Peculiarities of gas chromatographic analysis of 6N4 volatile hydrides using a helium ionization detector operated in the ionization amplification mode

A pneumovacuum circuit of a Tsvet-800-2 gas chromatograph with a helium ionization detector (HID) in the ionization amplification mode is proposed for controlling limiting trace impurities in ammonia, arsine, monosilane, and phosphine of grade 6N4. The conditions for the preparation and reliable operation of the chromatograph with the HID are systematized. The effect of an additive of (0.0–17.6) × 10^–4 mol % of hydrogen in the carrier gas of the detector on the polarity of its signal on the impurities of oxygen and nitrogen at a level of (0.5–20.0) × 10^–5 mol % is studied. Methods are proposed for eliminating systematic errors in the determination of the concentration of oxygen and nitrogen in the range from 0.5 × 10^–5 to 1 × 10^–3 mol % in 6N4 volatile hydrides, caused by “counter” impurities in the carrier gas, the mechanism of the heteropolar sensitivity of the HID, and irreversible chemical reactions of oxygen traces with phosphine and products of its decomposition on a CaA–ShM zeolite in a separating column of a chromatograph. Gas chromatography analysis of ammonia, arsine, monosilane, and phosphine of grade 6N4 was carried out.     

An atmospheric pressure ionization source based on desorption electrospray ionization technology (DESI) for ion cyclotron resonance mass spectrometry

An atmospheric pressure ionization source based on desorption electrospray ionization technology for a bench-top hybrid FTICR mass spectrometer is described. The ion source was characterized using low-molecular-weight-weight pharmaceutical samples. The dependences of signal intensities on various experimental parameters (solvent composition, surface temperature, spray voltage, etc.) were studied. Based on the results obtained, plausible mechanisms of desorption electrospray ionization for the analytes under the study are discussed.     

Single photo-electron and photon detection in a mercury resonance ionization photon detector (RID)

Avalanche detection of a laser enhanced ionization (LEI) signal has been studied in a resonance ionization detector (RID) cell containing mercury vapor at room temperature. An avalanche multiplication factor of more than 8000 was achieved. The limit of detection of Hg resonance radiation (λ = 253.7 nm) was at the level of 0.5 quantum during the lifetime of the excited 6³P₁⁰ state. Detection of radiation from a conventional CW Hg discharge lamp source with a signal to noise ratio of more than 10⁴ has been achieved.     

Interaction of piezoelectric lead zirconate titanate with 400 MeV/n xenon beam

The characteristics of radiation detector fabricated by stacking some piezoelectric lead zirconate titanate (PZT) elements were studied by irradiating it with a 400 MeV/n xenon (Xe) beam. Comparing between observed results from the detector and calculation results using Bethe–Bloch formula, it was found that the amplitude of the output voltage observed was dependent on the amount of ionization energy loss of Xe ion with PZT.     

Determination of Xenon in Air by a Pulse-discharge Helium Ionization Detector

A pulse-discharge helium ionization detector(Valco, PD-D3-I) was used to measure xenon concentration in air. The dependences of the detector relative response on various gas chromatograph parameters were investigated. Based on the well prepared gas connections for the detector system and optimized gas chromatography(GC) working conditions, the atmospheric xenon concentration could be measured by the cheap GC method with a detection level of 0.7?0^-9(parts by volume). Moreover, the xenon concentration in the ground level air around our laboratory was measured with the result of 0.085?0^-6(parts by volume) and RSD of 0.91%.     

Study of space charge phenomena in d.c. electron-capture detectors

The influence of space charge phenomena on the field and the potential in a d.c. electron-capture detector (ECD) under simplified conditions was studied. The results make it possible to explain the shape of the current-voltage characteristics of a d.c. ECD and the dependence of the sensitivity of such a detector on the electrode distance with positively and negatively polarized sources. All of these dependences studied using an ECD with variable geometry (electrode distances between 0.25 and 30 mm) and a changeable radioactive source (³H, ⁶³Ni, ²⁴¹Am).     

Operation modes of the helium dielectric barrier discharge for soft ionization

Among different applications of dielectric barrier discharge (DBD) plasma, the soft ionization ability is certainly one of the most interesting. In this paper the helium plasma jet, produced by a capillary DBD, penetrating in the ambient atmosphere, has been spectroscopically investigated in dependence on applied voltage and helium flow. It was found that the change of the applied voltage leads to different discharge modes. Based on the measurements of the emission spectra of atomic He and N₂⁺ and N₂ molecules in the capillary and in the plasma jet with high spatial resolution, it can be assessed in which mode, i.e. under which conditions the plasma jet is expected to be most effective for soft ionization of molecules.     

Temperature programmed decomposition studies: high-sensitivity determination of carbon monoxide,carbon dioxide and methane by gas chromatography

Carbon monoxide, carbon dioxide and methane, evolved in very low amount during temperature programmed decomposition of transition metal cluster catalysts, can be determined quickly (<3 min) by gas chromatography on a Porapak S column. Catalytic conversion of the CO and CO₂ to methane makes it possible to use a hydrogen fiame ionization detector. The advantages are that the limit of detection is about 1 ppm (ca. 4.4 × 10^?11 mol cm^?3, STP) and that the procedure is applicable to decompositions studied in helium/oxygen or other reactive gas mixtures.     

Gas spherical ionization chamber

A pressurized ionization chamber detector able to measure radioactive sources in internal 2π or 4π geometry was built in order to characterize alpha and beta radioactive sources, i.e. to calibrate these sources by a relative method, and to test the behavior of gas mixtures in pressurized-gas radiation detectors. The detector we made is of spherical shape and works by collecting in a quasi-uniform electric field the ionization charges resulting from the interaction of ionizing radiation with gas in the sensitive volume of the chamber. An ionizing current proportional to the activity of the radioactive source to be measured is obtained. Pressure inside the detector in standard conditions is maximum 6 × 10⁵ Pa at 22 °C and the maximum allowed voltage is 3000 V. It is presented as a spherical ionization chamber with gas under pressure, geometrical shape, dimensions and structural characteristics, functional and technical parameters and preliminary experimental results obtained from radiation measurements in the laboratory SALMROM of the IFIN-HH.     

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.     

Dissociative ionization of triethylamine molecules on a tungsten surface in an electric field

The surface ionization of triethylamine molecules (M) in accelerating fields of strength F from 2·10⁴ to 4·10⁶ V/cm has been studied under stationary conditions with the aid of mass spectrometry. The predominant formation of (M-H)⁺ fragment ions has been discovered. The logarithm of the relative intensity of the ion currents at T = const varies linearly with the value of F. The temperature dependence of the ion currents I(T) at F = const, which are in good agreement with the experimental dependences and make it possible to determine the kinetic parameters of the reaction, have been obtained with the aid of the theory of monomolecular dissociation of molecules in the gaseous phase and the theory of surface ionization.Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 24, No. 1, pp. 62–67, January–February, 1988.We thank N. D. Potekhina and é. Ya. Zandberg for some useful discussions.     

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.     

Spatially resolved spectroscopic measurements of a dielectric barrier discharge plasma jet applicable for soft ionization

An atmospheric pressure microplasma ionization source based on a dielectric barrier discharge with a helium plasma cone outside the electrode region has been developed for liquid chromatography/mass spectrometry and as ionization source for ion mobility spectrometry. It turned out that dielectric barrier discharge ionization could be regarded as a soft ionization technique characterized by only minor fragmentation similar to atmospheric pressure chemical ionization (APCI). Mainly protonated molecules were detected. In order to characterize the soft ionization mechanism spatially resolved optical emission spectrometry (OES) measurements were performed on plasma jets burning either in He or in Ar. Besides to spatial intensity distributions of noble gas spectral lines, in both cases a special attention was paid to lines of N₂⁺ and N₂. The obtained mapping of the plasma jet shows very different number density distributions of relevant excited species. In the case of helium plasma jet, strong N₂⁺ lines were observed. In contrast to that, the intensities of N₂ lines in Ar were below the present detection limit. The positions of N₂⁺ and N₂ distribution maxima in helium indicate the regions where the highest efficiency of the water ionization and the protonation process is expected.     

A novel and efficient excitation- and ionization-scheme for laser resonance ionization of mercury

A novel, efficient scheme for mercury atomic resonance ionization is proposed and experimentally studied with wavelengths λ₁=254 nm, λ₂=313 nm and λ₃=626 nm. The cross-sections of mercury photoionization from different excited states were estimated using a new imaging method of resonance ionization signal measurement. Almost 100% efficiency of Hg resonance ionization was achieved using the first harmonic of a dye laser at 626 nm to ionize mercury atoms excited into the 6³D₂ state. The photoionization cross-section from this state was found to be 1.5×10⁻¹⁸ cm². Suppression of the ionization signal by coherent effects (electromagnetically-induced transparency) and the efficiency of resonance ionization were also studied.     

A photoionization detector

Summary A photoionization detector (P.I.D.) with separated discharge and detection compartments, enabling detection of eluted substances under normal pressure, has been developed. A detection mechanism was formulated for these conditions and relations for the P.I.D. signal were derived. The detector can measure all substances with ionization potentials less than 11.4 eV. A detection limit of 10^–14 mol/s for benzene, with a linear dynamic range of 10⁴, was attained.     

Indirect hydrogen analysis by gas chromatography coupled to mass spectrometry (GC–MS)

Gas chromatography (GC) is an analytical tool very useful to investigate the composition of gaseous mixtures. The different gases are separated by specific columns but, if hydrogen (H₂) is present in the sample, its detection can be performed by a thermal conductivity detector or a helium ionization detector. Indeed, coupled to GC, no other detector can perform this detection except the expensive atomic emission detector. Based on the detection and analysis of H₂ isotopes by low‐pressure chemical ionization mass spectrometry (MS), a new method for H₂ detection by GC coupled to MS with an electron ionization ion source and a quadrupole analyser is presented. The presence of H₂ in a gaseous mixture could easily be put in evidence by the monitoring of the molecular ion of the protonated carrier gas. Copyright © 2013 John Wiley & Sons, Ltd.     

A novel 2-(2-methyl-2-nitrovinyl)-furan ectoparasitic drug: physicochemical characterization and determination of the raw material by gas chromatography mass spectrometry

2-(2-methyl-2-nitrovinyl)-furan (NVF) has recently been synthesized and the pharmaceutical industry interest in this compound has grown due to its antibacterial, fungicidal and anti-ectoparasitic activities. Therefore, the physicochemical characterization of new drug was conducted. In addition, two rapid, simple and suitable GC methods were developed for determination of NVF. Analyses were carried out with an Agilent DB-5ms capillary column (60 m × 0.25 mm i.d., 0.25 µm film thickness). The GC-FID analysis employed splitless mode of injection, oven/injector/detector temperature of 160/230/280°C and nitrogen carrier at the flow of 5.0 mL min^?1. The GC-MS analysis employed splitless mode of injection, helium carrier at the flow of 1.5 mL min^?1, column temperature program with 2 min at 100°C, ramp at 50°C min^?1 to 260°C and injector and detector temperature of 250 and 290°tC, respectively. The MS conditions were ionization voltage, 70 eV; mass range, m/z 40–350; and ion source temperature, 200°C. The analysis time took less than 6 min. The results obtained in the validation of the methods suggest that these methods are economic, precise, accurate and linear over the range of analysis. The methods were successfully employed during the synthesis of NVF in order to ensure the quality of the raw material.      

Effect of ammonia carrier gas on the response of the flame ionization detector

The effect of using ammonia as a carrier gas on the response of the flame ionization detector (FID) has been investigated. It was found that the FID response, calculated as the effective carbon number (ECN), increased for all the compounds studied when ammonia, rather than helium, was used. The change was 0–0. 9 carbon atom for hydrocarbons, one carbon atom for alcohols and diphenyl ether, and 0.4–1 carbon atom for phenols and ketones. The increase in ECN was larger for amines (0. 8–5 carbon atoms), but these numbers also reflected an improvement in chromatographic performance as a result of reduced adsorption on the column. The largest change in signal-to-noise ratio, a six-fold increase, was obtained for octyl-amine; ratios for hexyl methyl ketone, diisobutyl ketone, dihexyl-amine, dibutylamine, and N-methyloctylamine increased by a factor of 2–3 when ammonia was used as carrier gas. To determine the extent to which the effect on detector response was solely attributable to ammonia, a mixture of 5 % ammonia in nitrogen was used as detector make-up gas with helium as carrier gas. Under these conditions the noise in the FID increased but for most of the compounds studied the signal-to-noise ratio also increased.     

Development of an Atmospheric Pressure Glow Discharge Detector for Capillary Column Gas Chromatography

 The use of the change in the oscillation frequency of the current of a new atmospheric helium glow discharge for sensitive signal detection for gas chromatography is studied. The effluent of a capillary column is directed into the glow discharge cell perpendicular to the axis of the glow discharge that existed between a platinum anode and cathode. A stable discharge is obtained when several hundred volts are applied between the 0.2-mm gap between the anode and cathode. The effects of the electrode gap, discharge voltage and gas flow rate on the baseline frequency and discharge current were investigated. The chromatogram shows that the discharge current and discharge gap have a strong influence on the detector response. The discharge current shows positive peaks; however, frequency peaks are positive or negative depending on the discharge conditions. The response of the detector is in the femto-mole and pico-mole range for nonane and decane. Received August 5, 1997. Revision September 2, 1999