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Research ArticleHollow-Fibre-Supported Dispersive Liquid-LiquidMicroextraction for Determination of Atrazine and Triclosanin Aqueous Samples
Thabiso Letseka andMosotho J. George
Department of Chemistry and Chemical Technology, National University of Lesotho, P.O. Roma 180, Maseru, Lesotho
Correspondence should be addressed to Mosotho J. George; email@example.com
Received 30 April 2017; Revised 23 August 2017; Accepted 7 September 2017; Published 11 October 2017
Academic Editor: Mohamed Abdel-Rehim
Copyright 2017 Thabiso Letseka and Mosotho J. George. This is an open access article distributed under the Creative CommonsAttribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work isproperly cited.
We report the application of the dispersive liquid-liquid microextraction coupled to hollow-fibre membrane-assisted liquid-phasemicroextraction and its application for extraction of atrazine and triclosan. Under optimum conditions, namely, 25 L of a 1 : 4chlorobenzene : ethyl acetate mixture dispersed in 1mL of aqueous sample, 10% (m/v) NaCl, a magnetic stirrer speed at 600 rpm,and 10 minutes extraction time with toluene-filled fibre as the acceptor phase, the method demonstrates sufficient figures of merit.These include linearity (2 0.9975), intravial precision (%RSD 7.6), enrichment factors (127 and 142), limits of detection (0.0081and 0.0169 g/mL), and recovery from river water and sewerage (96101%).The relatively high detection limits are attributed to theflame ionization detector which is less preferred than amass spectrometer in trace analyses.This is the first report of a homogenousmixture of the dispersed organic solvent in aqueous solutions and its employment in extraction of organic compounds fromaqueoussolutions. It therefore adds yet another candidate in the pool of miniaturised solvent microextraction techniques.
The use and access to clean and safe water is a worldwideconcern as to prevent any water-borne illnesses, and this hasled to implementation of water quality regulations thus theneed for improvements in water treatment technologies.Thisis driven by the emerging contaminants in the environmentthat are present as a result of anthropogenic activities whichinclude agriculture, household processes, and industrial pro-cesses. These compounds inadvertently find their way intoenvironmental water through production, use, and final dis-posal of materials containing these compounds . They aregenerally discharged off in low concentrations into the envi-ronment; however as a result of their nonbiodegradabilitythey tend to bioaccumulate in the environment which theyare deposited in [2, 3]. It is essential therefore to monitor thepresence and concentrations of these compounds in theenvironment in order to reduce their effects on biodiversity.
Since these compounds are present in the environment atrelatively low concentrations and have to be isolated from
complex matrices, this necessitates sample preparation forremoval of interferences and preconcentration of target ana-lytes . Traditionally, liquid-liquid extraction was the mostwidely used sample preparation technique but had a numberof drawbacks which include chiefly utilization of large vol-umes of solvents and time consumption . In an effort toovercome the said drawbacks, a number of newminiaturisedtechniques have been developed and are continuously receiv-ing attention from analytical chemists.These techniques offerimprovements such as simplicity of operation, rapidity, lowcost, less hazards, and high enrichment factors .
There are principally three modes of miniaturised liquid-liquid extraction, sometimes called liquid-phase microex-traction (LPME) or solvent microextraction, namely, singledrop microextraction (SDME) [7, 8], hollow-fibre liquid-phase microextraction (HF-LPME) , and dispersive liq-uid-liquid-phase microextraction (DLLME) . Lastly,DLLMEentails the addition of appropriatemixture of extract-ing and dispersing solvents to an aqueous sample containinganalytes of interest; then formation of a cloudy solution
HindawiInternational Journal of Analytical ChemistryVolume 2017, Article ID 1451476, 8 pageshttps://doi.org/10.1155/2017/1451476
2 International Journal of Analytical Chemistry
occurs. When the cloudy solution is centrifuged, the extract-ed solvent will sediment at the bottom of the tube and is thenwithdrawn with a microsyringe for instrumental analysis. This method has received a wide acceptance for use inanalysis of environmental pollutants due to its unmatchedrapid extraction rates. However the need for precipitation ofthe organic solvent or aqueous to separate the two phases stillintroduces an extra step in the analysis time and as such thispresents another input cost in the form of a centrifuge.
Hollow-fibre liquid-phase microextraction on the otherhand involves the use of a hollow-fibre membrane to supportthe organic solvent. It is fast, efficient, sensitive, and easy tooperate and high enrichment process. The high efficiency ofHF-LPME is related to the high mass transfer rates of theprocess . The type of solvent to be filled and immobilizedin the pores of the hollow fibre is a critical factor to consideras the solvent must be compatible with the propylene fibre soas to easily fill the pores, and it should also be immiscible withthe water sample and provide high affinity of the target ana-lytes into it with low volatility to avoid evaporation during theextraction but have sufficient vapour pressure to be evapo-rated in the GC injection port . Usually the extractionkinetics and enhanced mass transfer of target analytes fromthe donor phase to the acceptor phase are achieved throughstirring of the sample .
Efforts to combine some of these techniques with poten-tial complementarity have demonstrated a promise in thisregard. For example, a combination of solid phase microex-traction with dispersive liquid-liquid microextraction and the combination of electromembrane extraction withDLLME  have been reported. Recently an attempt wasreported using a modified DLLME to drive the analytes intothe headspace followed by solid phase microextraction .The potential of yet another combination of two differenttechniques: DLLME with HF-LPME by introducing theorganic solvent filled fibre into the cloudyDLLME solution asa way of by-passing the extra step of phase separation hasbeen reported . Despite the reported challenge of theprecipitation of the more dense organic solvents, this methodwas applied in the determination of triclosan in sewagewater with considerable success . However, there wasstill a challenge of phase separation between the two sol-ventsaqueous solution and the organic solvent used in theDLLME.
As rigorous attempts were made to improve this situa-tionphase separation after the dispersion of the organicsolvents in the aqueous solutionwe herein report theoptimised coupled HF-LPME with DLLME using a binaryorganic solvent without any phase separation, thus achievingthe benefit of the two techniques as reported before as wellas a more improved precision which was a challenge with thepreviously reported method which had some precipitation ofthe organic solvent, thus posing a challenge of avoiding thesedimented droplets or suspended organic solvents. Atrazineand triclosan were used as model organic pollutants in thiswork as a follow-up to the previous exercise.
2.1. Materials and Reagents Used. Atrazine (1-chloro-3-ethylamino-5-isopropylamino-2,4,6-triazine, CAS 1912-24-9)
was purchased from Chem Service, Pennsylvania, USA, andtriclosan [5-chloro-2-(2,4-dichlorophenoxy)phenol, CAS3380-34-5], analytical grade diphenylamine, chlorobenzene,and ethyl acetate were obtained from Sigma Aldrich(Johannesburg, South Africa) while the HPLC grade sol-ventsmethanol, ethanol, toluene, and chloroformwereobtained from Riedel-de Haen (Seelze, Germany); analyticalgrade NaCl was obtained from ACE (Johannesburg SouthAfrica). The distilled water was prepared in house. TheAccruel Q3/2 PP polypropylene hollow-fibre membrane withthe dimensions of 600m (internal diameter) 200m (wallthickness) 0.2m pore size was obtained from MembranaGmbH (Wuppertal Germany) and cut into 1 cm strips usinga measuring ruler and a pair of scissors. Spinbar magneticstirring fleas with 5mm 2mm dimensions were obtainedfrom Sigma Aldrich (Steinheim, Germany).
Stock standard solutions were prepared by dissolving10mg of atrazine and triclosan standards in 1mL ethanol, andthis solution was further diluted serially to achieve lowerconcentrations using ethanol. Aqueous working solutions of5 g/mL were prepared by dilution of determined volumesof the stock standard solutions with distilled water. All thesolutions were stored in the refrigerator at temperature below5C when not in use.
2.2. Instrumentation. The analysis was carried out using aVarian 3800GasChromatograph (California, USA) equippedwith a flame ionization detector and a 30m 1 m 0.53mmSGE-BP5 (5% phenyl-95% dimethyl-polysiloxane) column(Texas, USA). Nitrogen gas (5.0 Grade) was used as a carriergas andmaintained at 5mL/min while hydrogen and air wereused for the detector. The injector and detector temperaturewere set at 250C and 200C, respectively. The column washeld at 100C for 2min, then ramped at 20C/min to 300C,and held for 3min to achieve a total run time of 15 minutes.
2.3. Extraction Procedure. The extraction procedure wasfollowed as described elsewhere . Firstly, 1 mL aliquotsof the 5 g/mL working solution were pipetted into a 2-mLsample vial with a screw-cap to which a 25 L mixture of1 : 4 chlorobenzene : ethyl acetate was then pipetted; 15mgNaCl was weighted and the