American Journal of Anal yt ical Chemistry, 2011, 2, 63-68
doi:10.4236/ajac.2011.228125 Published Online December 2011 (http://www.SciRP.org/journal/ajac)
A New Approach for Atrazine Desorption, Extraction and
Detection from a Clay-Silty Soil Sample
Rossy Feria-Reyes1, Paola Medina-Armenta2, M. Teutli-León3, M. G. García-Jiménez2, I. González1*
1UAM-Iztapalapa, Chemistry Department, Autonomous Metropolitan University, Mexico City, Mexico
2Chemistry Department, University of Guanajuato, Guanajuato, Mexico
3Engineering Department, Distinguished Autonomous University of Puebla, Puebla, Mexico
Received November 12, 2011; revised December 13, 2011; accepted December 23, 2011
Abstract
This paper reports an alternative method for extraction, detection and quantification of atrazine from a
clay-silty soil. Atrazine adsorption isotherm for this kind of soil fits to a Freundlich adsorption isotherm with
a correlation coefficient of 0.994, sorption intensity 1/n = 0.718 and Kf = 1, with a maximum soil adsorbed
atrazine concentration of 8 mg·g–1. Atrazine desorption was approached using several surfactants including
non-ionic (Triton X-100, Triton X-114, and Triton X-405), anionic (SDS) and cationic (CTAB), these sur-
factants were used at critical micellar concentration (CMC) and higher concentrations. Atrazine quantifica-
tion was done by high resolution liquid chromatography coupled to spectrophotometric detection
(HPLC-UV), optimized conditions correspond to a flow rate of 1.0 mL·min–1, λ = 260 nm, a C18 PAH
Agilent-Eclipse column with a mobile phase of CH3OH/1 × 10–3, a phosphate buffer, pH 3.2/CH3CN
55:30:15 (v/v). At these conditions it can be obtained a good chromatographic separation of atrazine and soil
organic matter. Atrazine desorption was aided by surfactants at CMC conditions, it can be claimed that
atrazine desorption was enhanced by surfactants since desorption, from higher to lower, goes as follows:
98.5% with Triton X-114, 98% with SDS, 89.5% with Triton X-405, 86.5% with Triton X-100; and 45%
with CTAB.
Keywords: Atrazine, Desorption, Soil, Surfactants
1. Introduction
In Mexico, it is estimated that annual pesticide applica-
tion amounts 55,000 tons [1], from which 28.7% corre-
sponds to herbicides, and in this class atrazine represents
12.8%, being the third most used herbicide. Atrazine
(2-chloride-4-ethylamino-6-isopropylamino-1,3,5-triazin
e) belongs to the S-triazine herbicide group. This herbi-
cide is practically non-volatile, at neutral state its average
half-life is 200 days, but its active state ranges from 4 to
57 weeks, its persistence is affected by environmental
factors such as pH, humidity, temperature and microbial
activity [2-8]. Health concerns about atrazine are related
to liver and heart, as well as endocrine and teratogenic
alterations.
Atrazine has been mainly used for weeds control in
corn, sorghum, pineapple and sugar cane farming. Ac-
cording to EPA, environmental concentration levels of
herbicides and pesticides are very low, therefore in EPA
508.1 method [9] it is recommended to include a solvent
aided extraction and pre-concentration stage so an in-
crease on selectivity is favored.
In the last decades methods for pre-concentration have
been studied in order to be implemented before analyti-
cal determination of compounds at trace level concentra-
tions. This approach pursued a minimization/elimination
of organic solvents of common use in liquid-liquid ex-
traction; some of the reported methodologies are: extrac-
tion with membranes [10-12], solid phase extraction
(SPE) [13,14], and solid phase micro-extraction (SPME).
Use of micellar systems (surfactants) has become a
common practice for either new analytical methods or
modification of old ones. Aqueous surfactant solutions
have been used in micellar extraction (ME) and cloud
point extraction (CPE), in the first methodology selective
extraction can be done because micellar aggregates have

R. FERIA-REYES ET AL. 64
a size which unable them to pass through ultrafiltration
membranes, this fact, plus micelle solubilization capacity
for a wide set of solutes, it is the basis of separation
methods. Most applications of CPE for organic com-
pounds extraction are usually complemented by HPLC,
since the obtained surfactant rich extraction phase is to-
tally compatible with the common hydro-organic phases
used in this type of chromatography [15].
Non-ionic surfactants like Genapol X-080 and Triton
X-114 have been used as extractive agents for organo-
phosphorate compounds such as methyl and ethyl-para-
thion, paraoxon, and fenitrothion, when the CPE method
is applied in their extraction, previously to HPLC deter-
mination [16,17].
Considering that in a soil sample, an analysis of herbi-
cide and pesticide it is though a challenge because pres-
ence of them, plus organic matter creates a highly com-
plex matrix. In this work it is presented evidence of a
modified methodology in which surfactants inclusion
allowed to get atrazine desorption and extraction from a
clay-silty soil, and left an extract which provides a clear
chromatographic separation signal between atrazine and
organic matter.
2. Methodology
2.1. Reagents
All reagents used in this study were analytical grade. A
1000 mg·L–1 standard atrazine (Sigma Aldrich, 99%)
solution was prepared with HPLC grade acetonitrile
(Caledon, 99%); this was storaged at –10˚C, in darkness
condition. One hour before experimentation reference
solution was allowed to warm at room temperature. A 5
mg·L–1 humic acid (Sigma Aldrich, 98%) solution was
prepared using 1 × 10–3 M NaOH. Additional reagents
for the mobile phase are methanol (J.T. Baker, 99.9%),
phosphoric acid (Sigma Aldrich, 98%), anhydrous mono-
basic sodium phosphate (Monterrey, 99.5%). Also, con-
sidered surfactants in the extraction stage were obtained
from Sigma Aldrich, three types were used: a) anionic
type: sodium dodecyl sulfate (SDS, 96%), b) cationic
type: cetyl trimethyl ammonium bromide (CTAB, 95%);
and c) non-ionic ones like octylphenol ethylene oxide
condensate (Triton X-100, 99%), tert-octylphenoxypoly
(ethoxyethanol) (Triton X-114, laboratory grade), Oc-
tylphenol ethoxylate (Triton X-405, 70% in water).
2.2. Soil Characterization
In order to assure that experiments will be run with a
clean soil, the sample used in this study was collected at
50 cm depth in a clean site. Soil particle characterization
was done following the ASTM-D2487 procedure, while
density and texture were determined by the Bouyoucos
hydrometer method [18]. Identification of soil minera-
logical phases were done with a Siemens D-500 powder
diffractometer, which has an X-ray tube, Cu cathode,
using a CuKα wavelength of 1.5418 Å and Ni filter; for
detection runs it was used 30 KV with 20 mA, the scan-
ning rate was done at 2˚ min–1 [19]. Analytical samples
were prepared by mixing soil with deionized Milli-Q
water in a proportion of 1:2.5; this samples were used to
measure pH and conductivity with a PC 45 conductivity
meter coupled to an Orion 710 A instrument provided
with a HI203 electrode, which is useful for in-situ soil
pH measurements. Organic matter content was deter-
mined using the ASTM-D 2974 procedure [20].
2.3. Atrazine Adsorption/Desorption
This study considered preparing a synthetic polluted
sample from clean soil (pesticide free), which was spiked
with an acetonitrile dissolved atrazine solution. After
adsorption, the extraction step was done using different
solvents, this with the purpose of establishing which one
provides the best characteristics for atrazine recovery and
analysis.
Atrazine impregnation (adsorption step) was realized
by a batch equilibrium method [22]. The sample is pre-
pared into centrifuge tubes, placing 1 g soil sample
which is mixed with atrazine solutions whose concentra-
tions go from 5 - 100 mg·L–1, in 10 mL of 0.01 M CaCl2,
tubes were stirred for 3 hrs at 25˚C ± 1˚C, centrifugated
at 3500 rpm during 30 min, the supernatant was decanted,
and atrazine equilibrium concentration is determined.
Later on, for extraction (desorption step), polluted soil
sample was added with 3 mL of extractant solution, be-
ing either acetonitrile or surfactants (SDS, CTAB, Triton
X-100, Triton X-114, Triton X-405), these mixed with
Milli-Q water at 1, 2 and 3 times critical micellar con-
centration (CMC).
Samples of soil plus extractant are placed in an ultra-
sound bath for 2 h, after doing that, a 1 mL aliquotat was
taken and centrifuged at 14,000 rpm for 30 min; then,
samples are filtered by a 0.2 mm Iso-DiscTM filters
N25-2 (Supelco), this step allowed suspended particle
separation. Afterwards, 20 μL of each filtered samples
were injected in the CC5-BAS Liquid Chromatographic
column coupled with an UV-116 BAS detector.
As a first step chromatographic separation was done
by using Carabias et al. reported procedure [12], later on
conditions were modified up to get the ones reported in
this paper which are a mobile phase of CH3OH: 1 mmol
L–1 NaH2PO4 pH 3.2:CH3CN (55:30:15), a flow rate of
0.4 mL·min–1, analysis performed in an Agilent Eclipse

R. FERIA-REYES ET AL.65
C18 PAH reverse phase column (100 mm × 4.6 mm 3 m
particle size). Spectrophotometric detection was done at
a 260 nm wavelength.
Soil adsorbed atrazine (Cs) is calculated from the dif-
ference between the initial concentration (Ci) and the
equilibrium concentration (Ce). Adsorption isotherms
were obtained by plotting the amount of adsorbed
atrazine per unit soil weight at equilibrium conditions (Cs,
mg·Kg–1), against the atrazine equilibrium concentration
in solution (Ce, mg·L–1). It was considered to fit the ex-
perimental data to the linear adsorption isotherm:
s
de
CKC (1)
where Kd = linear adsorption constant. And to the
Freundlich adsorption isotherm, which in linearized form
can be expressed as:
1
log loglog
s
Fe
CK C
n
 (2)
in this equation KF is Freundlich adsorption constant,
while 1/n is a measure of sorption intensity.
3. Results
3.1. Soil Characterization
The results of soil physical characterization, by the
Bouyoucus and X-Ray Diffraction methods, are reported
in Table 1. From these data it can be established that
used soil corresponds to a clay-silty soil with high feld-
spar content.
Table 1. Physical and textural soil properties.
Mineralogical characteristics
Feldspar 54.8%
Kaolinite 5.1%
Chlorite 8.3%
Carbonate 5.8%
Quartz 21.9%
Textural characteristics
Sand 29.0%
Clay 45.8%
Silt 23.9%
pH 8.6
C. E.a 0.334 S m–1
O. M.b 2.6%
a. Electrical conductivity; b. Organic matter.
3.2. Detection Method Calibration
In order to assess the precision of atrazine detection by
HPLC technique, it was necessary to get the calibration
curve, then a set of atrazine solutions, from 0.5 to 40
mg·L–1, was prepared using acetonitrile as a solvent. In
this concentration range it was possible to get a 0.999
correlation coefficient for atrazine detection.
3.3. Atrazine Adsorption onto Soil
Experimental approach considered batch experiments as
described in the methodology section. Considered con-
centrations were from 5 to 100 mg·L–1 of atrazine, results
allowed to calculate Ce and Cs values which are plotted
in Figure 1.
From the Figure 1 it becomes evident that adsorption
process is not a linear one, then experimental data was
fitted to the linearized form of Freundlich isotherm, after
doing the data conversion to get a log-log plot, and ap-
plying a linear regression the following data were ob-
tained: a correlation coefficient of 0.994, 1/n = 0.718, Kf
= 1. At this stage, it was determined that maximum
atrazine adsorbed concentration corresponds to 8 mg g–1,
which it is in the range of 5 - 10 mg·g–1, values reported
in published works [22,23].
In order to get the best chromatographic conditions to
detect atrazine in obtained soil extracts, it was used
HPLC grade acetonitrile as solvent.
In Figure 2(a) it is observed that the humic acid chro-
matogram presents an elution time of 1.9 min; while the
one for the unpolluted soil-acetonitrile extract, Figure
2(b), exhibits a signal at the same time, then this peak
was assigned to the organic matter in soil. Although,
C
e
(Atrazine mg·L
–
1
)
C
s
(Atra zin e m g /g so il)
Figure 1. Results of equilibrium adsorbed atrazine per unit
soil weight (Cs, mg·Kg–1) against liquid equilibrium atrazine
(Ce, mg·L–1), all batch ads orption exp erimen ts used 1 g clean soil
sample [22].

R. FERIA-REYES ET AL. 66
Figure 2. Chromatograms for extracts obtained from: (a) 5
mg·L–1 humic acid/CH3CN; (b) 1.0 g clean soil/ CH3CN; (c)
1.0 g soil previously contaminated with 10 mg·L–1 atraz-
ine/CH3CN, and experimental detection conditions: flow
rate: 0.4 ml·min–1,  = 260 nm, agilent eclipse C18PAH col-
umn. Mobile phase CH3OH/1 × 10–3, phosphate buffer, pH
3.2/CH3CN 60:30:10 (v/v).
when atrazine is present in soil, Figure 2(c), it is ob-
served a slight increase of the signal for the same posi-
tion; this phenomena can be attributed to the intermo-
lecular bonds between organic matter and atrazine, so the
last one enhances organic matter desorption, atrazine is
eluted at 3.1 min. In Table 2 it is shown the surfactant
used for this study and the aqueous applied concentra-
tions for atrazine desorption from soil. In the table are
explicit those values of the Critical Micellar Concentra-
tion (CMC) equivalent to the 1 CMC, 2 CMC and 3
CMC.
A first approach to determine atrazine desorption by
chromatographic analysis, was intended with the first 3
surfactants (SDS, CTAB, Tritón X-114), experimental
conditions were those reported by Carabias et al. [12],
results are shown in Figure 3.
As it can be observed in Figures 3(b) and (c), ob-
tained results with SDS and CTAB at CMC are quite
imprecise, it is considered that the obtained signal is in-
adequate since the organic matter was eluted a very short
times together with the atrazine; also, SDS and CTAB
absorbance peaks exhibit a wide signal masking onto the
required ones for organic matter and atrazine. An oppo-
site behavior is observed when the used surfactant is
non- ionic as Triton X-114, Figure 3(a), for this one it is
observed that the organic matter elutes at 3.1 min, while
the one for atrazine appears at 4.1 min; but as it can be
observed the signal for organic matter is broad and ex-
hibits 2 peaks, phenomena which can be accounted such
as a bad chromatographic separation.
Therefore, in order to improve the chromatographic
separation, the next set of experiments considered to in-
Table 2. Surfactants employed for atrazine desorption in
aqueous media.
Surfactant CMC (M) 2 CMC (M) 3 CMC (M)
SDS 8.1 × 10–3 1.6 × 10–2 0.0243
CTAB 9.2 × 10–4 1.8 × 10–3 0.00276
Triton X-1002.5 × 10–4 5.0 × 10–4 0.00075
Triton X-1143.5 × 10–4 ----- ------
Triton X-4058.1 × 10–4 ----- ------
Figure 3. Chromatograms of 1.0 g of soil contaminated with
an aqueous solution of 10 mg·L–1 atrazine, in its extraction
it was used (a) Triton X-114, (b) SDS and (c) CTAB, all at
CMC. Flow rate: 1.0 mL·min–1,  = 260 nm, in an agilent
eclipse C18 PAH column. Mobile phase CH3OH/ 1 × 10–3
phosphate buffer, pH 2. 6/CH3CN 60:30:10 (v/v).
crease surfactant concentrations up to 2 and 3 times the
CMC (results are not shown), for these it was observed
that the complex signal prevails, additionally it happens
that the absorbance peak increases as surfactant does it.
These behaviors could indicate that there is a molecu-
lar interaction between soil and extractant. Desorption
was estimated from the area under each peak, results are
presented in Table 3, in which it is reported the surfac-
tant, the concentration used and the attained desorption
expressed in percentage.
It can be observed that a 100% desorption is estimated
for Triton X-114 at 3 CMC (1.05 × 10–3 M). Also, 98%
desorption is obtained with a 3 CMC (2. 43 × 10–2 M)
SDS, finally, 57% desorption is obtained with a 3CMC
(2.76 × 10–3 M) CTAB. Although, again these values are
not trustable because the poor chromatographic separa-
tion of the peaks, that is why it was decided to modify
detection conditions. Optimized detection conditions cor-
respond to: a mobile phase of methanol/1 × 10–3 M pho-
sphate buffer, pH 3.2/acetonitrile, a volume relationship
of 55:30:15.

R. FERIA-REYES ET AL.67
Table 3. Atrazine desorption percentage for the different
surfactants.
Surfactant Desorption percentage
CMC 96
2 CMC 97
Triton X-114
3 CMC 100
CMC 91
2 CMC 96 SDS
3 CMC 98
CMC 42
2 CMC 55 CTAB
3 CMC 57
A new evaluation of atrazine desorption was done in-
cluding three non-ionic surfactants from the octylphenol
etholxilate group being: 1) Triton X-114; 2) Triton
X-100; and 3) Triton X-405; also the anionic 4) SDS,
and the cationic 5) CTAB; all of them were tried at the
CMC, under the optimized conditions. Results are shown
in Figure 4(a) for non-ionic surfactants, and in Figure
4(b) for the anionic and cationic surfactants.
In Figure 4(a) can be observed that extraction with the
non-ionic surfactants allowed for organic matter signal
occur at 1.7 min, and the one for atrazine at 3.2 min, both
with well defined peaks, then it becomes evident that
non-ionic surfactants allowed to realize atrazine extrac-
tion from soil. Obtained desorption percentage with Tri-
ton X-114 is 98.5%, Triton X-100 is 86.5%; and with
Triton X-405 is 89.5%. Even though atrazine signal is
similar for the three surfactants, it happens that Triton
X-100 affects the organic matter signal; then, this sur-
factant should be discarded.
In Figure 4(b) are presented the chromatograms for
the anionic surfactant (iv) SDS and the cationic one (v)
CTAB, it can be observed that for both the organic mat-
ter signal elutes at 1.7 min, and atrazine at 3.1 min. De-
sorption of atrazine with SDS amounts 98% and with
CTAB is only 54%. It is important to remark that, even
though the CTAB allowed a chromatographic separation
with clear peaks for the organic matter and atrazine the
obtained desorption was very low, phenomena which can
be attributed to a strong interaction between the hydro-
phobic part of CTAB with the laminar clay structures, as
a result atrazine desorption is diminished.
4. Conclusions
It was possible to optimize the condition for detection
and chromatographic separation of organic matter and
atrazine by HPLC-UV, from a clay-silty soil matrix. Soil
extracted atrazine determination and quantification was
1
2
3
(a)
4
5
(b)
Figure 4. Chromatograms of extraction from 1.0 g clean soil
contaminated with 10 mg·L–1 atrazine by using 3 mL of
aqueous extractant solution at CMC. (a) non ionic extrac-
tion: (1) X-114, (2) Triton X-100 and (3) TritonX-405; (b)
ionic extraction: (4) anionic SDS, (5) cationic CTAB at
CMC. Flow rate: 0.4 ml/min.,  = 260 nm, agilent eclipse
C18 PAH column. Mobile phase CH3OH/1 × 10–3 M. Phos-
phate buffer, pH 3.2/CH3CN 55:30:15 (v/v).
extracted atrazine determination and quantification was
done in aqueous samples containing surfactants, using a
methanol mobile phase/1 × 10–3 M, phosphate buffer pH
= 3.2/acetonitrile.
From desorption results it can be affirmed that use of
non-ionic surfactant Triton X-114 favors desorption and
extraction of atrazine from soil, being possible to attain
up to 98.5% recovery; also, this surfactant is the one with
lower affinity for soil organic matter, fact which provides
an advantage in respect to the other surfactants applied in
this study. One of the main advantages of this experi-
mental approach is that samples are prepared and ana-
lyzed in a simpler way, since it is not required special
conditions for extraction, cleaning or additional treat-

R. FERIA-REYES ET AL. 68
ments in order to determine atrazine in soil, which it can
be a good option for extracting organic compounds.
5. Acknowledgements
Author Rossy Feria is very thankful to CONACyT in
México, for sponsoring the post-doctoral fellowship un-
der which this work has been.
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