Dielectric barrier discharge-optical emission spectrometry for the simultaneous determination of halogens

Zhang, Deng-Ji; Cai, Yong; Chen, Mingli; Yu, Yong-Liang; Wang, Jianhua

doi:10.1039/c5ja00266d

Cited by 22 publications

(9 citation statements)

References 42 publications

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“…An atomic line of hydrogen at ∼656 nm (Balmer H-alpha) from the CH 3 OH/Ar mixture is significant besides the pronounced presence of the CH(A) band at ∼431 nm (Figure c). Similarly, CH(A) and the atomic line of hydrogen and bromine (at 827 nm) were observed in the case of CHBr 3 /Ar (Figure a).…”

Section: Resultssupporting

confidence: 57%

Formation of CN Radical from Nitrogen and Carbon Condensation and from Photodissociation in Femtosecond Laser-Induced Plasmas: Time-Resolved FT-UV–Vis Spectroscopic Study of the Violet Emission of CN Radical

et al. 2020

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Exploring the formation of diatomic radicals in femtosecond plasmas is important to establish the most dominant kinetic pathways following ionization and dissociation of small molecules. In this work, cyano radical formation has been studied from bromoform, acetonitrile, and methanol in nitrogen and argon plasmas created with a focused femtosecond laser beam operating at 100 kHz repetition rate and 1030 nm wavelength with 43 fs pulse length and 250 μJ pulse energy. Time-resolved Fourier transform fluorescence spectroscopy was applied in the ultraviolet−visible (UV−vis) spectral range for the characterization of the rotational and vibrational temperatures of the CN(B) radicals via fitting the experimental data. The high repetition rate of the laser allows efficient coupling with the step-scan Fourier transform spectroscopy method. Coulomb explosion at the very high intensity (∼10 16 W/cm 2 ) resulted in the formation of nascent atoms, ions, and electrons. The condensation reactions of carbon and reactive nitrogen species resulted in the formation of CN(B 2 Σ + ) radicals and C 2 (d 3 Π g ) dicarbon molecules/radicals. The CN(B) radicals were formed at the highest concentration in the case of bromoform because the weak carbon−bromine bonds resulted in reactive carbon atoms and CH radicals, which are reactive precursors for the CN(B) radical formation. In the case of acetonitrile, immediate production of CN(B) is observed with nanosecond resolution, which suggests that the CN is formed either via photodetachment or via roaming reaction associated with the Coulomb explosion of the parent molecule. The nascent rotational temperature was very high (∼6000−8500 K) and rapidly decreased in all instances within 40 ns with bromoform and acetonitrile. The highest vibrational temperature (∼7800 K) was observed in an acetonitrile/Ar mixture that decreased in about 30 ns and then increased in the observed time window. The vibrational temperature increased in all samples between 30 and 200 ns. The time dependence of fluorescence is described with a monoexponential decay in the case of acetonitrile/Ar and with biexponential decays in all other instances in the 0−250 mbar total pressure range. The shorter time constant is close to the radiative lifetime of CN(B) emission (∼60−80 ns), which can be attributed to the CN(B) radicals produced in the first few collisions at lower pressures. The longer CN(B) emission is from CN(B) created by slower chemical reactions involving carbon atoms, C 2 radicals, and reactive nitrogen-containing species.

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Section: Resultssupporting

confidence: 57%

Formation of CN Radical from Nitrogen and Carbon Condensation and from Photodissociation in Femtosecond Laser-Induced Plasmas: Time-Resolved FT-UV–Vis Spectroscopic Study of the Violet Emission of CN Radical

et al. 2020

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“…At oxygen levels above 110 ppm, the plasma reactive species are depleted, leading to a loss in analyte breakdown efficiency and consequent deviations from compound-independent response. Atomic chlorine has been detected in AP-DBD using optical methods in other studies, 12,29 indicating that atoms might be the precursors for the detected Cl − . Alternative precursors such as HCl might also play a role in ion formation.…”

Section: ■ Conclusionmentioning

confidence: 74%

Atmospheric-Pressure Dielectric Barrier Discharge as an Elemental Ion Source for Gas Chromatographic Analysis of Organochlorines

et al. 2018

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Atmospheric-pressure dielectric barrier discharge (AP-DBD) plasma has emerged in recent years as a versatile plasma for molecular ionization and elemental spectroscopy. However, its capabilities as an elemental ion source have been less explored, partly because of difficulties in the detection of positive elemental ions from this low-gas-temperature plasma. In this work, we investigate the detection of negative elemental ions to enable elemental mass spectrometry (MS) using AP-DBD. A gas chromatograph is coupled to a helium AP-DBD apparatus and positioned in front of an atmospheric-pressure-sampling mass spectrometer with no modifications to the ion sampling interface. We demonstrate that Cl ions are detected with a compound-independent efficiency, enabling elemental quantification of organochlorines. Further, addition of oxygen at low concentration (11 ppm, v/v) to the helium plasma improves the analytical performance by reducing postcolumn peak broadening, whereas high oxygen concentrations (>110 ppm, v/v) lead to loss of the compound-independent response. The optimized GC-AP-DBD-MS setup shows close to 2 orders of magnitude of linearity for its compound-independent Cl response and offers detection limits of 0.5-1 pg of Cl on column (0.6 pg/s), suitable for analysis of organochlorines in food samples. We demonstrate this capability by analyzing orange juice spiked with pesticides at 9 μg/L and a single internal standard. Importantly, we demonstrate that a quick, easy, cheap, effective, rugged, and safe (QuEChERS) extraction followed by GC-AP-DBD-MS quantification using the single standard provides acceptable recoveries (80-120%). These results highlight uniform QuEChERS extraction of a range of compounds and the compound-independent response of AP-DBD for Cl, making the combination of the two methods desirable for the rapid quantification of organochlorines. Furthermore, we discuss ionization matrix effects in AP-DBD for chlorine detection and offer strategies to flag matrix-impacted analytes. These results suggest that AP-DBD has the potential to become a unified ion source for both elemental quantification and molecular identification of GC eluents on a single MS platform.

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“…CH(A) radicals were identified from the peak observed at 431 nm in the overview spectrum (CH(A 2 Δ → X 2 Π, later referred to as CH(A–X), Figure a). The atomic lines of hydrogen (H-α, 656.8 nm) and bromine (827.8 nm) were also observed along with one of the C + ionic lines (392.5 nm) and C 2 bands (D 3 Π-A 3 Π, 450–475, 500–520, and 550–570 nm). − The inset shows the spectrum of CH in an enlarged form. The high-resolution continuous spectrum of this sample confirmed the CH(A–X) emission in the 22,500–24,000 cm –1 (444–417 nm) spectral range (Figure b).…”

Section: Resultsmentioning

confidence: 99%

Direct Production of CH(A²Δ) Radical from Intense Femtosecond Near-IR Laser Pulses

2020

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CH(A 2 Δ) radical formation was observed in bromoform and methanol vapor in argon plasma with near-infrared femtosecond laser pulses (43 fs, 1030 nm, 100 kHz, 250 μJ/pulse). The beam was focused with an achromatic lens, creating very high intensity in the plasma that caused Coulomb explosion (calculated intensity was ∼1.1 × 10 16 W/cm 2 in the focal point). The emitted fluorescence light was measured with high spectral (1−10 cm −1 ) and temporal resolution (5 ns) with an FT−Vis spectrometer. The step-scan technique allowed the reconstruction of the time-resolved fluorescence spectra from CH(A−X) emission. The emission from atomic lines such as H, Br, C, and O was observed and also from C + cations and CH and C 2 radicals. This indicates that in a significant portion of these organic molecules, all chemical bonds were cleaved in the Coulomb explosion. For both organics, the peak maximum of the CH(A) emission occurred at about 10 ns after excitation by the femtosecond pulse. After the maximum, a rapid emission decay was observed in the case of bromoform (monoexponential decay, t = 10 ns). The fluorescence decay was biexponential when methanol was used as the source for CH(A) generation. It can be assumed that CH(A) generation involved a fast and a slower path with some secondary reactions via the stepwise loss of hydrogen atoms from the CH 3 group. The time constants were t 1 = 7.8−8.3 ns and t 2 = 78−82 ns for the fast and slow components, respectively, and very similar values were obtained at 10 and 25 mbar total pressures. However, in the case of bromoform, the C−Br bonds are significantly weaker; therefore, these atoms can be removed even in a single step via multiphoton absorption. The rotational temperature of CH(A) radicals generated from methanol decreased rapidly in the 30−55 ns time period from 2770 ± 80 to 1530 ± 50 K. The vibrational temperature increased from 3530 ± 450 to 9810 ± 760 K in the 30−80 ns time period and then started to decrease (the average temperatures were T rot = 910 ± 20 K and T vib = 7490 ± 340 K at 100 ns). This initial increase of T vib is thought to be the result of electron collision with the CH radicals. The high temperatures of the fragment may indicate the roaming reaction associated with the Coulomb explosion of the parent molecule. We demonstrated that CH(A) radicals can be produced from both organic compounds, and the step-scan technique is ideal for the characterization of their time-resolved spectra using the 100 kHz high repetition rate near-infrared femtosecond laser pulses. The FT/UV−vis step-scan technique can detect neutral species directly with high spectral and time resolution, thus it is a complementary technique to the experiments utilizing ion detection schemes, such as velocity map imaging.

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Dielectric barrier discharge-optical emission spectrometry for the simultaneous determination of halogens

Abstract: Dielectric barrier discharge micro-plasma as a radiation source was used for the simultaneous determination of halogens by optical emission spectrometry.

Cited by 22 publications

References 42 publications

Formation of CN Radical from Nitrogen and Carbon Condensation and from Photodissociation in Femtosecond Laser-Induced Plasmas: Time-Resolved FT-UV–Vis Spectroscopic Study of the Violet Emission of CN Radical

Formation of CN Radical from Nitrogen and Carbon Condensation and from Photodissociation in Femtosecond Laser-Induced Plasmas: Time-Resolved FT-UV–Vis Spectroscopic Study of the Violet Emission of CN Radical

Atmospheric-Pressure Dielectric Barrier Discharge as an Elemental Ion Source for Gas Chromatographic Analysis of Organochlorines

Direct Production of CH(A²Δ) Radical from Intense Femtosecond Near-IR Laser Pulses

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Dielectric barrier discharge-optical emission spectrometry for the simultaneous determination of halogens

Abstract: Dielectric barrier discharge micro-plasma as a radiation source was used for the simultaneous determination of halogens by optical emission spectrometry.

Cited by 22 publications

References 42 publications

Formation of CN Radical from Nitrogen and Carbon Condensation and from Photodissociation in Femtosecond Laser-Induced Plasmas: Time-Resolved FT-UV–Vis Spectroscopic Study of the Violet Emission of CN Radical

Formation of CN Radical from Nitrogen and Carbon Condensation and from Photodissociation in Femtosecond Laser-Induced Plasmas: Time-Resolved FT-UV–Vis Spectroscopic Study of the Violet Emission of CN Radical

Atmospheric-Pressure Dielectric Barrier Discharge as an Elemental Ion Source for Gas Chromatographic Analysis of Organochlorines

Direct Production of CH(A2Δ) Radical from Intense Femtosecond Near-IR Laser Pulses

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Direct Production of CH(A²Δ) Radical from Intense Femtosecond Near-IR Laser Pulses