Purge-and-trap Research Articles

Volatile halogenated organics in swimming pools

This survey undertaken in Greece (Mytilene town) has shown that Volatile halogenated organics (VHO) are present in swimming pool water. Analysis was performed by purge‐and‐trap (PAT) gas chromatographic (GC) technique and samples from two public indoor swimming pools in Mytilene were analyzed for VHO. Water samples were collected every week for a period of three months, and have shown the occurrence of chloroform, dichlorobromomethane, chlorodi‐bromomethane, bromoform (all four are trihalomethanes [THMs]), as a result of the chlorination and the occurrence of tetrachloroethylene and 1,1,1,2‐tetrachloroethane is assigned to their introduction as impurities during the process treatment of water. The levels of concentrations ranged from 4.0 to 26.0 μg/1 for chloroform, from 0.26 to 7.0 μg/1 for dichlorobromomethane, from 0.5 to 3.0 μg/1 for chlorodibromomethane, from 0.07 to 0.9 μg/1 for bromoform, from no detectable levels to 0.07 μg/1 for tetrachloroethylene and from no detectable levels to 0.2 μg/1 for 1,1,1,2‐tetrachloroethane.

MultiSimplex optimisation and comparison of different purge-and-trap extractions of volatile organic compounds in soil samples

Two different purge-and-trap (PT) extraction methods have been optimised for nine volatile organic compounds (VOCs) (benzene, toluene, chlorobenzene, ethylbenzene, m-xylene, o-xylene, 1,3-dichlorobenzene, 1,4-dichlorobenzene and 1,2-dichlorbenzene) making use of the simplex method implemented in the MultiSimplex program. In both cases, the determination of the VOCs was performed by a coupled GC–FID system. In the first extraction method the soil sample was sonicated with methanol and 100 ml of the extract were analysed as an aqueous sample. Variables considered were heating temperature, heating time, purge time and concentration of sodium chloride and the optimum conditions were 4.3 min purge after a sample heating at 46°C for 7.5 min and a sodium chloride solution of 4.3 mol l −1. In the second method, the soil sample was directly introduced in the test tube for soils, heated and purged. Except for the concentration of sodium chloride, the previous variables were also considered and the optimum conditions were 51.1 min purge after 42.6 min heating at 61°C. These two methods are compared with a previously optimised method where soils samples were mixed with an aqueous phase and the VOCs were directly determined by the PT–GC–FID system.

Volatile organic compounds in the surface waters of Northern Greece

An investigation into the occurrence of volatile organic compounds (VOCs) was conducted for a period of two years in the surface waters of Northern Greece. Samples from four rivers and five lakes were taken seasonally and analyzed for VOCs. The analysis has been performed by purge-and-trap (PAT) gas chromatographic–mass spectrometric (GC–MS) technique. The most commonly encountered VOCs in surface waters were chloroform, carbon tetrachloride, trichloroethylene, dichlorobromomethane, tetrachloroethylene, and chlorodibromomethane.

Flavor release of diacetyl and 2-heptanone from cream style dressings in three mouth model systems.

The release of volatile compounds from a cream style dressing, which consisted of a thickening agent dispersed in the water phase of an oil in water (o/w) type of emulsion, was studied by the purge-and-trap (PT), dynamic head space mastication (DHM) and dynamic headspace (DH) model systems for diacetyl and 2-heptanone as two volatile compounds. Big differences were detected in the quantity of volatiles released by the three models for both diacetyl and 2-heptanone: PT released the most, followed by DHM and DH. Nitrogen gas bubbling in PT and plunger up-and-down motion in DHM mimic mouth movements and promoted volatile release more than DH. The quantity of volatiles released depended on the nitrogen gas flow rate and isolation period with both the PT and the DHM model. Static headspace measurements indicated that no interaction occurred between the volatiles and the dispersion thickening agent, nor between the volatiles and protein of saliva.

Evaluation of dynamic headspace and purge-and-trap techniques for the high-resolution gas chromatography analysis of nitrous oxide in seawater

The present study focuses on the effectiveness of dynamic headspace (DH) and purge-and-trap (PT), which are two commonly used techniques for determining volatile organic compounds in environmental samples, on the extraction and trace analysis of nitrous oxide in seawater. With the aim of obtaining reliable quantitative data in the DH and in the PT techniques, kinetics of these processes were studied; a first-order kinetic-like function is found to be followed for the extraction of nitrous oxide in both the DH and PT sampling methods. A three-way analysis of variance was carried out to evaluate the effect of the water sample composition on DH and PT analysis in order to systematically and accurately examine the effect of different factors on the chromatographic response of N 2O; a significant matrix effect proportional to the nitrous oxide concentration was observed when bidistilled water, synthetic and natural seawater were considered. The effects of different sampling procedures were evaluated in terms of linearity range, limit of detection, capability of detection, precision, extraction recovery and accuracy. Better results in terms of extraction recovery, sensitivity and detection limit were obtained when applying the purge-and-trap technique combined with GC–electron-capture detection; detection limits at very low pmol ml −1 levels were achieved, making this procedure suitable for trace nitrous oxide analysis in marine samples.

Effect of saliva dilution on the release of diacetyl and 2-heptanone from cream style dressings.

Aroma release from a cream style dressing, consisting of a thickening agent dispersed in the water phase of an oil in water (o/w) emulsion, has been studied by a purge-and-trap (PT) and a dynamic headspace mastication (DHM) model using two representative volatile compounds, viz. diacetyl and 2-heptanone. These isolations have been carried out from three systems: the dressing, the thickening agent dispersion and the o/w type of emulsion after adding different volumes of artificial saliva. Dilution of the samples with artificial saliva influences the amounts released for diacetyl and 2-heptanone differently: diacetyl decreases upon dilution of the thickening agent dispersion, emulsion and dressing. However, the amount of released 2-heptanone decreased only in the case of the thickening agent dispersion. These differences are caused by the distribution of diacetyl and 2-heptanone between the water and the oil phases. The distribution is not so important, when the DHM model is used for the release from dressings. The viscosity of the mixture of dressing and artificial saliva then plays an essential role. In general, the viscosity is considered to suppress the release of flavour. However, it has been found that the amount of volatile compounds released from the more viscous dressing was greater than from the emulsion. Most probably, the DHM model creates a large surface area by adhesion of the dressing on the wall of the sampling flask and the plunger head. This result suggests that the DHM equipment, which mimics the mouth movement, might be used to predict the real release of flavour in the mouth more precisely than other mouth models.

Volatile halogenated organics in the water supply system in Athens, Greece

A survey undertaken in Athens has shown that Volatile Halogenated Organics (VHO) are present in chlorinated drinking water; analysis has been performed by purge-and-trap (PAT) gas chromatographic (GC) technique. Samples from different points of the Menidi Treatment Plant (MTP) and the distribution network of Athens were taken and analyzed for VHO. Surface water samples have been collected every month for a period of eight months, and have shown the occurrence of chloroform, dichlorobromomethane, chlorodibromomethane as a result of the chlorination of raw water and of tetrachloroethylene and 1,1,1,2-tetrachloroethane.

Determination of benzene alkyl derivatives in heavily loaded environmental aqueous samples by means of combination of distillation and purge and trap‐gas chromatography‐mass spectrometry

AbstractSimple distillation was used to prepare aqueous environmental samples (especially those with high content of accompanying dissolved and suspended organic and inorganic matter) for determination of benzene, toluene, ethylbenzene, and xylenes (BTEX) by means of purge and trap (PT) coupled to gas chromatography‐mass spectrometry (GC‐MS). The PT step was carried out with a laboratory‐built device in which alalytes desorbed from a Primary trap (macrotrap) are focused in a microtrap (also with sorbent) and moisture is removed from purge gases by a Nafion tube (walls selectively permeable to water vapor). Recoveries, if only the first 10 ml distillate was collected, were of the order of 40% at optimum distillation parameters. At a probability level of 95% recoveries were independent of concentration in a studied concentration range of 0.50–30 ppb. Enrichment factors for distillation were of the order off 20. Real samples, i.e., raw and treated waste water were analyzedc for BTEX content by the developed medthod.

Volatile organo‐halogen trace analysis in beverages by thin‐layer headspace enrichment and electron‐capture gas‐chromatography

Applicability of thin‐layer headspace (TLHS) procedure giving an aqueous concentrate and also classical purge and trap (PT) in off‐line mode to isolate and enrich volatile organohalogen compounds in common beverages was tested. Both enrichment tech‐niques were used in combination with gas chromatography – electron capture detection (GC‐ECD). TLHS, combined with direct aqueous injection (DAI)‐GC‐ECD, proved applicable in the determination of volatile organohalogen compounds in all studied beverages, while the PT in a version with no preliminary sample pre‐treatment was of limited applicability. Detection limits of the TLHS‐based procedure were in the order of 1 ppt. Content of volatile organohalogen compounds in a number of beverages available on the Polish market including mineral waters, beers, juices, carbonated and non‐carbonated soft drinks, etc. was determined by means of TLHS‐DAI‐GC‐ECD.

Flavour release from rehydrated french beans (Phaseolus vulgaris) influenced by composition and volume of artificial saliva.

Influence of saliva composition and volume on flavour release from rehydrated French beans (Phaseolus vulgaris) was studied in three types of mouth model systems; dynamic headspace (DH), dynamic headspace and mastication (DHM) and a purge-and-trap (PT) model system. Volatile compounds were analysed by gas chromatography, using flame ionization detection (FID), mass spectrometry and sniffing port detection. Areas of FID peaks were largest in the PT system, followed by those of the DHM and DH systems, respectively. Saliva composition as well as volume influenced the release of volatile compounds from rehydrated French beans. Generally, FID data showed a decrease in release by the saliva component mucin, because of interactions between volatile compounds and protein, and in increase in release by its alpha-amylase, probably due to degradation of inclusion complexes of starch. The decrease in flavour release by the enlarged saliva volume was evaluated by a model study. Sniffing patterns of odour active compounds were barely influenced by either saliva composition or volume.

Changes in flavour release from rehydrated: Diced bell peppers (Capsicum annuum) by artificial saliva components in three mouth model systems

AbstractThe effect of artificial saliva components on flavour release from dehydrated diced red bell peppers (Capsicum annuum) was studied in a mouth model system. This measured the dynamic headspace under oral conditions, such as temperature, volume of the mouth, salivation, and mastication (DHM). The results were compared with a dynamic headspace (DH) and a purge‐and‐trap (PT) model system. Volatile compounds were analysed by gas chromatography, using flame ionisation detection (FID), mass spectrometry (MS), and sniffing port detection (SPD). SPD revealed that only 12 of the 47 compounds identified by MS and FID possessed odour activity. For all saliva compositions FID peak areas of volatile compounds were largest in the PT system, followed by DHM and DH, respectively. In the PT system the less volatile compounds were relatively better released than other volatile compounds in comparison with the DHM and DH system, for all salivas. The saliva components mucin and α‐amylase caused a relative decrease in release of the less volatile compounds in all model systems. An overall decrease in FID peak areas of volatile compounds by the latter components was observed in model system DH only.

Methylmercury determination by Purge and Trap–GC–FTIR–AAS after NaBH4 derivatization of an environmental thiosulfate extract

AbstractA method of detecting methylmercury species (MeHg) and dimethylmercury (DMM) has been studied. MeHg was transformed prior to its determination as methylmercury hydride (MMH) by use of NaBH4. The two volatile forms of organic mercury were detected by a purge and trap (PT) unit in‐line with a gas chromatograph (GC) connected with a Fourier transform infrared spectrometer (FTIR) which was also in‐line with an atomic absorption spectrometer (AAS). Environmental samples were analyzed by this technique. MeHg was detected in thiosulfate extracts of fish and sediment, and MeHg and DMM directly in water samples. Picogram levels of sensitivity were obtained, the limit of detection being 100 pg for MeHg and 50 pg for DMM. The calibration graph was linear for both compounds up to 10 ng as Hg.

Combined solvent extraction-purge and trap method for the determination of volatile organic compounds in sediments

A method involving methanol solvent extraction (SE) and purge and trap (PT) was evaluated for the determination of chlorinated volatile organic compounds (VOC) in sediments. The method was tested by means of standard solutions encompassing twenty chlorinated compounds with boiling points ranging between 24 and 150°C (at 1 atm = 101 325 Pa). Detection limits (0.05-0.4 μg/g), linearity ranges and recoveries (only 1% average losses by glassware manipulation and 7.5% losses after water sediment suspension with standards and methanol extraction) show the suitability of the method for the determination of chlorinated VOC in environmental samples. A specific advantage of this method is the possibility of storage of the VOC methanol extracts for long periods of time at −20°C without significant alteration of the quantitative results. In the conditions of the study, the average recovery of individual VOCs after storage for 50 days was 89%.

DIFFUSION METHOD FOR THE DETERMINATION OF ACID-VOLATILE SULFIDES (AVS) IN SEDIMENT

A simplified procedure using diffusion and a sulfide ion selective electrode is described for measuring acid-volatile sulfides (AVS) in sediment This method yielded at least 10% more AVS than the more common purge-and trap method The quantity of AVS (based on dry mass of sediment) was found to be dependent on acid concentration and on mass of wet sediment The mean recovery of known additions of sodium sulfide was 93 8 ± 6 7%

Methylmercury determination as volatile methylmercury hydride by purge and trap gas chromatography in line with Fourier transform infrared spectroscopy

We report a novel aqueous derivatization of methylmercury chloride by NaBH 4 to mehtymercury hydride (CH 3 HgH), a volatile and unexpectedly stable species which we determined has a half-life of approximately 2 h. The analytical apparatus consisted of a purge and trap (PT) unit linked to a gas chromatograph (GC), in line with a Fourier transform infrared spectrometer (FTIR). The sample was purged with nitrogen, and volatile compounds were concentrated in a cold trap