Gas Chromatography With Atomic Emission Detection Research Articles

Characterization and Identification of the most Refractory Nitrogen Compounds in Hydroprocessed Vacuum Gas Oil

There is currently a growing need to hydroprocess heavier and tougher crude oils with increased nitrogen content. Therefore, hydrodenitrogenation (HDN) has become a critical hydroprocessing reaction, making it essential to gain insight into which nitrogen-containing compounds are the most difficult to treat. In the present article, we describe the identification of nitrogen compounds in severely pretreated feed for hydrocracking (HC). The nitrogen compounds in the N-slip to the hydrocracker are isolated and concentrated on solid-phase extraction (SPE) columns and identified by gas chromatography mass spectrometry (GC-MS), gas chromatography with atomic emission detection (GC-AED), and nuclear magnetic resonance (NMR) spectroscopy. Density functional theory (DFT) calculations support the structural identification and are further used to investigate the reactivity. We find that the most refractory organic nitrogen compounds in the N-slip belong to the family of 4,8,9,10-tetrahydrocyclohepta[def]carbazoles. ...

Matrix solid-phase dispersion and solid-phase microextraction applied to study the distribution of fenbutatin oxide in grapes and white wine

The fate of the acaricide fenbutatin oxide (FBTO) during the elaboration of white wine is evaluated. Matrix solid-phase dispersion (MSPD) and solid-phase microextraction (SPME) were used as sample preparation techniques applied to the semi-solid and the liquid matrices involved in this research, respectively. Selective determination of FBTO was achieved by gas chromatography with atomic emission detection (GC-AED). GC coupled to mass spectrometry was also used to establish the identity of FBTO by-products detected in must and wine samples. MSPD extractions were accomplished using C18 as dispersant and co-sorbent. Sugars and other polar interferences were first removed with water and water/acetone mixtures, then FBTO was recovered with 8 mL of acetone. When used in combination with GC-AED, the MSPD method provided limits of quantification (LOQs) in the low nanogram per gram range, recoveries around 90% and relative standard deviations below 13% for extractions performed in different days. Performance of SPME for must and wine was mainly controlled by the extraction temperature, time and fibre coating. Under final conditions, FBTO was extracted in the headspace mode for 45 min at 100 degrees C, using a 100 microm poly(dimethylsiloxane)-coated fibre. The achieved LOQs remained around or below 0.1 ng mL(-1), depending on the type of sample, and the inter-day precision ranged from 10% to 13%. FBTO residues in grapes stayed mostly on the skin of the fruit. Although FBTO was not removed during must and white wine elaboration, it remained associated with suspended particles existing in must and lees, settled after must fermentation, with a negligible risk of being transferred to commercialised wine. On the other hand, two by-products of FBTO (bis and mono (2-methyl-2-phenylpropyl) tin) were identified, for first time, in must and final white wines obtained from FBTO treated grapes. Found values for the first species ranged from 0.03 to 0.9 ng mL(-1).

Pressurized liquid extraction followed by gas chromatography with atomic emission detection for the determination of fenbutatin oxide in soil samples

A novel method for the determination of the miticide bis[tris(2-methyl-2-phenylpropyl)tin] oxide, also known as fenbutatin oxide (FBTO), in agricultural soils is presented. Pressurized liquid extraction (PLE) followed by analyte derivatization and extraction into isooctane was the used sample preparation approach. Selective determination was achieved by gas chromatography with atomic emission detection (GC-AED). Influence of different parameters on the performance of the extraction process is thoroughly discussed; moreover, some relevant aspects related to derivatization, determination and quantification steps are also presented. As regards PLE, the type of solvent and the temperature were the most relevant variables. Under optimized conditions, acetone, without any acidic modifier, was employed as extractant at 80°C. Cells were pressurized at 1500psi, and 2 static cycles of 1min each were applied. Acetone extracts (ca. 25mL) were concentrated to 1mL, derivatized with sodium tetraethyl borate (NaBEt4) and the FBTO derivative, resulting from cleavage of the Sn–O–Sn bond followed by ethylation of the hydroxyl fragments, extracted into isooctane and determined by GC-AED. Under final working conditions, the proposed method provided recoveries from 76 to 99% for spiked soil samples, a limit of quantification of 2ngg−1 and an acceptable precision. Analysis of samples from vineyards sprayed with FBTO, confirmed the persistence of the miticide in soil for more than 1 year after being applied.

Isolation and quantification of dialkylmercury species by headspace solid phase microextraction and gas Chromatography with Atomic Emission detection

A methodology to quantify dialkylmercury compounds using Headspace Solid Phase Microextraction (HS-SPME) and Gas Chromatography with Atomic Emission Detection (GC-AED) was developed. The parameters for Hg detection were optimized by factorial design and response surfaces. Univariate experiments were employed to determine the HS-SPME conditions; 75 μm Carboxen / PDMS and 65 μm PDMS / DVB were the best fibers. However, the former was excluded from further experiments due to extensive thermal degradation of analytes during desorption. The optimized procedure allowed detection of the analytes from aqueous samples with LOD of 1.7 ng L-1 and 0.2 ng L-1 for dimethyl- and diethylmercury, respectively. The analytical curves are linear in the range from 36 to 180 ng L-1 (Me2Hg) and 38 to 190 ng L-1 (Et2Hg), with LOQ of 38 ng L-1 (Me2Hg) and 29 ng L-1 (Et2Hg) and correlation coefficients of 0.998 for Me2Hg and 0.999 for Et2Hg.

Influence of Puffing Parameters and Filter Vent Blocking Condition on Nicotine Fate in a Burning Cigarette - Part 1. Full Flavor Cigarettes

Abstract Cigarette testing regulations based on more intensive puffing conditions than standard Federal Trade Commission/International Organisation for Standardization (FTC/ISO) conditions, together with intentional filter vent-blocking of cigarettes during testing, are currently required in some countries. Recently, an initial recommendation under the auspices of the Framework Convention on Tobacco Control, has called for international machine-testing of cigarettes with a 55 cc/30 s/2 s puffing regimen after 100% filter vent-blocking. While much is currently known regarding changes in smoke yields with different machine smoking parameters, a more limited understanding of potential changes in smoke composition exists. In the present work, the influence of smoking conditions on nicotine fate in a burning cigarette was studied by gas chromatography with atomic emission detection (GC-AED) using core-injected nicotine-d4. Tobacco rods were injected via a syringe to a fixed length with a constant volume of a methanol solution of known concentration of deuterated nicotine. Four different puffing conditions and two different vent-blocking conditions were studied. GC with mass spectrometric detection was used to identify the deuterium-labeled compounds that gave an enhanced deuterium AED-response. A comparison of the distribution of compounds containing deuterium in the mainstream smoke, sidestream smoke, and cigarette remains (butt and ash) of a full flavor cigarette brand under the four smoking conditions studied indicated that a greater percentage of labeled nicotine remained intact during the smoking process as the intensity of the puffing regimen increased. As smoking regimen intensity increased, the amounts of nicotine pyrolysis and oxidation products detected in sidestream smoke decreased, while marginal increases in these compounds were observed in mainstream smoke and in the cigarette butt. The sidestream/mainstream nicotine ratio decreased significantly as smoking intensity increased. Small amounts of intact nicotine were observed in the sidestream vapor phase; however, nicotine was not observed in mainstream vapor phase samples.

Determination of the Elemental Composition of Hydrocarbon Mixtures by Gas Chromatography with Atomic Emission Detection: Increasing the Accuracy

In this work, the accuracy of the ratio of the numbers of carbon and hydrogen atoms (nC/nH) determined in the molecules of the components of aliphatic hydrocarbon mixtures by gas chromatography with atomic emission detection (GC-AED) is studied as a function of the oxygen concentration in helium. It is shown that the highest accuracy is achieved at about 9% of oxygen, which is the highest oxygen concentration possible for the Agilent model G2350A GC-AED device. At the standard oxygen concentration (about 1.5%) recommended by the manufacturer, the accuracy of the nC/nH ratios was five to ten times lower. It is shown that improving the accuracy of the nC/nH ratios at the maximum oxygen concentration in plasma is followed by an increase in the detection limit approximately by an order of magnitude.

Capillary gas chromatography with atomic emission detection for pesticide analysis in soil samples.

A method for the simultaneous determination of 10 pesticides (organochlorines, organophosphorus compounds, and pyrethrins) in soils using capillary gas chromatography with atomic emission detection (GC-AED) is reported. Soil samples are first "cleaned-up" with 25 mL of an ascorbic acid solution (pH 2.15). The aqueous phase is extracted with ethyl acetate, and the solid residue is then extracted twice with 10 mL of ethyl acetate. The three resultant organic extracts are combined, concentrated to dryness, and reconstituted in 1 mL of acetone. The pesticides are selectively detected by monitoring chlorine and bromine in the first run and sulfur emission line wavelength in the second run. Each chromatographic run takes 19 min. Detection limits are between 25 and 75 pg, depending on the compound, which corresponds to 1.7 and 5.0 ng/g in the soil samples, respectively. Recoveries of the pesticides from spiked preparations result in an overall mean recovery of 95.3% (n = 120) at fortification levels ranging from 10 to 60 ng/g, depending on the compound. The method is reliable and can be useful for routine monitoring in soils.

Determination of pesticides in waters by capillary gas chromatography with atomic emission detection.

Capillary gas chromatography with atomic emission detection (GC-AED) was successfully used to separate and quantify 14 pesticides (organochlorines, organophosphorus compounds and pyrethrins) in water samples after liquid-liquid extraction with ethyl acetate. Monitoring the emission lines for elements such as chlorine, bromine and sulfur ensures nearly specific chromatograms for these elements, and markedly increases selectivity. Calibration curves were obtained by plotting peak area versus concentration and the correlation coefficients relating to linearity were at least 0.999. Each chromatographic separation takes 21 min and, since two injections are necessary, it requires approximately 1 h to analyze one sample. The method shows a precision of 4.3-8.2% (RSD), depending on the compound. The application of liquid-liquid extraction with ethyl acetate led to recoveries from spiked samples ranging from 76 to 113%. The sensitivity and linearity for the elements chlorine, sulfur, nitrogen and phosphorus were checked under the optimized conditions at their customary emission wavelength. The sensitivity and linearity for these compounds decreased in the order (atom and emission wavelength) Cl (479 nm)>S (181 nm)>P (178 nm)>N (174 nm). A study of the GC-AED system's response to chlorine concentration in eight pesticide molecules was performed and a linear relationship was found with a correlation coefficient of 0.987.

Analysis of Malodorous Sulfur Gases and Volatile Organometalloid Compounds in Landfill Gas Emissions Using Capillary Gas Chromatography with Programmed Temperature Vaporization Injection and Atomic Emission Detection

Volatile compounds containing Group V and Group VI elements in landfill gases are of concern as a source of toxic pollutants and unpleasant odors. Conventional analytical techniques for these compounds e.g. ICP-MS, ICP-AES are complicated, expensive and time consuming. The use of a simple programmed temperature vaporization injection (PTV) technique coupled to gas chromatography with atomic emission detection (GC-AED) has been successfully demonstrated to identify compounds containing arsenic, antimony, and sulfur in landfill gas. With an adapted PTV injection system (using a combination of a ten-port and a six-port Valco valves), problems associated with AED discharge tube damage due to high carrier gas flow rate during sample loading can be overcome. The gas samples generated from both a laboratory biowaste digester and a domestic landfill site were characterized using these techniques. Large sample gas volumes were adsorbed onto a cooled sorbent trap containing Porapak Q, followed by rapid liberation onto a porous layer open tubular column (PLOT) using programmed thermal desorption. Arsenic and antimony were also detected in the landfill leachate collected from the same landfill site using hydride generation-atomic absorption spectrometry (Hy-AAS). The efficiency of different traps has also been compared.

Analysis and Occurrence of Polybrominated Diphenyl Ethers in Washington State Freshwater Fish

A method is described for analyzing polybrominated diphenyl ethers (PBDEs) in fish tissue using gas chromatography with atomic emission detection (GC/AED) and quantitation by compound independent calibration (CIC). The method has the advantage of an element-selective response, including selectivity between bromine and chlorine. An analysis of fish tissue samples from selected locations in Washington State showed total PBDE concentrations ranged from 1.4 microg/kg (wet weight) in rainbow trout from a remote spring-fed stream to 1,250 microg/kg in mountain whitefish from the urbanized Spokane River. Tetra and penta isomers were the major compounds present. There appear to be substantial between-species differences in the ability of fish to metabolize PBDEs.

Photochemical Desulfurization and Denitrogenation Process for Vacuum Gas Oil Using an Organic Two-Phase Extraction System

The simultaneous removal of sulfur- and nitrogen-containing compounds from vacuum gas oil (VGO), based on the combination of UV irradiation and liquid−liquid extraction using an oil/acetonitrile two-phase system, has been investigated. Detailed desulfurization and denitrogenation reactivities for the various compounds in VGO have also been studied by means of field ionization mass spectrometry (FI-MS) and gas chromatography with atomic emission detection (GC-AED), respectively. When VGO and acetonitrile are mixed and photoirradiated, the sulfur and nitrogen compounds in the VGO are distributed into the acetonitrile phase and photodecomposed there to form highly polarized compounds, which do not distribute into the lower-polarity VGO. The successive removal of these compounds from VGO to acetonitrile can therefore be carried out under moderate conditions, such that the sulfur and nitrogen contents for the VGO are decreased simultaneously to less than 1% of the feed values. FI-MS and GC-AED analyses reveal that dinaphthothiophenes, tetrahydrodinaphthothiophenes, tetrahydrodibenzothiophenes, and carbazoles, having large carbon numbers of the alkyl substituents, are the most difficult compounds to remove by the present photochemical organic two-phase extraction process. The removal efficiencies for sulfur and nitrogen compounds obtained from VGO were compared with the results obtained for light oil feedstocks, and the applicability of the present process to the refining of VGO was examined. From a consideration of the above results, a fully organized overall refining process for petroleum-derived middle and heavy feedstocks has been developed.

Multiresidue Screening of Pesticides in Foods Using Retention Time Locking, GC-AED, Database Search, and GC/MS Identification

Fruit and vegetable extracts were screened for over 400 pesticides by gas chromatography with atomic emission detection (GC-AED) and an experimental database. A technique called retention time locking was used to match GC-AED and GC with mass spectrometry (MS) retention times to those of the database. Samples were analyzed for sulfur, nitrogen, phosphorus, and chlorine by GC-AED. Possible pesticides were suggested by database search and identified by GC/MS. Forty-four pesticide standards were analyzed to determine the precision of retention time matching and the accuracy of the database search. Analytical retention times matched database retention times within 0.32 min. Using elemental criteria, the database search identified the correct compound for 41 of 44 pesticide standards. For blind spikes of fruit and vegetable extracts, the database suggested 22 of 26 spiked pesticides as matches. Nineteen were identified by GC/MS. The combination of retention time locking, GC-AED, database search, and GC/MS can be a powerful tool for identifying pesticides in a complex matrix.

Identification of Volatile and Extractable Chloroorganics in Rain and Snow

Organics enriched from samples of rain, snow, and glacier ice were analyzed to determine the chemical structure of the chloroorganic compounds that were most abundant in such media. Gas chromatography with atomic emission detection (GC-AED) was used to provide an overview of the presence of volatile and extractable chloroorganics at four sites in Europe and one site in Antarctica. Real samples and isomer-specific standards were then analyzed by gas chromatography with mass-spectrometric detection (GC-MS) to identify and confirm the structure of the chloroorganics that had been detected in the GC-AED analysis. The results revealed that of the volatile chloroorganics found in the samples, dichloronitromethane, a compound not previously reported to occur in the ambient environment, was often present in the highest concentration (up to 130 ng L-1). Chlorobenzenes were detected mainly as 1,4-dichlorobenzene and minor amounts of 1,3- and 1,2-dichlorobenzene and one isomer of tetrachlorobenzene (1,2,4,5- or 1,2,...

Improved Measurement of Sulfur and Nitrogen Compounds in Refinery Liquids Using Gas Chromatography--Atomic Emission Detection

The measurement of sulfur and nitrogen compounds in refinery liquids is an important analysis for the petroleum industry. Gas chromatography with atomic emission detection (GC-AED) provides a useful means of selectively detecting these compounds. This article presents a GC-AED method optimized for the analysis of sulfur and nitrogen compounds in gasoline through diesel-range materials. By optimizing such parameters as element wavelength, detector gas flow rates, and chromatographic conditions, the selectivity in the presence of hydrocarbons is increased 10-fold for sulfur and by more than 100-fold for nitrogen. These gains in selectivity result in the ability to measure sulfur and nitrogen at low parts-per-million levels.

Capillary gas chromatography combined with atomic emission detection for the analysis of DDT and metabolites

Capillary gas chromatography with atomic emission detection (GC-AED) was evaluated for the determination of DDT and metabolites in biological samples. Utilizing chlorine-selective detection at 479 nm, DDT, DDE, and DDD were quantified down to the 20 ng/g (fat weight) level ( S N = 10 ) in cod liver oil, while the detection limit was 6 ng/g ( S N = 3 ). With splitless injection performed in the pressure programmed mode, DDT and related compounds were quantified based on a single chlorine calibration curve (universal calibration). The quantitative data obtained by GC-AED were in excellent accordance with similar results from capillary gas chromatography with electron capture detection (GC-ECD), while the procedure for calibration was simplified with the former technique.

Interlaboratory evaluation of an off-line supercritical fluid extraction and gas chromatography with atomic emission detection method for the determination of organotin compounds in soil and sediments

A collaborative study was conducted, with eight laboratories participating, to determine the method accuracy and precision of an off-line supercritical fluid extraction (SFE) method for organotin compounds. This method involves extraction of organotin compounds from solid matrixes with supercritical carbon dioxide, modified with 5% methanol, at 450 atm and 60°C for 20 min in the static mode followed by 30 min in the dynamic mode. The extracted material was collected in either methylene chloride or on a C 18-bonded silica trap followed by a methylene chloride rinse. The extracted material was derivatized with pentyl magnesium bromide and analyzed by gas chromatography with atomic emission detection (GC-AED). The study design was based on the AOAC blind-replicate design with balanced replicates. The study samples consisted of three solid matrixes that were spiked with organotin compounds at 1000 ng/g (as Sn) and one unspiked matrix that contained dibutyltin and tributyltin compounds at independently determined levels. The results of this interlaboratory study indicate that the SFE method works satisfactorily for the tri- and tetra-substituted organotin compounds but that the di-and mono-substituted organotin compounds are quite difficult to extract under these conditions. Higher pressures and different modifiers may be required to enable extraction of the mono- and di-substituted organotin compounds from soils and sediments.

Possibilities of gas chromatography-atomic emission detection in pesticide multiresidue analysis Application to herbicide analysis in soils

The potential of gas chromatography with atomic emission detection (GC-AED) for pesticide multiresidue analysis is explored. Retention data of 181 phytochemicals of diverse properties and considerations about the identification reliability and sensitivity are provided, making a comparison with data obtained by mass spectrometric (MS) detection. The GC-AED system is applied to the determination of 11 herbicides in laboratory-spiked soils after extraction with ethyl acetate. Complementary use of MS is required in order to resolve some peak pairs undiscerned by AED.

Capillary gas chromatography combined with atomic emission detection for the analysis of polychlorinated biphenyls

Capillary gas chromatography with atomic emission detection (GC-AED) was evaluated for the analysis of polychlorinated biphenyls (PCBs). Since Cl-responses were almost independent of the PCB structure, individual PCBs were quantitated with an accuracy better than 10% utilizing a Cl-calibration plot based on a single randomly selected congener (universal calibration). In addition, within a 5–10% accuracy, GC-AED enabled estimation of total PCB residue levels and calculation of the percentage by weight of chlorine in contaminating PCB mixtures. Thus, although PCB detection limits were higher with GC-AED than with GC-ECD, the former technique was very attractive for PCB investigations and enabled significant simplification of PCB quantitation.

Allium chemistry: Natural abundance of organoselenium compounds from garlic, onion and related plants and in human garlic breath

Abstract

Simultaneous determination of organotin, organolead, and organomercury compounds in environmental samples using capillary gas chromatography with atomic emission detection

AbstractAs part of a continuing evaluation of new analytical and sample preparation techniques conducted by the US Environmental Protection Agency (EPA), the use of capillary gas chromatography with atomic emission detection (GC‐AED) for the simultaneous determination of organotin, organolead, and organomercury compounds in environmental samples was investigated. Pentylmagnesium bromide was used to pentylate ionic organotin, organolead, and organomercury compounds; the pentyl derivatives were then separated by GC and determined by AED. Several important GC‐AED parameters, including the type of injector inlet, carrier gas flow rate, and helium make‐up gas flow rate, were optimized for the simultaneous determination of these organometallic compounds. Their minimum detectable concentrations were approximately 1.0 to 2.5 ng/mL using a 0.5‐μL on‐column injection. The calibration curves exhibited good linearity between 2.5 and 2500 ng/mL for organotin and organolead compounds, and between 2.5 and 10000 ng/mL for organomercury compounds.