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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

Kr- and Ar-MPPI spectra for dacthal and 2,4,5-TP methyl ester.
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Related In: Results  -  Collection


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f2-aci-10-2015-001: Kr- and Ar-MPPI spectra for dacthal and 2,4,5-TP methyl ester.

Mentions: Figure 2 shows the mass spectra of dacthal and 2,4,5-TP methyl ester obtained with this soft ionization source using Kr and Ar plasmas. For both compounds, the molecular ion is the base peak on the Kr-MPI spectra and decreases in intensity, yielding fragment ions with Ar-MPPI. When there were only a few fragment ions in the Ar-MPPI spectra, we were able to search these spectra using the NIST library of low-resolution mass spectra and obtain compound identification. The NIST scores for dacthal and 2,4,5-TP were 82.76 and 76.82, respectively. Other compounds identified via NIST library search (score given in parentheses) include methyl esters of dichlorprop (81.66), 3,5-dichlorobenzoic acid (81.12), dicamba (68.24), chloramben (71.61), 2,4,5-T (63.57), 2,4-DB (70.85), picloram (62.74), and quiclorac (60.7). In order to obtain more fragmentation, Ne plasma is the next choice, and experiments done in our laboratory on a set of organic compounds concluded that fragmentation using Ne plasma is very similar to that while using 70-eV EI.


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)

Kr- and Ar-MPPI spectra for dacthal and 2,4,5-TP methyl ester.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2-aci-10-2015-001: Kr- and Ar-MPPI spectra for dacthal and 2,4,5-TP methyl ester.
Mentions: Figure 2 shows the mass spectra of dacthal and 2,4,5-TP methyl ester obtained with this soft ionization source using Kr and Ar plasmas. For both compounds, the molecular ion is the base peak on the Kr-MPI spectra and decreases in intensity, yielding fragment ions with Ar-MPPI. When there were only a few fragment ions in the Ar-MPPI spectra, we were able to search these spectra using the NIST library of low-resolution mass spectra and obtain compound identification. The NIST scores for dacthal and 2,4,5-TP were 82.76 and 76.82, respectively. Other compounds identified via NIST library search (score given in parentheses) include methyl esters of dichlorprop (81.66), 3,5-dichlorobenzoic acid (81.12), dicamba (68.24), chloramben (71.61), 2,4,5-T (63.57), 2,4-DB (70.85), picloram (62.74), and quiclorac (60.7). In order to obtain more fragmentation, Ne plasma is the next choice, and experiments done in our laboratory on a set of organic compounds concluded that fragmentation using Ne plasma is very similar to that while using 70-eV EI.

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