223
7.2.3 Analysis of Pesticides
7.2.3.1 GC Conditions
Separation conditions were the same in all experiments. The oven temperature
ramped from 60 °C for 2 min to 150 °C with an increment of 25 °C/min for 0 min,
ramped to 200 °C with an increment of 3 °C/min for 0 min, and ramped to 280 °C
with an increment of 20 °C/min for 10 min, for a total running time of 41.8 min. The
temperature of the injector was 250 °C, the temperature of the MS quadrupole was
150 °C, and the injection volume was 1 μl. Classical hot splitless injection versus
splitless injection using increased pressure from 10 to 50 psi at flow to split vent for
0.5 min and 1.5 min were evaluated for a better response of the analyte considering
the peak area and the response factor. For that purpose, each injection was conducted in three repetitions, and the mean value was used to calculate the percent of
improvement. The extraction of pesticides from the groundwater was made by continuous liquid-liquid extraction (LLE) using 1 l of water and 40 ml of dichloromethane (DCM) added in three portions of 20 ml, 10 ml, and 10 ml. First, the solvent was
added into the glass bottles to dissolve the pesticides adsorbed on a glass wall. Then
it was transferred into the separatory funnel of 2 l in which previously the groundwater sample of 1 l was added. Water was salted out with 10% of sodium chloride
(NaCl), and then the water and the solvent were shaken for 2 min and allowed to
stand for 10 min to separate the phases. After the extraction, the solvent was evaporated under the flow of nitrogen and collected in a 2 ml vial using DCM. The solvent
is evaporated again under the nitrogen flow, and the volume of 100 μl hexane was
added in the vial, vortexed for 10 s, and collected in a vial insert. For recovery
analysis water was spiked with pesticide standards in a concentration of 0.1 and
0.5 μg/l. Limit of detection (LOD) and limit of quantification (LOQ) were determined using regression ANOVA analysis. Quantification was done using triphenyl
phosphate (TPP) as an internal standard in a concentration of 0.05 ng/μl.
7.2.3.2 Solvents and Standards
Certified chemical standards (purity 95–99%) and solvents with HPLC grade were
obtained from Sigma-Aldrich. Pesticide stock solutions and working standards
were prepared in acetone. Calibration curves were prepared in the concentration
range of 0.1–3.2 ng/μl.
7.2.3.3 Apparatus and Instrumentation
Pesticide analyses were performed on gas chromatograph Agilent 6890N coupled to
a mass spectrometer and equipped with JAS UNIS split/splitless injector with electronic pressure control and Agilent 7683B Series Autoinjector. Glass liner type (JAS
7 Improving Quantitative Analysis of GC-MS for Tracking Potential Contaminants…
7.2.3 Analysis of Pesticides
7.2.3.1 GC Conditions
Separation conditions were the same in all experiments. The oven temperature
ramped from 60 °C for 2 min to 150 °C with an increment of 25 °C/min for 0 min,
ramped to 200 °C with an increment of 3 °C/min for 0 min, and ramped to 280 °C
with an increment of 20 °C/min for 10 min, for a total running time of 41.8 min. The
temperature of the injector was 250 °C, the temperature of the MS quadrupole was
150 °C, and the injection volume was 1 μl. Classical hot splitless injection versus
splitless injection using increased pressure from 10 to 50 psi at flow to split vent for
0.5 min and 1.5 min were evaluated for a better response of the analyte considering
the peak area and the response factor. For that purpose, each injection was conducted in three repetitions, and the mean value was used to calculate the percent of
improvement. The extraction of pesticides from the groundwater was made by continuous liquid-liquid extraction (LLE) using 1 l of water and 40 ml of dichloromethane (DCM) added in three portions of 20 ml, 10 ml, and 10 ml. First, the solvent was
added into the glass bottles to dissolve the pesticides adsorbed on a glass wall. Then
it was transferred into the separatory funnel of 2 l in which previously the groundwater sample of 1 l was added. Water was salted out with 10% of sodium chloride
(NaCl), and then the water and the solvent were shaken for 2 min and allowed to
stand for 10 min to separate the phases. After the extraction, the solvent was evaporated under the flow of nitrogen and collected in a 2 ml vial using DCM. The solvent
is evaporated again under the nitrogen flow, and the volume of 100 μl hexane was
added in the vial, vortexed for 10 s, and collected in a vial insert. For recovery
analysis water was spiked with pesticide standards in a concentration of 0.1 and
0.5 μg/l. Limit of detection (LOD) and limit of quantification (LOQ) were determined using regression ANOVA analysis. Quantification was done using triphenyl
phosphate (TPP) as an internal standard in a concentration of 0.05 ng/μl.
7.2.3.2 Solvents and Standards
Certified chemical standards (purity 95–99%) and solvents with HPLC grade were
obtained from Sigma-Aldrich. Pesticide stock solutions and working standards
were prepared in acetone. Calibration curves were prepared in the concentration
range of 0.1–3.2 ng/μl.
7.2.3.3 Apparatus and Instrumentation
Pesticide analyses were performed on gas chromatograph Agilent 6890N coupled to
a mass spectrometer and equipped with JAS UNIS split/splitless injector with electronic pressure control and Agilent 7683B Series Autoinjector. Glass liner type (JAS
7 Improving Quantitative Analysis of GC-MS for Tracking Potential Contaminants…