2.3.2 Internal standard curve
The matrix-matched calibration curve was prepared as in Section 2.3.1 with 1 μg L‒1 ISs. The external standard curve was drawing with the mass concentration of treated as abscissa and the ratio of the area of quality chromatographic peak of quantitative ion to the area of internal standard peak as the ordinate.
3 Results and discussion
3.1 Optimization of chromatographic conditions
PFAs contain a large group of highly stable compounds, which are amphiphilic and consist of a perfluorinated hydrophobic. A good separation of PFAs was achieved in C18 reversed chromatographic column of low silicon
hydroxyl active filler[14‒16]. In comparison with the columns
of Waters XTerra C18, Capcell Pak C18 and Atlantis T3 C18, Atlantis T3 C18 exhibited good chromatographic peak and resolution. In comparison with acetonitrile-water mobile phase, methanol- water mobile phase exhibited a better separation. As the PFAs were carboxylic acid or sulfonate, ammonium acetate was added into the mobile phase to keep pH and ionic strength constant[17], which could lead to a
better peak shape and decrease the trail on the chromatogram.
Some previous studies showed that high levels of NH4Ac had stronger inhibition in mass spectrometry detection[18]. Under the optimum experiment conditions such as Atlantis
T3 C18 column, 5 mM ammonium acetate in methanol and 5 mM ammonium acetate in water as mobile phase to gradient elution, 20 kinds of target objects were separated within 20 min. The retention time is summed in Table 2, and The MRM chromatograms of PFOA and L-PFOS standards are
shown in Fig.1.
2.3.2 Internal standard curveThe matrix-matched calibration curve was prepared as in Section 2.3.1 with 1 μg L‒1 ISs. The external standard curve was drawing with the mass concentration of treated as abscissa and the ratio of the area of quality chromatographic peak of quantitative ion to the area of internal standard peak as the ordinate.3 Results and discussion3.1 Optimization of chromatographic conditionsPFAs contain a large group of highly stable compounds, which are amphiphilic and consist of a perfluorinated hydrophobic. A good separation of PFAs was achieved in C18 reversed chromatographic column of low siliconhydroxyl active filler[14‒16]. In comparison with the columnsof Waters XTerra C18, Capcell Pak C18 and Atlantis T3 C18, Atlantis T3 C18 exhibited good chromatographic peak and resolution. In comparison with acetonitrile-water mobile phase, methanol- water mobile phase exhibited a better separation. As the PFAs were carboxylic acid or sulfonate, ammonium acetate was added into the mobile phase to keep pH and ionic strength constant[17], which could lead to abetter peak shape and decrease the trail on the chromatogram. Some previous studies showed that high levels of NH4Ac had stronger inhibition in mass spectrometry detection[18]. Under the optimum experiment conditions such as AtlantisT3 C18 column, 5 mM ammonium acetate in methanol and 5 mM ammonium acetate in water as mobile phase to gradient elution, 20 kinds of target objects were separated within 20 min. The retention time is summed in Table 2, and The MRM chromatograms of PFOA and L-PFOS standards areshown in Fig.1.
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