Esther Fernández-Fernández

Microwave-assisted extraction versus Soxhlet extraction in the analysis of 21 organochlorine pesticides in plants

A method to determine 21 organochlorine pesticides in vegetation samples using microwave-assisted extraction (MAE) is described and compared with Soxhlet extraction. Samples were extracted with hexane-acetone (1:1, v/v) and the extracts were cleaned using solid-phase extraction with Florisil and alumine as adsorbents. Pesticides were eluted with hexane-ethyl acetate (80:20, v/v) and determined by gas chromatography and electron-capture detection. Recoveries obtained (75.5-132.7% for Soxhlet extraction and 81.5-108.4% for MAE) show that both methods are suitable for the determination of chlorinated pesticides in vegetation samples. The method using microwave energy was applied to grass samples from parks of A Coruña (N.W. Spain) and to vegetation from the contaminated industrial area of Torneiros (Pontevedra, N.W. Spain).

Comparison of pressurized liquid extraction and microwave assisted extraction for the determination of organochlorine pesticides in vegetables.

A method to determine organochlorine pesticides in horticultural samples (lettuce, tomato, spinach, potato, turnip leaf and green bean) using pressurized liquid extraction (PLE) is described and compared with microwave assisted extraction (MAE). Significant parameters affecting PLE procedure such as temperature, static extraction time and extraction solvent were optimised and discussed. Clean-up of extracts was performed by solid phase extraction (SPE) using a carbon cartridge as adsorbent. Pesticides were determined by gas chromatography and electron capture detection (GC-ECD). Analytical recoveries obtained were ca. 100% and the relative standard deviations were lower than 15% for most of the studied pesticides with the proposed methods in each analysed matrix.

Distribution of volatile organic compounds during the combustion process in coal-fired power stations

This study concerns the distribution of volatile organic compounds (VOC) emitted during combustion processes in coal-fired power stations. Thermal desorption technique was employed to analyse VOC concentrations in gaseous emissions (trapped onto Carbotrap B sorbent) and solid samples (coal, fly ash and slag). An empirical parameter (Y) was employed to evaluate the relationships between the compounds emitted during a real combustion process and those obtained in coal analysis by thermal desorption. The Y calculation does not provide any information about VOC emissions through solid effluents as fly ash or slag. A comparison method was created for this purpose. The results obtained using this method confirm that combustion is almost complete for aromatic and aliphatic hydrocarbons. Chlorinated compounds are mainly formed during the combustion.

Multivariate optimisation of hydride generation procedures for single element determinations of As, Cd, Sb and Se in natural waters by electrothermal atomic absorption spectrometry

Continuous flow hydride generation procedures for As(III), total inorganic As, Cd, total inorganic Sb, Se(IV) and total inorganic Se from sea and hot-spring water samples were optimised by experimental designs. Ir-coated graphite tubes were used as preconcentration and atomisation medium of the hydrides generated. Several factors affecting the hydride generation efficiency were studied. Results obtained from Plackett-Burman designs suggest that sodium borohydride flow rate and reduction coil length, are significant factors for total inorganic arsenic hydride generation. For cadmium hydride generation the significant factors are hydrochloric acid concentration, hydrochloric acid and sodium borohydride flow rates and reduction coil length. For total inorganic antimony hydride generation the factors affecting the hydride generation procedure are hydrochloric acid and potassium iodide concentrations and reduction coil length; finally, pre-reduction coil length and oven temperature for the pre-reduction step are statistically significant factors for total inorganic selenium hydride generation. In addition, the factors studied for the arsenic and selenium hydride generation from As(III) and Se(IV) are not significant. From these studies, the significant variables were optimised by central composite designs. Validation carried out analysis on three reference materials: SLRS-4 (Riverie water), CASS-3 (seawater) and NIST-1643d.

Measurement of Volatile Organic Compounds in Urban Air of La Coruña, Spain

Twenty-eight volatile organic compounds have been measured in a 3-month monitoring campaign. The sampling point is locatedin the urban centre of La Coruña, a medium-size town in theNorthwest of Spain. Only a petrol refinery can be consideredas an important point VOCs source in its surrounding area.The municipal landfill collapsed in September 1996, and rebuilding works caused strong odour episodes at the urbancentre. We tried to check how this problem affected urban airquality. Samples were taken with Tenax-TA tubes and analysedby thermal desorption-GC-MS. From the results obtained, traffic emissions were recognised as the main VOCs source inthe sampling zone. On November 9th a contaminationepisode took place. Aromatic and aliphatic compounds levelswere probably affected by emissions from fuel treatmentprocesses in a nearby petrol refinery. No influence onquantified VOCs concentrations from the remaking landfillworks was observed. Several compounds (organosulphurs, estersand alcohols) were recognised as the cause of odour problems.

Development of an environmental friendly method for the analysis of organochlorine pesticides in sediments.

This work proposes a pressurized hot water extraction (PHWE) followed by solid phase microextraction (SPME) and determination by gas chromatography-mass spectrometry method for the analysis of organochlorine pesticides in sediment samples. For SPME, extraction temperature and time, desorption temperature and desorption time, and effect of an organic modifier were studied. For PHWE, parameters such as organic modifier, percentage of organic modifier, temperature, and static extraction time were studied. When these parameters were selected, the figures of merit were calculated in order to assess the performance of the proposed method. Quantitative recoveries (80-115%) and satisfactory precisions were obtained. The detection and quantification limits were between 0.11 and 16 microg kg(-1) and between 0.24 and 22 microg kg(-1), respectively with good linearity between LOQs and 500 microg kg(-1) for most of the studied pesticides. The method was validated by the analysis of a reference marine sediment material (SRM 1944). The obtained results are in excellent agreement with the certificate material. Another sediment reference material (SRM 1941b), with a very low concentration of pesticides was also analyzed with good results. In addition, this method was successfully applied to the analysis of three marine sediment samples. The developed method seems to be a nearly full automated, environmental friendly, sensitive, simple and less-time consuming method. Moreover this method, look for the implementation of the principles of green analytical chemistry and has demonstrated to be suitable for the analysis of organochlorine pesticides at trace levels in environmental matrices as sediment samples.

Pressurized liquid extraction followed by high performance liquid chromatography coupled to hydride generation atomic fluorescence spectrometry for arsenic and selenium speciation in atmospheric particulate matter.

This paper describes the development of a chelating solvent-based pressurized liquid extraction (PLE) method for the simultaneous extraction of As and Se species (As(III), As(V), Se(IV) and Se(VI)) in atmospheric particulate matter (PM(10)). The extracted As and Se species were evaluated by high performance liquid chromatography coupled to hydride generation atomic fluorescence spectrometry (HPLC-HG-AFS). The feasibility of several pressurized chelating solvents was recently investigated to leach As and Se species from atmospheric particulate matter. The best results (high recoveries) were obtained when using EDTA. Experimental design approaches were used to achieve the best compromise conditions for the simultaneous extraction of As and Se species by EDTA-PLE. Analytical performances, such as limits of detection (in the range of 0.01-0.02 ng m(-3)), quantification (in the range of 0.02-0.07 ng m(-3)), and repeatability of the over-all procedure ( approximately 10%) were established. Finally, As and Se species were determined in several atmospheric particulate matter (PM(10)) samples collected in an urban area of A Coruña city (northwest coast of Spain) in 2006. In all the atmospheric particulate matter samples that were analysed, As(V) and Se(IV) (in the range of 0.17-0.60 ng m(-3)) were the major species found.

Direct As, Bi, Ge, Hg and Se(IV) cold vapor/hydride generation from coal fly ash slurry samples and determination by electrothermal atomic absorption spectrometry

Abstract Direct cold vapor and hydride generation procedures for As, Bi, Ge, Hg and Se(IV) from aqueous slurry of coal fly ash samples have been developed by using a batch mode generation system. Ir-treated graphite tubes have been used as a preconcentration and atomization medium of the vapors generated. A Plackett–Burman experimental design has been used as a strategy for evaluation of the effects of several parameters affecting the vapor generation efficiency from solid particles, vapor trapping and atomization efficiency from Ir-treated graphite tubes. The effects of parameters such as hydrochloric acid and sodium tetrahydroborate, argon flow rate, trapping and atomization temperatures, trapping time, acid solution volume and mean particle size have been investigated. The significant parameters obtained (trapping and atomization temperatures for As and Ge; trapping temperature and trapping time for Bi; argon flow rate and atomization temperature for Se) have been optimized by 2 2 +star central composite design. For Hg, the trapping temperature has been also significant. Optimum values of the parameters have been selected for the development of direct cold vapor/hydride generation methods from slurry particles. The accuracy of methods have been verified by using NIST-1633a coal fly ash certified reference material. Absolute detection limits of 11.5, 48.0, 600, 55.0 and 11.0 ng l −1 for As, Bi, Ge, Hg and Se have been achieved, respectively. A particle size less than 50 μm has shown to be adequate to obtain total cold vapor/hydride generation of metals content in the aqueous slurry particles.

Determination of As, Bi and Se in acidified slurries of marine sediment, soil and coal samples by hydride generation electrothermal atomic absorption spectrometry

Ir-treated graphite tubes were used for preconcentration and atomisation of the As, Bi and Se hydrides generated from acidified slurries of marine sediment, soil and coal samples. A batch mode generation system was used for the hydride generation. The variables affecting the acidified slurry preparation procedure (assisted by ultrasonic energy) and the hydride generation/trapping/atomisation processes were studied by using a Plackett–Burman design. The sensitivity (characteristic masses of 65, 75 and 100 pg, for As, Bi and Se, respectively) and precision (RSD% lower than 10%) obtained were adequate for As, Bi and Se determination in slurry samples. The accuracy of the method was verified by analysing PACS-1 (Marine Sediment), GBW-07401 (Soil) and NIST SRM 1632c (Coal) certified reference materials.

As, Bi, Sb and Sn determination in atmospheric particulate matter by direct solid sampling-hydride generation-electrothermal atomic absorption spectrometry

A novel, rapid and simple method by hydride generation-electrothermal atomic absorption spectrometry (HG-ETAAS) after direct As, Bi, Sb and Sn hydrides generation from untreated filters of atmospheric particulate matter (PM(10) and PM(2.5)) was optimised. PM(10) and PM(2.5) were not subjected to any pre-treatment: circular portions between 0.28 and 6.28cm(2) were directly placed into the reaction vessel of a batch mode generation system. A 2(8)x3/64 Plackett-Burman design was used as a multivariate strategy for the evaluation of the effects of several variables affecting the hydride generation, trapping and atomisation efficiencies. Trapping temperature was the most statistically significant variable for As, Bi and Sn. Atomisation temperature was also statistically significant for Sb determination. Optimum values of significant variables were selected by using univariate optimisation approaches. An aqueous calibration method was used throughout. The developed method has been found to be precise with relative standard deviations of 6.2, 5.3, 9.1 and 7.5% for 11 determinations in a filter sample containing 0.7, 1.0, 1.4 and 1.7microg l(-1) for As, Bi, Sb and Sn, respectively. Results obtained by direct solid sampling-HG-ETAAS have been found statistically comparable with those obtained after conventional method based on an acid digestion followed to ICP-MS. Absolute detection limits were 37, 15, 30, and 41ng l(-1) for As, Bi, Sb and Sn, respectively. Detection limits referred to the air volume sampled (in the range of 0.020-0.050ng m(-3)) were low enough for the determination of several hydride-forming elements from PM(10) and PM(2.5) samples collected in a non-polluted suburban area of A Coruña (NW Spain).