Purge-and-trap Research Articles

Batch equilibrium experiments and modeling reveal weak temperature dependence of cyclic volatile methylsiloxane sorption in soil/sediment organic carbon-water systems

The organic carbon normalized partition coefficient, KOC, describes the equilibrium distribution of a chemical between water and organic carbon in soil or sediment. It is a key parameter in evaluating chemical persistence, mass distribution, and transport using multimedia fate and transport models. Considerable uncertainty remains about the KOC values of cyclic volatile methylsiloxane (cVMS) compounds, and in particular the dependence of KOC on temperature. In this study, we used a batch equilibrium (BE) method to measure KOC values and their temperature dependence between ∼5 and 25 °C for octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5) with soil and sediments. Approximate log KOC values at 25 °C were 4.5–5.0 for D4 and 5.5–6.1 for D5 with different sorbents, and decreased by 0.3 log units or less at 4–5 °C. Enthalpies of sorption, ΔHOC, obtained for the different sorbents ranged from +7.2 to +16 kJ mol−1, with average values of +7.9 and +13 kJ mol−1 for D4 and D5, respectively. These values differ in magnitude and direction from those reported elsewhere based on KOC values determined by a novel dynamic purge-and-trap (PnT) method, but are consistent with predictions based on their solvation properties. A new fugacity-based multimedia model incorporating sorption/desorption kinetics was developed and used to predict concentrations in the phases of BE and PnT systems during desorption of cVMS under different experimental and ideal conditions. Model simulations suggested that KOC values for cVMS compounds derived from the PnT systems could be influenced by sorption disequilibrium between water and solids controlled by desorption rates from the particle phase to water, and subsequent losses due to volatilization and degradation. This has the potential to result in overestimation of KOC values when fitting the experimental data of cVMS mass remaining in a PnT system over time, which could explain the observed differences between the methods.

Determination of potential volatile compounds in polyethylene terephthalate (PET) bottles and their short- and long-term migration into food simulants and soft drink

Head space (HS)-GC–MS was used to analyze possible migration of volatile compounds from polyethylene terephthalate (PET) bottles for soft drinks, and a total of six compounds were identified. Next, a rapid, simple, and accurate simultaneous method was established using purge-and-trap (PT)-GC–MS, to quantify their amounts in the liquid contents after short- and long-term storage in PET bottles. Starting with brand-new PET bottles, the maximum migration of 2-methyl-1,3-dioxolane into distilled water and 50 % aqueous ethanol after 2 years at 25 °C were 2.3 and 19 ng/mL, respectively. In commercially available bottled mineral water sold inside and outside Japan, we were able to detect 2-methyl-1,3-dioxolane in the same way. While nonanal was also detected in some products, 2-methyl-1,3-dioxolane was confirmed as the main volatile compound. Finally, the human exposure to 2-methyl-1,3-dioxolane was estimated based on the per capita intake of soft drinks in Japan and the migration amount in this study.

Method validation and measurement uncertainty of possible thirty volatile organic compounds (VOCs) presented in the polyethylene present in bottled drinking waters sold in Turkey

This study was actualized for the simultaneous determination of possible thirty VOCs presented in drinking waters in Turkey by direct injection to purge and trap (PT) gas chromatography-mass spectrometry (GC-MS). It consists of selectivity, linearity, the limit of detection (LOD) and limit of quantification (LOQ), accuracy (recovery), precision, trueness, and measurement uncertainty studies. In linearity, the values of correlation coefficients (r2) for the matrix-matched calibration curves were higher than 0.998 for all analytes. This method showed high sensitivity (LOD: 0.011–0.040 μg/L; LOQ: 0.035–0.133 μg/L), quite sufficient recovery (82.6% to 103.1%) for accuracy, and acceptable precision (intra-day recovery: 81.5–104.4%, relative standard deviation (RSD): 1.04–9.81%; inter-day recovery: 92.6–104.1%, RSD: 1.15–7.52%). All the recovery and RSD values obtained below 10% are evaluated agreeable in point of the AOAC and EURACHEM/CITAC validation guidelines. The recovery percentages of all analytes in CRM changed between 80.3 and 109.9% and the RSD (%) values for each analyte obtained below 10%. The proficiency test results were satisfactory and comparable (z score less than or equal to 2.0 is no questionable or satisfactory) to those obtained by other laboratories participating in the round. The calculated percentage of relative uncertainties for each analyte changed from 2.99 to 10.10% and the major contribution to uncertainty budget arises from the calibration curve and repeatability. Therefore, the results demonstrate that this method is applicable for the determination of possible thirty VOCs in drinking waters in routine analysis for custom laboratories.

Continuous underway measurements of dimethyl sulfide in seawater by purge and trap gas chromatography coupled with pulsed flame photometric detection

In this study, a conventional purge and trap (PT) system was modified with gas chromatography coupled with pulsed flame photometric detection (GC-PFPD) to achieve long-term continuous shipboard underway measurements of trace-level dimethyl sulfide (DMS) in unfiltered seawater. This PT system is automated, time-efficient and electronically temperature controlled. A complete analytical cycle for each sample only requires 8.5min. The critical aspects of the PT-GC-PFPD system were evaluated, and sharp peaks were observed for nanomolar levels of DMS with a low limit of detection (LOD) of 0.05nmolL−1. Unfiltered seawater samples were continuously supplied to the system because small deviations were observed in the responses between filtered and unfiltered seawater samples (ranging from 0.7% to 4.7%). Moreover, during 9days of continuous in-situ observations, a 6% deviation in the standards was observed, indicating that this system is reliable and stable. The successful application of this system in a field study suggested that the proposed DMS analysis method would significantly facilitate data collection in the field. In addition, dimethylsulfoniopropionate (DMSP) was also detected by this system after conversion to DMS. The required modifications are affordable and can be easily performed by laboratories that have traditional, non-commercial, purge and trap systems.

Determination of formaldehyde in aqueous samples with a miniaturized extraction capillary coupled to high-performance liquid chromatography.

A novel analytical method for determining formaldehyde (FA) in aqueous samples was developed with a miniaturized extraction capillary in high-performance liquid chromatography (HPLC). The extraction capillary was prepared by packing silica gel particles in a stainless steel capillary of 0.8 mm i.d. and 1.6 mm o.d. A derivatization reagent of 2,4-dinitrophenylhydrazine (DNPH) was impregnated on the silica gel particles by pumping a solution of DNPH to the capillary. Two extraction methods; dynamic extraction and purge-and-trap (PT) methods, were investigated for derivatizing and extracting FA from water samples onto the silica gel in the extraction capillary. The extraction capillary was directly connected to a six-port valve, and then desorption of the derivative from the capillary and injection to conventional HPLC system were simultaneously achieved with a flow of acetonitrile through the capillary. In the dynamic extraction, FA was determined with a simple sample preparation procedure, and the limit of detection (LOD) was 18 μg L(-1) at a sample volume of 20 mL, while several limitations were found in the method, such as bleeding of the derivatization reagent and the corresponding derivatized FA from the capillary during the sample load/extraction process. The sensitivity was significantly improved by introducing a PT technique, where the LOD was 6.9 μg L(-1) at a sample volume of 20 mL with a sampling time of approximately 20 min. With the PT method, successful recoveries of FA were confirmed for spiked tap water, river water and fruit juice samples.

Observation of the Variations of Very Short-Lived Halocarbon Emissions in Tropical Coastal Marine Boundary Layer

Halocarbons (methyl iodide, bromoform and dibromomethane) are produced naturally and the source has been found to be largely from the ocean. In recent years, the role of very short-lived halocarbons in the atmospheric chemistry has attracted many researchers in this field. Dissolved halocarbons in sea water and atmospheric halocarbons were taken at 73 different positions across South China Sea and Sulu Sea during the SHIVA measurement campaign on RV SONNE cruise from Singapore to Manila on the 15 to 29 November 2011. Both water and canister samples of air were analyzed on two different purge-and-trap (PT) gas chromatographic systems. Significant levels of halocarbons were observed during day-time and night-time in the tropical marine boundary layer. All of the halocarbons show higher concentrations at the coastal area compare to the location in the open sea.

Determination of Vinyl Chloride Monomer in Wastewater Using Purge and Trap Gas-Chromatograph Method

The analytical conditions of a purge and trap (PT) instrument have been optimized for determination of vinyl chloride monomer (VCM) in wastewater. The optimal purging pressure to purge VCM from wastewater was 10 kPa for a constant time of 10 minute at 30 °C purging temperature. The detection limit of VCM in wastewater is 0.5 μg/L. The reproducibility of replicate samples lies within 6.5%. The prominent feature of this method is the cheap cost of VCM standards and samples preparation. The fast and convenient system has been successfully employed for the determination of VCM in wastewater with good resolution and high recoveries.

Comparison of two methods for the determination of geosmin and 2-methylisoborneol in algae samples by stable isotope dilution assay through purge-and-trap or headspace solid-phase microextraction combined with GC/MS

Geosmin (1,2,7,7-tetramethyl-2-norborneol) (GSM) and 2-methylisoborneol (2-MIB), produced from the growth of blue-green algae, commonly found in lakes and reservoirs, are the major compounds responsible for the earthy and musty odours in drinking water. Two pre-extraction methods (purge-and-trap (PT) and headspace solid-phase microextraction (HS-SPME)) combined with gas chromatography/mass spectrometry (GC/MS), were introduced and compared in this study to establish simple, rapid, sensitive and selective methods for determination of GSM and 2-MIB in eutrophic water samples and algae cells. A stable isotope dilution assay (SIDA) was applied in these two methods to eliminate the matrix effect and improve the recoveries of the analytes. The deuterated compounds d5-GSM and d3-MIB were employed as internal standards for SIDA. SIDA-PT-GC/MS and SIDA-HS-SPME-GC/MS methods were evaluated and optimized for the extraction and detection of these two compounds. These two methods show good linearity over the concentration range of 10–500 ng L−1 and give detection limits of 3.60 ng L−1 of GSM and 4.12 ng L−1 of 2-MIB for SIDA-PT-GC/MS, and 3.00 ng L−1 of GSM and 3.10 ng L−1 of 2-MIB for SIDA-HS-SPME-GC/MS. The recoveries of spiked 20, 100 and 500 ng L−1 of GSM and 2-MIB from raw drinking water ranged from 81–104% for GSM and 89–111% for 2-MIB by means of SIDA-PT-GC/MS, and 83–98% for GSM and 85–121% for 2-MIB by SIDA-HS-SPME-GC/MS analysis. The SIDA-PT-GC/MS method is better used to analyze GSM and 2-MIB in clearer water samples, while SIDA-HS-SPME-GC/MS has some advantages in the determination of these two compounds in algae cells or eutrophic water samples.

Method Validation for the Trace Analysis of Geosmin and 2-Methylisoborneol in Water by ?Salt-Free? Purge-and-Trap Sampling/GC-MS, Using the Eclipse 4660 Sample Concentrator

The Eclipse 4660 purge-and trap sample concentrator, coupled to a gas chromatograph-mass spectrometer, was fully validated for trace analysis of the taste-odorants geosmin (GSM) and 2-methylisoborneol (2-MIB) in the absence of salt or methanol. The procedure involved purging a 25 mL sample volume, at 80°C, for 11 min. Quantitation was done by separation on an HP 5-MS capillary column (30 m × 0.25 mm × 0.25 μm), followed by mass spectrometric detection in the selected ion monitoring (SIM) mode. The method was found to be linear (r2 ≥ 0.995) over the calibration range 0-100 ng/L for both target analytes. The overall accuracy, determined by recovery, was 104.21% ± 19.46 (mean ± SD, range = 65.29-143.13%) for 2-MIB, and 85.24% ± 8.28 (mean ± SD, range = 68.66-101.82%) for GSM. The within-day precision averaged 7.97% for 2-MIB, and 8.77% for GSM. The day-to-day precision was 20.96% for 2-MIB, and 7.52% for GSM. The limit of quantitation (LOQ) was 6 ng/L and 5 ng/L for 2-MIB and GSM; the limit of detection (LOD) was 5 ng/L and 4 ng/L for 2-MIB and GSM respectively. Earlier findings regarding the dehydration of 2-MIB to 2-methyl-2-bornene (2-M-2-B) were confirmed. The average amount of 2-M-2-B formed was 27% (range: 15-50%), with RSD = 33.26%. There is evidence of dehydration of 2-MIB to 2-M-2-B at sample purge temperature of 40°C and higher. The poor day-to-day precision for 2-MIB has been proposed to be due to the inconsistent amount of 2-M-2-B formed. A minimum sample purge temperature of 40°C is required to purge 2-MIB and GSM from water, which can be detected by GC/MS under the purge-and-trap conditions at a concentration of 100 ng/L. The developed method was found to be sensitive, accurate, precise and reproducible for trace analysis of geosmin in water matrices.

Analysis of Volatile Compounds in Food and Cosmetic, Using the Purge and Trap Injector Coupled to a Gas Chromatograph with Photo Ionization Detector

A method was developed to analyze volatile organic compounds (VOCs) in food, beverages and cosmetic samples.VOCs were isolated from a standard solution or samples using a purge-and-trap (PT) system and identified andquantified by a gas chromatograph with Photo Ionization Detector (GC–PID). The experimental conditions wereoptimized and the performance of the system was evaluated. Linear calibration curves were obtained with correlationcoefficients of at least 0.9981. RSDs were less than 6%. Detection limits, calculated for 5 ml sample volume, rangedfrom 0.3056 ng ml-1 for toluene to 7.1373 ng ml-1 for propionaldehyde. The method was successfully applied to thequantitative analysis of food and cosmetic samples. Propionialdehyde and butyraldehyde were not found in food samples. Benzene and toluene were not detected in wine samples. Acetone was detected in all samples, except twosamples. The method is reliable and is used for routine monitoring in food, beverages and cosmetic.

Determination of 13C/12C Isotopic Ratios of Biogenic Organometal(loid) Compounds in Complex Matrixes

Methylated metal(loid) compounds are formed in the environment by abiotic as well as enzymatically catalyzed transfer of a methyl group. Due to the increased mobility and toxicity in comparison to the inorganic precursors, the investigation of the formation process is of high relevance. Though the natural abundance carbon isotope ratio can give important insights toward their origin as well as the biochemical methyl transfer process, so far, these species have not been investigated by carbon isotope ratio mass spectrometry (IRMS). This is due to the analytical challenge to precisely determine the natural isotope distribution of trace amounts of metal(loid)-bound carbon in complex organic matrixes. To overcome this problem, we tested the concept of selective derivatization of nonvolatile organometal(loid)s by hydride generation (HG) followed by purge and trap (P-T) enrichment, heart-cut gas chromatography (hcGC), and subsequent analysis by GC/IRMS. Parameter optimization of HG/P-T/hcGC was conducted using online coupling to element-sensitive ICPMS (inductively coupled plasma mass spectrometry) detection. The purity of the HG/P-T/hcGC fraction was verified by GC/MS. For the model substance trimethylarsine oxide (TMAsO), an excellent agreement of the delta(13)C-value analyzed by HG/P-T/hcGC-GC/IRMS was achieved in comparison to the bulk delta(13)C-value, which shows that no significant isotope fractionation occurred during hydride generation and subsequent separation. The optimized method showed good reproducibility and a satisfying absolute detection limit of 4.5 microg TMAsO (1.2 microg(carbon)). This method was applied to the analysis of TMAsO in compost. The low delta(13)C value of this compound (-48.38 +/- 0.41 per thousand) indicates that biomethylation leads to significant carbon fractionation. HG/P-T/hcGC-GC/IRMS is a promising tool for investigation of the biomethylation process in the environment.

Enrichment sampling methods for wine discrimination with gas sensors

A comparison between two sampling methods based on sample concentration (purge and trap (PT) and solid-phase micro-extraction (SPME)) applied to gas sensors (electronic nose) for wine discrimination is performed. Two different traps have been used in the Tekmar 3100 purge and trap concentrator: trap containing Tenax and Tenax/silica gel/charcoal. Four different types of fiber coating have been used for SPME method: 100 μm polydimethylsiloxane (PDMS), 65 μm polydimethylsiloxane/divinylbenzene (PDMS/DVB), 85 μm polyacrilate and 75 μm carboxen/polydimetilsiloxane (CAR/PDMS). The cell containing a tin dioxide multisensor was mounted inside the gas chromatograph (GC) oven, connected to the injector by replacing the chromatographic column. In this way, the GC injection port has been used to connect the purge and trap and fiber holder to sensors cell. Samples of five different wines elaborated with the major varieties of DO Vinos de Madrid were used for testing the discrimination capability of the systems. Multivariate analyses as principal component analysis (PCA) and artificial neural netwoks (ANN) have been applied to the data to discriminate among the different wine samples. Results show that purge and trap technique provide better response. Tenax trap and 85 μm polyacrilate fiber obtained the highest success rate in classification.

New approach based on solid-phase extraction for the assessment of organic compound pollutions in so-called pharmaceutically pure water

The application of a new kind of technique involving solid-phase extraction coupled with thermal desorption (SPE-TD) to the qualitative analysis of water used in pharmaceutical products was evaluated. Comparative analyses performed by the purge and trap (PT) technique were also conducted. The application of this SPE-TD technique resulted in the isolation of a large number of compounds from the water sample. The SPE-TD technique is applied to less volatile compounds, whereas the PT technique is used for more volatile and nonpolar ones. These two techniques should be applied in order to achieve complete identification and quantitative determination. Additionally, an attempt to identify organic compounds in pharmaceutical products was also conducted. The compounds present in such products include aldehydes, ketones, hydrocarbons, alcohols, esters. The influence of storage on the quality of water was also investigated. For samples characterized by a longer storage time, qualitatively richer chromatograms were obtained, which confirmed that components were released from the packaging (especially polyethylene) which entered the stored product.

Characterisation of volatile aroma compounds of orange juices by three dynamic and static headspace gas chromatography techniques

The influence of collection of volatiles by different headspace sampling techniques was compared for different orange juices, including one fresh unpasteurised, two reconstituted commercial juices and one juice freshly hand extracted in the laboratory. Dynamic headspace sampling from stirred juice samples (DH + S) and notably by purge and trap (PT) sampling gave the highest levels of analysed volatiles, but the composition of the isolated volatiles from the different types of juices varied depending on the volatiles collection method. Aroma sampling by dynamic headspace method without stirring (DH) gave results that reflected the equilibrium aroma composition as determined by static headspace better than that obtained by PT sampling. Totally, 67 aroma constituents were identified among all the orange juices. The largest amount of volatiles was isolated from the fresh commercial, unpasteurised juice, followed by the two reconstituted juices and the hand extracted juice. Limonene was the major constituent of all commercial juices comprising 72–93% of the total peak area of isolated volatiles, meanwhile its amount in the freshly hand extracted juices ranged from 25 to 62% depending on the method of isolation. Qualitatively, the aroma profiles of the freshly extracted oranges and the fresh, commercial unpasteurised juice were described by 62 and 55 aroma compounds, respectively, which included large proportions of esters and aldehydes. Only 41 and 34 aroma compounds, mainly terpenes, were identified in the reconstituted orange juices.

The comparison of physico‐chemical and textural properties, as well as volatile compounds, from low‐fat and regular‐fat sausages

SummaryIn order to determine the optimum method for extraction of the entire flavour profile of sausages, three extraction techniques, solvent extraction (SE), purge and trap (PT), and simultaneous distillation extraction (SDE), were compared. Similarly, to effectively analyse the volatile compounds of low‐fat (<3%) and regular‐fat (approximately 15%) sausages, three isolation techniques were investigated and gas chromatography (GC) and gas chromatography–mass spectrometry (GC/MS) were used for final identification of compounds. A total of thirty‐three volatile compounds were identified in the sausages by SDE, twelve by SE, and nine by PT. In the SE method, fats interfered in the extraction of some volatile components, resulting in lower recovery and longer isolation time when compared with the other two methods. The PT method might not be a good extraction method because of the loss of heterocyclic compounds. However, the SDE method showed greater yields and recognized more volatiles when compared with SE. Furfural, trans‐caryophyllene, and myristicine were the predominant volatile compounds extracted by SDE. These results suggest that the SDE method is the most efficient method in isolating volatile compounds in both regular‐ and low‐fat sausages. The amounts of volatile compounds, such as, 4‐acethyl‐3‐methyl pyrazole, 1,4‐dimethyl benzene, p‐ethylguaiacol and β‐caryophyllene were higher in regular‐fat sausages; however, the amounts of myristicine and hexadecanoic acid were higher in low‐fat sausages.

Purge-and-trap capillary gas chromatography with atomic emission detection for volatile halogenated organic compounds determination in waters and beverages

A method for the simultaneous determination of 10 volatile halogenated organic compounds (VHOCs), including four trihalomethanes (THMs), in waters and beverages was developed. The analytes were stripped from the aqueous sample by a flow of helium, preconcentrated in a capillary trap and thermally desorbed using a purge-and-trap (PT) system. This was followed by capillary gas chromatography with microwave-induced plasma atomic emission spectrometry (GC–AED). For element-specific detection, three wavelengths were monitored, corresponding to chlorine (479 nm), bromine (478 nm) and iodine (193 nm). Each chromatographic run took 21 min, including the purge time. After careful choice of the experimental conditions, the performance of the system was evaluated. Calibration curves were obtained by plotting peak area versus concentration and the correlation coefficients for linear calibration were at least 0.9987. Detection limits, calculated for 5 ml sample volume, ranged from 0.05 μg l −1 for chloroform to 0.5 μg l −1 for tetrachloromethane. The method was successfully applied to the quantitative analysis of water samples of different origin and also of several beer and juice samples. The tap water samples analyzed contain variable concentrations of the four trihalomethanes, ranging from 1.0 to 66.5 μg l −1, depending of the compound. Whereas chloroform, bromodichloromethane and bromoform were found in some of the juice samples, only chloroform was detected in the beer samples. The method is reliable and can be used for routine monitoring in water and beverages.

Construction and validation of an automated spray-and-trap gas chromatograph for the determination of volatile organic compounds in aqueous samples

An automated spray-and-trap (ST) chromatographic system was constructed for fast and efficient extraction of volatile organic compounds (VOCs) in aqueous samples with the capability to be deployed in the field for unattended continuous monitoring of surface or ground water. This system was built upon a commercial gas chromatograph with full automation capability using self-developed hardware and software. For sample analysis, fine droplets of the aqueous solution were generated in the extraction chamber by pressure expansion of a clean air stream through a spray nozzle. A portion of the VOCs distributed into the gas phase was retained by a multi-sorbent micro-trap kept at ambient temperature. Flash heating of the sorbent trap desorbed the enriched VOCs onto the gas chromatography (GC) with flame ionization detection (FID) for hydrocarbons or electron-capture detection (ECD) for halocarbons. In order to validate the performance of the ST method, it was compared with a more conventional method, i.e., a purge-and-trap (PT), by analyzing a serious of standard solutions containing benzene, toluene, ethylene, and o-, m-xylenes. Using a purge-and-trap method as a reference for complete extraction, the ST method showed less sensitivity. Extraction recoveries are in consistent with Henry’s law constants. To test response time the ST–GC–ECD was periodically switched between tap and underground waters. Negligible carry-over of halogenated species and reproducibility better than 2% relative standard deviation (R.S.D.) can be achieved regardless of large concentration difference between the two sources, thus demonstrating applicability of the ST system for on-site monitoring.

Trace sulfide determination in oxic freshwaters

A simplified method for determination of reduced sulfur species in natural waters is presented. Reduced sulfur species were separated from a natural water matrix, using purge-and-trap (PT), after reacting with acid (acid volatile sulfide—AVS) or Cr(II) in acidic medium (chromium reducible sulfur—CRS). Sulfide in the trapping medium (0.05 M NaOH), was analyzed spectrophotometrically after derivatization to form methylene blue (MB). AVS precision for Na 2S and zinc sulfide clusters in synthetic solutions was ≤8.5% RSD at concentrations ranging from 48 to 503 nM. Spike recoveries of zinc sulfide clusters were 75–98% in a variety of freshwaters using the AVS procedure. Spike recoveries of Cu sulfide colloids were 94–109% in the same freshwater samples using the CRS procedure. During the analytical procedure an interfering compound was produced due to the reaction of mixed diamine reagent with itself. Lowering the pH of the reaction mixture minimized the formation of this compound. Minimizing contamination from particulates was necessary to achieve sub-nanomolar detection limits. The detection limit for AVS in a 500 ml sample with a 10 cm spectrophotometer cell was 0.1–0.3 nM (3×S.D. blank). The CRS procedure was calibrated with a synthetic CuS colloid. Interferences to the CRS method included finely divided pyrite, polysulfide, thiosulfate, sulfite and some elemental sulfur. The Cr(II) reagent did not reduce sulfate under our experimental conditions. The degree to which zinc sulfide clusters were adsorbed on membrane filters during filtration was mitigated if the clusters were synthesized in the presence of natural organic matter. Examples of AVS and CRS concentrations determined in oxygenated waters using the PT method were comparable to those reported recently by other methods. This method offers greater simplicity than other methods for trace dissolved sulfide determination in natural waters.

Comparison of methods for determination of volatile organic compounds in drinking water

Comparison of four methods including liquid–liquid extraction (LLE), direct aqueous injection (DAI), purge and trap (PAT) and head space (HS) were carried out in this work for determination of volatile organic compounds (VOCs) including trihalomethanes (THMs) in drinking water. This comparison is made especially to show the advantages and disadvantages and specifically the different detection limits (DL) that can be obtained for a given type of analysis. LLE is applicable only for determination of the THMs concentrations, while DAI, PAT, HS methods with different DL each of them are applicable for all VOCs, with PAT to be the most sensitive. Sampling apparatus and procedure for all these methods except of PAT are very simple and easy, but possible disadvantages for LLE and DAI are the low sensitivity and especially the detection only of THMs with LLE.

DISINFECTION BY-PRODUCTS AND VOLATILE ORGANIC COMPOUNDS IN THE WATER SUPPLY SYSTEM IN ATHENS, GREECE

On a monthly basis, on a one year period, disinfection by-products (DBPs) and volatile organic compounds (VOCs) were measured in raw water and in treated water of four water treatment plants (WTP) as well as from eight representative points of the distribution network of Athens. Liquid-liquid extraction (LLE) method followed by gas chromatography (GC) with electron capture detection (ECD) and mass spectrometry (MS) was used for the determination of the DBPs, while the purge-and-trap (PAT) technique followed by GC-MS was used for the determination of the VOCs. The DBPs that have been studied included trihalomethanes (THMs), haloacetonitriles (HANs), haloketones (HKs), chlorate hydrate (CH) and chloropicrin (CP), while forty one VOCs were also studied including THMs. Chloroform (CM), dichlorobromomethane (DCBM), chlorodibromomethane (CDBM) were the major organic compounds found in all treated water samples. HANs, HKs, CH and CP were detected in treated samples but at lower concentrations.