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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

S/N and calibration data for 3,5-dichlorobenzoic acid methyl ester (conc. 0.5; 2.5, 5.0, 50, 500, and 5,000 pg/μL; vol. injected 1 μL. The two calibrations were performed at 1-week interval).
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f3-aci-10-2015-001: S/N and calibration data for 3,5-dichlorobenzoic acid methyl ester (conc. 0.5; 2.5, 5.0, 50, 500, and 5,000 pg/μL; vol. injected 1 μL. The two calibrations were performed at 1-week interval).

Mentions: Table 4 summarizes the slopes of the calibration curves, the linear regression correlation coefficients (reported as R2), the noise level reported as root-mean-squared (rms) noise, and the signal-to-noise (S/N) values for each test compound. The highest sensitivity, defined as the highest slope of the calibration curve, was exhibited by pentachloroanisole, and the lowest sensitivity by bentazon and acifluorfen. All calibration curves were linear at least over three orders of magnitude in concentration. The S/N values, which are at least 20, indicate that most chlorinated acid methyl esters can be detected at 1–5 pg per injection into the GC and a few of them (ie, pentachloroanisole and 2,4,5-T) even at subpicogram levels. Figure 3 shows the S/N values and the noise levels for 3,5-dichloro-benzoic acid and two calibration curves performed at 1-week interval. The noise levels for three replicate injections at 0.5 pg/μL were 4.0, 2.8, and 6.4 counts, and the S/N values were 83, 89, and 50, respectively. The ratio of the slopes of the calibration curves performed at 7-day intervals with the same calibration solutions was 0.94, which is well within the measurement error for such type of analyses. Overall, the determination of the chlorinated acid methyl esters by GC-QTOFMS with the Ar plasma delivers instrument detection levels at low picogram levels per injection into the GC.


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)

S/N and calibration data for 3,5-dichlorobenzoic acid methyl ester (conc. 0.5; 2.5, 5.0, 50, 500, and 5,000 pg/μL; vol. injected 1 μL. The two calibrations were performed at 1-week interval).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3-aci-10-2015-001: S/N and calibration data for 3,5-dichlorobenzoic acid methyl ester (conc. 0.5; 2.5, 5.0, 50, 500, and 5,000 pg/μL; vol. injected 1 μL. The two calibrations were performed at 1-week interval).
Mentions: Table 4 summarizes the slopes of the calibration curves, the linear regression correlation coefficients (reported as R2), the noise level reported as root-mean-squared (rms) noise, and the signal-to-noise (S/N) values for each test compound. The highest sensitivity, defined as the highest slope of the calibration curve, was exhibited by pentachloroanisole, and the lowest sensitivity by bentazon and acifluorfen. All calibration curves were linear at least over three orders of magnitude in concentration. The S/N values, which are at least 20, indicate that most chlorinated acid methyl esters can be detected at 1–5 pg per injection into the GC and a few of them (ie, pentachloroanisole and 2,4,5-T) even at subpicogram levels. Figure 3 shows the S/N values and the noise levels for 3,5-dichloro-benzoic acid and two calibration curves performed at 1-week interval. The noise levels for three replicate injections at 0.5 pg/μL were 4.0, 2.8, and 6.4 counts, and the S/N values were 83, 89, and 50, respectively. The ratio of the slopes of the calibration curves performed at 7-day intervals with the same calibration solutions was 0.94, which is well within the measurement error for such type of analyses. Overall, the determination of the chlorinated acid methyl esters by GC-QTOFMS with the Ar plasma delivers instrument detection levels at low picogram levels per injection into the GC.

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