Application of Headspace Liquid-Phase Microextraction to the Analysis of Volatile Halocarbons in Water

The determination of four volatile halocarbons (CHCl₃, CCl₄, C₂HCl₃ and C₂Cl₄) in water by headspace liquid-phase microextraction (HS-LPME) with gas chromatography using a micro electron capture detector (GC-μECD) is described. The effects of the type and volume of the extraction solvent, headspace volume, stirring rate, extraction temperature and time and ionic strength on the extraction performance are investigated and optimized. The developed protocol yields a linear calibration curve in the concentration range from 0.05 to 50 µg L^?1 for the target analytes; the detection limits ranged from 0.003 to 0.146 µg L^?1 and the relative standard deviation (R.S.D.) values below 8.45%. The results demonstrate that HS-LPME followed with GC-μECD is a simple and reliable technique for the determination of volatile halocarbons in water samples.     

Flow-injection analysis based on a membrane separation module and a bulk acoustic wave impedance sensor – determination of the volatile acidity of fermentation products

A novel flow-injection analysis (FIA) system has been developed for the rapid determination of the volatile acidity of some fermentation products like vinegars and juices. The proposed method is based on the diffusion of volatile acids, mainly acetic acid, across a PTFE gas-permeable membrane from an acid stream into an alkaline stream, and the acids trapped in the acceptor solution are determined online by a bulk acoustic wave impedance sensor based on changes in the conductivity of the solution. It exhibited a linear frequency response up to 10 mmol · L^–1 acetic acid with a detection limit of 50 μmol · L^–1, and the precision was better than 1% (RSD) at a through-put of 72 h^–1. The effects of operating voltage for the detector, cell constant of the electrode, composition of acceptor stream, flow rates and temperature on the FIA performance were also investigated.     

Determination of breath gas composition of lung cancer patients using gas chromatography/mass spectrometry with monolithic material sorptive extraction

A gas chromatographic–mass spectrometric method with monolithic material sorptive extraction (MMSE) pretreatment was developed to determine the breath gas composition in lung cancer patients. MonoTrap silica monolithic and hybrid adsorbent was selected as the extraction medium during MMSE, given its strong capacity to extract volatile organic compounds (VOC) from exhaled gas. Under the appropriate conditions, high extraction efficiency was achieved. Using the selected ion‐monitoring mode, the limit of detection (signal‐to‐noise ratio 3) for the benzene series was 0.012–2.172 ng L^?1. The limit of quantitation (signal‐to‐noise ratio, 10) was 0.042–7.24 ng L^?1. The linearity range of the method was 4–400 ng L^?1. Average recovery of the benzene series at lower concentrations was 65–74% (20 ng L^?1). The relative standard deviation of benzene series contents determined within the linear range of detection was <10% of the mean level determined. Our proposed method is simple, rapid and sensitive, and can be competently applied to determine the breath gas composition of lung cancer patients. Copyright © 2014 John Wiley & Sons, Ltd.     

Miniaturized dielectric barrier discharge induced chemiluminescence for detection of volatile chlorinated hydrocarbons separated by gas chromatography

A new analytical method was proposed for the detection of volatile chlorinated hydrocarbons (VCHCs) including dichloromethane, 1,2-dichloroethane, chloroform, tetrachloromethane, perfluoromethane and bromoform after gas chromatographic (GC) separation. Atmospheric pressure dielectric barrier discharge (DBD) was miniaturized and used as a GC detector by using chemiluminescence (CL) emission from the reaction of DBD-split VCHCs with luminol solution. The miniaturized DBD-CL detector possessed the advantages of simple construction, very low power consumption, and high sensitivity to many volatile halocarbons, especially VCHCs. The parameters of the detector were optimized by using dichloromethane as a typical analyte. Under the optimized experimental conditions, the limit of detection (LOD) down to sub-nmol can be achieved.     

Determination of Uric Acid in Human Urine by Ion‐exclusion Chromatography with UV Detection Using Pure Water as Mobile Phase

A simple, rapid and accurate ion‐exclusion chromatographic method coupled with a UV detector for the determination of uric acid in human urine samples has been developed. The separation was carried out on an ion‐exclusion column using only pure water as mobile phase. The detection wavelength was 254 nm and urine sample was injected directly without any pretreatment. Furthermore, the retention behavior of uric acid on the ion‐exclusion column was researched when pure water and 1 mmol·L^?1 HCl were used as mobile phase, respectively. The stability of uric acid was also further investigated within 28 days. In this method, the linear range of the calibration curve for uric acid was 0.25–100 mg·L^?1, and the detection limit calculated at S/N=3 was 0.02 mg·L^?1. The proposed ion‐exclusion chromatographic method has been used for the determination of uric acid in human urine.     

Element selective detection of chlorine in capillary gas chromatography by wavelength modulation diode laser atomic absorption spectrometry in a microwave induced plasma

A new element selective detector for gas chromatography is presented. The detector, based on wavelength modulation diode laser atomic absorption spectrometry in a microwave induced helium plasma, is used for measurements of chlorinated hydrocarbons by absorption of excited, metastable chlorine atoms. Indications of complete dissociation of the halocarbons in the plasma have been found. Preliminary detection limits of the order of 1 μg ml⁻¹ or 80 pg s⁻¹ have been found for different halocarbons.     

Determination of chlorinated and brominated micropollutants by capillary gas chromatography coupled with on-column radio frequency plasma atomic emission detection

Capillary gas chromatography (GC) combined with on-column radio frequency plasma atomic emission detection was evaluated for the determination of polychlorinated and polybrominated biphenyls (PCBs and PBBs). Quantitation was possible utilizing a single chlorine or bromine calibration curve based on a randomly selected reference compound, because the signal per ng of halogen ranged within 17 % for 29 congeners. Combined with an internal standard to correct for potential plasma quenching from matrix components, this type of universal quantitation represented a sub-stantial simplification of current calibration procedures. In combi-nation with relatively low detection limits (1–5 pg/s of halogen), the present work suggested that GC, coupled with on-column atomic emission detection is a promising technique for the determination of halogenated micropollutants.     

Construction and validation of automated purge-and-trap-gas chromatography for the determination of volatile organic compounds

An automated purge-and-trap chromatographic system for the determination of dissolved volatile organic compounds in aqueous samples was built in the laboratory with minimum cost both in the construction and routine operation. This system was built upon a commercial gas chromatograph with full automation capability using self-developed hardware and software. The use of a multi-sorbent bed quantitatively trapped a wide range of volatile organic compounds at ambient temperature, including the extremely volatile ones such as dichlorofluoromethane (CFC-12). Flash heating for rapid desorption and adequate plumbing for minimizing dead volume resulted in excellent chromatographic separation at above-ambient temperatures, which eliminated the need for cryogen for cooling at the head of the column, a second refocusing stage, or entire GC oven for refocusing. This cryogen-free system was tested with standard solutions and environmental samples for determining hydrocarbons with flame ionization detection, and halogenated compounds with electron-capture detection. An innovative method was also developed for validating the system's linearity for extremely volatile compounds. By introducing ambient air, which usually contains constant levels of anthropogenic halocarbons, e.g., CFC-12 and CFC-11 (CCl3F), the need to prepare aqueous standards containing extremely volatile compounds is avoided, hence providing a convenient method for evaluating a purge-and-trap system.     

Determination of methylcyclopentadienylmanganesetricarbonyl by gas chromatography—atomic absorption spectrometry at ng m-3 levels in air samples

A procedure is given for the determination of methylcyclopentadienylmanganese tricarbonyl (MMT) at ng m^-3 concentrations in air. The method involves trapping of MMT in a small segment of gas chromatographic column and then determination by gas chromatography with an electrothermal atomic absorption detector. The detection limit of the procedure is 0.05 ng m^-3. Air samples from an underground car-park (when MMT was detected) were found to contain between 0.1 and 0.3 ng m^-3 MMT. MMT was not detected in any of the street air samples taken.     

Enhancement of ruthenium determination by inductively coupled plasma/atomic emission spectrometry by addition of periodic acid

A sensitive method for the determination of ruthenium involving the formation of volatile species in solution and subsequent nebulization for inductively coupled plasma/atomic emission spectrometry is proposed. The sensitivity of the determination of ruthenium was increased by a factor of 70 with the addition of 1×10^?2 M periodic acid as an oxidizing agent. The detection limit was 5 ng ml^?1 of ruthenium and the calibration was linear over the range 0.01–0.5 μg ml^?1 of ruthenium. Serious interferences were not found except from reducing agents.     

Determination of acid volatile sulphur in river sediments by ICP-OES coupled with purge and trap method

The developed and tested method is based on the acid volatile sulphur (AVS) releasing from a sample of sediment by acidification with hydrochloric acid and sequential absorption of released hydrogen sulphide into the absorption solution of sodium hydroxide. Total sulphur absorbed in the absorption solution is subsequently determined by inductively coupled plasma optical emission spectrometry (ICP-OES) technique. The method was tested using both model and real samples of the river sediment. Obtained results were compared with the results of iodometric determination as the method routinely used for the AVS determination. In case of using ICP-OES with purge and trap, there is no spectral interference of calcium; therefore for the determination of sulphur, it is possible to use atomic emission line of sulphur S I 180.7 nm. The tested method provides the results comparable with the iodometric method within the range of tested concentrations. The detection limit (LOD) of this method is 0.09 mg· S^2? ? L^?1 in the absorption solution which corresponds to 0.23 mg S^2?·kg^?1 in a sediment. Value of LOD is comparable with the iodometric determination.     

Two-dimensional on-line detection of brominated and iodinated volatile organic compounds by ECD and ICP-MS after GC separation

Inductively coupled plasma-mass spectrometry (ICP-MS) was coupled to a gas chromatographic (GC) system with electron capture detector (ECD), which enables relatively easy characterization and quantification of brominated and iodinated (halogenated) volatile organic compounds (HVOCs) in aquatic and air samples. The GC-ECD system is connected in series with an ICP-MS by a directly heated transfer line and an outlet port-hole for elimination of the ECD make-up gas during ignition of the plasma. The hyphenated GC-ECD/ICP-MS system provides high selectivity and sensitivity for monitoring individual HVOCs under fast chromatographic conditions. The ECD is most sensitive for the detection of chlorinated and brominated but the ICP-MS for iodinated compounds. The greatest advantage of the use of an ICP-MS is its element-specific detection, which allows clear identification of compounds in most cases. The absolute detection limits for ICP-MS are 0.5 pg for iodinated, 10 pg for brominated, and 50 pg for chlorinated HVOCs with the additional advantage that calibration is almost independent on different compounds of the same halogen. In contrast to that detection limits for ECD vary for the different halogenated compounds and lie in the range of 0.03-11 pg. The two-dimensional GC-ECD/ICP-MS instrumentation is compared with electron impact mass spectrometry (EI-MS) and microwave induced plasma atomic emission detection (MIP-AED). Even if EI-MS has additional power in identifying unknown peaks by its scan mode, the detection limits are much higher compared with GC-ECD/ICP-MS, whereas the selective ion monitoring mode (SIM) reaches similar detection limits. The MIP-AED detection limits are at the same level as EI-MS in the scan mode.     

Flow-injection analysis based on a membrane separation module and a bulk acoustic wave impedance sensor – determination of the volatile acidity of fermentation products

A novel flow-injection analysis (FIA) system has been developed for the rapid determination of the volatile acidity of some fermentation products like vinegars and juices. The proposed method is based on the diffusion of volatile acids, mainly acetic acid, across a PTFE gas-permeable membrane from an acid stream into an alkaline stream, and the acids trapped in the acceptor solution are determined online by a bulk acoustic wave impedance sensor based on changes in the conductivity of the solution. It exhibited a linear frequency response up to 10 mmol · L^–1 acetic acid with a detection limit of 50 μmol · L^–1, and the precision was better than 1% (RSD) at a through-put of 72 h^–1. The effects of operating voltage for the detector, cell constant of the electrode, composition of acceptor stream, flow rates and temperature on the FIA performance were also investigated. Received: 2 June 1997 / Revised: 7 July 1997 / Accepted: 12 July 1997     

Single Laboratory Validation of a Method for the Determination of Total Inorganic Arsenic by Hydride Generation Atomic Absorption Spectrometry

The purpose of this study consists in reporting of single laboratory validation of a method for the determination of total inorganic arsenic by hydride generation atomic absorption spectrometry from natural and residual water samples. Applicability, fitness for purpose, selectivity, and sensitivity were discussed. A calibration study was realized, linear working range (0.4–4 μg·L^?1), detection (0.11 μg·L^?1), and quantification (0.38 μg·L^?1) limits being determined. It was also proven that the method is accurate and precise. Following the bottom-up approach measurement, uncertainty was estimated (method validation data were used).     

Determination of hypericin and pseudohypericin in extracts fromHypericum Perforatum L. and pharmaceutical preparations by liquid chromatography-fluorescence detection

Summary An isocratic reversed-phase liquid chromatographic method for the simultaneous determination of hypericin and pseudohypericin, two of the main constituents ofHypericum Perforatum L., has been developed. The compounds were eluted from an Inertsil ODS-3, column by triethylammonium acetate-methanol-acetonirile (5:15:80) eluent and detected fluorimetrically, excitation 478, emission 598 nm. Hypericin and pseudohypericin were extracted from flowring tops by Soxhlet and pseudohypericin was isolated from the extract by collecting its chromatographic peak from the eluent flow. Identification of peaks was by HPLC coupled to a diode array detector and electrospray MS. The method was applied to the determination of hypericin and pseudohypericin in plant extract and in pharmaceutical tablets. For the latter a solid-phase extraction procedure was adopted. Riboflavin (0.1 ng.μL⁻¹) was used as internal standard. The linear working range of the method is 0.025–4 ng.μL⁻¹ and limit of detection 0.2 ng injected on-column. A comparative SPE study for hypericin is presented.     

Determination of Polyethylene Glycol Monoester Acrylate and Polyethylene Glycol Diester Acrylate Using Reversed-Phase High-Performance Liquid Chromatography

A procedure was developed for the determination of polyethylene glycol monoester acrylate (PEGMA) and polyethylene glycol diester acrylate (PEGDA) by reversed-phase high performance liquid chromatographic (RP-HPLC) with UV detector. Sample was well separated on an SinoChrom ODS-BP (C-18) column (200 × 4.6 mm i.d., 5 μm) with mobile phases composed of acetonitrile-phosphate buffer solution (0.05 mol · L^?1 pH = 6.86) in the ratio of 42:58 (v/v). The PEGMA and PEGDA were detected by UV detector at 205 nm, and quantitatively analyzed with an external standard of methyl acrylate. For PEGMA, the linear response ranged from 0.40 × 10^?5 mol · L^?1 to 2.00 × 10^?3mol · L^?1 (r² > 0.999), the detection limit was 0.12 × 10^?5 mol · L^?1, the recovery rate was found to be 93.4%–99.7%. For PEGDA, the linear response ranged from 0.20 × 10^?5 mol · L^?1 to 1.00 × 10^?3mol · L^?1 (r² > 0.999), the detection limit was 0.04 × 10^?5 mol · L^?1, the recovery rate was found to be 99.1% ～ 105.8%. This quantitative method can also be used in the HPLC analysis of other α,β-unsaturated esters.     

Determination of Procymidone, Pentachloroaniline and Methyl-pentachloro-phenylsulfide Residues in Wine by MSPD-GC-ECD

A rapid method based on matrix solid-phase dispersion (MSPD) was developed for the determination of procymidone, pentachloroaniline and methyl-pentachloro-phenylsulfide in wine. After the optimisation of different parameters such as the type of adsorbent, the extraction solvent, and the extraction assistance by sonication. The analysis of samples was accomplished using gas chromatography with electron-capture detector (GC-ECD). Spiked blank samples were used as standards to counteract the matrix effect observed in the chromatographic determination. The recovery of the method was in the range 82.4–93.7% and a good linear relationship (R ² ≥ 0.9992) with relative standard deviations lower than 8%. The limits of detection (LOD) ranged from 0.1 to 0.4 μg L^?1. The proposed method was applied to the analysis of these compounds in commercial wine samples.     

Development of chromatographic methods by using direct-sampling procedure for the quantification of cyclic and linear volatile methylsiloxanes in biogas as perspective for application in online systems.

By empirically examining the persistent theme, we hope to produce a more complete understanding of methods for determination of volatile methylsiloxanes in biogas stream. Therefore, we made an attempt to investigate a rapid and sensitive method for simultaneous analysis of linear and cyclic volatile methylsiloxanes in sewage biogas in the context of the perspective for application in online systems. The gas chromatographic (GC) parameters were optimised, and sampling of volatile methylsiloxanes from biogas was performed using novel direct sampling procedure with applying of three kinds of liquid-media. Through application of well-established gas chromatography technique coupled with two types of detector – flamed ionisation detector and mass spectrometer detector – we developed the characterisation of the presented methods. Moreover, during the samples preparation the extraction procedure was consistently excluded, as well as the time of analysis was significantly reduced. The analyses were carried out by applying special constructed sampling train where the absorbed VMSs were trapped and analysed directly by GC technique, afterwards. The instrumental analytical protocol was found to yield a linear calibration in the range 0.1–55.13 (µg g^?1) with R² values 0.996 and in the range from 0.1 to 65.17 µg g^?1) with R² values > 0.99 for GC-FID and GC-MS method respectively. In all analysed samples linear and cyclic VMSs were found in sewage gas with quantities exceeding 4.6 mg Nm^?3 and 19.9 mg Nm^?3, respectively Furthermore, estimation of VMSs solvent absorption efficiency was tested and the highest absorption efficiency was obtained when acetone was used as a primary solvent. High range of linearity (0.1–65.17 µg/g), and low values of limit of detection (0.01 µg/g), limit of quantification (0.04 µg/g) clearly indicate that the analysis can be successfully repeated in other independent laboratory. The proposed method creates the real perspective for analyis of VMSs in on-line system.     

Identification of halocarbons in the Tiber and Marta rivers by static headspace and liquid–liquid extraction analysis

Volatile organochlorine compounds in the Tiber and Marta rivers have been analyzed by liquid–liquid extraction and headspace gas chromatography. Several different halogenated compounds were identified, in particular chloroform, bromoform, trichloroethane, trichloroethene, and tetrachloroethene. The concentrations of the halocarbons varied between 0.05 and 4.5 μg L^–1 with a relative standard deviation ≤4.0%. The highest concentrations were observed for chloroform, bromoform, and tetrachloroethene in the Marta and Tiber rivers. The results obtained by use of the two analytical methods were similar.     

Direct acetylation followed by solid-phase disk extraction and GC-ITDMS for the determination of trace phenols in water

Summary A rapid, accurate and sensitive method is described for the analysis of phenolic compounds, including phenol, alkylphenols, halogenated phenols and nitrophenols in tap, ground and river water samples. The method consists in direct acetylation of the aqueous phenols with acetic anhydride, extraction of the phenol acetates with a C₁₈ disk and analysis by gas chromatography with an ion-trap detector mass spectrometer. Using this method, the sample preparation time was approximately 1.5 h for six 1-L water samples, and recoveries for most of the phenolic compounds studied were more than 80% at concentration levels of 0.1 and 1.0g L^–1. The detection limits were in the range 2 to 15 ng L^–1 for phenol, alkylphenols and halogenated phenols, and 25 to 50 ng L^–1 for nitrophenols.