University of North Florida
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Stuart Chalk, Ph.D.
Department of Chemistry
University of North Florida
Phone: 1-904-620-1938
Fax: 1-904-620-3535
Email: schalk@unf.edu
Website: @unf

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Carlos Bendicho

Abbrev:
Bendicho, C.
Other Names:
C. Bendicho
Address:
Departamento de Quimica Analitica y Alimentaria, Facultad de Ciencias de Vigo, Universidad de Vigo, As Lagoas-Marcosende, E-36200, Vigo, Spain
Phone:
+34-986-812281
Fax:
+34-986-812382

Citations 18

"Photolytic Oxidation Of As Species For Determination Of Total As (including The 'hidden' As Fraction) In Coastal Seawater By Hydride Generation-atomic Fluorescence Spectrometry"
Talanta 2007 Volume 71, Issue 1 Pages 51-55
E. Castro, I. Lavilla and C. Bendicho

Abstract: Ultraviolet irradiation (photolysis) in alkaline medium was applied for pretreatment of seawater samples so as to accurately determine total As by continuous-flow hydride generation-atomic fluorescence spectrometry. This sample pretreatment is meant to convert non-reducible As forms into inorganic As, which easily forms arsine. The optimized parameters were the treatment time and the pH of the medium. The behavior of four hydride-reactive As species [As(III), As(V), MMA, DMA], and AsB, i.e. a typical non-hydride-reactive As species, when subjected to UV irradiation was studied. UV irradiation at pH 1 lead to conversion of all species into As(V) with the exception of AsB and DMA. Conversions of DMA and AsB into As(V) at pH 11 in less than 30 min were observed under UV irradiation. The limit of detection of As (measured as As(V)) by hydride generation-atomic fluorescence spectrometry was 0.1 ?g/L and the repeatability of the oxidation procedure was about 10%. The method was applied to determination of total and directly reducible As at 11 sampling points of the Galician Coast (Atlantic Ocean, Spain). Total As concentrations were in the range 1.4-4.8 ?g/L. A significant As fraction, between 20 and 44%, depending on the sampling point, corresponded to non-reducible As which was converted by UV irradiation into hydride-reactive As. This fraction should represent the sum of DMA, which yields a low sensitivity in the continuous flow-AFS system, and the hidden As fraction. © 2006 Elsevier B.V. All rights reserved.

"Evaluation Of Non-chromatographic Approaches For Speciation Of Extractable As(III) And As(V) In Environmental Solid Samples By FI-HGAAS"
Talanta 2003 Volume 59, Issue 3 Pages 525-534
J. Carlos González, Isela Lavilla and Carlos Bendicho

Abstract: Non-chromatographic speciation approaches have been developed for determination of water-soluble and phosphate-exchangeable As(III) and As(V) in certified reference materials of coal fly ash and sediments by FI-HGAAS. A 2IV6-2 fractional factorial design was employed for screening optimization of the flow injection manifold. A simple two-stage sequential extraction protocol involving deionized water and a phosphate buffer as extractants was employed. Determination of both oxidation states of As in the extracts could be accomplished following arsine generation under different reaction conditions, namely, (i) selective determination of As(III) in citric acid medium or using soft generation conditions (i.e. low HCl and NaBH4 concentrations); (ii) determination of total As in each extract using thioglycollic acid as reaction medium or after pre-reduction of As(V) to As(III) with a KI+ascorbic acid mixture. The As(V) content was estimated by difference between both measurements. Reaction conditions were previously optimized and analytical parameters in each reaction medium were established. Overall, the extractable As content was less than 5% in sediment and fly ash CRMs. The LOD of As was around 0.07 µg L-1 for As(III) determination, and 0.06 µg L-1 for total As determination after prereduction. Liquid chromatography coupled to atomic fluorescence spectrometry with post-column hydride generation was used for comparison.

"Ultrasonic Extraction-ozonation Sequential Sample Treatment For The Determination Of Arsenic In Environmental Certified Reference Materials By Hydride Generation-atomic Fluorescence Spectrometry"
Spectrosc. Lett. 2006 Volume 39, Issue 6 Pages 713-725
Carmen Fernández-Costas; Isela Lavilla; Carlos Bendicho

Abstract: A sample pretreatment method based on ultrasound-assisted extraction followed by ozonation is developed for sensitive determination of total As in biological and environmental certified reference materials and an unknown plant sample (Acacia dealbata) by flow injection and continuous-flow hydride generation-atomic fluorescence spectrometry. The method is meant to minimize the use of corrosive and oxidizing acids for sample decomposition and common errors in trace analysis. Problems derived from introduction of sonicated extracts in continuous flow and flow injection manifolds in combination with an atomic fluorescence detector, such as excessive foaming and flame instability, are addressed. The following certified reference materials (CRMs) were employed for method assessment: BCR CRM 482 lichen; BCR CRM 60 and 61 aquatic plants; BCR CRM 279 sea lettuce; NIST 1633b fly ash; BCR 320 river sediment; RTC CRM 024-050 soil. Effect of variables such as extraction time, ultrasound amplitude, concentration of extractant acid, sample mass, drying mode, and particle size was investigated. Leaves of Acacia dealbata were also employed for method development. Limits of detection ranged from 0.03 to 0.15 ?g/g As depending on the sample. Between-batch precision values ranged from 2% to 11%. Sample throughput was 40 hr-1 with flow injection. Copyright © Taylor & Francis Group, LLC.

"Determination Of Methylmercury By Electrothermal Atomic Absorption Spectrometry Using Headspace Single-drop Microextraction With In Situ Hydride Generation"
Spectrochim. Acta B 2005 Volume 60, Issue 1 Pages 145-150
Sandra Gil, Sandra Fragueiro, Isela Lavilla and Carlos Bendicho

Abstract: A new method is proposed for pre-concentration and matrix separation of methylmercury prior to its determination by electrothermal atomic absorption spectrometry (ETAAS). Generation of methylmercury hydride (MeHgH) from a 5 mL solution is carried out in a closed vial and trapped onto an aqueous single drop (3-?l volume) containing Pd(II) or Pt(IV) (50 and 10 mg/l, respectively). The hydrogen evolved in the headspace (HS) after decomposition of sodium tetrahydroborate (III) injected for hydride generation caused the formation of finely dispersed Pd(0) or Pt(0) in the drop, which in turn, were responsible for the sequestration of MeHgH. A pre-concentration factor of ~40 is achieved with both noble metals used as trapping agents. The limit of detection of methylmercury was 5 and 4 ng/ml (as Hg) with Pd(II) or Pt(IV) as trapping agents, and the precision expressed as relative standard deviation was about 7%. The pre-concentration system was fully characterized through optimization of the following variables: Pd(II) or Pt(IV) concentration in the drop, extraction time, pH of the medium, temperatures of both sample solution and drop, concentration of salt in the sample solution, sodium tetrahydroborate (III) concentration in the drop and stirring rate. The method has been successfully validated against two fish certified reference materials (CRM 464 tuna fish and CRM DORM-2 dogfish muscle) following selective extraction of methylmercury in 2 mol/l HCl medium. © 2004 Elsevier B.V. All rights reserved.

"Headspace Sequestration Of Arsine Onto A Pd(II)-containing Aqueous Drop As A Preconcentration Method For Electrothermal Atomic Absorption Spectrometry"
Spectrochim. Acta B 2004 Volume 59, Issue 6 Pages 851-855
Sandra Fragueiro, Isela Lavilla and Carlos Bendicho

Abstract: A new method based on arsine pre-concentration onto a single drop (3 µl) containing a Pd(II) solution (30 mg/l) is combined with electrothermal atomic absorption spectrometry (ETAAS) for the determination of As. Hydride generation is carried out in a vial containing an As solution (20 ml) in hydrochloric or citric acid medium. The drop was suspended at the tip of a microsyringe fixed above an extraction vial with a septum such that the tip of the needle was located in a consistent position in the headspace. The presence of Pd2+ in the hanging aqueous drop was seen to be highly effective for sequestration of the arsine formed, a pre-concentration factor of 70 being achieved for As(III). The pre-concentration method was fully characterized through optimization of the following variables: Palladium concentration in the drop, sample volume, extraction time, stirring rate, extraction temperature, sodium tetrahydroborate (III) concentration, hydrochloric and citric acid concentration, drop volume and sample temperature. Preconcentration of other hydride-forming elements such as Se and Sb proved also effective under the conditions optimized for arsine. The limit of detection (LOD) (3s criterion) of As(III), Se(IV) and Sb(III) were 0.1 (As), 0.15 (Se) and 0.2 (Sb) ng/ml. The relative standard deviations (RDS) (%) for As, Se and Sb were 3.5%, 2.5% and 3.0%, respectively.

"Determination Of Total And Inorganic Mercury In Biological And Environmental Samples With Online Oxidation Coupled To Flow Injection-cold Vapor Atomic Absorption Spectrometry"
Spectrochim. Acta B 1999 Volume 54, Issue 8 Pages 1129-1139
Susana Río-Segade and Carlos Bendicho

Abstract: A method for determination of inorganic and total mercury by flow injection-cold vapor atomic absorption spectrometry (FI-CVAAS) with online oxidation was developed. Potassium peroxodisulfate and sulfuric acid were used as oxidizing agents so that decomposition of organomercury compounds could be achieved. Depending on the temperature selected, inorganic or total mercury could be determined with the same FI manifold. In order to assess the method performance, synthetic wastewater, wastewater, urine and saline water samples were spiked with inorganic mercury, methylmercury and phenylmercury. Quantitative recoveries were obtained for the three mercury species, except with the synthetic wastewater when the chemical oxygen demand value was higher than 1000 mg L-1. In most cases, the standard addition method was usually needed for calibration. LODs calculated as 3s/m were 0.47 µg L-1 for inorganic mercury and 0.45 µg L-1 for total mercury. RSD values corresponding to peak height measurements were 1.5 and 2.2% for inorganic mercury and total mercury, respectively The accuracy of the method was tested by analyzing 5 mol L-1 hydrochloric acid extracts of seven biological and environmental CRMs. LODs in the solid CRMs ranged from 0.032 to 0.074 µg g-1.
FIMS

"On-line Photoassisted Vapour Generation Implemented In An Automated Flow-injection/stopped-flow Manifold Coupled To An Atomic Detector For Determination Of Selenium"
J. Anal. At. Spectrom. 2006 Volume 21, Issue 6 Pages 582-587
M. García, R. Figueroa, I. Lavilla and C. Bendicho

Abstract: A flow-through UV reactor has been implemented in an automated flow-injection/stopped-flow manifold, and used for on-line generation of Se volatile derivatives prior to detection by quartz furnace atomic absorption spectrometry. The presence of a low molecular weight organic acid (formic or acetic) in the carrier was a necessary requirement so that efficient vapor generation was achieved. Stopped-flow conditions were employed with the aim of increasing the time for which the sample zone was subjected to UV irradiation while it was transported to the detector. The simultaneous formation of H 2 during the photochemical decomposition of formic acid facilitated the atomization of the Se derivatives in the quartz furnace, and therefore the addition of H2 to the carrier gas, which is necessary for efficient atomisation, could be eliminated. Nevertheless, the presence of H2 in the carrier gas (Ar) was required for efficient atomisation when using acetic acid as carrier. This manifold allowed a sample throughput of 26 h-1 with a detection limit of 0.5 ng mL-1 Se and a repeatability, expressed as relative standard deviation, of 4%. Effect of concomitants in the online generation of Se vapors with the new manifold was investigated. Chloride salts of alkaline and alkaline-earth elements did not interfere at concentrations up to 10000 mg L-1, but nitrate salts caused a positive effect. Tolerance of typical hydride-forming elements such as As and Sn was much higher with UV vapor generation as compared to chemical hydride generation. The presence of Cu(ii) was critical since interference effects are observed from 0.05 mg L-1, but tolerance of Ni(ii) was greater with UV vapor generation. © The Royal Society of Chemistry 2006.

"Mild Sample Pretreatment Procedures Based On Photolysis And Sonolysis-promoted Redox Reactions As A New Approach For Determination Of Se(IV), Se(VI) And Se(-II) In Model Solutions By The Hydride Generation Technique With Atomic Absorption And Fluorescence"
J. Anal. At. Spectrom. 2004 Volume 19, Issue 10 Pages 1379-1385
Hortensia Méndez, Isela Lavilla and Carlos Bendicho

Abstract: Ultraviolet and ultrasound irradiation-induced redox reactions have been assessed for the determination of Se(IV), Se(VI), selenomethionine and selenocystine in model waters, enriched natural waters and soil/fly ash extracts by the hydride-generation technique with atomic absorption and fluorescence detection. Photooxidation of Se-methionine and Se-cystine into Se(IV) by UV irradiation in HCl medium (pH 0.4) can be achieved within 10 min, whilst Se(IV), the only Se species reactive towards NaBH4, leading to SeH 2 formation, remains unaffected. Photoreduction of Se(VI) to Se(IV) required at least 45 min under the same conditions. Higher pH values yielded incomplete conversions of the Se species into Se(IV). Se(VI) photoreduction was completely inhibited by the presence of 10000 mg L-1 nitrate as KNO3. Ultrasonic oxidation of Se-cystine to Se(IV) is seen to occur, the remaining Se species remaining unaffected. According to the above redox reactions, a four-stage model for speciation of Se is proposed. The combination of these reactions could be the basis for a new speciation approach that is advantageous in terms of sensitivity and simplicity over methods involving chromatographic separations. The LOD of each Se species was 40 pg mL -1 and 2 pg mL-1 with detection by atomic absorption and fluorescence, respectively. The repeatability expressed as relative standard deviation was in the range 2-5% for natural waters and 4-10% for phosphate extracts. © The Royal Society of Chemistry 2004.

"Direct Coupling Of Solid Phase Microextraction And Quartz Tube-atomic Absorption Spectrometry For Selective And Sensitive Determination Of Methylmercury In Seafood: An Assessment Of Chloride And Hydride Generation"
J. Anal. At. Spectrom. 2004 Volume 19, Issue 2 Pages 250-254
Sandra Fragueiro, Isela Lavilla and Carlos Bendicho

Abstract: The direct coupling between headspace solid phase microextraction and quartz tube-atomic absorption spectrometry detection has been evaluated for speciation of methylmercury in seafood after volatilization of its hydride or chloride derivative. Following variable optimization in both procedures, a critical influence of the fiber sorbent material was observed. Liquid-phase coatings such as polydimethylsiloxane (PDMS) and 'solid' phase coatings such as polydimethylsiloxane-divinylbenzene (PDMS/DVB) or fused silica were compared. Best LODs were provided by the silica fiber for CH3HgH (0.4 ng mL-1) and by the PDMS/DVB fiber for CH3HgCl (0.06 ng mL-1). In general, repeatability was about 6% for the pre-concentration of both Hg derivatives in the different fiber coatings. The affinity to sorption of CH3HgH was slightly improved when using silica fibers loaded with L-cysteine or palladium nitrate. Sorption/desorption studies with fused silica fibers allowed us to hypothesise that CH 3HgH formed upon reaction of MeHg+ with NaBH 4-NaOH suffered from decomposition onto the fiber to yield Hg 0 like direct reaction between Hg2+ and NaBH 4-NaOH. Generation of the chloride derivative showed an enhanced selectivity as compared with generation of the hydride. Nevertheless, experimental evidence of decomposition of the chloride derivative upon heating is also given. For methylmercury determination in seafood, hydride or chloride generation and headspace SPME were applied after ultrasound assisted extraction 'of methylmercury in 2 mol L-1 HCl. Validation was carried out against CRM DORM-2 (dogfish muscle) and CRM 464 (Tuna fish), demonstrating good trueness of the methods proposed. A better LOD of MeHg+ is obtained as compared with other SPME couplings described in the literature. © The Royal Society of Chemistry 2004.

"Total As In Seafood As Determined By Transverse Heated Electrothermal Atomic Absorption Spectrometry-longitudinal Zeeman Background Correction: An Evaluation Of Automated Ultrasonic Slurry Sampling, Ultrasound-assisted Extraction And Microwave-assisted Digestion Methods"
J. Anal. At. Spectrom. 2000 Volume 15, Issue 8 Pages 987-994
Catalina Santos, F. Alava-Moreno, Isela Lavilla and Carlos Bendicho

Abstract: Two sample pretreatment methods based on the use of ultrasound [i.e., automated ultrasonic slurry sampling (USS method) and ultrasound-assisted extraction (UAE method)] were developed for determination of total As in eleven fresh and frozen seafood samples by transverse heated electrothermal atomic absorption spectrometry with longitudinal Zeeman background correction and compared with the conventional microwave-assisted digestion method using the H2O2-HNO3 mixture (MAD method). Non-parametric tests (i.e., Kruskal-Wallis test and Wilcoxon rank sum test) were used in order to compare analytical results obtained, thus avoiding the influence of outliers. In general, no significant differences in accuracy were observed when comparing the UAE and MAD methods. Significantly lower arsenic concentrations were observed for several seafood samples with the USS method even using large amounts of matrix modifier [i.e., 22.5 µg Pd + 13.5 µg Mg(NO3)(2)] which were attributed to non-spectral interferences caused by the sample matrix. When the solid particles were allowed to settle in the USS method, an improved arsenic recovery was obtained; the concentration found being similar to that obtained by the UAE and MAD methods. Plackett-Burman designs were used to assess the robustness of the USS and UAE methods. The slurry concentration was seen to cause a significant negative effect on As recovery in both the slurry and solid-liquid extraction techniques, whereas nitric acid concentration caused a significant positive effect only in the solid-liquid extraction techniques. The LOD of arsenic with the USS and UAE methods was 0.5 µg g-1 and the between-batch precision expressed as relative standard deviation (RSD) was in the range of 1-6%.

"Determination Of Tetraethyllead By Solid Phase Microextraction-thermal Desorption-quartz Furnace Atomic Absorption Spectrometry"
J. Anal. At. Spectrom. 2000 Volume 15, Issue 6 Pages 705-709
María Sandra Fragueiro, Fausto Alava-Moreno, Isela Lavilla and Carlos Bendicho

Abstract: A new procedure that uses a pre-concentration system based on solid phase microextraction (SPME) and detection by quartz furnace atomic absorption spectrometry after thermal desorption from the microextraction fiber has been proposed for the determination of tetraethyllead in gasoline (leaded and unleaded) and water. Three different volatilizators were designed and their influence in the thermal desorption of tetraethyllead was studied. Working tetraethyllead solutions were prepared in 40 mL amber vials and sampling was performed by exposing the SPME fiber to the headspace over vigorously stirred samples for 10 min. The analytical performance characteristics of the proposed procedure were as follows: the detection limit for tetraethyllead was 0.43 ng mL-1, with a relative standard deviation of 6% for determination of 10 ng mL-1 of tetraethyllead (n = 5) while the calibration curve was linear up to 50 ng mL-1 range. The proposed procedure was finally applied to the determination of tetraethyllead in gasoline and water samples obtaining a good agreement with those values obtained by an alternative method that included the direct injection of tetraethyllead, via a septum, in the heated volatilizator with a gas chromatographic syringe, the tetraethyllead volatilisation and its transport by the gas carrier to the quartz furnace, where the analytical signal was observed. This procedure could be easily adapted for the speciation of ionic lead and tetraethyllead.
Speciation

"Slurry Sampling Combined With Ultrasonic Pretreatment For Total Mercury Determination In Samples Containing Inorganic And Methylmercury By Flow Injection-cold Vapor-atomic Absorption Spectrometry"
J. Anal. At. Spectrom. 1999 Volume 14, Issue 12 Pages 1907-1912
S. Río-Segade and C. Bendicho

Abstract: A method for the determination of total mercury in solid biological and environmental samples by slurry sampling combined with flow injection-cold vapor-atomic absorption spectrometry (FI-CV-AAS) was developed. The slurries were prepared in 15% m/m nitric acid (mussel tissue, aquatic plant) or a (9 + 1) 15% m/m nitric acid-15% m/m hydrochloric acid mixture (river sediment, sewage sludge) containing 0.02% v/v Triton X-100 as dispersing agent, and subjected to ultrasonic pretreatment before being injected into the FI manifold. Ultrasonic pretreatment of slurries was proved to be necessary in order to improve the low mercury recoveries obtained. The effect of several FI parameters on the effectiveness of cold vapor generation for total mercury determination in slurries of mussel tissue was investigated. Mercury concentrations obtained by the proposed method were compared with those obtained after microwave-assisted digestion of mussel tissue samples. The method was validated against CRM BCR 278 mussel tissue, CRM BCR 60 aquatic plant, CRM BCR 320 river sediment and CRM BCR 145R sewage sludge. LODs were 3, 26, 28 and 8 ng g-1 for mussel tissue, river sediment, sewage sludge and aquatic plant, respectively. The precision, expressed as relative standard deviation [RSD (%)], ranged from 4 to 7% for three replicates of each sample analyzed by the standard additions method.

"Ultrasound-assisted Extraction For Mercury Speciation By The Flow Injection Cold Vapor Technique"
J. Anal. At. Spectrom. 1999 Volume 14, Issue 2 Pages 263-268
Susana Río-Segade and Carlos Bendicho

Abstract: A simple and rapid ultrasound-assisted extraction method with hydrochloric acid for mercury speciation in fish tissues was developed. Centrifuged extracts were directly injected into a flow injection-cold vapor atomic absorption spectrometry system. First, methylmercury was separately determined using sodium tetrahydroborate as reducing agent after selective extraction with 2 mol L-1 hydrochloric acid. Second, inorganic mercury was determined by selective reduction with stannous chloride in 5 mol L-1 hydrochloric acid extracts containing both mercury species. Total mercury could not be determined in the sonicated acid extracts using sodium tetrahydroborate as reducing agent because the methylmercury and inorganic mercury sensitivities were different. The detection limit was 11 and 5 ng g-1 for methylmercury and inorganic mercury, respectively. The recovery was >92% and the precision (RSD) ranged from 5 to 10% for three replicates of each sample analyzed by the standard additions method. Total mercury, calculated as the sum of methylmercury and inorganic mercury, was in agreement with the total mercury content determined after microwave digestion. The method was validated by means of three fish certified reference materials. The concentrations found were in good agreement with the certified values.

"Selective Reduction Method For Separate Determination Of Inorganic And Total Mercury In Mussel Tissue By Flow Injectioncold Vapor Technique"
Ecotoxicol. Environ. Saf. 1999 Volume 42, Issue 3 Pages 245-252
S. Río-Segade and C. Bendicho

Abstract: A flow injection cold vapor atomic absorption spectrometry (FI-CV-AAS) method was developed to determine inorganic mercury and total mercury in mussel samples obtained from the Galicia coasts. The mussel samples were digested in a microwave oven using an HNO3/H2O2 mixture and then total mercury was determined using sodium borohydride as reducing agent. In a separate subsample, following ultrasonic extraction in hydrochloric acid medium, inorganic mercury was determined by selective reduction using stannous chloride in acid medium as reducing agent. The accuracy of the digestion method was checked by analyzing BCR Reference Material No. 278 Mussel Tissue (Mytilus edulis). There were no significant differences between the certified and found concentration values. As a certified reference material of mussel tissue containing both methylmercury and inorganic mercury was not available, recovery studies on mussel tissue samples spiked with inorganic mercury and methylmercury were done to check the reliability of the method. The results revealed that the mercury contained in mussel samples was methylmercury. Copyright 1999 Academic Press.
Speciation Microwave Ultrasound Calibration

"Chemometric Approach For The Optimization Of A Flow Injection Manifold Applied To The Determination Of Total Hg In Seafood By Cold Vapor AAS"
Atom. Spectrosc. 2000 Volume 21, Issue 6 Pages 229-233
JL CAPELO, I LAVILLA, C BENDICHO

Abstract: A flow injection manifold was optimized using factorial design for the determination of mercury in seafood after microwave- assisted digestion by cold vapor atomic absorption spectrometry. The 2v5?1 fractional factorial allowed to estimate main factor and two-factor interactions with only 16 experiments. The HCl flow rate displayed the highest influence on sensitivity, the effect being positive and independent of other factors. The sodium borohydride concentration showed a significant negative effect, which could not be individually interpreted as there was interaction between the reducing agent concentration and the reducing agent flow rate. This interaction arose from the different influence of the reducing agent concentration depending on the reducing agent flow rate. Low reducing agent concentration together with high reducing agent flow rate is recommended. The HCl concentration and carrier gas flow rate did not show any significant effect. With a sample loop of 500 µL, a LOD of 0.4 ?g L-1 could be reached, the precision expressed as the relative standard deviation for 20 ?g L-1 Hg solution being 1.5%. The manifold was applied to the determination of total Hg in five seafood samples, using microwave-assisted decomposition with the HNO3 + H2O2 mixture. The method was validated against two certified reference materials.

"Ultrasonic Extraction Followed By Sonolysis-ozonolysis As A Sample Pretreatment Method For Determination Of Reactive Arsenic Toward Sodium Tetrahydroborate By Flow Injection-hydride Generation AAS"
Anal. Chem. 2001 Volume 73, Issue 15 Pages 3732-3736
J. L. Capelo, I. Lavilla, and C. Bendicho

Abstract: A new sample pretreatment method based on ultrasonic extraction in HCl medium and subsequent oxidation of the extracts by sonozone (i.e., sonolysis-ozonolysis) has been developed for determination of reactive arsenic toward sodium tetrahydroborate [mainly As(III) + As(V)] by flow injection-hydride generation atomic absorption spectrometry. This method avoids the use of intensive treatments with concentrated and corrosive acids, high pressures, and temperatures that are inherent with traditional wet or dry ashing procedures and entails reduced waste production and reagent consumption. A sonozone process at room temperature was optimized to break the bond of As to proteins and macromolecular constituents which was an essential requirement for effective reduction by L-cysteine prior to arsine generation. Spiking experiments showed that As(III), As(V), MMA, and DMA were fully recovered from several matrixes on applying the above treatment. On the other hand, a nonreducible As species such as arsenobetaine that is predominant in some biological samples remained unchanged. Application of the method to sediment, soil, fly ash, and plant CRMs demonstrated that, in general, a good agreement existed between certified and found As contents, thereby indicating the absence of nonreducible As forms. Low As recoveries were observed for fish CRMs, as a result of the nondegradability of arsenobetaine by sonozone. The detection limit of As in the samples investigated was in the range 0.19-2.8 µg g-1.
Speciation Optimization

"Room Temperature Sonolysis-based Advanced Oxidation Process For Degradation Of Organomercurials: Application To Determination Of Inorganic And Total Mercury In Waters By Flow Injection-cold Vapor Atomic Absorption Spectrometry"
Anal. Chem. 2000 Volume 72, Issue 20 Pages 4979-4984
J. L. Capelo, I. Lavilla, and C. Bendicho

Abstract: A new oxidation method based on room-temperature ultrasonic irradiation (sonolysis) is proposed for Conversion of organomercurials into inorganic mercury and subsequent determination by now injection-cold vapor atomic absorption spectrometry. This advanced oxidation process eliminates the need for chemical oxidants, high temperature, and pressure for degradation of organomercurials so that total mercury can be determined with sodium tetrahydroborate(III) or tin(II) chloride as reducing agents. Complete oxidations can be accomplished within 3 min, using a 40% sonication amplitude (100 W nominal power) provided by a probe ultrasonic device (20 kHz frequency) and a 1. mol L-1 HCl liquid medium. The presence of HCl was seen to be necessary for fast oxidation of organomercurials, in contrast to other chemical oxidants such as H2O2 or HNO3 which yielded incomplete oxidation. Further advantages of the proposed method over existing methods which are currently employed for oxidation prior to total Hg determination are the removal of hazardous wastes and the decreased risk of Hg losses by volatilization. Oxidation kinetics indicated a pseudo first-order reaction with apparent rate constants (k) of 3.2 x 10^-2 and 1.6 x 10^-2 s-1 for methylmercury and phenylmercury, respectively. Oxidation experiments in the presence of foreign substances acting as OH radical scavengers showed a tolerance at least up to a concentration of 1000 mg L-1. likewise, model wastewaters with chemical oxygen demand of up to 1000 mg L-1 could be processed without diminishing the oxidation efficiency. The method was applied to determination of inorganic and total mercury in simulated wastewaters and spiked environmental waters in combination with selective reduction.

"Use Of Flow Injection Sample-to-standard Addition Methods For Quantification Of Metals Leached By Selective Chemical Extraction From Sewage Sludge"
Anal. Chim. Acta 1999 Volume 381, Issue 2-3 Pages 297-305
I. Lavilla, B. Perez-Cid and C. Bendicho

Abstract: The flow injection sample-to-standard addition method (FI-SAM) proposed by Israel and Barnes and a modification of it was employed for determination of the extractable contents of chromium, lead, nickel and zinc in a sewage sludge sample obtained from an urban wastewater processing plant. The new calibration method was a modification of the one established by Israel and Barnes in which the sample was injected into a blank solution and two different standard solutions. The advantages of this modified calibration method were: (i) sample consumption was minimized in comparison with the reverse flow injection method since the sample was not used as carrier; (ii) a blank that was matrix matched to the sample was not required; (iii) a similar precision was observed in comparison with the original procedure. For studying FI-SAM calibration strategies, extractable metals obtained by using two known sequential extraction schemes (Tessier and BCR) were determined. Only fractions that required calibration with the standard addition method for metal determination were considered. FI-SAMs compensate for interference effects caused by concomitants co-extracted at each stage of the sequential extraction scheme from sewage sludge, for all metals studied except for chromium.
Chromium Lead Nickel Zinc Sludge Spectrophotometry Standard additions calibration Extraction Reverse Interferences Method comparison