Hall Electrolytic Conductivity Research Articles

Determination of organochlorine and organophosphorus pesticide residues in low moisture, nonfatty products using a solid phase extraction cleanup and gas chromatography

A multiresidue solid‐phase extraction (SPE) method for the isolation and subsequent gas Chromatographie determination of organochlorine and organophosphorus pesticide residues in low‐moisture, nonfatty products is described. Residues are extracted from samples with an acetonitrile/water mixture. Cleanup of the extract is performed using graphitized carbon black and anion exchange SPE columns, and analysis is performed by gas chromatography with Hall electrolytic conductivity and flame photometric detection. Recovery data was obtained by fortifying corn, oats and wheat with pesticides. The average recoveries were 79–123% for eight organochlorine and 51–122% for 28 organophosphorus pesticide residues. The limit of quantitation for chlorpyriphos was 0.05 ppm using the Hall electrolytic conductivity detector and <0.005 ppm using the flame photometric detector.

GC determination of halogenated olefins by photoionization and hall electrolytic conductivity detectors in series in matrices of hydrofluorocarbons and hydrochlorofluorocarbons

Gas chromatography (GC) with photoionization (PI) and Hall electrolytic conductivity (E1C) detectors connected in series, has been used for the determination of chlorofluorinated olefins. The separation of different standard solutions containing eight chlorofluorinated ethenes in nitrogen and in halogenated matrices has been performed in wide bore capillaries, 0.53 mm i.d., and normal capillaries, 0.32 mm i.d. The quality of separation is obviously influenced by their limited load capacity and by the response time of the Hall detector. At concentrations 1–150 μL L−1 halogenated olefins, both PI and ElC detectors have linear response and can detect minimum levels of 0.2–0.5 ng and 0.4–1.2 ng, respectively. The PID is particularly selective toward halogenated olefins and is extremely useful for the determination of traces of unsaturated halogenated hydrocarbons in a matrix of saturated homologues. The results of this work are of great interest for the detection of chorofluorinated olefins, highly toxic compounds usually formed as by-products in the industrial production of hydrofluorocarbons and hydrochloro-flurocarbons.

Comprehensive, quantitative, congener-specific analyses of eight aroclors and complete PCB congener assignments on DB-1 capillary GC columns

We have determined complete polychlorinated biphenyl (PCB) congener assignments and weight percent distributions for all major (> 0.5 wt %) PCB components of Aroclors 1221, 1232, 1242, 1016, 1248, 1254, 1260, 1262 that are resolved by DB-1 (polydimethylsiloxane) capillary GC columns. Aroclor components present between 0.05 and 0.5 wt % were also identified but not quantified. Quantitation was done using a combination of GC-ELCD (Hall electrolytic conductivity detector) and GC-MS measurements. All 209 PCB congeners have been assigned to the 124 peaks that can be resolved on DB-1 columns. The data support use of these eight Aroclors individually or in customized standards for calibrating the comprehensive, quantitative, congener-specific PCB analyses that are necessary for accurate quantitation of the complex and often radically altered mixtures of PCBs typically found in the environment.

Methyl Bromide Determination in Selected Foods by Headspace Technique

A headspace method used earlier for determining methyl bromide (MB) in assorted nuts and peanut butters has been successfully applied to other foods that could potentially contain traces of this toxic fumigant. The foods tested include 63 off-the-shelf spices and seasonings, 83 table-ready items (grain-based, dried, or highly seasoned), 30 dried fruits and trail mixes, and 38 oil-based items (oil-seeds, cooking oils, or spicy oil-based dressings). Sample headspace gas is produced by blending < or = 50 g sample in 250 +/- 50 mL aqueous solution in a sealed 1000 mL blender cup. After equilibration at 25 degrees C, the headspace is sampled with a gas-tight syringe and injected into a dual column-dual detector gas chromatograph. One determination is made with a 20% OV-101 packed column and a 63Ni electron capture detector (ECD), the other with a GS-Q wide-bore capillary column and a Hall electrolytic conductivity detector (HECD). Of the approximately 200 samples tested, none contained detectable MB residue at a quantitation limit < 100 ng/g sample. All fortified samples yielded MB recovery. Samples were fortified at levels ranging from 78 to 3250 ng MB/g. Recoveries ranged from a mean high of 56% for spices and seasonings to a mean low of 30% for oil-based foods. The overall recovery and CV, including the results from assorted nuts and peanut butters, were 46 and 33%, respectively.

Capillary gas chromatographic method for the determination of the thromboxane A 2 receptor antagonist S-1452 and its metabolites in human urine

A capillary gas chromatographic method using a sulphur-specific detector (Hall's electrolytic conductivity detector) was established to determine the thromboxane A 2 antagonist S-1452 and its metabolites in human urine. The target species were the free acid (+)-S-145 of the drug and its nine metabolites: the three hydroxyl forms of (+)-S-145 (I, II and III), bisnor-(+)-S-145 (IV) the hydroxylated forms of IV (V and VI), tetranor-(+)-S-145 (VII) and the hydroxylated forms of VII (VIII and IX). These ten compounds, which have the same sulphur-containing functional group in common, were determined simultaneously. Their conjugated forms, which were assumed to be glucuronides, were also assayed after hydrolysis. The first derivatization was esterification with diazomethane. The second, for the hydroxylated compounds, was trimethylsilylation with bis(trimethylsilyl)trifuloroacetamide. The ten analytes appeared as separate peaks without mutual interference during 5 min. Hall's detector distinguished the ten analytes selectively from the other urinary components, which removed the need for complex clean-up procedures and led to higher sensitivity with a lower noise level. The method is sensitive enough for the assay of substances present at more than 0.1 μg/ml of urine. All the compounds could be determined with a high level of precision and accuracy, with 2–5% relative standard deviation and within ±5% deviation from the actual value. Day-to-day measurements verified the reproducibility of the method. Recovered substances were quantified by following the time course, and the analytical data together with previously obtained plasma data clarified the metabolism pharmacokinetically.

Identification of chlorinated fatty acids in fish lipids by partitioning studies and by gas chromatography with Hall electrolytic conductivity detection

Chlorinated compounds in fish lipids [determined by neutron activation analysis as extractable, organically bound chlorine (EOCl)] were characterized by liquidliquid extractions after enzymatic hydrolysis and after forming fatty acid methyl esters (FAMEs). Most of the chlorinated compounds in lipids from four different fish samples could be hydrolysed. Comparison with results of methanolysis of two of the fish lipids indicated that chlorinated fatty acids made up the major portion of EOCl. Using gas chromatography (GC) with electrolytic conductivity detection (ELCD), chlorinated compounds were found among FAMEs of ee] lipids containing 1200 ppm of EOCl. Approximately 90% of EOCl was detected by GC-ELCD. The GC-detectable compounds are suggested to be methyl esters of chlorinated fatty acids and 9,10-dichlorostearic acid was tentatively identified after co-injection of the synthesized compound.

Headspace Method for Rapid Determination of Methyl Bromide in Assorted Nut Samples

Abstract A headspace method has been developed for the rapid, safe determination of methyl bromide (MeBr) in raw and processed nuts. Fifty grams of frozen nut meats is blended 3 min at high speed in 200-250 mL aqueous solution in a sealed 1 L blender cup fitted with a septum port on its cover. The cup is equilibrated 10 min in a 25C water bath. Two 250 ±150 μL aliquots of the sample headspace gas are sequentially removed with a gas-tight syringe and injected into a dual column/ dual detector gas chromatograph. One determination is made with a GS-Q wide-bore capillary column and a Hall electrolytic conductivity detector, the other with a packed column, 20% OV-101 on Chromosorb W(HP), and a 63Ni electron capture detector. The average variation for the manual injections is about 5% for both column/detector systems. To prevent random emission of MeBr during the determination, dated standards, headspace wastes, and electron capture detection effluent are passed through liquid traps. The overall recovery of MeBr from fortified samples is about 40%; the coefficient of variation is 29%. Eighteen assorted nut samples were analyzed on both systems at a quantitation limit of ᑉ100 ng/g; no detectable MeBr was found.

Gas Chromatographic Method for Determination of Chlorpyrifos and Its Metabolite 3,5,6-Trichloro-2-Pyridinol (TCP) in Dates

A method is described for the determination of the insecticide chlorpyrifos and its metabolite TCP in green, unprocessed, and processed dates with the seeds incorporated. After extraction, chloropyrifos is cleaned up using Florisil and analyzed using a gas chromatography (GC) equipped with a nitrogen/phosphorus detector. TCP is derivatized using bis-(trimethylsilyl)-acetamide (BSA) to form the TCP-derivative and analyzed by a gas chromatograph equipped with a Hall electrolytic conductivity detector. Recoveries of chlorpyrifos from all fortified dates (0.05 and 0.1 ppm) ranged from 86 to 110% with an average of 94.5%. Recoveries of TCP from all fortified dates (0.1 and 0.2 ppm) ranged from 79 to 99% with an average of 86%. Limits of detection for chlorpyrifos and TCP in green, unprocessed, and processed dates were 0.02 and 0.05 ppm, respectively.

Residue Analysis of Organochlorine Pesticides by Gas Chromatography Equipped with a Hall Electrolytic Conductivity Detector (Halogen Mode)

Residue Analysis of Organochlorine Pesticides by Gas Chromatography Equipped with a Hall Electrolytic Conductivity Detector (Halogen Mode)

Determination of the total amount sulfur in petroleum fractions by capillary gas chromatography in combination with cold trapping and a total sulfur analyzer

The distribution of sulfur compounds among fractions of a petroleum liquid has been quantitatively determined by capillary gas chromatographic techniques, including on-column injection, cold-trapping of effluent, and measurement of effective recovery. In this study the amount of sulfur was determined in the gasoline (0–450°F), light cycle oil (450–650°F), and heavy cycle oil (650–11OO°F) fractions of a refinery stream liquid. Knowledge of the amount of sulfur in the various fractions of this material can be valuable in determining how to process this material in the refinery. The petroleum liquid was separated by an on-column injection into a fused-silica capillary column, and the sulfur in each of the three cold-trapped fractions was measured by a hydrogen sulfide total sulfur analyzer. A detection limit of 50 ppm was achieved with quantitative recoveries of almost 100%. The sulfur distributions determined for a series of these petroleum liquids were 0.01–0.02 wt.-% in the 0–450°F fraction, 0.13–0.23 wt.-% in the 450–650°F fraction, and 0.50–1.20 wt.-% in the 650–1100°F fraction. The reproducibility for duplicate samples was 3%, and the reproducibility for the same sample with multiple cold-trap separations was also within 3%. This method obviates the complicated calibration step, which is necessary when sulfur-specific detectors, such as the flame-photometric detector and the Hall electrolytic conductivity detector are used.

Gas chromatographic determination of volatile sulfides at trace levels in natural freshwaters

Volatile sulfides in the aqueous phase were analyzed by degassing the solution and cryogenically trapping the volatiles. A gas chromatograph equipped with a Hall electrolytic conductivity detector is used in the sulfur mode. Water samples were analyzed with the internal standard method because of variable recoveries. Recovery efficiencies of the internal standard show a good linear relationship with the analytes. Detection limits (as S) of 0.03 ng/L for H/sub 2/S, 0.02 ng/L for COS, 0.06 ng/L for CH/sub 3/SH, 0.09 ng/L for CS/sub 2/, 0.05 ng/L for CH/sub 3/SCH/sub 3/, 0.07 ng/L for CH/sub 3/CH/sub 2/CH/sub 2/SH, and 0.10 ng/L for CH/sub 3/SSCH/sub 3/ can be achieved for a 100-mL sample. The precision is better than 10% for the range of 1-4000 ng of S/L.

Multiresidue procedures for the determination of chlorinated dibenzodioxins and dibenzofurans in a variety of foods using capillary gas chromatography-electron-capture detection

Multiresidue digestion-extraction procedures for the determination of chlorinated dioxins and furans in a wide variety of products are presented. Procedure selection is dependent upon the residue(s) of interest, and on the fat content of the product. Additional cleanup is accomplished using column chromatography and a Florisil trap. The separation of residues is achieved by fraction collection off of two high-performance liquid chromatographic systems. Capillary gas chromatography employing electron-capture detecton is used for quantitation. The extracts are suitable for gas chromatography-mass spectrometry or gas chromatography with Hall electrolytic conductivity detection. Results of analysis, recovery data, and interlaboratory comparisons are presented. Spike recoveries will typically average 90% ± 10%.

Factorial optimization for flows in the hall electrolytic conductivity detector

Statistical optimization of flows is carried out for a Hall electrolytic conductivity detector (HECD). Yates' method was used to quickly estimate main factors affecting HECD response to organochlorine. Also, more detailed evaluation of variations of HECD response for three flow variables was performed via central composite design factorial experiments. Corresponding three-factor, three-level factorial experiments provided data for least-squares regression analyses. The resulting fitted-polynomial yielded an appropriate mathematical model of the HECD response surface for the corresponding three dimensions in flow-space. Optimum values for three detector flows are thereby selected from the response surface to provide maximum HECD sensitivity, i.e., response to organochlorine in the halogen mode. Supplemental data then allow for flow optimization with respect to other criteria, e.g., signal-to-noise ratios and resolution of eluates.

Residue Level Determination of the Aquatic Herbicide Fluridone and a Potential Photoproduct (N-Methylformamide) in Water

Methods are presented for the determination of the aquatic herbicide fluridone and N-methylformamide (NMF), a potential photoproduct of fluridone which has thus far been observed only in a laboratory aqueous photolysis study. Water samples are passed through a Sep-Pak C18 cartridge to extract fluridone while NMF passes unretained through the cartridge with the water. Fluridone is eluted from the cartridge with methanol, which is then concentrated for analysis by liquid chromatography with UV detection at 313 nm. The water eluate containing NMF is concentrated for analysis by rotary vacuum evaporation at 40-46 degrees C. Methanol is added to help evaporate the water, and glycerol is added as a keeper solvent to retain NMF during the evaporation. The residual NMF is dissolved in methanol for analysis by gas chromatography with a Hall electrolytic conductivity detector operated in the nitrogen mode. The assay limits of detection are 1 and 2 ppb for fluridone and NMF, respectively. Recoveries averaged 98% for fluridone at 1-400 ppb and 87% for NMF at 2-50 ppb.

Ethyl carbamate analysis in fermented products - A comparison of measurements of mass-spectrometry, thermal-energy analyzer, and hall electrolytic conductivity detector

4. References > 1000 jAg/L. Typically, the concentration is low in wine and high in some spirits; the concentration is particularly high in some plum brandies but is low in gin and vodka. Literature methods [1,2,31 rely on sample clean-up followed by packedcolumn GC and detection by FID, alkali flame ionisation, electron capture, or Coulson electrolytic conductivity detector and allow measurements down to 10 Itg/L. The clean-up procedure required for levels below 100 jg/L is extensive and MS confirmation is still required. I.5 I~a 21 In the course of a study of ethyl carbamate levels in alcoholic beverages on sale in U.K., different methods of separation and measurement were as-

Determination of Purgeable Halocarbons and Aromatics by Photoionization and Hall Electrolytic Conductivity Detectors Connected in Series

The applicability of the purge-and-trap technique, combined with a photo ionization detector (PID) and a Hall electrolytic conductivity detector (EICD) connected in series to the determination of 46 volatile organic compounds, is investigated. Both packed and open tubular capillary columns are evaluated. Twenty compounds arranged in nine groups coelute on the 1% SP-1000 on Carbopack B column, and 15 compounds arranged in five groups coelute on the n-octane/Porosil column. Preliminary experiments with wide-bore capillary columns indicate that either the VOCOL or the DB-624 open tubular capillary column can be used for the primary analysis of Methods 8010 and 8020 compounds. However, neither column is able to completely resolve all compounds. Twenty compounds arranged in eight groups coelute on the VOCOL (diphenyl dimethyl polysiloxane with crosslinking moieties, Supelco, Inc.) open tubular capillary column and 11 compounds arranged in five groups coelute on the DB-624 (cyanopropyl phenyl dimethyl polysiloxane, J&W Scientific) open tubular capillary column. Method precision of the purge-and-trap technique with a PID and a Hall EICD connected in series, as assessed from the instrument response at a known concentration per compound, is better than ± 30% (except for dichloromethane) and has a mean value of ± 12%. Method accuracy ranges from 82 to 104% for groundwater samples. Method detection limits vary with each compound and range from 0.1 to 0.9 ppb for water samples and 1 to 5 ppm for soil samples.

Capillary Column Gas Chromatographic Determination of Ethyl Carbamate in Alcoholic Beverages with Confirmation by Gas Chromatography/Mass Spectrometry

A method is described for determining ethyl carbamate at low microgram/kg levels in several types of alcoholic beverages by capillary column gas chromatography with Hall electrolytic conductivity detection and confirmation by mass spectrometry. Samples are diluted to obtain a uniform concentration of ethanol (ca 10%) then saturated with NaCl and extracted with methylene chloride. Extracts are evaporated to a small volume and injected in ethyl acetate solution for chromatographic analysis. The method was evaluated by 5 laboratories, 4 employing the Hall detector and one using mass spectrometric detection. Overall between-laboratory mean percent recoveries were: wine, 85.3 +/- 21.0% coefficient of variation (CV) (spiking level 20-45 micrograms/kg); sherry, 83.8 +/- 16.1% CV (spiking level, 81-142 micrograms/kg); whiskey, 79.5 +/- 13.9% CV (spiking level 127-190 micrograms/kg); and brandy, 85.0 +/- 12.5% CV (spiking level 297-446 micrograms/kg). Mass spectrometric results agreed well with the Hall results for all commodities. Detection limits were about 5 micrograms/kg for the Hall detector and about 0.5 microgram/kg for mass spectrometric detection.

Capillary Column Gas Chromatographic Determination of Ethyl Carbamate in Alcoholic Beverages with Confirmation by Gas Chromatography/Mass Spectrometry

Abstract A method is described for determining ethyl carbamate at low \i%l kg levels in several types of alcoholic beverages by capillary column gas chromatography with Hall electrolytic conductivity detection and confirmation by mass spectrometry. Samples are diluted to obtain a uniform concentration of ethanol (ca 10%) then saturated with NaCl and extracted with methylene chloride. Extracts are evaporated to a small volume and injected in ethyl acetate solution for chromatographic analysis. The method was evaluated by 5 laboratories, 4 employing the Hall detector and one using mass spectrometric detection. Overall between-laboratory mean percent recoveries were: wine, 85.3 ± 21.0% coefficient of variation (CV) (spiking level 20- 45 μg/kg); sherry, 83.8 ± 16.1% CV (spiking level, 81-142 μg/kg);whiskey, 79.5 ± 13.9% CV (spiking level 127-190 Mg/kg); and brandy, 85.0 ± 12.5% CV (spiking level 297-446 μg/kg). Mass spectrometric results agreed well with the Hall results for all commodities. Detection limits were about 5 μg/kg for the Hall detector and about 0.5 μg/kg for mass spectrometric detection.

Purge and Trap Method for Determination of Volatile Halocarbons and Carbon Disulfide in Table-Ready Foods

A method developed for the determination of ethylene dibromide in table-ready foods has been modified and expanded to include 7 other volatile halocarbons and carbon disulfide. Samples are stirred with water and purged with nitrogen for 0.5 h in a water bath at 100 degrees C. The analytes collected on a duplex trap composed of Tenax TA and XAD-4 resin are eluted with hexane and determined by gas chromatography with electron capture detection or Hall electrolytic conductivity detection. Flame photometric detection in the sulfur mode is used to determine carbon disulfide. Thick-film, wide-bore capillary columns are used exclusively in both the determination and confirmation of the halogenated analytes. The higher levels of analytes are also confirmed by full scan gas chromatography mass spectrometry (GC/MS). Samples are analyzed for carbon disulfide, methylene chloride, chloroform, 1,2-dichloroethane, methyl chloroform, carbon tetrachloride, trichloroethylene, 1,2-dibromoethane, and tetrachloroethylene. Initially, 19 table-ready foods from the Food and Drug Administration's Total Diet Study were analyzed by this method. A limited survey of those food items exhibiting high levels of analytes was conducted. Samples exhibited levels up to 3300 ppb (methyl chloroform in Parmesan cheese). Recoveries of all 9 analytes from fortified samples ranged from 83 to 104%. Chromatograms from this purge and trap method are clean, enabling quantitation levels of low parts per billion and sub-parts per billion to be achieved for the halogenated analytes. The quantitation limit for carbon disulfide is 12 ppb. Two compounds found in drinking water were identified by GC/MS as bromodichloromethane and chlorodibromomethane. Drinking water from several cities was analyzed for these trihalomethanes as well as for bromoform. Levels of up to 17 ppb bromodichloromethane were found. Recoveries ranged from 96 to 103%.

Comparative study of high-performance liquid chromatography with ultraviolet detection and gas chromatography with the Hall electrolytic conductivity d

Comparative study of high-performance liquid chromatography with ultraviolet detection and gas chromatography with the Hall electrolytic conductivity d