patiala, India
Received November 26, 2010; revised December 29, 2010; accepted March 1, 2011
Abstract
A highly sensitive fourth derivative spectrophotometric method is presented for the residue analysis of ethy-
lenebis dithiocarbamate fungicide Maneb. The fungicide maneb forms a blue complex with sodium molyb-
date on heating which is studied spectrophotometrically. The method has been successfully applied to maneb
determination in wheat grains and soft drinks with high recoveries. The analytical sensitivity of the present
method has been found to be 0.0011 μg/mL.
Keywords: Derivative Spectrophotometry, Maneb, Sodium Molybdate
1. Introduction
Maneb (manganese ethylenebisdithiocarbamate) (Figure 1)
is a common dithiocarbamate (DTC) fungicide available as
dust and dispersible powder [1]. Maneb is active against
a wide range of bacterial and fungal species, so, it is
widely used on vegetable crops, in fields, orchards and
vines, greenhouses, forestry and also for seed treatment
[2]. Maneb is not systemic but rather a protective fungi-
cide. Hence, its residues can be found on the fodder, fruit
and other crops where it is sprayed. Ethylene-
bisdi-thiocarbamate (EBDC) fungicides like maneb have
low human toxicity but their degradation to Ethylene
thiourea (ETU) is of great toxicological concern [3-5] as
it is associated with carcinogenic and teratogenic proper-
ties [6]. DTC complexes are toxic and have mutational
effect [7]. Rathore et al. [8] have studied the mobility of
DTC pesticides through soil and this aspect of their be-
havior presents severe hazards for the mankind as they
can be washed in to drinking water sources thus entering
our food chain. In the wake of above knowledge, it is im-
perative that highly sensitive and efficient methods be
developed for the residue analysis of dithiocarbamate
pesticides like maneb in various food and environmental
samples. Most of the developed methods like spectro-
photometry and gas chromatography [9] are based on the
analysis of CS2, H2S or amines, which are evolved dur-
ing decomposition of EBDCs.
One of the earliest colorimetric methods for Maneb
determination was developed by Hylin et al. [10] Türker
et al. devised a flame atomic absorption spectrometry
method for indirect determination of dithiocarbamate
fungicides [11]. Crnogorac and Schwack have provided
insight into the various methods for the residue analysis
of dithiocarbamate fungicides [12]. Waseem et al. have
used a flow-injection method for the analysis of DTC
fungicides with chemiluminescence detection [13]. A
microwave assisted extraction method involving hy-
drolysis of dithiocarbamates and their analysis in tobacco
leaves was developed by Vryzas et al. [14] A DPP (Dif-
ferential pulse polarographic) technique has been em-
ployed for the determination of DTC residues by
Schwack et al. [15] Lo et al. have determined propineb,
zineb, maneb and mancozeb by an HPLC method [16].
Česnik et al. have developed validation for a GC-MS
Figure 1. Structure of maneb.

M. KAUR ET AL.159
method for the determination of DTCs in foodstuffs [17].
Cronogorac et al. have presented a method using hydro-
philic interaction-LC-Tandem Mass Spectrometry for the
determination for DTC fungicide residues in fruit and
vegetables [18]. Dithiocarbamates (DTCs) can also be
determined by methods, like iodometry [19,20], indirect
complexometry [21] and FTIR spectrometry [22]. But
the methods discussed above have various disadvantages
like:
1) Most of the methods except for the gas chromatog-
raphy are indirect, time consuming and less sensitive.
2) The Gas chromatographic methods are sensitive but
not selective as all the dithiocarbamate pesticides evolve
carbon disulphide on acid hydrolysis.
3) HPLC methods are out of bounds for several re-
searchers as these are expensive and use toxic and ex-
pensive solvents.
In the present work, a relatively fast, simple, sensitive
and selective derivative spectrophotometric method is
presented for the analysis of Maneb by converting it into
molybdenum complex. Maneb reacts with sodium mo-
lybdate on heating to form a blue coloured complex.
Maneb and sodium molybdate combine in the ratio 1:2 to
form complex. Maneb releases Mn2+ and dithiocar- ba-
mate unit, the latter forms complex with sodium mo-
lybdate, which is then extracted into methyl isobutyl ke-
tone (MIBK) and determined by derivative spectropho-
tometry. The significant advantage of this method over
the gas chromatographic methods is that it can be applied
for the direct determination of Maneb in the presence of
other dithiocarbamates like Ziram, Nabam and Zineb.
2. Materials and Methods
2.1. Equipment and Reagents
Elico SL-164, Double Beam UV-Vis spectrophotometer
was used. Maneb standard was obtained from Riedel de
Haën, Germany. A stock solution was prepared by heat-
ing 100 mg of Maneb in 100 mL of 0.1 molL−1 of NaOH.
Further dilutions were carried out with 0.1 molL−1 of
NaOH as required. A 2% (m/v) solution of sodium mo-
lybdate was prepared in doubly distilled water.
2.2. Procedures
2.2.1. Absorption Spectra
2 mL of 2% sodium molybdate solution and 1 mL of
2 molL−1 of H2SO4 were added to an aliquot containing
100 g of Maneb. The mixture was boiled for 5 minutes,
cooled and water was added to make the volume 5 mL.
The blue complex formed was extracted into 5 mL of
MIBK (methyl isobutyl ketone) with shaking. The or-
ganic layer was collected into a test tube containing
fused CaCl2 to remove any moisture. The solution was
then decanted into a 1 cm cell and the spectra were taken
against a reagent blank. The molybdenum complex
shows peaks at 670 nm and 956 nm (Figure 2), but the
peak at 956 nm has much higher absorbance; hence all
the measurements were made at this wavelength. The
first derivative, second derivative, third derivative and
fourth derivative curves were given in Figures 3-6 re-
spectively.
Figure 2. Zero order absorption spectra of Maneb-molyb-
date complex.
Figure 3. 1st derivative curves of molybdenum-ethylenebis-
dithiocarbamate complex: a, b, c, d representing the
amounts of Maneb in final solutions (a: 10, b: 20, c: 30 and
d: 40 μgmL−1).
Figure 4. 2nd derivative curves of molybdenum-ethylenebis-
dithiocarbamate complex: a, b, c, d representing the
amounts of Maneb in final solutions (a: 10, b: 20, c: 30 and
d: 40 μgmL−1).

M. KAUR ET AL. 160
Figures 3-6 show the derivative spectrum of different
orders. The comparison of calibration curves of different
derivative spectra are provided in the Table 2.
3. Results and Discussion
3.1. Beer’s Law and Sensitivity
The optimum wavelength interval was found to be 9 nm
for high resolution and sensitivity. The wavelength range
to obtain spectra was selected from 600 nm to 1100 nm.
The calibration curve was obtained by measuring the
peak height between wavelength of 850 and 938 nm.
Absorbance of sodium molybdate complex with Maneb
recorded against a reagent blank was linear over the
concentration range from 2 µg/5 mL−1 to 40 µg/5 mL−1
of the final solution. The detection limit is 0.0011 µgmL−1
for Maneb when S/N ratio was 3.
Figure 5. 3rd derivative curves of molybdenum-ethylenebis-
dithiocarbamate complex: a, b, c, d representing the
amounts of Maneb in final solutions (a: 10, b: 20, c: 30 and
d: 40 μgmL−1).
3.2. Effect of Heating Time
It was observed that the absorbance of the complex in-
creased up to a certain extent on increasing the heating
time. Therefore, the reaction mixture was heated for dif-
ferent intervals of time. It was observed that an optimum
heating time of 5 minutes was sufficient to obtain maxi-
mum absorbance. Increasing the heating time beyond
this did not increase the absorbance as the complete
complexation was achieved by heating for 5 minutes.
Figure 6. 4th derivative curves of molybdenum-ethylenebis-
dithiocarbamate complex: a, b, c, d representing the
amounts of Maneb in final solutions (a: 10, b: 20, c: 30 and
d: 40 μgmL−1).
3.3. Effect of Acid Concentration
In DS (Derivative Spectrophotometry), the λ repro-
ducibility and S to N ratio are quite important. The fea-
tures like peak height and noise level depend on parame-
ters chosen like order of derivative; scan speed and inte-
gration time during recording of spectra. The use of op-
timum parameters will give better resolution and more
sensitivity. For the 4th derivative spectra, Δλ = 9 nm was
found to be ideal.
Maximum absorbance was observed when volume of
acid added was between 1 mL to 1.5 mL. A decrease in
absorbance was observed on further increasing the
amount of acid added as higher acid concentration is not
conducive for complex formation.
Table 1. Different parameters of zero order spectrum.
Serial
No. Parameter
Zero order spectrum of
maneb-sodium
molybdate complex
1.
2.
3.
4.
Molar Absorptivity (Lmol−1cm−1)
Sandell’s Sensitivity (μgmL−1)
Analytical Sensitivity (μgmL−1)
Linear Range (μgmL−1)
8.16 × 104
0.0049
0.0011
2 to 40
2.2.2. Preparation of Calibration Curve
The known volumes of sample solutions having 10 - 250 µg
of Maneb were analysed by general procedure and the
derivative spectra were obtained against a reagent blank
prepared under the similar conditions. The characteristics
of zero order spectrum are summarized in Table 1. The
Table 2. Comparison of calibration curves of Maneb using different derivative spectra.
Zineb Complex Order of Derivative λ (nm) Regression Equation R2 S.D. of Slope Analytical Sensitivity μgmL−1
1.
2.
3.
4.
1st
2nd
3rd
4th
814
950
932
904
y = 4 × 10−5x – 0.0001
y = 7 × 10−6x – 0.0002
y = 3 × 10−6x – 5 ×10−5
y = 8 × 10−7x + 7 ×10−6
0.9997
0.9992
0.9995
0.9994
1.2 × 10−6
2.4 × 10−7
1.4 × 10−8
2.3 × 10−9
1.4
0.9
0.032
0.0011

M. KAUR ET AL. 161
3.4. Effect of Other Ions
Sample solutions containing 5 μgmL−1 of Maneb and
various amounts of different alkali metal salts or metal
ions were prepared and the general procedure was ap-
plied. It was observed that 20 mg of following foreign
anions didn't interfere in the determination of Maneb:
bromide (11 mg), acetate (15 mg), chloride (3.5 mg),
fluoride (2 mg), citrate (20 mg) and EDTA (0.06 mg). Of
the metal ions examined, Mn(II) (0.066 mg), Mo(IV)
(0.14 mg), Ni(II) (0.30 mg), Co(II) (0.009 mg) did not
interfere. Fe(II) and Zn(II) were masked with 1 mL of
5% NaF solution and 1 mL of 5% KCN solution respect-
tively. 1 mL of 5% potassium iodide and thiourea were
used to mask Hg(II) and Cu(II) respectively. It is thus
clear that several ions like Fe, Zn, Hg etc. interfered in
maneb determination
3.5. Effect of Standing Time
It was observed that the absorbance of the solution be-
came constant after 2 - 3 min. so after extracting into
MIBK a 5 min. standing time was selected. The absorb-
ance of the complex remained practically constant for
about 30 minutes with the R.S.D. of absorbance values
varying between 0.69% to 1.6% for different concentra-
tions.
4. Applications
4.1. Determination of Maneb from Fortified
Samples of Wheat Grains and Soft Drinks
The method was applied to the determination of Maneb
from fortified samples of wheat grains, cabbage and soft
drink samples.
4.1.1. Sample Preparation for Food Stuffs
20 grams of the foodstuff was finely crushed and solu-
tion containing a known amount of maneb was added, it
was mechanically shaken with 100 mL of ACN (Ace-
tonitrile) for 1 hour. This mixture was filtered and the
residue in funnel was washed with 3 × 10 mL portions of
ACN. The extracts were evaporated on a water bath (70 -
90˚C). The last traces of solvent were removed using a
current of dry air. The Maneb content in the residue was
determined by the general procedure and the results in-
dicated good recoveries in all cases. The results of the
determinations were given in Table 3.
4.1.2. Sample Preparation for Soft Drinks
The soft drinks (coke and limca) were locally obtained.
These were diluted ten times, filtered and spiked with
known amount of maneb solution. The maneb content
was determined by the general procedure using a reagent
blank prepared under similar conditions.
4.2. Determination of Maneb in Commercial
Samples
The method was applied for determination of Maneb in a
commercial samples and. The formulated product sample
solutions were prepared as discussed earlier and deter-
mined by the general procedure. The results of the de-
terminations were given in Table 4.
4.3. Simultaneous Determination of Maneb in
Presence of Ziram in Synthetic Mixtures
The method was applied for the simultaneous determina-
tion of Ziram and Maneb in synthetic mixtures. Ziram
forms a yellow complex with sodium molybdate in cold,
which absorbs at 420 nm (21) whereas Maneb forms
complex on heating, all other conditions remaining the
same. Synthetic mixtures of maneb and ziram were made
in different proportions. To the binary mixture, 0.15 mL
of 2 molL−1 of H2SO4 and 2 mL of 2% sodium molybdate
were added. Molybdenum-ziram complex was extracted
Table 3. Determination of Maneb in fortified samples (mean values and standard deviations, n = 5).
Fungicide Sample Maneb added (μg)Maneb found (μg) Recovery (%) ± RSD (%)
Wheat
10
15
20
9.8
14.9
19.8
98 ± 2.1
99.3 ± 1.9
99 ± 1.9
Cabbage 8
10
7.8
9.7
97.5 ± 2.2
97 ± 1.9
Coke
10
20
25
9.1
18.6
23.9
91 ± 2.4
93 ± 2.1
95.6 ± 2.5
Maneb
Limca
10
20
25
9.0
18.2
23.6
90 ± 2.2
91 ± 1.8
94.4 ± 1.8

M. KAUR ET AL. 162
Table 4. Determination of Maneb in commercial samples (mean values and standard deviations, n = 5).
Rangaswamy et al. method22
Commercial
Sample
Maneb taken
(μg)
Maneb found
(μg) Recovery (%) ± RSD (%)
Maneb found (μg) Recovery %
Dithiane
M-45 (80% W.P.)
20
30
40
19.9
30
39.9
99.5 ±1.5
100 ± 1.8
99.8 ± 1.6
19.7
29.8
39.8
98.5
99.3
99.5
Dithiane
M-22 (80% W.P.)
20
30
40
19.8
29.8
39.9
99 ± 1.6
99.3 ± 1.4
99.8 ± 1.5
19.7
29.6
39.8
98.5
98.7
99.5
Table 5. Determination of Maneb and Ziram in synthetic mixtures (mean values and standard deviations, n = 5).
Recovery (%) ± RSD (%)
Maneb added
(μg)
Ziram added
(μg)
Maneb found
(μg)
Ziram found
(μg) Maneb Ziram
30
20
15
40
30
20
29.5
19.6
14.5
38.8
29.0
19.0
98.3 ± 2.3
98.0 ± 2.6
96.7 ± 2.1
97 ± 2.3
96.7 ± 2.5
95 ± 2.6
Table 6. Comparison of molar absorptivities of Maneb complexes.
Procedure Molar Absorptivity
(Lmol−1cm−1) Remarks Reference
Molybdenum 0.4 × 104 Low sensitivity and selectivity 23
Rangaswamy et al. method _
Low sensitivity, long tedious
procedure 24
Complex formation with diphenylcarbazone
and pyridine 6.5 × 104 Extraction not rapid and uses toxic pyridine 25
Complex formation with PAN 4.1 × 104 Less sensitive than present me-
thod 26
Molybdenum (at 956 nm) and derivative
spectrophotometry 8.1 × 104 Better sensitivity Present work
into 5 mL MIBK and maneb remained in aqueous phase.
The absorbance of ziram-molybdenum complex was
measured at 420 nm. To the aqueous phase containing
maneb was added 1mL 4 molL−1 H2SO4 and 2 mL of 2%
Na2MoO4 solution. The solution was boiled for 5 minutes,
cooled and extracted into 5 mL MIBK, the spectra of
blue complex of maneb was taken between 600 nm and
1100 nm. Thus, this method was applied for the simulta-
neous determination of ziram and maneb. Ziram was
determined from the standard calibration curve. The re-
sults of the determinations are given in Table 5.
5. Conclusions
The present method is more sensitive than the carbon
disulphide evolution methods. It is superior to the re-
ported methods and the direct simultaneous determina-
tion of ziram and maneb is possible. The sensitivity of
the present method is comparable to other spectropho-
tometric methods (Table 6). The selectivity of the pre-
sent method is superior to other methods. The wide ap-
plicability of this method makes it suitable for dithiocar-
bamate analysis in foodstuffs and in commercial sam-
ples.
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M. KAUR ET AL.163
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