The stock standard solutions were prepared in acetone at concentrations of 2.0 mg/ml for each compound and stored at - 4°C.. Stock solutions 1000 µg/ml were prepared by dissolving the so
Trang 12 Chapter Two
Experimental Section
This chapter describes the instrumentation, chemicals and procedures used throughout this work, unless specified otherwise in a particular chapter
2.1 INSTRUMENTATION
2.1.1 Sample Preparation Techniques: MAE and SFE
Microwave-assisted extraction was carried out using a MarsX (CEM, Matthews, NC, USA, 1200-Watt) laboratory microwave extraction system equipped with a solvent detector The instrument is able to extract concurrently fourteen solid samples in PTFE extraction vessels under identical extraction conditions It controls either pressure or temperature depending on which parameter reaches its control set point first
SFE in the dynamic mode was performed using a Jasco (Tokyo, Japan) PU-980 HPLC pump A Trace ThermoQuest (Rodano, Italy) Series 2000 GC oven was used to produce the required critical temperature of CO2 A 10-ml stainless steel sample cell (Jasco) was installed in the GC oven Methanol was added to the CO2 at intervals with a second
PU-980 HPLC pump
Trang 22.1.2 Sample Measurement Systems: HPLC-UV, LC-MS and GC-ECD
The HPLC system consisted of a Shimadzu (Kyoto, Japan) LC-6A pump, a Rheodyne (Cotati, CA, USA) 7010 injector equipped with a 20-µl loop, a Shimadzu SPD-6AV UV-VIS detector and a Shimadzu C-R6A integrator
The LC-API-MS analyses were performed with a Thermo Separation gradient HPLC system (Model SCM 1000) coupled to a Finnigan MAT LCQ ion-trap mass spectrometer (all ThermoQuest, San Jose, CA, USA) The instrument was initially tuned based on a mixture of caffeine, L-methionyl-arginyl-phenylananyl-alanine acetate·H2O and a mixture of perfluoroalkoxycyclotriphosphazenes in both positive and negative ionization modes as suggested by the manufacturer
GC analysis was performed by a Hewlett-Packard (Palo Alto, CA, USA) 5890 Series II gas chromatograph equipped with a 63Ni electron-capture detector Separations were conducted using a DB-5, 30 m × 0.32 mI.D capillary column (0.25 µm stationary phase thickness) (J&W, Folsom, CA, USA) The carrier gas was purified nitrogen at a flow rate 1.5ml/min
Trang 32.2 REAGENTS
Analytical-grade PAHs (naphthalene and phenanthrene) were purchased from Supelco (Bellefonte, PA, USA) or Ultra-Scientific (North Kingston, RI, USA) The stock standard solutions were prepared in acetone at concentrations of 2.0 mg/ml for each compound and stored at - 4°C Working solutions were prepared by diluting the stock solutions with acetone
Polychlorinated biphenyls (PCB-1242 and PCB-1248) were purchased as individual standard stock solutions containing a nominal concentration of 100 µg/ml in methanol from Ultra-Scientific
Atrazine (purity 98%) and simazine (purity 99%) were purchased from Supelco Stock solutions (1000 µg/ml) were prepared by dissolving the solid standards in acetone and stored under refrigeration Working solutions were obtained by diluting with acetone
The carbamates: propoxur (purity 99%), methiocarb (purity 99%), propham (purity 99.5%), thiuram (purity 98%) and chlorpropham (purity 99.5%) were supplied by ChemService (West Chester, PA, USA) The stock solutions containing each compound
at 1000 µg /ml were prepared in methanol and diluted with the same solvent to obtain working solutions at various concentrations They were stored at 4°C
Trang 4All solvents used in this study were either pesticide-grade or HPLC-grade and obtained from Fischer Scientific (Fair Lawn, NJ, USA) The water used (thereafter referred to as ultrapure water) was purified using a Milli-Q (Millipore, Bedford, MA, USA) water purification system All the samples (solutions and extracts) were filtered through 0.45-m membranes (Millipore) and degassed in an ultrasonic bath before use
2.3 PROCEDURES
2.3.1 Preparation of Water Samples
Natural water samples were collected from local sites They were filtered through a
0.45-µm membrane (Millipore) to remove particulate matter before use
Freshly spiked water samples were prepared by adding an appropriate volume of spiking solutions into the natural water samples prepared above and ultrapure water All the samples were degassed by an ultrasonic bath before LC-MS analysis
2.3.2 Preparation of Soil Samples
2.3.2.1 Blank soils
Blank soils, collected from local sites were air-dried, pulverized and sieved through a 60-mesh sieve In order to remove possible traces of PAHs, PCBs, triazines, carbamates and
Trang 5each of methanol, acetone, dichloromethane and n-hexane for at least 24 hr sequentially The treated soil was spread out on a tray and air-dried for 8 hr in a fume hood to remove
as much solvent as possible Finally, it was determined that there were no detectable levels of the target analysts in soil samples before spiking
2.3.2.2 Freshly spiked soils
Freshly spiked soil samples were prepared by adding an appropriate volume of spiking solutions into the soils To ensure that the analytes were well distributed, a reasonable amount of acetone was added to moisten the soil and careful agitation was performed These standards were prepared 10-14 days prior to soil analysis
2.3.2.3 Aged spiked soils
Aged spiked soil samples were obtained by storing the above spiked soil in bottles in a dry, dark location for 60 days It was assumed that the contaminants were uniformly distributed in the sample and that, because the soil still retained residual moisture throughout the storage period, any analyte-matrix interactions would have occurred, over the weathering period, to a similar extent to those in real contaminated soil with similar properties
Trang 62.3.3 Preparation of Biological Samples
Goldfish, tortoises (Trachemys scripta elegans), and green alga (Sea lettuce: Ulva lactuca) were purchased in a local market In order to remove possible trace organic
contaminants prior to preparation, all of them were washed in fresh running water and then rinsed with deionized water
The fish samples were grinded in a mortar and pestle with liquid nitrogen until a homogenous fine powder was obtained In order to meet the fortification standards for recovery and analytical precision, a portion of each fish sample was added an appropriate volume of standard solution, thereby obtaining the required levels of target analytes To ensure that the analytes were well distributed, enough methanol was added to just moisten the samples that were then stirred After freeze-drying for 24 hours, the fine powders were accurately weighed and placed in polyethylene flasks
Tortoises were removed from their shells after being submerged in liquid nitrogen, and tissues were then crushed and lyophilized Spiked tortoise samples were prepared in a similar manner as the fish The remainders of the fish and tortoise samples were stored at -20 °C for later analyses All samples were analyzed as freeze-dried powders
Sea lettuce was crushed until a homogeneous mass was obtained Spiked samples used for recovery determination were prepared via the addition of standard stock solutions to
Trang 7solution to penetrate the material The samples were then immediately freeze-dried for 24h, and finally stored in polyethylene bottles after being weighed accurately No sieving was performed before analysis
To assess possible contamination from sample preparation, together with each series of samples, blanks were made to ensure there were no detectable levels of the target analytes in each freeze-dried blank samples before spiking