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Simultaneous Determinationof Atrazine and Chlorpyrifosin Pesticide Formulations, inSoils and Waters by DerivativeSpectrophotometry and RatioSpectra DerivativeM. Martínez Galera a , J. L. Martínez Vidal a & A.Garrido Frenich aa Department of Analytical Chemistry , Faculty ofSciences of Almería , 04021 Almería, SpainPublished online: 22 Aug 2006.

To cite this article: M. Martínez Galera , J. L. Martínez Vidal & A. Garrido Frenich(1994) Simultaneous Determination of Atrazine and Chlorpyrifos in PesticideFormulations, in Soils and Waters by Derivative Spectrophotometry and Ratio SpectraDerivative, Analytical Letters, 27:4, 807-818, DOI: 10.1080/00032719408000273

To link to this article: http://dx.doi.org/10.1080/00032719408000273

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ANALYTICAL LETERS, 27(4), 807-818 (1994)

SIMULTANEOUS DETERMINATION OF ATRAZINE AND CHLORPYRIFOS IN PESTICIDE FORMULATIONS, IN SOILS AND WATERS BY DERIVATIVE SPECTROPHOTOMETRY

AND RATIO SPECTRA DERIVATIVE

Keywords: Atrazine, Chlorpyrifos, simultaneous determination, derivative spectrophotometry, derivative ratio spectra.

M. Martinez Galera, J.L. Martinez Vidal and A. Garrido Frenich

Department of Analytical Chemistry, Faculty of Sciences of Almeria. 04021 Almeria (Spain).

SUMMARY

A new method is described to analyse a binary mixture of atrazine and chlorpyrifos, using first-derivative spectrophotometry for atrazine and first derivative of the ratio spectra for chlorpyrifos. The procedure does not require any separation ste Calibration graphs were linear up to 15 pg.mL-' of atrazine and to 10 pg.mCP'of chlorpyrifos. The method has been applied to determine both compounds in pesticide formulations, in soils and waters.

INTRODUCTION

The use of derivative UV-vis spectrophotometry for the simultaneous determination of analytes increases with the availability of spectrophotometers with software in order to produce derivative spectra . The fundamental principles have been described in some previous papers 2-5 and the interest in the analytical applications of derivative spectrophotometry has increased . This possibilit is today widely ap lied to determine organic compound mixtures such as drug$-' ' and pesticidesy2-' among others, with overlapping spectra. In some cases, the first or the higher order derivatives of the absorption spectra of the analytes are not sufficiently well resolved to allow their determination due to the spectra overlapping. In this way, Salinas and coworkers16 have developed a new spectrophotometric method based on the use of the first derivative of the ratio spectra. The absorption spectrum of the mixture is obtained and divided by

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Copyright 0 1994 by Marcel Dekker, Inc.

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808 MART~NEZ GALERA, MART~NEZ VIDAL, AND GARRIDO FRENICH

the absorption spectrum of a standard solution of one of the components (amplitudes by amplitudes at each wavelength) and the first derivative of the ratio spectra is obtained. The concentration of the other component is determined from a calibration graph obtained previously. This method has been applied for the determination of drug binary mixtures in pharmaceutical products with good

Atrazine is a selective herbicide highly used (in the USA it is the second most applied)’ ’, whereas chlorpyrifos has a broad range of insecticidal activity, effective by contact, ingestion and vapour action. They are present simultaneously in environmental samples due to their persistence (higher than one month). Because of the possible effect on health, EPA has proposed 3 ppb of atrazine as Maximum Contaminant Level Goals in drinking water *’. Atrazine and chlorpyrifos are usually analyzed by GLC or HPLC, previous liquid-liquid or solid phase extraction. In this work we present the results obtained in the study of a new, easy and fast spectrophotometric method to determine atrazine and chlorpyrifos in waters, in soils and commercial formulations.

Some pesticides are persistent in soils and they leach to ground water during decades after their application2’. so, triazine herbicides have been encountered contaminating ground ~ a t e r ~ ’ . ~ ~ . Almeria (Spain) is an area with intensive

practice of agricultural exploitations in greenhouses. In this way, chemicals are used in important amounts for control of pests in cultures under plastic house and they are distributed in the environmental compartment : soil, water, air and vegetables. Degradation studies of several pesticides in vegetables have been reported prev i~us ly ’~ - *~ . In this work, we have focused attention on a triazine herbicide, the atrazine, and on an organochlorine pesticide, the chlorpyrifos, which have been very used in the last years.

EXPERIMENTAL

Apparatus

A Milton Roy 3000 diode array spectrophotometer and an Olivetti PCS 386 were used for all measurements and data treatment.

Chemicals and solvents

Atrazine and chlorpyrifos standard solutions of 50 pg.mL-’ in acetonitrile were prepared from the products of Riedel-de Haen (Pestanal). Commercial formulations of atrazine and chlorpyrifos were supplied by lnagra and Argos, respectively. All organic solvents used were Panreac UV-vis grade. Cartridges Sep-Pack C18 Cromlab. Distilled water was obtained from a Millipore water purification Milli-Q system.

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ATRAZINE AND CHLORF’YRIFOS 809

Procedure for determining atrazine and chlorpyrifos in synthetic mixtures

Samples are prepared in 25-mL volumetric flasks, containing between 25-375 pg of atrazine and/or between 25-250 Lig of chlorpyrifos in acetonitrile and methanol 1:l (vlv).

To determine atrazine, the absorption spectra of the samples are recorded between 200 and 350 nm, smoothed through 1 1 experimental points and the first derivatives are calculated with Ah=9 nm. The concentration of atrazine is proportional to the amplitude of the signal at 228.3 nm (’D228.3).

To determine chlorpyrifos, the stored spectra of the mixtures, recorded between 200 and 350 nm, are divided by a standard spectrum of atrazine of 8 pg.mL-’. The obtained ratio spectra are smoothed through the use of 1 1 experimental points and the first derivatives calculated with Ah=9 nm are recorded. The concentration of chlorpyrifos is proportional from peak to peak amplitude, (’DD287.8, 303.6).

Procedure to determine atrazine and chlorpyrifos in water

500 mL samples of ground water are filtered out through a 0.45 pm filter, connected with PTFE tubes to the conditioned cartridges, passed through of them at a rate of 3-5 mL.min” and then sucked dry for 5 minutes. The cartridges are preconditioned with 5 mL of acetonitri1e:methanoI 1:l (v/v), followed by 5 mL of ultrapure water without allowing the cartridges to dry out. The samples thus concentrated are extracted with 5 mL of acetonitri1e:methanoI 1:1 (v/v) and atrazine and chlorpyrifos are determined as described above.

Procedure to determine atrazine and chlorpyrifos in soils

Weigh 25.0 g of ground air-dry soil passed through a 55 mesh sieve into 200 mL flask. Add 1 0 0 rnL of CH2C12, stir for 2 h, filter through a Buchner and wash well with two aliquots of 1 0 mL of CH2CI2. Evaporate CHzC12 to dryness using rotatory vacuum evaporator, dissolve the residue in 1 mL of acetonitri1e:methanol I :I (v/v) and determine both pesticides as described above .

Procedure to determine atrazine and chlorpyrifos in commercial formulations

Weigh a suitable portion of commercial products and dissolve in acetonitrile in a 25-mL volumetric flask; transfer aliquots containing not more than 375 pg of atrazine and 250 pg of chlorpyrifos to a 25-mL volumetric flask, dilute with acetonitrile and methanol to give a 1:l (v/v) solution and determine both pesticides as described above.

RESULTS AND DISCUSSION

The absorption spectra corresponding to atrazine, chlorpyrifos and a mixture of them can be seen in figure 1. The absorption maxima for chlorpyrifos are

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8 10 MARTiNEZ GALERA, MARTiNEZ VIDAL, AND GARRIDO FRENICH

Figure 1.- Absorption spectra of (1) 10 pg.rnL-' of chlorpyrifos; (2) 5 pg.mL-' of atrazine; (3) their mixture in acetonitri1e:methanoI 1 : I (v/v).

situated at 289, 229.5 and 202.5 nm, when measuring an acetonitri1e:petroleum ether solution 1:l (v/v); these maxima do not change with pH between 2 and 10. The absorption maxima for atrazine, at the same operatory conditions, are encountered at 264 and 219.5 nm and do not change significatively with the pH. The maxima remain constant when the solvent is acetonitri1e:methanoI 1:l (v/v) but they change when the solvent used is acetonitri1e:methylene chloride 1:l (v/v).

Acetonitri1e:methanoI 1 : l (v/v) has been chosen as solvent due to the optimum characteristics of the first derivative absorption spectra. We checked that the absorbances are constant for both pesticides during 10 days at least.

The first derivatives of the absorption spectra of both pesticides and a mixture of them can be seen in figure 2. It is possible to measure the atrazine concentration from its first derivative signal at the zero-crossing point for chlorpyrifos, but it is difficult to measure the first derivative signal of chlorpyrifos due to the overlapping of the first derivative signal of the atrazine spectrum.

Figure 3 shows the first derivative of the spectrum of 4 pg.mL-' of chlorpyrifos divided by the spectrum of 8 pg.mL-' of atrazine. Atrazine does not interfere in the measurement of chlorpyrifos at 287.8 nm ('DD287.8), 303.7 nm ('DD303.7) and peak-to-peak ('DD287.8, 303.7).

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ATRAZINE AND CHLORF’YRIFOS 811

Figure 2.- First derivative of (1) 10 pg.rnL” of chlorpyrifos; (2) 5 pg.mL-’ of atrazine; (3) Their mixture.

1 .oooo

0.5000

0,

u -2 8 0.0000

f 0,

Q u -0.5000 2 c

I -1.0000

-1.50001 I I I I I I , I I I I I I I I I I I I I I I I I

200 240 280 32 0 Wavelength (nrn)

Figure 3.- First derivative of the spectrum of 4 pg.mL-’ of chlorpyrifos divided by 8 pg.mL- of atrazine. 1

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812 MARTiNEZ GALERA, MARGNEZ VIDAL, AND GARRIDO FRENICH

'0217.3 =0.0022A + 0.0020 0.9927 1 . 0 6 ~ 1 0 - ~

'D228.3 =- 0.0039A - 0.0006 0.9998 2 .87~1 0-5

Table 1 .- Calibration data for atrazine and chlorpyrifos. r I

9.14~10"

2.47~10"

Equation I

CHLORPYRIFOS

'DD287.8 =0.1247C i0.0061 0.9997 1 .2zX1 o - ~ 1 . 0 5 ~ 1 0 - ~

'DD303.7 =0.2032(3 - 0.01 74 0.9998 1.56~1 0-3 1 . 3 4 ~ 1 0 . ~

1DD287.8.303.7=0.3279C +0.0235 0.9999 1 .71~10 .~ 1 . 4 5 ~ 1 0 - ~ 1 ~~~

The results were obtained from 8 points; 1 A(Atrazine concentration: pg.rnL-'); C(Ch1orpyrifos concentration: pg.mL- )

Table 2.-Statistical parameters for the determination of atrazine and chlorpyrifos.

'D217.3 i D228.3 I 1.27

0.93

1 0.420 I 1.400 I 1 0.129 j 0.430 ii

U CHLORPYRIFOS I

Absorption spectra were smoothed with 11 experimental points (the Milton Roy software is provided with a Savitzky-Golay smoothing function to avoid degradation of the signal noise ratio) and A h = 9 nm was considered suitable for both pesticides.

CALIBRATION

Calibration graphs for atrazine were made by measuring the first derivative signal at the zero-crossing point for chlorpyrifos (l Dg i 7.3 and D228.3 ).

On the other hand, calibration graphs for chlorpyrifos were made by measuring the amplitude from the maximum at 287.8 nm ( DD287.8), from the minimum at 303.7 nm (lDD303.7) and from peak-to-peak ('DD287.8, 303.7) of the first

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ATRAZINE AND CHLORPYMFOS 813

Table 3.- Results obtained in the determination of atrazine and chlorpyrifos in synthetic mixtures by using the proposed methods.

derivative ratio spectra. The concentration of atrazine as divisor was modified between 1 and 15 yg.mL-' obtaining different calibration graphs; the higher values of the correlation coefficient were obtained using 8 pg.mL-' of atrazine as divisor.

Table 1 summarizes the statistical data obtained from the different calibration graphs in the range 1-15 pg.mL-' of atrazine and to 1-10 pg.mL-' of chlorpyrifos. To check the precision of the methods, the signals for replicate samples (n = 1 1) containing 5 pg.mL-l of atrazine and 5 @g.rnL"of chlorpyrifos were measured individually (Table 2). In all cases good results were obtained and these parameters do not change if the determination of one compound is carried out i n presence of the other one.

The proposed methods were applied for resolving several binary mixtures. The results corresponding to these determinations are summarized in Table 3. The best results are obtained measuring atrazine at 228.3 nm ('D228.3) (recoveries between 88.4% and 10 .7%, except the mixture containing 2.4 pg.rnL-' of atrazine and 8 pg.mL3 of chlorpyrifos) and measuring chlorpyrifos at peak-to-peak amplitude ('DD227.8, 303.6) (recoveries between 91.9% and 104.9% in all cases); besides this, the correlation coefficients are higher and the relative standard deviations (r.s.d.) are lower. For all the above mentioned reasons we propose to determine atrazine at 228.3 nm ('D228.3) and determine chlorpyrifos by peak-to-peak amplitude (' DD227.8.303.6).

INTERFERENCES

According to the proposed method, 5 pg.mL-l of: chlor yrifos, diuron, captan, methiocarb, carbophenothion and buprofezin, 2.5 pg.mL-' of: dieldrin, tetradifon and triazophos, and 1 pg.mL-' of: methomyl ethylenethiourea, benomyl,

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814 MART~NEZ GALERA, MART~NEZ VIDAL, AND GARRIDO FRENICH

Table 4.- Results obtained in the determination of atrazine and chlorpyrifos in spiked groundwater by using the proposed method.

N.D.: <determination limit; The results are average of three determinations

dichloran and vinclozoline, do not interfere in the determination of 5 pg.mL-' of atrazine, but 0.25 pg.mL-l of folpet interferes. On the other hand, 5 pg.mL-' of: atrazine, benomyl and vinclozoline, 2.5 g.mL-' of: captan, triazophos, dieldrin, methiocarb and methomyl and 1 pg.mL- of: buprofezin, carbophenotion, diuron, folpet, tetradifon and ethylenethiourea, do not interfere in the determination of 5 pg.mL-' of chlorpyrifos, but 0.25 pg.mL-' of dichloran do.

P

APPLICATIONS

Simultaneous determination of atrazine and chlorpyrifos in ground water

The proposed method was applied to determine both pesticides, in ground water of the aquifer system of "Aguadulce", Almeria (Spain)27, whose TOC (Total Organic Carbon) was 2.1 rng.L-'. The preconcentration step was realized with C i8 Sep Pack cartridges preconditioned with 5 mL of acetonitri1e:methanoI 1 :I (v/v) followed by 5 mL of ultrapure water. The study was carried out operating with spiked samples of ultrapure water with both pesticides. A flow rate of 3-5 mL.min-' through the cartridge was found to be optimum. At a flow rate higher than 20 rnL.min-' the breakthrough of atrazine occurred. The calibration curves were linear between 10 - 160 ng.mL-lof atrazine and 10 - 110 ng.mL-'of chlorpyrifos. The correlation coefficients, obtained from 8 calibration points are better than 0.9996 in all cases. The determination limits are 8 and 7 ng.mL-' for atrazine and chlorpyrifos respectively and the relative standard deviations (r.s.d. t are 2.3 and 2.5% at a spiked level of 50 ng.mL-' of each one of them.

The suitability of the proposed method to determine both pesticides was evaluated by the standard addition method. Operating on ground water at a

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ATRAZINE AND CHLORPYRIFOS 815

Table 5.-Results obtained in the determination of atrazine and chlorpyrifos in soils usina the DroDosed method

1 Atrazine (mglKg) I Chlorpyrifos (mglKg) Soil I

Recovery R.S.D. (%I (%I Spike Found Recovery R.S.D.

(%) Spike Found (%) , I , I 1 I

0.00 N.D. 0.00 N.D.

N.D.: <determination limit; The results are average of three determinations

Table 6.- Results obtained in the determination of atrazine and chlorpyrifos in two commercial formulations mixtures using the proposed method.

Chlorpyrifos (r(g.mC')

Spike Found R.S.D. (%) Spike Found Recovery R.S.D. (%I (%I l o 3.80 0 I 2.30

2 5.67 93.50 4.3 2 4.00 85.00 2.9

4 7.12 83.00 2.9 4 6.70 110.00 3.2

0 1 .80 0 5.04

2 3.77 98.50 4.4 2 7.24 110.00 3.6

4 5.40 90.00 3.4 4 9.41 109.25 3.0

The results are average of three determinations

spiked level between 10 and 120 p9.L-l of atrazine and between 1 0 and 50 pg.L-' of chlorpyrifos, the recoveries ranges are between 99.6 and 124.0% for atrazine, with a relative standard deviation (r.s.d.) from 2.5 to 5.7%, and between 80.0-121 .O% for chlorpyrifos with a r.s.d. from 2.9 to 5.3% (Table 4). On the other hand, the obtained results indicate that both pesticides were not detected in the analyzed waters.

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816 MART~NEZ GALERA, MART~NEZ VIDAL, AND GARRIDO FRENICH

Simultaneous determination of atrazine and chlorpyrifos in soils

The proposed method was applied to determine both pesticides in soils. TWO kinds of soils (AL-08 and AL-04) were collected from the top 15 cm of a greenhouse from Almeria (Spain), after six months without agricultural activity. Their characteristics and composition arez8: AI-08: pH(Hz.0, KCI): 8.0, 7.9; % C: 0.91; YO N: 0.10; % Organic Matter: 1.57; Texture: 12% clay, 44% lime, 44 % sand. AL-04: pH(Hz0, KCI): 8.2, 8.2; % C: 1.65; % N: 0.15; % Organic Matter: 2.84; Texture:4% clay, 54% lime, 42% sand. The suitability of the proposed method to determine both pesticides was evaluated by the standard addition method. The obtained results can be seen in table 5.

When CHzCIz is used as extractant, the recoveries of both pesticides are between 94.2-120.0 % for atrazine with r.s.d.'s from 3.1 to 5.2% and between 92.7-108.0 YO for chlorpyrifos with r.s.d. from 3.0 to 4.9%. This shows the suitability of CHzCIz for the atrazine and chlorpyrifos extraction from soils. On the other hand, the obtained results indicate that both pesticides were not detected in the analyzed soils.

Simultaneous determination of atrazine and chlorpyrifos in commercial formulations

In addition, atrazine and chlorpyrifos were determined in commercial formulations by the proposed method. Because of the difficulties encountered to obtain dosage forms containing both of the pesticides tested, the proposed method was applied to the determination of these pesticides in commercial formulation mixtures. The suitability of the method has been evaluated by the standard addition method. Table 6 summarizes the obtained results. It can be observed that both pesticides are recovered quite satisfactory.

The authors gratefully acknowledge financial support from the FIAPA foundation. Almeria (Spain).

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Received February 28, 1993 Accepted October 11, 1993

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