Make-up Gas Research Articles

Gas chromatography coupled with atomic absorption spectrometry — a sensitive instrumentation for mercury speciation

New instrumentation for the speciation of mercury is described, and is applied to the analysis of natural water samples. The separation of mercury species is effected using gas chromatography of derivatized mercury species on a widebore capillary column. The solvent is vented using a bypass valve and the separated mercury species are pyrolysed on-line at 800°C for production of mercury atoms. These are then detected by atomic absorption spectrometry (AAS) at the 253.7 and 184.9 nm lines simultaneously in a quartz cuvette. The use of the 184.9 nm line provides a more than five-fold increase in sensitivity compared with the conventional 253.7 nm line and an absolute detection limit of 0.5 pg of mercury. The dynamic range of the combined analytical lines provides a linear response over more than three orders of magnitude. A number of organic compounds not containing mercury are also detected following pyrolysis, especially at the 184.9 nm line. These background species must not co-elute at the retention times for methyl- and inorganic mercury, as otherwise a positive interference would result. By maximizing the chromatographic resolution and minimizing the band broadening in the cuvette by use of a make-up gas, the retention times of interest are freed from co-eluting background peaks. The instrumentation has been applied to the determination of ng l −1 concentrations of methyl- and inorganic mercury in Lake Constance, Germany and within the Lake Constance drinking water supply organization, Bodenseewasserversorgung (BWV). The accuracy for the sum of methyl- and inorganic mercury has been assessed by comparison with an independent method for total mercury based on AAS detection implemented at BWV. Relative detection limits using 1 litre water samples and 15 ml injections of the final hexane extract were 0.03 ng l −1 for methylmercury and 0.4 ng l −1 for inorganic mercury based on the 3j criterion.

Design and Optimization of a Corona Discharge Ion Source for Supercritical Fluid Chromatography Time-of-Flight Mass Spectrometry

The interfacing of capillary column supercritical fluid chromatography (SFC) to time-of-flight mass spectrometry (TOFMS) through atmospheric pressure chemical ionization (APCI) was investigated. An ion source chamber and a new, flexible, and efficient transfer line from the SFC to the TOFMS system were designed to accommodate the requirements of this study. Ionization of analytes was performed using a corona discharge needle. The interface was equipped with two multiple-axis translation stages for positioning of the transfer line tip and the discharge needle inside the ion chamber. The investigations were oriented toward the optimization of parameters which have a strong effect on the intensity and stability of the analyte signal, including background stability, corona discharge needle positioning in the ion source, transfer line tip and discharge needle relative positioning, curtain gas and makeup gas flow interactions, ion chamber temperature, and elution pressure of analytes from the SFC system.

Evaporative Light Scattering Detection for Supercritical Fluid Chromatography

A high-performance liquid chromatograph-evaporative light scattering detector is modified and interfaced with a supercritical fluid chromatograph. The detector performance is evaluated by monitoring the response of several steroids. Specifically the effects of nitrogen makeup gas flow rate, carbon dioxide modifier type, modifier concentration, evaporative light scattering detector orifice size, and detector temperature are determined. As the nitrogen gas flow rate increases, the response of the analyte decreases, but the increased flow improves peak shape to mimic that obtained with ultraviolet detection. Furthermore, increasing the detector temperature causes the response of the analytes to decrease. A detection limit of 10 ng or less is determined for progesterone and testosterone with 2% and 20% (v/v) methanol-modified carbon dioxide on a Deltabond cyano column (4.6 mm × 15 cm, 5 µm) at 150 mL/min and 1000 mL/min decompressed carbon dioxide. The separations of polyethylene glycols and ginko biloba leaf extract with the optimized conditions

Calculation of elemental ratios by on-column radiofrequency plasma atomic emission detection coupled with capillary gas chromatography

Atomic emission from a 350-kHz helium plasma was evaluated for the calculation of C/Cl and C/Br ratios in compounds separated by capillary gas chromatography. When the plasma was sustained inside the end of a 0.32 mm I.D. fused-silica GC column in 2 ml/min of GC carrier gas + 18 ml/min of make-up gas (helium), 94% of the elemental ratios obtained deviated by less than 20% from the theoretical values. These results with the on-column r.f. discharge were comparable to data obtained with a commercial GC-atomic emission detection system based on a microwave-induced plasma.

Effect of make-up gas in on-column atomic emission spectrometric detection for capillary gas chromatography

The effect of make-up gas was studied for capillary gas chromatography (GC) coupled with on-column atomic emission spectrometric detection (AED), where a 350 kHz plasma was sustained inside the end of a 0.32 mm i.d. capillary GC column. For selective detection of Cl and Br both the plasma background characteristics and elemental responses were stabilized during temperature programmed analysis when 10–15 ml min–1 of helium were added as a make-up gas. In addition, chromatographic peaks were protected against tailing, while Cl and Br were detected at the 4 pg s–1 level.

Gas chromatographic determination of organometallic compounds with atomic emission detection

We describe the effect of a modified gas chromatography-atomic emission detection (GC-AED) instrumental setup on the analysis of organometallic compounds. It is shown that the installment of an additional makeup gas flow positively effects the performance of the Hewlett Packard (HP) atomic emission detector. In addition, a partially sealed transfer line capillary end providing a narrowed central flow substantially improved the sensitivity. Lower detectable levels were achieved for several of the investigated elements. The parameters makeup gas flow, additional makeup gas flow, and transfer line outlet diameter were optimized and their effects on the peak shapes and detectable levels were evaluated. GC-AED analysis was performed for the first time for the speciation of volatile metal-containing compounds present in diesel particulate matter. Compounds containing iron, chromium, and manganese were successfully detected. © 1996 John Wiley & Sons, Inc.

Methanol synthesis from carbon dioxide on CuO-ZnO-A [formula omitted]2O 3 catalysts

Activities and durabilities of CuO-ZnO-A l 2O 3 catalysts for methanol synthesis from H 2, CO 2 and CO were measured in the once-through reaction test using a microreactor. Catalysts of different compositions were prepared by the precipitation method. Activity tests were conducted under the following conditions: temperatures, 210, 230, 250°C; pressures, 40, 80 kgf/cmG; GHSV, 6000 h −1; feed gas composition, H 2/CO 2/CO=77/17/6 (mole%). The result at 250°C, 40kgf/cmG showed that the rates of CO 2 and CO conversion into CH 3 OH were 22–24 % and these values were roughly equal to the equilibrium value (25%). Durability tests at 230°C, 40kgf/cmG found that these catalysts were roughly the same in initial activity for methanol synthesis but considerably different in durability. Additional durability test has been made on the catalyst selected on the basis of the microreactor tests results by recycling unreacted gases, using a bench-scale test plant. The recycling test with this catalyst, conducted for 1000 hours, showed that more than 90% of supplied CO 2 were converted into CH 3 OH under the following conditions: temperature, 240°C; pressure, 80kgf/cmG; make-up gas composition, H 2/CO 2=75/25; GHSV, 5000h −1; recycle ratio, 4 N l /N l .

Electron-capture detection in reversed-phase liquid chromatography using packed-capillary columns

A new type of interface has been developed for the direct coupling of packed-capillary reversed-phase liquid chromatography with electron-capture detection. This interface allows the detection of relatively non-volatile and/or polar compounds, and simply consists of a fused-silica capillary (50 μm I.D.) inside of a stainless-steel capillary (0.32 mm I.D.) connecting the analytical column with the detector through the oven wall. The make-up gas is used for cooling of the fused-silica capillary. With flow-injection analysis the influence of several parameters (e.g. flow-rate of the make-up gas and mobile phase, oven temperature) on the performance of the total system (i.e. band broadening, sensitivity) has been studied. Using optimal conditions (flow-rate 2 μl min −1, make-up gas 40 ml N 2 min −1, oven temperature 300 °C, injection volume 60 nl) separation and detection of mononitroanilines, chlorophenols, pesticides and benzodiazepines have been performed. Detection limits are in the range of 10–450 pg (0.2–7 mg 1 −1) under reversed-phase conditions. Large-volume injections up to 15 μl, using a non-eluting solvent (water) to focus the analytes on top of the column, have been performed to increase the sensitivity of the system. This technique increased the concentration sensitivity with 2–3 orders of magnitude allowing the detection of ca. 150 ng 1 −1 of chlorophenols in river Meuse water.

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.

Effect of ammonia on the response of the nitrogen phosphorus detector (NPD)

AbstractThe effect of ammonia as a carrier gas and as a make‐up gas on the response of the nitrogen phosphorus detector (NPD) was investigated. This study showed that the response of the NPD increased 2.2 to 10.3 fold for all studied aliphatic amines when 5% ammonia in nitrogen was used as a make‐up gas. This increase was about 5.3 to 22.8 fold when ammonia was used as a carrier gas. The response of the NPD for nitro‐aromatic compounds increased 1.8 to 3.1 fold using 5% ammonia as a make‐up gas and 4.2 fold when ammonia was used as a carrier gas. The higher response obtained using ammonia as the carrier gas is related to improvements in the chromatographic performance (reduced tailing). The response of the NPD to phosphorus compounds was about 1.5 times higher using ammonia either as a carrier gas or as a make‐up gas compared to nitrogen. Although the noise of the NPD increased, the signal‐to‐noise ratios for both amines and phosphorus compounds improved with the use of ammonia.

Fast, high temperature and thermolabile GC—MS in supersonic molecular beams

This work describes and evaluates the coupling of a fast gas chromatograph (GC) based on a short column and high carrier gas flow rate to a supersonic molecular beam mass spectrometer (MS). A 50 cm long megabore column serves for fast GC separation and connects the injector to the supersonic nozzle source. Sampling is achieved with a conventional syringe based splitless sample injection. The injector contains no septum and is open to the atmosphere. The linear velocity of the carrier gas is controlled by a by-pass (make-up) gas flow introduced after the column and prior to the supersonic nozzle. The supersonic expansion serves as a jet separator and the skimmed supersonic molecular beam (SMB) is highly enriched with the heavier organic molecules. The supersonic molecular beam constituents are ionized either by electron impact (EI) or hyperthermal surface ionization (HSI) and mass analyzed. A 1 s fast GC—MS of four aromatic molecules in methanol is demonstrated and some fundamental aspects of fast GC—MS with time limit constraints are outlined. The flow control (programming) of the speed of analysis is shown and the analysis of thermolabile and relatively non-volatile molecules is demonstrated and discussed. The tail-free, fast GC—MS of several mixtures is shown and peak tailing of caffeine is compared with that of conventional GC—MS. The improvement of the peak shapes with the SMB—MS is analyzed with the respect to the elimination of thermal vacuum chamber background. The extrapolated minimum detected amount was about 400 ag of anthracence- d 10, with an elution time which was shorter than 2s. Repetitive injections could be performed within less than 10 s. The fast GC—MS in SMB seems to be ideal for fast target compound analysis even in real world, complex mixtures. The few seconds GC—MS separation and quantification of lead (as tetraethyllead) in gasoline, caffeine in coffee, and codeine in a drug is demonstrated. Controlled HSI selectivity is demonstrated in the range of 10 1 to 10 4 anthracene/decane which helped to simplify the selective analysis of aromatic molecules in gasoline. The contribution of SMB to the operation of the fast GC—MS is summarized and the compatibility with conventional GC having a megabore column is shown. Splitless injections of 100 μL sample solutions for trace level concentration detection is also presented (with a conventional GC).

Determination of oxygen-containing additives in gasoline by gas chromatography–microwave-induced plasma atomic emission spectrometry

The development and characterization of a method for the determination of oxygen-containing (oxygenated) species in a complex mixture of hydrocarbons is described. A microwave-induced plasma (MIP) atomic emission detector is coupled to a gas chromatograph, and atomic oxygen emission is monitored as an indication of oxygenated compounds in the gas chromatograph effluent. On-line helium purification and the use of a tangential-flow torch provide conditions ideal for oxygen-selective analysis without make-up gases or extensive background correction. Furthermore, large amounts of solvent or sample do not extinguish the plasma so samples can be analysed directly without dilution, addition of reagent gases or solvent venting procedures. Both axial and lateral viewing positions were investigated for analytical use. Detection limits for oxygen were 1 ng s–1 for both axial and lateral positions but sensitivity was higher in the axial position. However, selectivity over carbon in the lateral position was 4850 : 1 compared with 155 : 1 in the axial position. The gas chromatography MIP method was applied, using lateral viewing, to the analysis of alcohols in National Institute of Standards and Technology (NIST) reference fuel standards and to commercial gasoline samples collected from Columbia, SC, USA and Greensboro, NC, USA. Experimental results of oxygen-selective analysis of NIST reference fuel are in good agreement with the certified values. Results obtained for the determination of oxygenated compounds in gasoline samples further demonstrate the usefulness of the method for the analysis of a complex mixture of hydrocarbons. Most spike recoveries were within 10% of the expected values. Examples of oxygen-selective chromatograms are presented to demonstrate the usefulness and selectivity of the method.

Performance of a silica T-tube interface for the determination of cadmium, copper, lead, zinc and mercury in flowing liquid streams by atomic absorption spectrometry

An all-silica interface for coupling flowing liquid streams with on-line monitoring by atomic absorption spectrometry (AAS), was evaluated for the determination of Cd, Cu, Pb, Zn and Hg. In operation, the mobile phase was nebulized by thermospray effect into a hydrogen–oxygen diffused flame maintained within a heated pyrolysis chamber. The expanding gases entrained the combustion products into an optical tube mounted within the optical beam of the spectrometer. Low to sub-nanogram limits of detection for each of the elements were achieved with either an aqueous or a methanolic mobile phase. Although optimal operating conditions of the interface were somewhat different for each analyte element, the optimum total flow of make-up gases and the ratio of H2:O2, as predicted by response surface models, were surprisingly similar for Cd, Cu, Pb and Zn detection. Yet the ratio of O2:H2 flow to the interface was important only for the determination of Pb. By contrast to the other metals, determination of Hg was optimized by turning off the flows of these gases to the interface. The response to Hg was increased 6-fold by substituting methanol for water as the mobile phase carrier. By contrast, the AAS responses to the other elements was unaffected by this change in carrier solvent. The utility of the high-performance liquid chromatography (HPLC)–AAS interface was demonstrated by monitoring the Cd, Zn or Cu bound to a crude metallothionein isolate from a single freshwater mollusc by gel permeation HPLC.

Design and use of a thermal conductivity detector at reduced pressure for temperature-programmed capillary gas chromatography

Based on a systematic study of the response characteristics of a thermal conductivity detector (TCD) at reduced pressure, a newly designed TCD was constructed and evaluated for use in temperature-programmed capillary gas chromatography. The effective cell volume is as low as 1.3 μl (physical volume 100 μl), and there is no dead corner along the sensing path. Capillary columns of I.D. ⩾0.25 mm can couple directly with the TCD without a make-up gas. The detector response time is less than 0.1 s, the linear dynamic range is about four orders of magnitude and the detection limit is about 10 ppm (v/v) for octadecane. In the split injection mode, a simple configuration of the capillary inlet system offers a constant carrier gas flow-rate through the column with temperature-programmed operation. Practical examples are given that demonstrate the applicability of this detector and the system.

On-column bromine- and chlorine-selected detection for capillary gas chromatography using a radio frequency plasma

A 350-kHz rf plasma sustained inside the end of a 0.25- or 0.32-mm-i.d. fused-silica GC column was evaluated for element-selective detection of brominated and chlorinated compounds separated by gas chromatography. Due to the small volume of the plasma cell, dilution of the GC efluent with make-up gas was unnecessary and a stable 25-W plasma was maintained in only 1.5-5 mL/min GC carrier gas. With the plasma sustained in pure helium, carbon formed from eluting material was deposited in the plasma region causing serious peak tailing and loss of sample

Sensitive flame ionization detector for the determination of traces of atmospheric hydrocarbons by capillary column gas chromatography

A sensitive flame ionization detector was developed for capillary column gas chromatography. The detector used no make-up gas and lower flow-rates of hydrogen and air to suppress detector noise and to achieve maximum response. The detector was responsive down to the 10 −13 g level for C 2–C 11 hydrocarbons. Atmospheric hydrocarbons could be determined at parts per billion or parts per trillion levels by using gas chromatography with the detector via cryogenic concentration of a small volume of air sample.

Operation of adsorbers for purifying ammonia synthesis make-up gas

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTOperation of adsorbers for purifying ammonia synthesis make-up gasGregory R. SchoofsCite this: Ind. Eng. Chem. Res. 1993, 32, 4, 613–619Publication Date (Print):April 1, 1993Publication History Published online1 May 2002Published inissue 1 April 1993https://doi.org/10.1021/ie00016a007RIGHTS & PERMISSIONSArticle Views84Altmetric-Citations2LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts Get e-Alerts

The atomic emission detector in gas chromatographic trace analysis

The atomic emission detector for element-selective detection in gas chromatography shows high selectivities for many elements vs. carbon, coupled with a large dynamic range and relatively low limits of detection. In this work we report on our experience with the detector with respect to the response in dependence on the chemical form of the element monitored, the limit of detection, the selectivity vs. carbon and efforts to improve the limit of detection by varying the flow rate of the make-up gas. Applications discussed include the quantification of a dibenzodioxin/dibenzofuran standard solution, dual-isotope monitoring and the determination of elemental ratios in organic compounds. The work centers on the elements carbon, sulphur, chlorine, bromine and oxygen.

Response characteristics and operating limits of thermal conductivity detectors at reduced pressure in capillary gas chromatography

The response characteristics of thermal conductivity detectors (TCDs) at reduced pressure, especially in the pressure range 0.2–25 Torr, was studied systematically. It was found that there existed an operational pressure limit ( P min) below which the gas flow in the detector cell was no longer laminar and the detector response became pressure dependent. In addition, the noise level increased exponentially as the pressure decreased below P min. When the detector was operated at pressures above P min, both the responses and relative responses of the TCD were constant for a given concentration of a sample. P min as a function of temperature, cell structure and carrier gas properties was interpreted theoretically and verified experimentally. Using this technique, coupling of capillary columns directly with a conventional TCD without make-up gas was realized while maintaining the efficiency of the capillary columns and the concentration sensitivity of the detector.

Optimizing electron-capture detector performance for gas chromatographic analysis of polychlorinated biphenyls

A modified simplex technique has been applied to optimize the performance of an electron-capture detector under constant-current and constant-frequency pulse modes for the gas chromatographic analysis of polychlorinated biphenyls. Optimal performance was obtained by adjusting the four experimental parameters of pulse voltage, detector temperature, make-up gas flow rate, and reference current (or pulse frequency) using the signal-to-noise ratio of the eluting peak as the criterion. The results show that constant-current pulse mode has better sensitivity and dynamic range whereas the constant-frequency pulse mode has the lower detection limit. Subsequent principal component factor analysis indicated that similar performance is achievable using only three parameters.