2.2. Solid-phase extraction (SPE) and liquid chromatography/mass spectrometric detector (LC/MSD) analytical method
The Spark Holland on-line equipment was used for SPE. The analytes were extracted using the Prospekt™ Oasis HLB cartridges (10 mm × 2 mm, Waters, U.S.A.). These cartridges were preconditioned with 1 mL of methyl alcohol, 1 mL of 0.5N HCl, and 1 mL of deionized water. After sampling, 0.2 mL of 5% Na2EDTA was added to 50 mL of the filtered water for the extraction preparation. After the EDTA addition, the sample pH was adjusted to less than 3.0 by adding 40% sulfuric acid. The water sample of 10 mL was then passed through the cartridges at the flow rate of 2 mL/min. The cartridges were connected to the LC/MSD on-line, so that all antibiotics in the water sample could be passed to LC/MSD without any loss. Such connection enabled the analysis of the antibiotics at very low concentration despite the extracted sample volume being small. Detailed information about this analytical method can be found elsewhere [8]. The Agilent 1100 LC/MSD (Agilent, U.S.A.) was used with the diode array detector. The ultraviolet wavelength was 360 nm. The separation column was the Atlantis dC18® (2.1 mm × 50 mm, C18 column) with a pore size of 3 μm (Waters, U.S.A.).
2.2. Solid-phase extraction (SPE) and liquid chromatography/mass spectrometric detector (LC/MSD) analytical methodThe Spark Holland on-line equipment was used for SPE. The analytes were extracted using the Prospekt™ Oasis HLB cartridges (10 mm × 2 mm, Waters, U.S.A.). These cartridges were preconditioned with 1 mL of methyl alcohol, 1 mL of 0.5N HCl, and 1 mL of deionized water. After sampling, 0.2 mL of 5% Na2EDTA was added to 50 mL of the filtered water for the extraction preparation. After the EDTA addition, the sample pH was adjusted to less than 3.0 by adding 40% sulfuric acid. The water sample of 10 mL was then passed through the cartridges at the flow rate of 2 mL/min. The cartridges were connected to the LC/MSD on-line, so that all antibiotics in the water sample could be passed to LC/MSD without any loss. Such connection enabled the analysis of the antibiotics at very low concentration despite the extracted sample volume being small. Detailed information about this analytical method can be found elsewhere [8]. The Agilent 1100 LC/MSD (Agilent, U.S.A.) was used with the diode array detector. The ultraviolet wavelength was 360 nm. The separation column was the Atlantis dC18® (2.1 mm × 50 mm, C18 column) with a pore size of 3 μm (Waters, U.S.A.).
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