Microchim Acta (2011) 173:477–483DOI 10.1007/s00604-011-0587-2 ORIGINAL PAPER Ultratrace determination of carbamate pesticides in water samples by temperature controlled ionic liquid dispersive liquid phase microextraction combined with high performance liquid phase chromatography Qingxiang Zhou & Long Pang & Junping Xiao Received: 22 December 2010 / Accepted: 4 March 2011 / Published online: 16 March 2011 # Springer-Verlag 2011 Abstract A simple and sensitive method was developed Keywords 1-Hexyl-3-methylimidazolium for the determination of three carbamate pesticides in water hexafluorophosphate . Carbamate pesticides . Temperature samples. It is based on temperature controlled ionic liquid controlled ionic liquid dispersive liquid phase dispersive liquid phase microextraction combined with high- microextraction . High performance liquid chromatography performance liquid chromatography. The ionic liquid 1-hexyl- 3-methylimidazolium hexafluorophosphate was used as the extractant, and the factors affecting the extraction were Introduction investigated in detail. The detection limits obtained for isoprocarb, diethofencarb and fenothiocarb are 0.91, 0.45, Ionic liquids (ILs) consisted of the combination of organic and 1.40 μgL-1, respectively, and the precisions are in the cations with delocalized charges and various anions [1]. range between 1.0 and 1.8% (n=6). The method was Owing to their special properties, they have represented a validated with environmental water samples and the results type of novel solvents at the beginning of the 21st century indicate that it represents a viable alternative to existing [2]. Recently, ILs have become the focus of many academic methods. and industrial investigations, and mainly utilized as reaction media for a number of organic synthesis reactions, catalysis, separation processes and polymerization [3–11]. Compared to traditional organic solvents, they are nonvol- atile, nonflammable, possess high thermal stability and are Q. Zhou (*) excellent solvents for a wide range of inorganic and organic State Laboratory of Petroeum Resource and Prospecting, materials. Due to these advantages, ILs have been widely College of Geosciences, China University of Petroleum, Beijing Capmus(CUP), known as “green solvents” and good alternatives to Beijing 102249, China conventional organic solvents. e-mail:
[email protected] In general, environmental pollutants are present at e-mail:
[email protected] trace levels in environmental samples, which bring Q. Zhou : L. Pang difficulties in direct instrumental analysis. According to School of Chemistry and Environmental Sciences, Henan Key this, sample pretreatment procedure prior to instrumental Laboratory for Environmental pollution Control, Key Laboratory analysis is necessary. Carbamate pesticides are mainly for Yellow River and Huaihe River Water Environment and used in agriculture, and most of them are prone to Pollution Control, Ministry of Education, Henan Normal University, distribute in the aqueous environments due to their high Xinxiang 453007, People’s Republic of China solubility in water. Recently, increasing evidences confirmed that carbamates are potential contaminants J. Xiao of the ecosystem and human health [12]. Therefore, it is Department of Chemistry, University of Science and Technology Beijing, of great importance to monitor their residual concentration Beijing 100083, China in environmental waters. There have been several sample pretreatment methods for the analysis of carbamate Ministry (Beijing. In general. Lake water sample was collected from Shouxihu [PF6]) was prepared in lab [31]. respectively. Liquid phase microextraction (LPME) developed in recent years A high-performance liquid chromatography system. Then the cloudy solution was named temperature controlled ionic liquid dispersive centrifuged for 15 min at 3. diethofencarb and fenothiocarb were set at and the results confirmed that it was an ingenious sample 200. Detection wavelengths for for the determination of environmental pollutants firstly. A reversed-phase Waters LPME methods are single drop microextraction (SDME) SunFireTM C18 column (4. toxic and volatile organic solvents such as at 70 °C.3 and 225 nm. Due to the merits. and 10 mL ultra-pure triazine herbicides [26]. diethofencarb park. respectively. organophosporus pesticides [27]. Ltd (Huaian. sensitivity. DDT and its main metabolites [25].478 Q. high enrichment factors and less consumption of organic Temperature controlled ionic liquid dispersive liquid phase solvents. Then the and determination of three organophosphorus pesticides conical tubes were heated with the temperature controlled [30].6×150 mm. Four real water samples were collected and utilized for validating the method. high enrichment factor and inexpensiveness diode-array detector (Waters.525 pumps and a Waters 2998 tion. Zhou et al. Methanol and acetonitrile of pesticides including solid-phase microextraction (SPME) HPLC grade were obtained from Jiangsu Guoda Chemical [13. liquid-liquid extrac. 14]. 40 μL 1-hexy-3. typic for the separation and analysis. 243. Melted snow water was collected from Experimental Henan Normal University. concentration of 200. and a homogenous solution formed. 5 μm) was used for [19]. All the real water and fenothiocarb were purchased from Institute of Envi. Henan Province. v/v). 16]. USA).45 μm micro-pore mem- ronmental Prevention and Monitoring of Agriculture branes and stored for use. . Assadi and microextraction coworkers. pretreatment method with advantage of simplicity. matrix Reagent Co. high-performance liquid Bedford. DLLME In the experimental procedure.6 mLmin-1. Jiangsu Province. isoprocarb. prepared by a Milli-Q purification system (Millipore. samples were filtered through 0. and chloroform were often completely. The tube was on the environment human health. Yangzhou city. etc. and 20 μL. Recently. phase was removed with a syringe and the residue was methylimidazolium hexafluorophosphate ([C6MIM] [PF6]) dissolved in 200 μL methanol and 20 μL was injected into was utilized as the extractant and the temperature was used the HPLC system for analysis. Tap water was collected from our laboratory. Wastewater Reagents sample was taken from the exit of Xiaoshangzhuang wastewater treatment factory in Xinxiang city. The employed as the extraction solvent in DLLME. Then IL was dispersed into the aqueous solution benzene. Milford. DLLME was developed by Rezaee. chlorobenzene. added into a 10 mL glass conical tube. tion (LLE) [18]. 18] were the popularly used Apparatus techniques for the analysis of carbamate pesticides. China). which is a novel technique which has merit such as simplifica. 125 and 150 μgL-1 for isoprocarb. 17] or ultraviolet detector [16. consisted of two Waters 1.meth- has been widely used for the analysis of heterocyclic ylimidazolium hexafluorophosphate ([C6MIM] [PF6]) was insecticides [24]. palladium and cobalt [29] and so on. MA. The upper aqueous liquid phase microextraction was described. which analytes would migrate into the IL in a short time because would generate secondary pollution and put a severe threat of the higher solubility of analytes in IL. DLLME was also developed for the enrichment diethofencarb and fenothiocarb. injection volume were methanol/water (60/40. Isoprocarb. chromatography coupled with mass spectrometry [15. hollow fiber microextraction (HF-LPME) [20] and separation at 25 °C. This solution was spiked with different Cadmium [28]. and has been regarded as a novel liquid phase microextraction method [23]. the flow rate and the dispersive liquid-liquid microextraction (DLLME) [21]. The factors that would influence the extraction were investigated in Real water samples detail.000 rpm. The mobile phase. the special thereafter cooled with ice water and kept for 20 min and a characteristics of ILs were utilized and a new method cloudy solution formed. etc. Ultrapure water was solid-phase dispersion (MSPD) [17]. solid-phase extraction (SPE) [15. water was added. SDME was developed by Jeannot and Cantwell [22] 0. However. Nowadays. USA).. Xinxiang city. China). was utilized and gradually attracted much more attention. Therefore. 1-hexyl-3. as the driving force in the dispersing procedure. Henan 1-Hexyl-3-methylimidazolium hexafluorophosphate ([C6MIM] Province. extraction sample volume. The reason was that some IL would adsorb onto the tube wall when the IL volume exceeded a certain value. salt addition. extraction temperature. 10 mL. Extraction condition: spiked level. it was found that the peak areas of increase of temperature. 3 The effect of extraction temperature. 70 °C. 70 °C. 20 min. 1 The effect of ionic liquid volume. isoprocarb was disap. This accounted for the Here the optimization of temperature was conducted fact that these compounds were stable in acidic and neutral between 60–100 °C and the results were exhibited in environment. which determined the present form of target analytes in In this special enrichment procedure. However. [C6MIM][PF6] volume. According to these facts. ture is very important for developing a reliable method. 40 μL. centrifuging time. The results were exhibited in Fig. 3. pH 6. temperature was the aqueous solution. extraction time. extraction time. 20 min. 0% (w/v). It is easy to see that the optimal temperature was Hence. peared in alkalescent environment. The pH was investigated over the analytes from aqueous solution to IL phase. salt addition. 0% (w/v) Effect of sample pH Effect of dissolving temperature Sample pH is another important factor in LLE procedure. 1. 40 μL. high temperature will these three compounds changed very slightly when the also lead to the loss of some target analytes by sample was in acidic or neutral conditions. 20 min. In general. sample volume. 2. The effect of IL volume on the extraction procedure was investigated over the range of 25–45 μL. 10 mL. 20 min. extraction time. 20 min. 2 The effect of sample pH. and decreased in volatilization in some cases. pH 6 was used in the following experiments.Ultratrace determination of carbamate pesticides in water samples 479 Results and discussion Effect of the volume of ionic liquid IL volume is an essential factor in the procedure. salt addition. Fig. which can accelerate the transformation of target achieve the optimal pH. Fig. Hence a suitable tempera- alkalescent conditions. and instable in alkalescent environment. which can influence the formation of the cloudy solution and also affect the enrichment performance. 70 °C. temperature. Moreover. Fig. pH 6. Extraction condition: sample volume. centrifuging time. the range of pH 2–8 and the experimental results were shown in recoveries of the analytes would be enhanced with the Fig. 40 μL [C6MIM][PF6] was 10 mL. ■isoprocarb ●fenothiocarb ▲fenothiocarb 0% (w/v) . [C6MIM][PF6] volume. 200 μgL-1 (isoprocarb). 2. selected in the subsequent experiments. From the Fig. centrifuging time. Fig. The results indicated that the peak areas of target analytes also increased in the range of 25–40 μL and slightly decreased in the range of 40–45 μL with the increase of of IL volume. Extraction condition: 150 μgL-1(fenothiocarb). 20 min. 125 μgL-1 (diethofencarb). A series of experiments were carried out to key factor. 000. which has significant influence on Real water sample analysis the extraction efficiency.0 – 95.0±1.7 – No detection Diethofencarb – 95.8–750 μgL-1 for isoprocarb. Maybe parts of [C6MIM] [PF6] drops were extractions at the same concentration under optimal redissolved in the solution due to the heat generation extraction condition.4 – 84.0 – 95. Herein ILs phase can be easily obtained experimental results exhibited that there were good linearity by centrifugation after a certain extraction time. and good precisions performance at 15 min.000 0.40 Effect of extraction time sodium chloride in the range of 0–15%. four environmental water samples such as melted step. From Table 3. diethofencarb and fenothio- performance.1–625.7 a spiked recovery. extraction procedure is a time consum. detection limits Compound Linear range (μg L-1) R2 RSDs (n=6) (%) LOD (μg L-1) of the established method Isoprocarb 5.0 0. 15% addition of sodium chloride part of [C6MIM][PF6] was dissolved in aqueous solution was used in this experiment. which Phase separation is a popular procedure in liquid phase significant influence the extraction performance.5 – 99. but cooled to centrifuging.6±1. the convenient means. over the concentration range of 5.1–625 0. tap water. Addition of a proper In this experiment. 20 min was selected as the optimal extraction time. Zhou et al. which means the time from the solution to be tion of analytes from sample solution to the ILs drops.9 – 101. the peak area were achieved in the range of 1. amount of sodium chloride would promote the transforma- ing process. precisions and detection limits. it was found that this developed method utilized conventional and low cost Effect of salting-out effect instrument LC-UV and developed a new method with much lower LODs for the determination of carbamate pesticides. mean value (%)± Fenothiocarb – 108. The effect of extraction time was some of sodium chloride would salt out at low temperature examined in the range of 10–50 min and the results showed when the amount of sodium chloride was over 15%. The detection limits (LODs) demonstrated that it could reach the optimal extraction were in the range of 0.4±3. Hence.64±3. 15 min was adopted. gradually. These samples Table 2 Spiked recoveries of four environmental water Compounds Melted snow water Tap water Xiaoshangzhuang Shouxihu Lake water samples wastewater blank spiked blank spiked blank spiked blank spiked Isoprocarb – 82. and obviously declined when further addition.5±7.45 Fenothiocarb 3. Analytical parameters of the developed method Effect of centrifuging time Under the optimal conditions.4±2. A series experiments were designed in order carb. precisions.9993 1.8–750 0. The experiments in the range of 99. The results exhibited that the peak areas of target snow water. The comparison of this method with resulted from longer centrifugation time. and centrifugation is an often used and investigated.480 Q.0–1. Tables 2 and 3.8a – 104.89–99.93%. and gation time is also of great importance to the enrichment 3.4±3. The peak would adsorb part of analytes and lead to the decrease of areas slightly decreased during 20–50 min largely because recoveries finally.8±3. respectively and the correlation coefficients (R2) were to achieve the optimal centrifuging time. Salting-out effect is a popular parameter in the sample pretreatment procedures. In order to obtain existing method for different matrices was demonstrated in the best extraction performance.6 – 97.1 – 99.6 1.4±4.9991 1. which that the best results were achieved at 20 min. It can be seen from the Table 1. wastewater and lake water samples analytes increased with the increase of the concentration of were analyzed with the developed method. were extraction methods.8 0. some important parameters such as linear range. Table 1 Linear ranges. According to these results. Centrifu. 3.40 μg L-1.0–1.0–1.9989 1.7±2.1 – 93.8% by performing six decreased.45–1. So it was studied in detail in the range of 0–20% (w/v) with addition of sodium chloride In order to validate the applicability of the developed with the temperature was controlled at 70 °C at dispersing method.6±2. With a longer time.0±3.91 Diethofencarb 3.0 standard deviation . fenothiocarb .000.01 mgkg-1 [17] C18 μSPE HPLC-UV Soil 2–200 ngg-1 0.0 μgkg-1 [35] temperature partitioning DLLME-sweeping MEKC apples 6–500.0–15 μgL-1 [33] LLE-LTPa HPLC-UV Water 0. 10 mL.8–750 μgL-1 microextraction were spiked with isoprocarb.0–3. The carb at the concentration of 200.56–108. Method Matrix Analytical range LOD Ref.6%. It can be samples versus the blank water samples were shown in seen that the spiked recoveries were satisfied over the range Fig. 9–500 ngg-1 2. Conditions: sample volume. 1.0–1. mination of carbamate pesticides Matrix -SPE LC-MS Fruits vegetables 0. extraction time. 20–600 μgkg-1 0.01–10 mgkg-1 0. salt addition.4 ngg-1 [32] In-tube SPME HPLC-UV water 5–10. pH 6. 15%. 0.40 μgL-1 Present study uid dispersive liquid phase 3. extraction temperature.000 μgL-1 1. 70 °C. TCILDLPMEb-HPLC-UV water 5. [C6MIM][PF6] volume. diethofencarb. Fig. 4 The representative spiked chromatogram from Melted snow water sample.Ultratrace determination of carbamate pesticides in water samples 481 Table 3 Figures of merits of comparable methods for deter. 15 min. 125 and 150 μg L-1.5–3. 40 μL. isoprocarb. typical chromatograms of target analytes in spiked water respectively.033–10 mgL-1 5–10 μgL-1 [34] a liquid–liquid extraction with low DLLME HPLC-DAD vegetables 10–300. of 82. 2. 3.0 ngg-1 [36] b temperature controlled ionic liq.70% with the precisions of 1. diethofencarb and fenothio. 3.7–7. centrifuging time. 20 min. 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