Evaluating on-line solid-phase extraction coupled to liquid chromatography-ion trap mass spectrometry for reliable quantification and confirmation of several classes of antibiotics in urban wastewaters.

This study provides an evaluation of on-line solid-phase extraction (SPE) and liquid chromatography (LC) in combination with ion trap (IT) mass spectrometry for the simultaneous routine analysis of 12 antibiotics belonging to multiple classes together with carbamazepine and propranolol in sewage treatment effluents. The on-line SPE step warranted high sensitivity and high sample throughput while IT mass detection provided high selectivity for confirmation of positive samples. A single extraction procedure resulted in recoveries ranging from 40% to 120%. Limits of detection were in the 1-46 ng/L range, which constitutes an improvement of a factor of 10 with respect to the off-line SPE procedure.

An experimental set up of a PAH vapour generator and its use to test an annular denuder.

The aim of this work is to develop and test a dynamic gas generator for semi-volatile organic compounds (SVOC). A single compound, naphthalene, is used as a surrogate PAH to test the system. The dynamic generation of PAH is based on the permeation technique [Analyst 106 (1981) 817; Am. Ind. Hyg. Assoc. J. 38 (1977) 712]. Monitoring the temperature and measuring the mass of PAH present in the permeation chamber every 48 h gives a direct measurement of the sublimation rate of the PAH. Knowing the flow rate, gives an accurate value of the concentration of PAH from the generator. It was found stable over a period of time under constant operating conditions. This concentration is diluted down to between 0.3 and 30 ppbv by a controlled flow of pure air. The diluting airflow is a mixture of dry and wet air, making it possible to control the relative humidity of the flow from the generator as well as its concentration in PAH. We used this generator to calibrate an annular denuder tube, based on the study by Gundel et al. [Atmos. Environ. 29 (1995) 1719]. Although this technique has been shown to be artefact-free for sampling gaseous PAH [Polycyclic Aromatic Compounds 9 (1996) 67; Atmos. Environ. 28 (1994) 3083], its trapping efficiency still depends on environmental parameters (temperature, relative humidity and sampling duration). Accordingly, we used our generator to calibrate a single annular denuder under controlled conditions (T degrees C, HR%, CPAH, sampling duration). The trapping efficiency of the denuder was calculated by two independent methods. Firstly, by comparing the amount trapped on a denuder with the measured mass sublimated in the generator. Secondly, by putting two denuders in series and comparing the mass collected on the first and the second tube. These two methods gave similar results, within the 10% relative uncertainties of both methods. The first results obtained show that, in environmental conditions, the efficiency ranges between 90 and 100%.

Intrinsic biodegradation potential of aromatic hydrocarbons in an alluvial aquifer--potentials and limits of signature metabolite analysis and two stable isotope-based techniques.

Three independent techniques were used to assess the biodegradation of monoaromatic hydrocarbons and low-molecular weight polyaromatic hydrocarbons in the alluvial aquifer at the site of a former cokery (Flémalle, Belgium). Firstly, a stable carbon isotope-based field method allowed quantifying biodegradation of monoaromatic compounds in situ and confirmed the degradation of naphthalene. No evidence could be deduced from stable isotope shifts for the intrinsic biodegradation of larger molecules such as methylnaphthalenes or acenaphthene. Secondly, using signature metabolite analysis, various intermediates of the anaerobic degradation of (poly-) aromatic and heterocyclic compounds were identified. The discovery of a novel metabolite of acenaphthene in groundwater samples permitted deeper insights into the anaerobic biodegradation of almost persistent environmental contaminants. A third method, microcosm incubations with 13C-labeled compounds under in situ-like conditions, complemented techniques one and two by providing quantitative information on contaminant biodegradation independent of molecule size and sorption properties. Thanks to stable isotope labels, the sensitivity of this method was much higher compared to classical microcosm studies. The 13C-microcosm approach allowed the determination of first-order rate constants for 13C-labeled benzene, naphthalene, or acenaphthene even in cases when degradation activities were only small. The plausibility of the third method was checked by comparing 13C-microcosm-derived rates to field-derived rates of the first approach. Further advantage of the use of 13C-labels in microcosms is that novel metabolites can be linked more easily to specific mother compounds even in complex systems. This was achieved using alluvial sediments where 13C-acenaphthyl methylsuccinate was identified as transformation product of the anaerobic degradation of acenaphthene.

Effect of relative humidity on gas/particle partitioning and aerosol mass yield in the photooxidation of p-xylene.

The formation of secondary organic aerosol and gas/particle partitioning of carbonyl products from the photooxidation of p-xylene has been investigated as a function of relative humidity. Experiments were performed in an atmospheric simulation chamber at atmospheric pressure and ambient temperature in the presence of NOx. Aerosol yields increased by a factor of approximately two over the relative humidity range 5-75% and were found to correlate with initial water vapor concentration and hydroxyl radical (OH) concentration. The results indicate that an increase in relative humidity results in higher levels of HONO formation in the chamber which leads to increased OH concentration, a faster p-xylene decay rate, and higher aerosol mass yields. A recently developed denuder-filter sampling technique was used to investigate the gas/ particle partitioning behavior of the carbonyl photooxidation products. The identified products accounted for up to 18% of the aerosol mass formed. Dicarbonyls with at least one aldehyde functionality (e.g., glyoxal and methylglyoxal) exhibited gas/ particle partitioning coefficients several orders of magnitude higher than expected from absorptive partitioning theory, suggesting that reactive uptake and particle phase reactions are important processes for aerosol formation from these species. Experimental gas/particle partitioning coefficients were also found to be dependent on relative humidity, with every dicarbonyl exhibiting much lower values when the relative humidity was increased from 50% to 75%.

A denuder-filter sampling technique for the detection of gas and particle phase carbonyl compounds.

A denuder-filter sampling technique for the simultaneous collection of gas and particle phase carbonyl compounds has been developed and tested. The denuder was coated with XAD-4 resin and the derivatizing agent O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) to enable on-tube conversion of gas-phase carbonyls to their oxime derivatives which were extracted and identified by GC-MS. The performance of the PFBHA-coated denuder was tested on a range of carbonyls, dicarbonyls, aromatic aldehydes, carbonyl-containing furans, and benzoquinones. The collection efficiency of the PFBHA-coated denuder was over 90% for sampling times of 10 min and significantly higher than when using only XAD-4 as the sorbent. The collection efficiency and rate of on-tube derivatization was highest for aldehydes and lowest for ketones, consistent with the expected reactivity of carbonyls with PFBHA. The method was used to separate the gas and particle phase carbonyl products formed during the photooxidation of toluene in order to assess its potential for application to simulation chamber experiments of VOC oxidation. The results indicate that when compared to a conventional filter sampling setup, the PFBHA-coated denuder-filter reduced the extent of gas phase adsorption onto the filter by at least a factor of 2 for each of the carbonyls formed. Further potential applications of the denuder-filter sampling method are discussed.