Determination Of Organic Pollutants In Environment By High Performance Liquid Chromatography

Organic pollutants may affact human health and normal growth of animals and plants, and also disturb or destroy the ecological balance. Although the concentration of organic pollutants is not high in the environment, they can cause physiological hazard like chronic poisoning, carcinogenic, teratogenic, mutagenic, and so on. Hence, it is important to establish a simple, rapid, and reliable method to determine organic pollutants in environmental samples. Up to now, many analytical techniques have been introduced for the determination of organic pollutants in environmental samples, including gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS), high performance liquid chromatography (HPLC), high performance liquid chromatography-mass spectrometry (HPLC-MS) and capillary electrophoresis (CE). HPLC becomes a widely used detection technique in modern separation and analysis because of its high separation efficiency, fast analysis speed, good selectivity, good sensitivity, and automatic operation, and it has been widely applied in the area of production of medicine, foodstuff, and environment, etc.Organic pollutants are commonly present in actual environmental samples at very low concentration with complex sample matrices. Therefore, in order to improve the sensitivity and selectivity, a complicated preconcentration step is always required prior to the analysis and determination of organic pollutants in actual environmental samples.As an alternative to in-tube solid phase microextration technique, polymer monolith microextraction (PMME) is a miniaturized sample pretreatment method using tube capillary polymer materials as the extraction medium. It integrates sample extraction, purification and concentration of analytes into one single step and it has several advantages such as solvent-free extraction, small sample volume, high enrichment, convenience and flexibility operation, and easy automation.Cloud point extraction (CPE) is a kind of new sample pretreatment technique developed in recent years. CPE uses surfactant solvent as the extraction solvent and can be performed without the use of toxic organic solvents. CPE, based on the solubilization and cloud point phenomenon of surfactants, causes the separation of a surfactant-rich phase and an aqueous phase by changing the experimental parameters including surfactant concentration, salt concentration, equilibrium temperature, incubation time, centrifugation time, and sample pH in order to realize the analytes separation and enrichment.In this paper, we mianly study the application of PMME and CPE coupled to HPLC-DAD for the determination of organic pollutants. It includes the following two sections.1. Determination of methylcarbamate pesticides (carbaryl, pirimicarb, and isoprocarb) in vegetables by coupling PMME to HPLC. In this experiment, a poly(methacrylic acid-co-ethylene glycol dimethacrylate) capillary monolithic column is selected as the extraction medium for PMME. We have investigated and optimized the experimental parameters and apply this method to determine methylcarbamate pesticides in vegetables. Optimization of HPLC conditions:a reverse phase Agilent Zorbax Eclipse XDB-Cis column (4.6×250mm,5μm) is used as analytical column, the optimized mobile phase is methanol-water (60-40, v/v), the flow rate is maintained at1.0mL/min, the preferential wavelength is set to210nm, the column temperature is35℃and the injection volume is5.0μL. The conditions of PMME have also been optimized. Firstly, in order to equilibrate the monolith,0.20mL methanol and0.50mL Na2HPO4(pH6.00,0.02mol/L) are ejected via the monolithic capillary tube by the syringe pump at0.05mL/min and0.16mL/min, respectively. Secondly,1.0mL sample solution is pushed through the monolith capillary at a flow rate of0.15mL/min. To eliminate the residual sample solution and the adsorbed sample matrix,0.20mL Na2HPO4(pH6.00,0.02mol/L) is kept to flow through the monolithic capillary tube at a flow rate of0.16mL/min. Finally,0.10mL acetonitrile is used to elute the analytes from the monolith at a flow rate of0.125mL/min and the eluate is collected into a vial for HPLC analysis. Under the optimal experimental conditions, the method provides an acceptable linearity (5-5000μg/kg), low limits of detection (0.36-2.6μg/kg), and good precision (intraday and interday relative standard deviations are lower than2.53%and6.36%, respectively). Moreover, this method is successfully applied to the determination of methylcarbamate pesticides in vegetables with the recovery range of70.4-98.5%.2. Ultrasound-assisted CPE method coupled with HPLC-DAD has also been applied to the determination of phenolic compounds, phenol, hydroquinol, resorcinol, catechol, m-cresol, and o-cresol in environmental water samples. In this study, a non-ionic surfactant, Tergitol15-S-7, is introduced as the extraction solvent. Several important parameters, which affect the extraction efficiency of CPE, including surfactant concentration, salt concentration, equilibrium temperature, incubation time, centrifugation time, ultrasonic time, sample pH, and dilution solvent are systematically evaluated and optimized. Optimization of HPLC conditions:a reverse phase Agilent Zorbax Eclipse XDB-C18column (4.6×250mm,5μm) is used as analytical column, the optimized mobile phase is methanol-water (55-45, v/v), the flow rate is maintained at0.7mL/min, the preferential wavelength is set to275nm, the column temperature is35℃and the injection volume is5.0μL. Under the optimum conditions, the linear regression coefficients of the standard curves are greater than0.9986and the limits of detection are very low within the range of1.7-6.0μg/L. This method is shown to be reproducible and reliable with intraday and interday relative standard deviations less than4.0%and5.8%, respectively. Finally, the developed method is applied for the quantitative analysis of phenolic compounds in environmental water samples and the recoveries are in the range of81.1-109.4%.