S. Muniategui Lorenzo

Simultaneous determination of 11 polycyclic aromatic hydrocarbons (PAHs) by second-derivative synchronous spectrofluorimetry considering the possibility of quenching by some PAHs in the mixture

A method capable of determining 11 PAHs (acenaphthene, anthracene, benz[a]anthracene, benzo[a]pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene, chrysene, phenanthrene, fluoranthene, indeno[1,2,3-cd]pyrene and perylene) in a mixture of 18 by second-derivative synchronous spectrofluorimetry in the constant wavelength mode was developed. It has not been possible to determine the following PAHs in the mixture: dibenz[a,h]anthracene, fluorene, indene, naphthalene, pyrene, triphenylene and 1,12-benzoperylene. The possibility of selective quenching of some molecules by others in the mixture was considered and it was found that the fluorescent signal of fluorene is quenched by indeno[1,2,3-cd]pyrene. Other papers related to complex mixtures have not taken this possibility into account; on the other hand, the identification and quantification of PAHs in such a complex mixture (18 compounds) has never been attempted before. The approach studied allows the sensitive, rapid, easy and inexpensive identification and quantification of 11 PAHs in a solution of hexane. The detection limits are between 0.01 and 0.70 ng ml–1 in most cases (except for indeno[1,2,3-cd]pyrene with a detection limit of 4.95 ng ml–1) and a short analysis time (four PAHs were determined in one interval alone, Δλ = 95 nm), the total identification and quantification of the PAHs taking only 10 min.

Optimization of microwave-assisted extraction of hydrocarbons in marine sediments: comparison with the Soxhlet extraction method

Abstract Microwave energy was applied to extract polycyclic aromatic hydrocarbons (PAHs) and linear aliphatic hydrocarbons (LAHs) from marine sediments. The influence of experimental conditions, such as different extracting solvents and mixtures, microwave power, irradiation time and number of samples extracted per run has been tested using real marine sediment samples; volume of the solvent, sample quantity and matrix effects were also evaluated. The yield of extracted compounds obtained by microwave irradiation was compared with that obtained using the traditional Soxhlet extraction. The best results were achieved with a mixture of acetone and hexane ¶(1 : 1), and recoveries ranged from 92 to 106%. The extraction time is dependent on the irradiation power and the number of samples extracted per run, so when the irradiation power was set to 500 W, the extraction times varied from 6 min for 1 sample to 18 min for 8 samples. Analytical determinations were carried out by high-performance liquid chromatography (HPLC) with an ultraviolet-visible photodiode-array detector for PAHs and gas chromatography (GC) using a FID detector for LAHs. To test the accuracy of the microwave-assisted extraction (MAE) technique, optimized methodology was applied to the analysis of standard reference material (SRM 1941), obtaining acceptable results.

Determination of polycyclic aromatic hydrocarbons (PAHs) in a complex mixture by second-derivative constant-energy synchronous spectrofluorimetry

In this work, the combination of the excellent band narrowing features of derivative spectrometry with constant-energy synchronous fluorescence spectrometry for the simultaneous determination of different polycyclic aromatic hydrocarbons (PAHs) in a mixture of 18 is assessed. This mode of scanning allowed for the identification and quantification of 10 PAHs and the grouping of some of these.

Simultaneous determination of carbonyl compounds and polycyclic aromatic hydrocarbons in atmospheric particulate matter by liquid chromatography–diode array detection–fluorescence detection

Simultaneous analysis of 24 carbonyl compounds (alkanals, unsaturated, dicarbonylic and aromatic aldehydes and ketones) derivatized with 2,4-dinitrophenylhydrazine and 16 polycyclic aromatic hydrocarbons (PAHs) using a photodiode-array (PDA) and a fluorescence (FL) detector in series is proposed. The separation is carried out with a reversed-phase column and gradient elution using four solvents (acetonitrile, water, tetrahydrofuran and methanol) in less than 35 min. Several critical pairs of carbonyl compounds with 3 and 4 carbon atoms and different functional groups, isomers of tolualdehyde, aromatic and aliphatic aldehydes were conditional on the gradient elution. Common pre-treatment for two groups of compounds consists in a step of extraction and derivatization in aqueous medium and a further clean-up using a polymeric phase SPE and concentration in a mixture of dichloromethane:methanol. A pre-concentration factor of 50 was achieved by this procedure. Acetone and formaldehyde blanks were minimized and remain controlled with a specific cleaning of glass material and washing the SPE cartridge. The limits of detection (LOD) ranged from 0.006 to 0.18 ng mL(-1) for PAHs and from 2.4 to 10.1 ng mL(-1) for carbonyl compounds and method precision was <or=15% for all analysed compounds. Recoveries were within the range of 95-104% for PAHs except for more volatile compounds (acenaphthene and fluorene) and within the range of 72-113% for carbonyl compounds. The method was applied in water-soluble fraction of PM(10) (atmospheric particulate matter with an aerodynamic diameter less than 10 microm) and the spectral contrast technique was used in the identification of carbonyl compounds.

Application of programmed-temperature split/splitless injection to the trace analysis of aliphatic hydrocarbons by gas chromatography

Abstract The dependence of the programmed-temperature solvent split sampling technique using a PSS (programmed-split/splitless) injection mode on different variables affecting the introduction of large sample volumes for a mixture of alkanes in capillary GC was evaluated. Apart from the studies found in the literature on different factors such as speed of injection, presence of adsorbent in the liner, internal diameter of the liner, initial and final injector temperature, split flow-rate and initial split time, affecting the chromatographic signal of different compounds, others were studied whose influence has not been considered until now. They include length of the microsyringe needle, adsorbent distribution in the liner, injection volume on analyte discrimination, speed of injector heating, time which the column stays at the initial temperature and time that the injector stays at the final temperature. Once finalised, the study of the PSS injection mode was compared with the conventional mode of gas chromatography splitless injection, and found that the proposed method increases sensitivity in GC trace analysis. Finally, the application of both injection modes in the determination of aliphatic hydrocarbons was tested in an atmospheric particulate sample.

Resolution of benzo[a]pyrene in complex mixtures of other polycyclic aromatic hydrocarbons. Comparison of two spectrofluorimetric methods applied to water samples

Two spectrofluorimetric methods, second-derivative constant-energy synchronous luminescence (SDCESL) and constant-wavelength synchronous luminescence (CWSL) in combination with multiple linear regression (MLR), for the quantification of benzo[a]pyrene (BaP) at sub-ng mL−1 levels, in the presence of benzo[b]fluoranthene (BbFt), benzo[k]fluoranthene (BkFt), benzo[ghi]perylene (BghiP) and indeno[1,2,3-cd]pyrene (IP), were developed and compared in detail. SDCESL presents lower limits of detection and quantification than CWSL/MLR and also gives more exact and precise results for levels close to the quantification limit. For BaP, SDCESL achieved quantification limits of 0.019 ng mL−1 in river waters and 0.007 ng mL−1 in drinking waters. This work offers a sensitive, precise, accurate, rapid, simple and economic methodology for monitoring BaP in waters for public consumption, meeting all the requirements of the EC Directive 98/83/CE that fixes the maximum admissible limit for this polycyclic aromatic hydrocarbon in drinking waters at of 0.010 ng mL−1.

Capillary zone electrophoresis for the determination of light-absorbing anions in environmental samples

Abstract A rapid and simple method for separation and determination of inorganic anions by capillary zone electrophoresis was described. The detection was carried out directly with a diode array detector. The experimental conditions, such as concentration of carrier electrolyte, capillary length, voltage, and temperature were optimized. In order to improve selectivity, different organic modifiers were also investigated. The baseline separation of 10 light-absorbing anions was accomplished within 3.5 min with a background electrolyte consisting of 50 mM sodium tetraborate containing 5% MeOH. Linear plots were obtained in the concentration range of 0.1–10 μg/ml. With sample stacking injection, the quantitation limits of the anions were found to be in the range of 0.02–0.1 μg/ml. The proposed method was successfully applied to the determination of inorganic anions in environmental samples and in effluents of a power plant.

Optimizing Resolution in Constant-Energy Synchronous Spectrofluorimetry

Constant-energy synchronous luminescence (CESL) offers significant improvements in selectivity and sensitivity compared to the more conventional constant-wavelength synchronous luminescence (CWSL) technique. Despite this consideration, practical problems can be encountered that have not been reported in the literature. This paper offers an explanation of these technical issues—why they occur and how they can be avoided—and the method optimized to take full advantage of this powerful technique. Polycyclic aromatic hydrocarbons (PAHs) were selected for demonstrating all our conclusions, because of their carcinogenic activity; 16 of them appear in the EPA (Environmental Protection Agency) list as PAHs for which it is necessary to develop efficient methods for their precise and accurate quantification at low levels. The technique can be applied to other complex fluorescent mixtures.

Ion-Exchange Method for Analysis of Four Arsenic Species and its Application to Tap Water Analysis

Abstract Arsenic (III), arsenic (V), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA) were separated by ion-exchange chromatography. The elution sequence was as follows: 1.5 M ammonia followed by 0.12 M hydrochloric acid yielding As(III); 1 M hydrochloric acid followed by water yielding first As(V) and then MMA. Detection was performed by hydride generation-atomic absorption spectrometry. The possible interferences of 13 metallic ions have been studied and none of them was found to interfere. The method provides good linearity, precision, accuracy, and sensitivity. It has been applied to the speciation of arsenic in tap water samples from North West of Spain (a region about 29500 Km2).

Separation of alkylbenzyl quaternary ammonium compounds by capillary zone electrophoresis with sample stacking injection

A systematic investigation of operational buffer systems, sample preparation and instrument parameters for achieving the best possible performance for determinating an homologous series of N-benzyl-N-alkyl-N,N-dimethylammonium chloride compounds by capillary zone electrophoresis with direct UV detection. The most effective separation was achieved within 3.5 min with the addition of acetonitrile (40%) in a phosphate buffer (20 mM pH 5.2) using a 40 cm fused-silica capillary operating at 25 KV and 20°C. Degassing of all electrolyte solutions and samples was very important. The linearity and repeatability for each compounds were satisfactory. To improve detection limits, on-column sample preconcentration, sample stacking, was investigated achieving a tenfold enrichment factor and quantitation limits about 10−7M.