Anal Let 2014

Preconcentration Techniques

DETERMINATION OF ORGANOCHLORIDE ANDTRIAZINE PESTICIDES IN NATURAL WATERSBY SOLVENT BAR MICROEXTRACTION

C. Vergel, E. J. Guerrero, C. Mendigucha, and C. MorenoDepartment of Analytical Chemistry, Faculty of Marine andEnvironmental Sciences, University of Cadiz, Puerto Real, Spain

A new analytical methodology based on solvent bar microextraction has been developed to

preconcentrate two triazine and two organochloride pesticides in natural waters prior to

analysis by gas chromatography. The method was optimized for the organic solvent, sample

pH, sample agitation, length of the fiber, extraction time, and salt concentration. The

optimized methodology provides high enrichment factors, ranging between 40.2 (aldrin) to

107.0 (lindane). Since no salinity effects were observed, this method may be used to analyze

fresh and salt water. Thus, three real samples with different salinities were analyzed with

pesticide recoveries higher than 80%. As this methodology agreed with the principles of

green analytical chemistry, it offers low solvent and sample consumption, simplicity, and

compatibility with current analytical techniques.

Keywords: Hollow fiber; Liquid phase microextraction; Natural waters; Organochloride pesticides;

Triazines

INTRODUCTION

Over the past decades, the extensive use of chemical reagents to exterminateinsects in agriculture has been an increasing source of contamination to naturalwaters. Once these compounds have reached the environment, they may be adsorbedby organisms and accumulated in the food chain. Therefore, most of thesecompounds have been prohibited in the majority of developed countries, reducingtheir concentrations in the aquatic environment. However, several current analysiscarried out in natural waters have shown the presence of these prohibitedreagents, so that their identification and quantification continues to be an importanttask (Belmonte, Garrido, and Martnez 2005).

Among these organic compounds, triazine and organochloride pesticides area cause of concern because of their toxicity. In fact, a high number of these

Received 8 January 2014; accepted 3 March 2014.

Address correspondence to C. Mendigucha, Department of Analytical Chemistry, Faculty of

Marine and Environmental Sciences, University of Cadiz, 11510 Puerto Real, Spain. E-mail: carolina.

[email protected]

Analytical Letters, 47: 22092220, 2014

Copyright # Taylor & Francis Group, LLCISSN: 0003-2719 print=1532-236X online

DOI: 10.1080/00032719.2014.902462

2209

compounds are listed as persistent, bioaccumulative, and toxic reagents (PBT), asdefined in the EPAs Toxic Release Inventory (EPA 2012). Their presence in naturalwaters is regulated by Directive 2008=105=CE on environmental quality standards inthe field of water policy (Directive 2008=105=CE). Specifically, triazines present highmobility, great solubility in water, and tendency to be absorbed in soils (Shen andLee 2003). In addition, one of these compounds, atrazine, has been classified asa possible human carcinogen (Shen and Lee 2002). Organochloride pesticides havealso shown great toxicity for humans, showing a modulating effect on the humanendocrine system (Li et al. 2008).

Although several techniques are available to extract and determine thesepesticides from natural waters, liquid=liquid extraction continues being the mostpopular in routine sample preparation (Lambroupoulou and Albanis 2007). How-ever, this technique presents several disadvantages mainly related to the high volumesof organic solvent needed, moving it away of the principles of Green Chemistry(Armenta, Garrigues, and de la Guardia 2008; Anastas and Warner 1998). Toovercome this drawback, miniaturized extraction techniques have been developedto reduce the volume of organic solvents and the waste generated. High enrichmentfactors have been obtained with minimum consumption of sample (Ghambarian,Yamini, and Esrafili 2012). The use of a hollow fiber as support for the organicsolvent has been widely used recently to avoid the loss of solvent observed in othermicroextraction approaches (Psillakis andKalogerakis 2003; Rasmussen and Pedersen-Bjergaard 2004; Lambroupoulou and Albanis 2007; Pena-Pereira, Lavilla, andBendicho 2009; Dadfarnia and Shabani 2010; Tankiewicz, Fenik, and Biziuk 2011).The two phase mode is the most extensively used for pesticide analysis, because theorganic solvent is placed in the lumen of a microporous polymeric support and theextraction is performed through the organic phase filling the pores. Once the extrac-tion is complete, the organic solvent is extracted from the lumen and directly injectedinto a chromatography system for analysis. Although several configurations areavailable, the so-called solvent bar microextraction has been presented as a simplemode of microextraction (Jiang and Lee 2004). The preparation of the extraction unitis very easy and requires minimal manipulation of the sample. As it consists ina solvent bar tumbling freely in the solution, this methodology allows the analysisof organic compounds in different samples with complex matrices, such as slurries,wine, and wastewater (Jiang and Lee 2004; Chia and Huang 2006; Kamarei,Ebrahimzadeh, and Yamini 2010). Jiang and Lee (2004) obtained better relativestandard deviations for the analysis of slurry samples with this technique than bysolid phase microextraction. Moreover, the solvent bar microextraction agrees withthe principles of green chemistry because the solvent volume is drastically reducedin comparison with traditional extraction. However, the reduction in solvent isinsufficient for the technique to be considered green (Keith, Gron, and Young 2007).

Although solvent bar microextraction and similar approaches have beenpreviously used to determine organochloride pesticides in wine and triazines in water(Chia and Huang 2006; Peng et al. 2007; Hu et al. 2009) usually other hollow fiberliquid phase microextraction configurations has been used to determine thesecompounds. None of these approaches allowed their simultaneous analysis(Lambroupoulou and Albanis 2007; Basheer, Lee, and Obbard 2002; Shen and Lee2002; Yan and Wu 2004).

2210 C. VERGEL ET AL.

In the present work, a solvent bar microextraction technique was developed todetermine triazines and organochloride pesticides in natural waters with different sali-nities. As examples of these contaminants, atrazine, terbuthylazine, lindane, and aldrinwere selected due to their extensive use and their persistence in the environment. Atra-zine and lindane are included as priority hazardous substances in the Water FrameDirective (Directive 2008=105=CE). The most influent parameters in the extractionprocess were studied, such as organic solvent used, the sample pH, stirring rate, fiberlength, extraction time, and sample salinity. Once the conditions were optimized, themethod was employed for the analysis of real samples.

EXPERIMENTAL

Materials and Chemicals

Toluene, octanol, octane, hexane, and the pesticides were obtained from Sigma-Aldrich (Steinheim, Germany). The preparation of the pesticide standards was carriedout by weighing the appropriate amount of each pesticide followed by dissolution inmethanol (Scharlab, Barcelona, Spain). Sodium hydroxide and sodium chloride werealso obtained from Scharlab (Barcelona, Spain) (analytical-reagent grade).

The solvent bar microextraction experiments were performed using an AccurelPP S6=2 polypropylene hydrophobic capillary fiber with the following characteristics:wall thickness 450mm, porosity 72% and inner diameter 1800mm. It was purchasedfrom Membrane (Wuppertal, Germany).

All synthetic solutions were prepared with Milli-Q water. For optimizationpurposes, the concentration of pesticides in the source solution was 1 mg L1 oflindane and aldrin, 20 mg L1 of terbuthylazine, and 50 mg L1 of atrazine. Inaddition, a simulated seawater matrix was produced by adding 35 g L1 of sodiumchloride to the samples. The pH of the samples was controlled by a model 2001pH-meter with a combined glass Ag=AgCl electrode (Crison, Spain).

Solvent Bar Microextraction

A piece of the hollow fiber was cut to the desired length. One end of the fiberwas sealed with heat before immersing it in the solvent. It was then introduced freelyin the sample placed in tubes stirred in a model Reax 2 tubing stirrer (Heidolph,Germany) that allowed agitation rates between 20 and 100 rpm. In this configur-ation, loss of solvent is avoided due to the hydrophobic characteristics of the supportmaterial and the surface tension. After the selected extraction time, the solvent wasextracted from the fiber with a microsyringe and 1mL was injected in a gas chroma-tograph with an electron capture detector.

The effects of the solvent, sample pH, stirring rate, fiber length, and extractiontime were studied using a univariate optimization. The parameter to be maximizedwas the enrichment factor defined as follows (Pedersen-Bjergaard, Rasmussen, andJonsson 2010):

Ee CacceptorCsample

1

ORGANOCHLORIDE AND TRIAZINE PESTICIDES IN WATER 2211

where Cacceptor and Csample are the concentration of pesticides in the solvent andsample, respectively. The effects of sample salinity, analytical characteristics, andapplicability to real sample analysis were investigated.

Chromatographic Analysis

The analysis of the pesticides extracts was performed by an Agilent 7820A gaschromatograph (GC) (USA), equipped with a micro electron capture detector. Thecapillary column was a HP-5 (5% phenyl and 95% methylpolysiloxane)30m 0.32mm 0.25 mm (Agilent Technologies, DE, USA). The injection of 1mLof sample was carried out in splitless mode, using nitrogen as carrier gas at a flowof 25 psi. The GC temperature program was as follows: initial temperature 150C,held for 1 minute, and then increased by 5C min1 to 190C. The detector tempera-ture was maintained at 300C.

Sample Collection

Three real samples were used to test the applicability of the method. Two werecollected from Cadiz (SW, Spain), one of seawater from the San Pedro River and theother freshwater from the Guadalete River. The third was tap water. The sampleswere passed through a 0.7 mm pore size glass filter prior to the extraction.

RESULTS AND DISCUSSION

Optimization of the method was performed using a univariate approach for theorganic solvent, the sample pH, the stirring rate, the fiber length, the extraction time,and the sample salinity.

Selection of Organic Solvent

The first parameter studied was the type of solvent used as extractant. Thesolvents from most to least polar included octanol, toluene, hexane, and iso-octane.As shown in Figure 1, different behaviors were observed for the different pesticides.In general, the enrichments increased when the polarity of solvent decreased, asexpected due to the low polarity of these pesticides. However, atrazine showed minorextraction for iso-octane and hexane, probably due to the higher polarity of thispesticide (Perez-Carrera et al. 2007). However, a low enrichment factor for atrazinewas also observed for octanol, the most polar solvent. This could be related to thehigh viscosity of octanol (6.49 103 Pa s), in comparison with the other solvents(between 3.72 104 5.90 104 Pa s), which could affect the diffusion coefficientsof the analytes and the kinetics of mass transfer (Kokosa Przyjazny, and Jeannot2009). For this reason, toluene was selected as the most appropriate solvent forthe extraction of the analytes. This solvent has been widely used in other techniquesfor pesticides because of its suitable immobilization in the hollow fiber pores andits high solubility for the analytes (Basheer et al. 2002; Shen and Lee 2002;Lambroupoulou and Albanis 2007; Sanagi et al. 2010; Young et al. 2011; Sarafraz-Yazdi, Assadi, and Ibrahim 2012).


Effect of Sample pH

The pH of the sample plays an important role to modify the ionic form of theanalytes, influencing the solubility and extraction efficiency. The pH should allowthe analytes to remain in neutral states to achieve better extraction (Lambroupoulouand Albanis 2007). The effect of the pH on the enrichment factor was evaluated inthe range from 2 to 8. As Figure 2 shows, the triazine herbicides presented higherenrichment factors in the intermediate range of pH values probably due to thepossible hydrolysis of these compounds at extreme values. Similar behavior wasobserved by Trtic-Petrovic et al. (2010) for atrazine, although Shen and Lee (2002)observed the same extraction efficiency for this pesticide regardless of the pH value.Although other authors have observed a reduction in the extraction efficiency fororganochloride pesticides at alkaline pH range due to decomposition (Basheer et al.2002), Figure 2 shows slight differences in the enrichment factors of lindane and aldrinat basic pH. A small increase was observed for lindane at pH values greater than 6. ApH of 6 was selected as optimum.

Figure 2. Effect of sample pH on the enrichment factor. (^) Atrazine, (&) Terbutylazine, (~) Lindane, (x)Aldrin. Aqueous solution: 35 g l1 NaCl. Fiber length: 4 cm; stirring rate: 40 rpm; extraction time: 30min.

Figure 1. Effect of extraction solvent on the enrichment factor. Aqueous solution: pH 8; 35 g l1 NaCl.Fiber length: 4 cm; stirring rate: 40 rpm; extraction time: 30min.


Effect of Stirring Rate

The agitation of the sample is an important parameter to consider becausemass transfer of the analytes may be improved by agitation (Lambroupoulou andAlbanis 2007; Pena-Pereira, Duarte, and Duarte 2012). However, a negative effecthas been observed for high stirring rates due to a less stability of the organic solventin the fiber and the appearance of air bubbles on the surface of the hollow fiber(Sanagi et al. 2010; Sarafraz-Yazdi et al. 2012). In this work, different behaviorwas observed for the pesticides. As shown in Figure 3, for organochloride pesticides,the enrichment factor was independent of stirring rate, probably because themaximum enrichment factor for these pesticides was obtained at lower stirring rates.However, triazines showed higher enrichment factors at intermediate stirring rates.A stirring rate of 40 rpm was selected for subsequent experiments.

Effect of Fiber Length

The next parameter studied was the fiber length used for the extraction.A shorter length may improve the enrichment factor due to a higher volume betweenthe donor and received phases, but may increase the time of sample preparationdue to the lower surface area (Sanagi et al. 2010). In this case, the fiber length wasvaried from 1 to 9.5 cm, which was the maximum length allowed for the selectedconfiguration. Figure 4 shows that better enrichment factors were achieved byreducing the length of the fiber. Nevertheless, aldrin showed a minor enrichmentfactor for the shortest length (1 cm) so that an optimum length of 2 cm was chosenfor the following experiments.

Selection of Extraction Time

A study of extraction time was performed to evaluate the interval required forthe system to reach equilibrium. Figure 5 shows that the enrichment factor increaseswith extraction time up to 60 minutes and remains constant for times up to 400min.For longer times, a decrease was observed, probably due to the instability of the

Figure 3. Dependence of enrichment factor on the stirring rate. (^) Atrazine, (&) Terbuthylazine, (~)Lindane, (x) Aldrin. Aqueous solution: pH 6; 35 g l1 NaCl. Fiber length: 4 cm; stirring rate: 40 rpm;extraction time: 30min.


organic phase. Previous studies have suggested that the optimum extraction timefor these systems to be between 15 and 30min due to instability at longer times(Lambroupoulou and Albanis 2007; Sanagi et al. 2010). The enrichment factorobtained in this work was constant from 60 to 400min, and it was significantlyhigher than at lower times. As instability problems were not observed, a time of60min was selected as optimum.

Effect of Sample Salinity

As the system has been developed to extract pesticides from saline waters(35 g l1 NaCl), the effect of NaCl concentration was investigated. Although someauthors found an increase in the efficiency at high NaCl concentrations, otherbehavior has been observed in liquid phase microextraction (Lambroupoulou andAlbanis 2007). In this case, the enrichment factors for the four pesticides wereconstant with the salinity over the range from 0 to 35 g l1, as has been observedin previous reports of organochloride pesticides and triazines with liquid phase

Figure 4. Effect of the fiber length on the enrichment factor. (^) Atrazine, (&) Terbuthylazine, (~)Lindane, (x) Aldrin. Aqueous solution: pH 6; 35 g l1 NaCl. Fiber length: 4 cm; stirring rate: 40 rpm;extraction time: 30min.

Figure 5. Effect of extraction time on the enrichment factor. (^) Atrazine, (&) Terbuthylazine, (~)Lindane, (x) Aldrin. Aqueous solution: pH 6; 35 g l1 NaCl. Fiber length: 2 cm; stirring rate: 40 rpm.


microextraction (Shen and Lee 2002; Sarafraz-Yazdi et al. 2012). Lampropoulosreported two effects when NaCl is added to samples (Lambroupoulou and Albanis2007). The salting-out effect improves the extraction due to a reduction in thesolubility of the pesticides and a subsequent increase of their partitioning into theorganic phase. The other is related to changes in the physicochemical properties ofthe extraction film reducing the diffusion rates of analytes into the organic phase.In the present work, the combination of these effects may be responsible for theconstant enrichment factors with different salinities. Therefore, this methodologyallows the simultaneous extraction of pesticides selected in saline or fresh water.

Analytical Performance

Once the main factors influencing the extraction process were investigated, themethods linearity, precision and detection limits were evaluated, as shown inTable 1. The linearity was studied over the ranges of 2.550 mg L1 atrazine,120 mg L1 terbuthylazine, and 0.051 mg L1 lindane and aldrin. The calibrationcurves were linear for the pesticides, with a linear determination coefficients from0.964 (aldrin) to 0.997 (lindane). Each measurement was performed three timesunder the optimized conditions, obtaining relative standard deviations from 2.8%(terbuthylazine) to 9.6% (aldrin), comparable with those obtained by other research-ers (Basheer et al. 2002; Lambroupoulou and Albanis 2007). The limits of detectionwere calculated from the calibration curve as 3 sb=m, where sb is the standard devi-ation of the y-intercept and m represents the slope of the line (Miller and Miller2010). The enrichment factor for each pesticide was also considered. These limitsof detection are below the environmental quality standards for priority substancesin the field of the Water Frame Directive that included atrazine and lindane (Direc-tive 2008=105=CE). Under optimized conditions, the enrichment factors obtainedwere between 40.2 (aldrin) and 107.0 (lindane).

In comparison with other similar hollow fiber liquid phase microextractionapproaches, the reported method provides low limits of detection for atrazine andaldrin and also high enrichment factors for atrazine and lindane (Peng et al. 2007;Basheer et al. 2002). In addition, in some cases, the time necessary to perform theextraction was reduced (Trtic-Petrovic et al. 2010). In addition, the method maybe presented as a green alternative to the traditional solvent extraction due to thereduction of the waste generated, although toluene is included in the EPAs ToxicRelease Inventory as a persistent, bioaccumulative, and toxic reagent in the F andU hazardous waste list of the Resource Conservation and Recovery Act. The

Table 1. Analytical performance of the optimized methodology

Pesticide Linear range (mg L1) r2 LOD (mg L1) RSD (%) Ee

Atrazine 2.550 0.988 0.086 5.6 63.7

Lindane 0.051 0.997 0.001 3.6 107.0

Terbuthylazine 120 0.996 0.012 2.8 100.1

Aldrin 0.051 0.964 0.005 9.6 40.2

LOD: limit of detection; RSD: relative standard deviation; Ee: enrichment factor.


replacement of the organic solvent for other greener alternative could implya reduction in the enrichment factors or in the analytical characteristics of themethodology, which is not recommended.

Real Sample Analysis

Under the optimized conditions, the system was applied to real samples ofvarying salinities. Since the analytes were not found in these samples, the sampleswere spiked with pesticides at concentrations of 0.1 mg L1 of lindane and aldrin,2 mg L1 of terbuthylazine, and 5 mg L1 of atrazine. A typical chromatogram fora spiked seawater sample is shown in Figure 6.

Figure 6. Typical chromatogram of spiked seawater. Peaks: (1) 5 mg l1 atrazine, (2) 0.1 mg l1 lindane,(3) 2mg l1 terbuthylazine, and (4) 0.1mg l1 aldrin.

Table 2. Analysis of spiked samples, recoveries, and relative standard deviations (RSD) for five replicates

Seawater Tap water River water

Atrazine Spiked, mg L1 5.0 5.0 5.0Found, mg L1 4.34 5.64 5.56Recovery, % 87 113 111

RSD, % 16.6 6.7 6.5

Terbuthylazine Spiked, mg L1 2.0 2.0 2.0Found, mg L1 1.82 2.15 1.95Recovery, % 92 109 99

RSD, % 15.3 14.5 7.4

Lindane Spiked, mg L1 0.1 0.1 0.1Found, mg L1 0.09 0.11 0.09Recovery, % 93 106 92

RSD, % 7.7 15.9 4.3

Aldrin Spiked, mg L1 0.1 0.1 0.1Found, mg L1 0.1 0.09 0.08Recovery, % 105 85 79

RSD, % 6.2 20.5 6.5


The recoveries values and relative standard deviations are shown in Table 2(Lambroupoulou and Albanis 2007; Pena-Pereira et al. 2012). Although previousmethods presented similar analytical characteristics, the application to real seawatersamples has not been performed (Shen and Lee 2002; Yan and Wu 2004; Peng et al.2007; Basher et al. 2010, Trtic-Petrovic et al. 2010). As acceptable recoveriesand relative standard deviations were obtained, the methodology is an attractivetool for the determination of pesticides in natural waters.

CONCLUSIONS

A solvent bar microextraction method for pesticide analyses has been reportedas a greener alternative to the traditional liquid-liquid extraction due to thereduction of solvent and waste. In addition, it presents advantages of simplicity,low-cost, good stability of organic phase, high enrichment factors, and goodprecision. The detection limits are sufficiently low to meet the environmental qualitystandards for priority substances in the field of the Water Frame Directive.Moreover, the application of this methodology to real water samples with differentsalinities has been satisfactorily performed.

FUNDING

The authors thank the Spanish Ministry of Economy and Competitiveness(CTM2010-15618) for support of this work.

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