Anna Godayol

Headspace needle-trap analysis of priority volatile organic compounds from aqueous samples: Application to the analysis of natural and waste waters

Combining headspace (HS) sampling with a needle-trap device (NTD) to determine priority volatile organic compounds (VOCs) in water samples results in improved sensitivity and efficiency when compared to conventional static HS sampling. A 22 gauge stainless steel, 51-mm needle packed with Tenax TA and Carboxen 1000 particles is used as the NTD. Three different HS-NTD sampling methodologies are evaluated and all give limits of detection for the target VOCs in the ng L⁻¹ range. Active (purge-and-trap) HS-NTD sampling is found to give the best sensitivity but requires exhaustive control of the sampling conditions. The use of the NTD to collect the headspace gas sample results in a combined adsorption/desorption mechanism. The testing of different temperatures for the HS thermostating reveals a greater desorption effect when the sample is allowed to diffuse, whether passively or actively, through the sorbent particles. The limits of detection obtained in the simplest sampling methodology, static HS-NTD (5 mL aqueous sample in 20 mL HS vials, thermostating at 50 °C for 30 min with agitation), are sufficiently low as to permit its application to the analysis of 18 priority VOCs in natural and waste waters. In all cases compounds were detected below regulated levels.

Sorbent-packed needle microextraction trap for benzene, toluene, ethylbenzene, and xylenes determination in aqueous samples.

A needle trap (NT) device filled with Carbopack X as a sorbent material is evaluated for the static headspace analysis of benzene, toluene, ethylbenzene, and xylene (BTEX) compounds in aqueous samples. Injection parameters used with the NT device (e.g. volume of carrier gas and time to open the split valve) are evaluated to determine the mechanism involved during the desorption and transferring of the target compounds into the GC column. Furthermore, different parameters affecting the adsorption capacity of the sorbent are studied (e.g. sampling time and temperature, headspace/sample volume ratio, salting-out, and stirring). The evaluation of the method with aqueous samples shows that repeatability and recoveries with the NT device are equivalent to those obtained using solid-phase microextraction with a carboxen/PDMS (CAR/PDMS) coating. LODs obtained with flame ionization detection are in the range of 10-25 μg/L, and in the range of hundredths of μg/L with MS detection. The method developed is satisfactorily applied to the analysis of aqueous samples obtained from wastewater treatment plants.

Needle microextraction trap for on-site analysis of airborne volatile compounds at ultra-trace levels in gaseous samples.

Different capillary needle trap (NT) configurations are studied and compared to evaluate the suitability of this methodology for screening in the analysis of volatile organic compounds (VOCs) in air samples at ultra-trace levels. Totally, 22 gauge needles with side holes give the best performance and results, resulting in good sampling flow reproducibility as well as fast and complete NT conditioning and cleaning. Two different types of sorbent are evaluated: a graphitized carbon (Carbopack X) and a polymeric sorbent (Tenax TA). Optimized experimental conditions were desorption in the GC injector at 300°C, no make-up gas to help the transport of the desorbed compounds to the GC column, 1 min splitless time for injection/desorption, and leaving the NT in the hot injector for about 20 min. Cross-contamination is avoided when samples containing high VOC levels (above likely breakthrough values) are evaluated. Neither carryover nor contamination is detected for storage times up to 48 h at 4°C. The method developed is applied for the analysis of indoor air, outdoor air and breath samples. The results obtained are equivalent to those obtained with other thermal desorption devices but have the advantage of using small sample volumes, being simpler, more economical and more robust than conventional methodologies used for VOC analysis in air samples.

Monitoring of sixteen fragrance allergens and two polycyclic musks in wastewater treatment plants by solid phase microextraction coupled to gas chromatography

A methodology based on headspace solid phase microextraction (HS-SPME) and gas chromatography-mass spectrometry (GC-MS) determination was developed for the monitoring and evaluation of the removal efficiency of 16 common fragrance allergens and two polycyclic musks in wastewater treatment plants (WWTPs). An experimental design with a full factorial model was applied to evaluate the effects of the experimental parameters on the extraction (e.g., salt content, time and extraction temperature). After determining the optimum conditions (2.4 g NaCl, 45 min at 90 °C), an external calibration was performed and quality parameters of the proposed method were evaluated. Method detection limits in the range of 0.01-1.7 μg L(-1) were obtained. Satisfactory inter-day precision values between 4% and 23% (n=5) were obtained for most compounds. The method was applied to the monitoring of the target analytes in samples from two WWTPs. Seven target compounds were detected at the primary effluent of both plants at μg L(-1) levels. Limonene, linalool and eugenol were quantitatively eliminated during the secondary treatments of both WWTPs, while lilial, benzyl salicylate, galaxolide, and tonalide were still detected at the effluent waters.

Assessment of environmental tobacco smoke contamination in public premises: significance of 2,5-dimethylfuran as an effective marker.

Contamination by environmental tobacco smoke (ETS) on premises where smoking is permitted is evaluated. Although all target VOCs evaluated show significant differences between smoking and nonsmoking indoors, the results obtained indicate that 2,5-dimethylfuran is the most appropriate and effective marker of ETS contamination given that this compound is only detected in environments where people have smoked and so the detection of this compound cannot be attributed to other contamination sources such as traffic. Moreover, the air levels of this compound due to coffee aroma are below the detection limits for this methodology. A preliminary study is performed to evaluate whether 2,5-dimethylfuran, a smoking breath biomarker, can be detected in passive smokers working in smoking environments. The compound was continuously detected in the breath of nonsmoking employees after being in direct contact with ETS for just a few hours. The Tedlar gas sampling bags had 5% loss of 2,5-dimethylfuran after 3 h of storage, which we took as the maximum recommended period for air sample storage.

Odour-causing organic compounds in wastewater treatment plants: Evaluation of headspace solid-phase microextraction as a concentration technique

Odorous emissions from wastewater collection systems and treatment facilities affecting quality of life have given local populations reasons to complain for decades. In order to characterise the composition of such malodorous emissions, a method based on headspace solid-phase microextraction (HS-SPME) and gas chromatography coupled to mass spectrometry (GC-MS) has been developed to determine a list of compounds belonging to different chemical families, which have been previously described as potentially responsible for odour complaints, in wastewater matrices. Some parameters affecting the chromatographic behaviour of the target compounds were studied (e.g. splitless time). Experimental conditions affecting the extraction process (temperature, time and salt content) were evaluated by applying a factorial design at two levels. Using a DVB/CAR/PDMS fibre and the optimised HS-SPME conditions, calibration curves were constructed with detection limits in the range of 0.003-0.6 μg L(-1). Recovery values higher than 70% and relative standard deviation values between 5 and 16% (n=5) were obtained for all compounds and found to be satisfactory. In wastewater samples, a decrease in the concentration of the analysed compounds through the different treatments was observed. Most of the target analytes were found in influent samples while only octanal and carvone were detected in samples from the plant effluent.

Assessment of the effect of UV and chlorination in the transformation of fragrances in aqueous samples

The removal and transformation of 15 common fragrance allergens and two polycyclic musks in water samples were studied using UV irradiation and chlorination treatments. The monitoring of the reaction was carried out by a HS-SPME method coupled to GC-MS analysis. Different behaviours were observed depending on the compound and the treatment applied. Elimination experiments showed that all target compounds were affected by at least one of the two treatments. A total of 15 UV transformation products were detected and chemical structures were proposed for five of them. In the chlorination experiments, only galaxolide and benzyl cinnamate transformation products were observed.

Odour-causing compounds in air samples: gas-liquid partition coefficients and determination using solid-phase microextraction and GC with mass spectrometric detection.

A quantification method based on solid-phase microextraction followed by GC coupled to MS was developed for the determination of gas-liquid partition coefficients and for the air monitoring of a group of odour-causing compounds that had previously been found in wastewater samples including dimethyl disulphide, phenol, indole, skatole, octanal, nonanal, benzothiazole and some terpenes. Using a divinylbenzene/carboxen/polydimethylsiloxane fibre, adsorption kinetics have been studied to define an extraction time that would avoid coating saturation. It was found that for an extraction time of 10 min, external calibration could be performed in the range of 0.4-100 μg/m(3), with detection limits between 0.1 and 20 μg/m(3). Inter-day precision of the developed method was evaluated (n = 5) and RSD values between 12 and 24% were obtained for all compounds. The proposed method has been applied to the analysis of air samples surrounding a wastewater treatment plant in Catalonia (Spain). In all air samples evaluated, dimethyl disulphide, limonene and phenol were detected, and the first two were the compounds that showed the highest partition coefficients.

Mass spectrometry identification of alkyl-substituted pyrazines produced by Pseudomonas spp. isolates obtained from wine corks

We investigated the pyrazine production of 23 Pseudomonas isolates obtained from cork in order to assess their implications in off-flavour development. Off-flavour development in cork stoppers is a crucial process in maintaining the high quality of some wines. Pyrazine production was analyzed by headspace solid-phase-microextraction (HS-SPME) and gas chromatography coupled with mass spectrometry (GC-MS). Five out of the 23 isolates, i.e. Pseudomonas koreensis TCA20, Pseudomonas palleroniana TCA16, Pseudomonas putida TCA23 and N7, and Pseudomonas stutzeri TRA27a were able to produce branched alkyl-substituted pyrazines. For isolates N7 and TCA16, 14 compounds could be identified as pyrazines. The use of mineral media supplemented with different carbon and nitrogen sources resulted in changes in the pyrazine production capacity. In the two strains the amount of pyrazines produced was higher with glucose and decreased significantly with lactate. In all cases, 2,5-di(1-methylethyl)pyrazine was found to be dominant and independent of amino acid addition, suggesting a completely de novo synthesis. Aroma descriptions of most alkyl substituted pyrazines include mild vegetal aromas, not necessarily undesirable for the cork manufacturing industry. Methoxypyrazines, exhibiting earthy and musty aromas, could not be detected in any of the strains analysed.

Development of a method for the monitoring of odor-causing compounds in atmospheres surrounding wastewater treatment plants

This study describes the development of an analytical method based on active collection in a multisorbent Tenax TA/Carbograph 1TD tube, followed by thermal desorption and GC-MS for the determination of 16 volatile organic compounds in air samples. The analyzed compounds include ozone precursors and odor-causing compounds belonging to different chemical families (sulfur- and nitrogen-containing compounds, aldehydes, and terpenes). Two types of sorbents were tested and desorption conditions (temperature, time, and sampling, and desorption flow) were evaluated. External calibration was carried out using the multisorbent bed. Method detection limits in the range 0.2-2.0 μg m(-3) for 1 L samples were obtained. The method was applied for determining the target compounds in air samples from two different wastewater treatment plants. Most compounds were detected and toluene, limonene, and nonanal were found in particularly high concentrations with maximum values of 438, 233, and 382 μg m(-3), respectively.