The plasma emission detector (PED) as an element-selective detector for supercritical fluid chromatography

The plasma emission detector (PED) has been shown to be an element specific detector for supercritical fluid chromatography (SFC). The commonly used eluents (CO₂ and N₂O) tend to disturb the He plasma; two different discharge tubes were tested in an attempt to overcome this problem. Promising results were obtained with a concentric dual flow torch design for the element specific detection of Cl, H, and C containing analytes using N₂O as SFC mobile phase.     

Application of an atmospheric pressure helium microwave-induced plasma as an element-selective detector for gas chromatography

An atmospheric pressure helium microwave-induced plasma (MIP) was combined with a gas chromatograph (GC). and used as an element-selective detector for GC. The detection limits, dynamic ranges and selectivities were obtained for H, C, F, Cl, Br, I and S. Such data for nitrogen and oxygen could not be obtained because of the interference from air which was entrained into the system through the leakages of the tubing and the valve system. The detection limits and dynamic ranges for all the elements investigated were in a range between 1.8 and 39pgs^?1 and between 1.6 × 10³ and 1.1 × 10⁵, respectively. Furthermore, the relative sensitivities of C, H, Cl and Br for various compounds were examined. In the cases of carbon and hydrogen, the relative sensitivities were not the same for different compounds containing oxygen and nitrogen. This result may be explained by the incomplete decomposition of such compounds due to the low microwave power (75 W) applied in the present system.     

Development and characterization of chlorine-selective pulsed discharge emission detector for gas chromatography

A novel chlorine-selective pulsed discharge emission detector (Cl-PDED) for gas chromatography has been developed based on a reaction of krypton with chlorine and a unique design of the detector. A krypton ion produced in the krypton-doped helium pulsed discharge reacts with chlorinated compounds within the pulsed discharge to produce an excited species of KrCl* which emits at 221-222 nm. The reaction has the following advantages in respect to the detection of chlorinated compounds: (1) the reaction is an ion-molecule reaction that is 100-1000 times faster than a reaction of neutrals, which greatly enhances the sensitivity; (2) the KrCl* emission wavelength is far separated from interfering C emissions at 193. and 247.3 nm; (3) the KrCl* emission is transparent to air and can be recorded without a helium purge of the monochromator. The detector itself has been designed to have the following features: (1) the detector has a microvolume of the pulsed discharge region, ca. 0.35 microl, which increases the discharge power density to enhance the sensitivity; (2) this microvolume detector allows the use of a low flow-rate of approximately 5 ml/min, which enhances the sensitivity by the lower dilution of the column effluent; (3) the pulsed discharge is sufficiently narrow to replace the monochromator entrance slit, which gives much greater light gathering power; (4) the discharge electrodes are protected with a helium purge to prevent carbon deposition on the electrodes. This new Cl-PDED is the most sensitive chlorine-selective detector with a minimum detectability of approximately 50 fg Cl/s. The selectivity to carbon is 1000. There are no significant carbon emission lines in the KrCl* emission wavelength region, but the carbon continuum interference (stray light) limits the selectivity. The selectivity could be increased if a double monochromator were used to diminish the stray light. The detector linear range is over three orders of magnitude from 40 fg Cl to approximately 130 pg Cl, and the dynamic range is approximately 4 orders of magnitude. The relative standard deviation of the elemental response to chlorinated compounds is about 5%.     

Applications of gas chromatography with an atomic emission detector

An atomic emission detector for gas chromatography has been developed which is, in principle, capable of detecting selectively any element (except helium) which can elute from a gas chromatographic column. Software methods have been developed so far for 23 elements and on isotope, including all of the organic elements along with mercury, lead, tin, silicon, and deuterium. Element-specific analyses are shown for several petroleum, environmental, and aroma samples. A table for the detector's element-specific detection limits, selectivities, and linear dynamic ranges is given for 12 elements and deuterium.     

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.     

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 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.     

Gas chromatography of organic mixtures using an atomic emission detector

Specific features of the combination of gas chromatography with atomic emission detection and the prospects for the determination of components of organic mixtures are considered. Attention is mainly focused on the application of a commercial system developed in 1990 by the Hewlett-Packard Company. The scope and limitations of the method are scrutinized; methods for improving the reliability of the results of analyses are discussed.     

Iodine-doped selective ionization detector for gas chromatography

During initial investigations of a detector for gas chromatography based on modifications of a field-emission argon ionization detector an intriguing selective response phenomenon was identified when iodine vapor was continuously introduced into the detection chamber. The detector was of a simple design consisting of two 1.5 × 0.5 cm concave electrodes mounted in a concentrical ceramic housing. With iodine continuously introduced into the housing via a thermally controlled diffusion tube, certain test compounds of interest, such as valeric acid, triethylphosphate, or aniline, provided analytically significant ionization responses while their hydrocarbon solvents and test compounds went undetected.     

A new photoionization detector for gas chromatography

Summary A new photoionization detector for gas chromatography is discribed. The source of vacuum ultra-violet (VUV) radiation is separated from the ionization chamber by a window and thus the ionization chamber may be run at atmospheric pressure using an intense source of ionizing radiation. The operation consequently is improved and considerably simplified. Except for a ten times reduction in linearity, the performance characteristics of the detector are comparable to those of the flame ionization detector. Filtration of the VUV radiation allows the selectivity to be varied without affecting the dynamic properties of the detector.Z. ternberg, N. Ostoji, Yug. Pat. Appl.     

Direct determination of chromium(III) and chromium(VI) with ion chromatography using direct current plasma emission as element-selective detector

A method is described that utilizes direct current plasma atomic emission spectrometry as an element-selective method of detection for ion chromatographic determination of chromium(III) and chromium(VI) species. The eluting chromium-containing species are detected on the basis of the atomic emission of chromium without any species conversion. Both anion and cation separator columns give similar results when used with varying sample matrices. By employing an on-column preconcentration procedure, the detectable concentrations of the chromium species are reduced to less than 1.0 ppb. This method is applied to the determination of chromium species in human serum, natural water, and industrial process stream samples.     

Hyphenation of a near-infrared Echelle spectrometer to a microplasma for element-selective detection in gas chromatography

The coupling of a near-infrared Echelle spectrometer (NIRES) with a gas chromatograph for element-selective detection is introduced. The miniaturized capacitive plasma device is operated at a frequency of 40.68 MHz and is mounted directly on an Hewlett-Packard HP6890 GC. First results with a mixture of halogenated standard compounds are presented and discussed in terms of the advantages and problems with this system.     

Improved synchronized accumulating radioisotope detector for gas chromatography

A synchronized accumulating radioisotope detector for radio gas chromatography was developed. It comprised seven gas-flow proportional counters each with an inner volume of 10 ml. Every counter tube was connected by a mutual anti-coincidence circuit to reduce the background. The transit time of gas particles in one counter tube could be set to an optimal value between 1 and 4 s by regulating the flow-rate of the counting gas, according to analytical requirements. The improved detector maintained high chromatographic resolution, which suggested the applicability of the apparatus to capillary gas chromatography.     

An improved flame photometric detector for gas chromatography

A simple modification in the flame photometric detector is reported. This modification enables liquid sample injections of up to 50 μl without solvent flame out. The signal to noise ratio is also increased, the baseline has increased stability and dynamic working range and linearity are improved. No loss in specificity is reported for either the phosphorus (526 nm) or sulfur (394 nm) modes. Detection of picogram quantities of chromium is possible using this detector and a 520 nm filter. The modification now allows automatic analysis of pesticide extracts and liquid samples without the use of flame autoignitors.     

A surface ionization detector for capillary gas chromatography

A novel surface ionization detector using a reducing quartz liner and a Mo emitter with a quartz enclosed internal heater for selective measurement of alkylamines by gas chromatography is designed and evaluated.     

An atmospheric-pressure,argon-afterglow detector for gas chromatography

The development of an atmospheric-pressure argon-afterglow, produced from an ozonizer-type discharge tube, for element-selective, multielement detection in gas chromatography is described. Characteristic atomic emission is observed from chlorine, bromine, iodine, carbon, sulfur and phosphorus in organic compounds, with limits of detection ranging from 0.02 ng for phosphorus to 20 ng for bromine. Element-selective detection for several pesticides is demonstrated.     

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.     

Microplasma-based atomic emission detectors for gas chromatography

This paper is an update on the development of microplasmas as detectors for gas chromatography. Direct current (dc), alternating current (ac), and radio frequency (rf) microplasmas developed in recent years will be described with their significant analytical results, which mostly concern the detection of halogens and sulfur. New results will be added which employ a microhollow cathode discharge (MHCD) as excitation source. Emphasis will be given to this microplasma which has already been implemented as an element-selective detector for emission spectrometry and as ionization source for mass spectrometry. The possibility to use it as a multielement-selective detector for gas chromatography will be presented. A discussion of the published detection limits of all these microplasmas is given.     

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.