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Determination of Chlorophenoxy Acid Methyl Esters and Other Chlorinated Herbicides by GC High-resolution QTOFMS and Soft lonization.

Lopez-Avila V, Roach P, Urdahl R - Anal Chem Insights (2015)

Bottom Line: Gas chromatography with quadrupole time-of-flight mass spectrometry (GC-QTOFMS) and soft ionization generated by a rare-gas plasma is described here for the determination of various chlorophenoxy acid methyl esters and a few chlorinated herbicides.This plasma-based, wavelength-selectable ionization source, which can use Xe, Kr, Ar, Ne, or He as the plasma gas, enables ionization of GC-amenable compounds with ionization energies below 8.4, 10, 11.6, 16.5, or 22.4 eV, respectively.Data generated with the Ar plasma and real matrices such as a peppermint extract, a plum extract, and an orange peel extract, spiked with 16 test compounds, indicate that the test compounds can be detected at 1-10 pg/μL of extract, and compounds such as menthone, limonene, eucalyptol, pinene, caryophylene, and other C15H24 isomers, which are present in the peppermint and the orange peel extracts at ppm to percent levels, do not appear to interfere with the determination of the chlorophenoxy acid methyl esters or the chlorinated herbicides, although there were matrix effects when the test compounds were spiked at 1-10 pg/μL of extract.

View Article: PubMed Central - PubMed

Affiliation: Agilent Technologies, Santa Clara, CA, USA.

ABSTRACT
Gas chromatography with quadrupole time-of-flight mass spectrometry (GC-QTOFMS) and soft ionization generated by a rare-gas plasma is described here for the determination of various chlorophenoxy acid methyl esters and a few chlorinated herbicides. This plasma-based, wavelength-selectable ionization source, which can use Xe, Kr, Ar, Ne, or He as the plasma gas, enables ionization of GC-amenable compounds with ionization energies below 8.4, 10, 11.6, 16.5, or 22.4 eV, respectively. The advantages of soft ionization include enhanced molecular ions, reduced fragmentation, and reduced background noise as compared to electron ionization. In the study presented here for two plasma gases, we demonstrate that Kr plasma, which is softer than Ar plasma, yields molecular ions with a relative intensity >60% for 11 of the 16 test compounds. When using this "tunable" plasma to ionize the analytes, there is the possibility for selective ionization and less fragmentation, which may lead to increased sensitivity and may help structure elucidation, especially when using high-resolution mass spectrometry that generates accurate masses within a few parts per million (ppm) mass errors. Data generated with the Ar plasma and real matrices such as a peppermint extract, a plum extract, and an orange peel extract, spiked with 16 test compounds, indicate that the test compounds can be detected at 1-10 pg/μL of extract, and compounds such as menthone, limonene, eucalyptol, pinene, caryophylene, and other C15H24 isomers, which are present in the peppermint and the orange peel extracts at ppm to percent levels, do not appear to interfere with the determination of the chlorophenoxy acid methyl esters or the chlorinated herbicides, although there were matrix effects when the test compounds were spiked at 1-10 pg/μL of extract.

No MeSH data available.


Related in: MedlinePlus

GC-QTOFMS chromatogram of the 16 chlorinated acid methyl esters analyzed using the MPPI source with Ar as plasma gas (conc. 2.5–10 ng/μL).
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f1-aci-10-2015-001: GC-QTOFMS chromatogram of the 16 chlorinated acid methyl esters analyzed using the MPPI source with Ar as plasma gas (conc. 2.5–10 ng/μL).

Mentions: Figure 1 shows a GC-QTOF total ion chromatogram of the 16 test compounds using a 30-m HP-5MS capillary column and the Ar plasma. Fourteen compounds are fully resolved chromatographically on the HP-5MS capillary column. 2,4-DB methyl ester (peak 6) and the dinoseb methyl ether (peak 11) slightly overlap, but they can be easily identified because there are no overlapping fragment ions with the same mass-to-charge (m/z) ratio. The retention times of the 16 test compounds are given in Table 1, together with the CAS numbers, chemical formulae, the calculated m/z values for the monoisotopic mass of each test compound, and the quantitation ions used in this study. A DB-5MS capillary column of the same dimensions as the HP-5MS column was used to analyze the spiked orange peel extracts using the same GC operating conditions. The elution order of the 16 test compounds from the DB-5MS column is the same as on the HP-5MS column with the exception of 2,4-DB and dinoseb. On the HP-5MS column, 2,4-DB methyl ester elutes before bentazon methyl derivative, whereas on the DB-5MS column the elution order of the two compounds is reversed. During the study, we had to replace the HP-5MS capillary column because the HP-5MS capillary column was inadvertently broken when removing the MPPI source for troubleshooting. Although the HP-5MS and the DB-5MS capillary columns have the same dimensions in terms of length, internal diameter, and film thickness, and in principle they are equivalent because they use the same stationary phase consisting of 5% phenyl and 95% methylsiloxane, they do not give identical performance in terms of analyte elution order, as shown here for 2,4-DB methyl ester and bentazon methyl. The slight difference in performance between these low-bleed columns appears to be due to the fact that the HP-5MS column is coated with 5% phenyl/95% methylsiloxane stationary phase whereas the DB-5MS is coated with 5% phenyl/95% methyl arylenesiloxane.


Determination of Chlorophenoxy Acid Methyl Esters and Other Chlorinated Herbicides by GC High-resolution QTOFMS and Soft lonization.

Lopez-Avila V, Roach P, Urdahl R - Anal Chem Insights (2015)

GC-QTOFMS chromatogram of the 16 chlorinated acid methyl esters analyzed using the MPPI source with Ar as plasma gas (conc. 2.5–10 ng/μL).
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4325682&req=5

f1-aci-10-2015-001: GC-QTOFMS chromatogram of the 16 chlorinated acid methyl esters analyzed using the MPPI source with Ar as plasma gas (conc. 2.5–10 ng/μL).
Mentions: Figure 1 shows a GC-QTOF total ion chromatogram of the 16 test compounds using a 30-m HP-5MS capillary column and the Ar plasma. Fourteen compounds are fully resolved chromatographically on the HP-5MS capillary column. 2,4-DB methyl ester (peak 6) and the dinoseb methyl ether (peak 11) slightly overlap, but they can be easily identified because there are no overlapping fragment ions with the same mass-to-charge (m/z) ratio. The retention times of the 16 test compounds are given in Table 1, together with the CAS numbers, chemical formulae, the calculated m/z values for the monoisotopic mass of each test compound, and the quantitation ions used in this study. A DB-5MS capillary column of the same dimensions as the HP-5MS column was used to analyze the spiked orange peel extracts using the same GC operating conditions. The elution order of the 16 test compounds from the DB-5MS column is the same as on the HP-5MS column with the exception of 2,4-DB and dinoseb. On the HP-5MS column, 2,4-DB methyl ester elutes before bentazon methyl derivative, whereas on the DB-5MS column the elution order of the two compounds is reversed. During the study, we had to replace the HP-5MS capillary column because the HP-5MS capillary column was inadvertently broken when removing the MPPI source for troubleshooting. Although the HP-5MS and the DB-5MS capillary columns have the same dimensions in terms of length, internal diameter, and film thickness, and in principle they are equivalent because they use the same stationary phase consisting of 5% phenyl and 95% methylsiloxane, they do not give identical performance in terms of analyte elution order, as shown here for 2,4-DB methyl ester and bentazon methyl. The slight difference in performance between these low-bleed columns appears to be due to the fact that the HP-5MS column is coated with 5% phenyl/95% methylsiloxane stationary phase whereas the DB-5MS is coated with 5% phenyl/95% methyl arylenesiloxane.

Bottom Line: Gas chromatography with quadrupole time-of-flight mass spectrometry (GC-QTOFMS) and soft ionization generated by a rare-gas plasma is described here for the determination of various chlorophenoxy acid methyl esters and a few chlorinated herbicides.This plasma-based, wavelength-selectable ionization source, which can use Xe, Kr, Ar, Ne, or He as the plasma gas, enables ionization of GC-amenable compounds with ionization energies below 8.4, 10, 11.6, 16.5, or 22.4 eV, respectively.Data generated with the Ar plasma and real matrices such as a peppermint extract, a plum extract, and an orange peel extract, spiked with 16 test compounds, indicate that the test compounds can be detected at 1-10 pg/μL of extract, and compounds such as menthone, limonene, eucalyptol, pinene, caryophylene, and other C15H24 isomers, which are present in the peppermint and the orange peel extracts at ppm to percent levels, do not appear to interfere with the determination of the chlorophenoxy acid methyl esters or the chlorinated herbicides, although there were matrix effects when the test compounds were spiked at 1-10 pg/μL of extract.

View Article: PubMed Central - PubMed

Affiliation: Agilent Technologies, Santa Clara, CA, USA.

ABSTRACT
Gas chromatography with quadrupole time-of-flight mass spectrometry (GC-QTOFMS) and soft ionization generated by a rare-gas plasma is described here for the determination of various chlorophenoxy acid methyl esters and a few chlorinated herbicides. This plasma-based, wavelength-selectable ionization source, which can use Xe, Kr, Ar, Ne, or He as the plasma gas, enables ionization of GC-amenable compounds with ionization energies below 8.4, 10, 11.6, 16.5, or 22.4 eV, respectively. The advantages of soft ionization include enhanced molecular ions, reduced fragmentation, and reduced background noise as compared to electron ionization. In the study presented here for two plasma gases, we demonstrate that Kr plasma, which is softer than Ar plasma, yields molecular ions with a relative intensity >60% for 11 of the 16 test compounds. When using this "tunable" plasma to ionize the analytes, there is the possibility for selective ionization and less fragmentation, which may lead to increased sensitivity and may help structure elucidation, especially when using high-resolution mass spectrometry that generates accurate masses within a few parts per million (ppm) mass errors. Data generated with the Ar plasma and real matrices such as a peppermint extract, a plum extract, and an orange peel extract, spiked with 16 test compounds, indicate that the test compounds can be detected at 1-10 pg/μL of extract, and compounds such as menthone, limonene, eucalyptol, pinene, caryophylene, and other C15H24 isomers, which are present in the peppermint and the orange peel extracts at ppm to percent levels, do not appear to interfere with the determination of the chlorophenoxy acid methyl esters or the chlorinated herbicides, although there were matrix effects when the test compounds were spiked at 1-10 pg/μL of extract.

No MeSH data available.


Related in: MedlinePlus