Applications using the chlorine-selective pulsed discharge emission detector

The use of the chlorine-selective pulsed discharge emission detector (Cl-PDED) for the GC analyses of EPA mixtures 502, 612, 624, organochlorine pesticides, and polychlorinated biphenyls has been demonstrated. The Cl-PDED is the most sensitive chlorine-selective detector with a minimum detectability of 50 fg Cl/s. A constant response/pg Cl was observed for these mixtures regardless of the number of Cl atoms/molecule and structure of the compound to which the Cl atoms are attached. The analysis of standard samples of polychlorinated biphenyls using the Cl-PDED have sensitivities comparable to those of the electron-capture detector; however, the predictable response/pg Cl from the Cl-PDED is preferred over the extremely variable response from the electron capture detector.     

Characterization of chlorinated compounds using a dual chlorine-selective pulsed discharge emission detector-helium-pulsed discharge photoionization detector system

The Cl-selective pulsed discharge emission detector (Cl-PDED) response is dependent only upon the Cl content, irrespective of the molecular structures of the compounds. This provides a simple, fast quantitative method of analysis for chlorinated compounds. The response of the helium-pulsed discharge photoionization detector (He-PDPID) is a function of the molecular structure and the number of photoionizable electrons using the He2 band at 13.5-17.5 eV. The ratio of the responses of the two detectors is independent of concentration and can be used to characterize the Cl-containing compounds along with the retention time, or the ratio can be used as evidence for coelution. The dual Cl-PDED-He-PDPID detector system is a useful tool for peak identification. The effect of coeluting hydrocarbons on the Cl-PDED response was evaluated by spiking a gasoline sample with US Environmental Protection Agency mixture 502. All Cl-PDED responses were greater than 90% of the response in the absence of the hydrocarbons.     

Pulsed discharge emission detector: an element-selective detector for gas chromatography

An element-specific pulsed discharge emission detector (PDED) has been coupled directly with a vacuum UV monochromator so that vacuum UV atomic emissions from Cl, Br, I and S can be observed. The observed sensitivities for the elements are in the range of mid to high pg/s, but can be lowered by direct absorption of the radiation using a vacuum UV radiation photomultiplier tube. A helium pulsed discharge photoionization detector (He-PDPID) was run simultaneously in parallel with the PDED. The chromatograms recorded with the two detectors had similar peak shapes, suggesting that there is no peak tailing in the PDED. The ratio of the detector responses PDED/He-PDPID can be used for qualitative identification of the Cl-, Br-, I- or S-containing compounds.     

Pulsed discharge detector: theory and applications

The pulsed discharge detector (PDD) is a significant advancement in gas chromatography (GC) detector design which can be operated in three different modes: pulsed discharge helium ionization (He-PDPID), pulsed discharge electron capture (PDECD) and helium ionization emission (PDED). The He-PDPID can detect permanent gases, volatile inorganics and other compounds which give little or no response with the flame ionization detector (FID) and has significantly better limits of detection (minimum detectable quantities (MDQs) in low picogram range) than can be achieved with a thermal conductivity detector (typically not lower than 1 ng). The PDECD has similar or better sensitivity (MDQs of 10(-15) to 10(-12) g) than radioactive source ECD but does not require licensing, wipe tests and other administrative or safety requirements which have increased over security concerns. The PDED shows promise as an extremely selective and sensitive elemental detector but a commercial unit is not presently available. In this report, the theory of operation, applications of the PDD and the practical aspects of using this novel detector are presented.     

Pulsed discharge photoionization detector: Application to analysis of chloro alkanes/alkenes

A windowless pulsed discharge photoionization detector (PDPID) is described which uses the emission spectra from the discharge in helium and Ar/Kr doped helium. The emission from helium is a continuum ranging from 13.5–17.7 eV which ionizes all compounds except neon. The emission from 5.4% Ar/He ranges from 9.3–11.8 eV and ionizes most organic compounds and many inorganic compounds. The emission from 1.36% Kr/He consists principally of the resonance lines at 10.6 and 10.1 eV. These PDPIDs are used to analyze a 12 component mixture containing principally chloro alkane/alkene. The relative responses of the PDPID combined with the relative retention time can be used to qualitatively identify the chloro compounds.     

Universal and discriminative detection using a miniaturized pulsed discharge detector in comprehensive two-dimensional GC

A miniaturized pulsed discharge detector (Mini-PDD) has been successfully demonstrated for comprehensive 2-D GC (GC x GC) analysis of pyrolysis gasoline and the pyrolysis GC x GC analysis of a polyethylene copolymer. The detector cell volume of the Mini-PDD is reduced to 25% of the Valco plug-in PDD D-3. An n-C11 peak width at base is 96 ms for the Mini-PDD, about 23% larger than a peak width of 78 ms detected by a flame ionization detector (FID). The Mini-PDD has sufficient response time for most GC x GC applications. When Mini-PDD is operated in helium photoionization mode (Mini He-PDD), it is a universal detector for both inorganic and organic compounds. This is especially useful when detection of water is needed in GC x GC applications. When krypton is doped in the helium discharge gas (Mini Kr-PDD), it can suppress signals of compounds having higher ionization potentials and enhance relative signal intensities of aromatic compounds. The determination of aliphatic to aromatic hydrocarbon ratios is essential to the operation of petroleum crackers. Comparison of the signal from two modes of the Mini-PDD is a simple and fast way to verify the location of aromatics in comprehensive 2-D gas chromatograms.     

Pulsed discharge emission detector — Application to analytical spectroscopy of permanent gases

Summary This publication contains our initial development of a pulsed discharge emission detector (PDED) (patent pending). It uses a pulsed high voltage discharge in helium, which provides a stable source for atomic and polyatomic emission spectroscopy. We have evaluated this detector for both quantitative and qualitative analysis of a range of chemical compounds. Emission spectra observed from the pulsed high voltage discharge are valuable for spectral analysis. The results obtained for selected permanent gases in the ultraviolet, visible and infrared regions of the optical spectrum indicate that these spectra can be used for compound identification after a chromatographic separation. The data are unique in our opinion and serve as a basis for the future development and investigation of the analytical significance of this detection method.Dedicated to Professor Leslie S. Ettre on the occasion of his 70th birthday.     

UV Inactivation of Common Pathogens and Surrogates Under 222 nm Irradiation from KrCl* Excimer Lamps

Germicidal ultraviolet (UV) devices have been widely used for pathogen disinfection in water, air, and on food and surfaces. Emerging UV technologies, like the krypton chloride (KrCl*) excimer emitting at 222 nm, are rapidly gaining popularity due to their minimal adverse effects on skin and eyes compared with conventional UV lamps emitting at 254 nm, opening opportunities for UV disinfection in occupied public spaces. In this study, inactivation of seven bacteria and five viruses, including waterborne, foodborne and respiratory pathogens, was determined in a thin-film aqueous solution using a filtered KrCl* excimer emitting primarily at 222 nm. Our results show that the KrCl* excimer can effectively inactivate all tested bacteria and viruses, with most microorganisms achieving more than 4-log (99.99%) reduction with a UV dose of 10 mJ cm⁻². Compared with conventional UV lamps, the KrCl* excimer lamp exhibited better disinfection performance for viruses but was slightly less effective for bacteria. The relationships between UV sensitivities at 222 and 254 nm for bacteria and viruses were evaluated using regression analysis, resulting in factors that could be used to estimate the KrCl* excimer disinfection performance from well-documented UV kinetics using conventional 254 nm UV lamps. This study provides fundamental information for pathogen disinfection when employing KrCl* excimers.     

Emission spectra of an argon inductively coupled plasma in the vacuum ultraviolet: background spectra from 85 to 200 nm

The background spectra emitted from an argon ICP discharge have been recorded over the spectral range 85 to 200 nm. These vacuum ultraviolet spectra were acquired by coupling the ICP to a 0.5-m Seya-Namioka vacuum monochromator, through a helium purged side-arm. Background features observed include emission from the resonance lines of ArI, and emission from gas impurities such as oxygen, nitrogen, carbon and hydrogen.     

Relative Responses of Noble Gases Using a Pulsed Discharge Helium Photoionization Detector:Theoretical Calculation and Experimental Determination

The relative response factors（RRFs） for noble gas（Ng） were determined on a pulsed discharge helium photoionization detector. Using ab initio method, the atomic orbitals of noble gas were calculated and used to determine the number of ionizable electrons on the basis of the continuous emission of He2. The molar responses of noble gases is well correlated with the number of ionizable electrons.     

气相色谱法测定大气中氪和氙

设计了一套测定气体的可调压进样装置,提出了气相色谱法-脉冲放电氦离子化检测器测定大气中氪和氙的含量。通过采用低温分离、柱程序升温及高效吸气柱消除了样品中基体气体对氪、氙测定的干扰。氪和氙的检出限(3S/N)分别为11 pg和24 pg。     

Multi-element selective radio frequency plasma detector for capillary gas chromatography

A radio frequency plasma detector for element specific detection in gas chromatography is described. The detector is comprised of a radio frequency (300 kHz) discharge between electrodes in helium, and utilizes a low-resolution emission spectrometer to monitor selected spectral emission lines produced when the helium discharge decomposes and excites the atomic constituents in the chromatographic column effluent. The spectrometer is tuned to an atomic emission line in the near-infrared portion of the spectrum, and the emission intensity from the discharge region of a selected line is used to monitor the concentration of the element producing that line. Acceptable detector sensitivity was achieved by the use of a high-throughput optical system. Selectivity was achieved by a combination of correct line selection, plasma and carrier gas purification, and plasma gas doping.     

Pulsed discharge helium ionization detector

Summary A pulsed discharge helium ionization detector (PDHID) (patent pending) for gas chromatography has been developed. This detector uses a non-radioactive pulsed high voltage discharge source for generation of electrons and pulsed collection of these electrons. We have evaluated this detector for the analysis of a wide range of chemical compounds. In this paper the analytes are passed through the discharge since the permanent gases are difficult to ionize. The initial results for the permanent gases indicate that the PDHID can be used as a universal detector of contaminant traces at detection levels on the order of 1–20 pg. The response in this mode of operation is linear over four orders of magnitude.Dedicated to Professor Leslie S. Ettre on the occasion of his 70th birthday.     

Emission spectra of a direct current plasma in the vacuum ultraviolet spectral region from 100 to 200 nm

DCP emission spectra have been recorded over the spectral range, extending from 100 to 200 nm. These spectra were acquired by coupling the DCP to a 0.5-m Seya-Namioka vacuum monochromator through a specially designed, helium purged, glass/quartz side arm. DCP background lines and emission lines of P, S and Cl have been identified and tabulated.     

Helium microwave-induced plasma mass spectrometric detection for reversed-phase high-performance liquid chromatography

Reversed-phase high-performance liquid chromatography (HPLC) is directly coupled to helium microwave-induced plasma mass spectrometry (He MIP-MS) for the element-selective detection of halogenated organic compounds. Absolute detection limits are approximately 50 pg Br for brominated compounds, 1 pg I for iodinated compounds, and 10 ng Cl for chlorinated compounds. The linear dynamic range for Br- and I-containing compounds is 3-4 orders of magnitude. However, the linear range for chlorinated species is severely limited by high background at m/z = 35. The relative standard deviation for repetitive injections is less than 10%. The helium microwave-induced plasma is operated at moderate powers (300-350 W) and with a total helium consumption of 6-8 L/min. The effect of organic solvents on the background mass spectrum is investigated.     

Microwave-induced plasma emission spectrophotometer combined with a photodiode array monitor for capillary column gas chromatography

A microwave-induced plasma emission spectrophotometric detector (MIPD) was used as an element-specific detector for capillary column gas chromatography. The atmospheric pressure microwave helium plasma generated with an original device called a SURFATRON was used as an atomization and excitation source. Combining a photodiode array spectrophotometer with the above system made the emission spectrophotometric detector very powerful. A wide range of spectra could be instantly monitored without any mechanical device. However, the spectrum of atmospheric helium emission plasma was complicated by the presence of air around the plasma discharge. An on-line background correction scheme was developed to handle such complicated spectra.     

Computational study of the reaction of chlorinated vinyl radical with molecular oxygen (C2Cl3 + O2)

Eight exothermic product channels of the reaction of chlorinated vinyl radical (C2Cl3) with molecular oxygen (O2) have been investigated using ab initio quantum chemistry methods. The energetics of the reaction pathways were calculated at the second-order Moller-Plesset Gaussian-3 level of theory (G3MP2) using the B3LYP/6-311G(d) optimized geometries. It has been shown that the C2Cl3 + O2 reaction takes place via a barrierless addition to form the chlorinated vinylperoxy radical complex, which can decompose or isomerize to various products via the complicated mechanisms. Two major reaction routes were revealed, i.e., the three-member-ring reaction mechanism leading to ClCO + CCl2O, CO + CCl3O, CO2 + CCl3, Cl + (ClCO)2, etc., and the OO bond cleavage mechanism leading to O(3P) + C2Cl3O. The other mechanisms are shown to be unimportant. The results are validated by the calculations using the restricted coupled cluster theory [RCCSD(T)] with the complete basis set extrapolation. Variational transition state theory was employed to calculate the individual and total rate coefficients as a function of temperature and pressure (helium). The theoretical rate coefficients are in good agreement with the available experimental data. It was found that the total rate coefficients show strong negative temperature dependence in the range 200-2000 K. At room temperature (297 K), the total rate coefficients are shown to be nearly pressure independent over a wide range of helium pressures (1-10(9) Torr). The deactivation of the initial adduct, C2Cl3O2, is only significant at pressures higher than 1000 Torr. The three-member-ring reaction mechanism is always predominant over the OO bond cleavage.     

Miniaturized dielectric barrier discharge induced chemiluminescence for detection of volatile chlorinated hydrocarbons separated by gas chromatography

A new analytical method was proposed for the detection of volatile chlorinated hydrocarbons (VCHCs) including dichloromethane, 1,2-dichloroethane, chloroform, tetrachloromethane, perfluoromethane and bromoform after gas chromatographic (GC) separation. Atmospheric pressure dielectric barrier discharge (DBD) was miniaturized and used as a GC detector by using chemiluminescence (CL) emission from the reaction of DBD-split VCHCs with luminol solution. The miniaturized DBD-CL detector possessed the advantages of simple construction, very low power consumption, and high sensitivity to many volatile halocarbons, especially VCHCs. The parameters of the detector were optimized by using dichloromethane as a typical analyte. Under the optimized experimental conditions, the limit of detection (LOD) down to sub-nmol can be achieved.     

Chlorine-Selective Detection in Supercritical Fluid Chromatography using a Coulson Electrolytic Conductivity Detector

Abstract

A Coulson electrolytic conductivity detector has been coupled successfully to a supercritical fluid chromatograph, providing chlorine-selective detection. This involves minimal modification of the detector and no modification of the SFC or its operation. The general operating parameters of the SFC/CECD system were established by direct injection of three probe compounds: chlordane, γ-lindane, and hexachlorobenzene. Next, the SFC separation of a test mixture containing phenol, γ-lindane, and several chlorinated phenols and related compounds was optimized using UV-Vis and FID detection. The mixture was then separated using the same chromatographic method but with the CECD in line with the UV-Vis detector. The response of the CECD was linear and selective for chlorinated compounds. Limits of detection for the test mixture by CECD ranged from 80 – 250 ng/μL, corresponding to approximately 14 – 44 ng of chlorine on column, and were dependent on chromatographic conditions, but independent of analyte structure.     

脉冲放电氦光离子化检测器分析有机化合物的性能研究

研究本实验室组装的脉冲放电氦光离子化检测系统上PDPID的性能、各种操作参数对信号的影响、操作最佳化及信号线性。用该系统分析了汽油、酮醇混合物和痕量挥发性有机化合物等样品,它们的色谱图可以同FID相比。