University of North Florida
Browse the Citations
-OR-

Contact Info

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

View Stuart Chalk's profile on LinkedIn

Pilar Bermejo Barrera

Abbrev:
Bermejo Barrera, P.
Other Names:
Ma Pilar Bermejo Barrera, Pilar Bermejo-Barrera
Address:
Department of Analytical Chemistry, Nutrition and Bromatology, University of Santiago de Compostela, Santiago de Compostela E-15706,, Spain
Phone:
+34-98-156-3100 x14266
Fax:
+34-98-159-5012

Citations 12

"Multivariate Optimization Of Solvent Extraction With 1,1,1-trifluoroacetylacetonates For The Determination Of Total And Labile Cu And Fe In River Surface Water By Flame Atomic Absorption Spectrometry"
Spectrochim. Acta B 2002 Volume 57, Issue 12 Pages 1951-1966
Pilar Bermejo-Barrera, Antonio Moreda-Piñeiro, Ricardo González-Iglesias and Adela Bermejo-Barrera

Abstract: A procedure for simultaneous solvent extraction of Cu(II) and Fe(III) from river surface waters as diethyldithiocarbamates (DDC) 1,1,1-trifluoroacetylacetonates into isobutyl methyl ketone (IBMK) has been developed prior to their determination by flame atomic absorption spectrometry. Experimental design approaches were used in order to obtain the best compromise conditions for simultaneous solvent extraction. Variables such as pH, sodium DDC or 1,1,1-trifluoro-2,4-pentanodione (H(TFA)) concentrations, reaction time, IBMK volume and extraction time have been optimized. First, Plackett-Burman designs involving 13 experiments and 2 replicates were used as screening designs to determine which variables were significant. DDC or H(TFA) concentration, as well as pH and IBMK volume were found statistically significant and they were finally optimized by applying a central composite design (15 experiments and 2 replicates). Optimum values for these variables were selected for compromise extraction conditions of Cu(II) and Fe(III) species. An optimum pH of 5.3 was chosen for Cu-H(TFA) and Fe-H(TFA) formation with an optimum H(TFA) concentration of 0.20% (m/v). The optimum IBMK volume for extraction was 8 ml, allowing a pre-concentration factor of 10. A microwave-assisted peroxydisulfate oxidation was used to break down the metal-organic matter complexes in river surface waters in order to assess the total Cu and Fe contents. Applying the experimental design approach, optimum conditions was an irradiation for 5.0 min at a microwave power of 500 W using 0.5 g of ammonium peroxydisulfate. The method was applied to determine total Cu and Fe contents and also labile Cu(II) and Fe(III) contents in several river surface water samples.

"Optimization Of A Microwave-pseudo-digestion Procedure By Experimental Designs For The Determination Of Trace Elements In Seafood Products By Atomic Absorption Spectrometry"
Spectrochim. Acta B 2000 Volume 55, Issue 8 Pages 1351-1371
P. Bermejo-Barrera, A. Moreda-Piñeiro, O. Muñiz-Naveiro, A. M. J. Gómez-Fernández and A. Bermejo-Barrera

Abstract: A Plackett-Burman 2(7) X 3/32 design for seven factors (nitric acid concentration, hydrochloride acid concentration, hydrogen peroxide concentration, acid solution volume, particle size, microwave power, and exposure time to microwave energy) was carried out in order to find the significant variables affecting the metals acid leaching after a pseudo-digestion procedure by microwave energy from mussel. Nitric acid concentration, hydrochloride concentration or hydrogen peroxide, and exposure time to microwave energy were the most significant variables, and a 2(3) + star central composite design was used for their optimization. Nitric and hydrochloric acid concentrations between 4.1 and 5.3 M, and between 2.8 and 3.8 M, respectively, were found as optimum for many elements (Ca, Cd, Cr, Cu, Fe, Mg, Mn, Pb and Zn) yielding the acid leaching process for times in the 1.2-3.2 min range. However, As was quantitatively leached with hydrochloric acid concentrations between 4.8 and 5.3 M and an exposure time of 2.0 min, while Co and Se were extracted using nitric acid (1.0 and 5.0 M, respectively) and hydrogen peroxide (5.0 M) solution and an exposure time of 2.0 min. Finally, Hg was extracted using a hydrochloric acid/hydrogen peroxide solution at 3.5:2.0 M, and also for an optimum time of microwave radiation of 1.75 min. Trace metals were determined using flame atomic absorption spectrometry, electrothermal atomic absorption spectrometry and cold vapor - atomic absorption spectrometry. The methods were finally applied to several reference materials (DORM-1, DOLT-1 and TORT-1), achieving good accuracy.
Extraction

"Use Of Lanthanum Hydroxide As A Trapping Agent To Determine Of Hydrides By HG-ICP-OES"
J. Anal. At. Spectrom. 2005 Volume 20, Issue 12 Pages 1344-1349
Elena Peña-Vázquez, Adela Bermejo-Barrera and Pilar Bermejo-Barrera

Abstract: The level of arsenic and antimony was determined in sea-water by axial ICP-OES with continuous hydride generation after performing pre-reduction with thiourea and carrying out a pre-concentration by co-precipitation with lanthanum in a PTFE knotted reactor (KR). Optimization of the whole system was performed using experimental design and with on-line pre-concentration and ultimate hydride generation. Using a pre-concentration time of two minutes and consuming 16 mL of sample, the LOD and LOQ were 0.17 and 0.56 ?g L-1, respectively, for As, and 0.27 and 0.88 ?g L-1 for Sb. Pre-concentration was carried out off-line in the KR in order to decrease the LOD and LOQ to 0.031 and 0.10 ?g L-1 (As 188.979 nm) and 0.043 and 0.15 ?g L-1 (Sb 217.582 nm) (sample volume 83 mL). The method was precise, with RSDs (n = 11) of 5.7% for As and 9.4% for Sb. The method was accurate, with a recovery of 108.5% for As and 106.0% for Sb. Moreover, values of 3.0 ±0.5 ?g As L-1 and 14.7 ±1.5 ?g Sb L -1 were obtained for a reference material with certified content of 2.7 ±1.0 ?g As L-1 and 13.7 ± 8.5 ?g Sb L -1. The method can be applied to element determination in unpolluted sea-water samples. © The Royal Society of Chemistry 2005.

"Flow On-line Sorption Preconcentration In A Knotted Reactor Coupled With Electrothermal Atomic Absorption Spectrometry For Selective AS(III) Determination In Sea-water Samples"
J. Anal. At. Spectrom. 2005 Volume 20, Issue 7 Pages 662-664
Paloma Herbello-Hermelo, M. Carmen Barciela-Alonso, Adela Bermejo-Barrera and Pilar Bermejo-Barrera

Abstract: A flow injection on-line sorption pre-concentration system using a polytetrafluoroethylene (PTFE) knotted reactor was coupled with electrothermal atomic absorption spectrometry (ETAAS) to determine selectively AS(III) in sea-water samples. Separation of arsenic inorganic species was achieved by the on-line formation of As(III)-pyrrolidine dithiocarbamate (PDC) complex in an acid medium, its sorption onto the inner walls of the knotted reactor (KR) and elution with 40 µL of ethanol. An enhancement factor (EF) of 44 was obtained compared with the slope of the linear portion of the calibration curve before and after pre-concentration The detection limit (3 s) was 0.008 ?g 1 -1 As(III). The precision (RSD n = 11) was 4.5% at 0.1 ?g 1 -1 As(III). The accuracy was demonstrated by total arsenic determination in certificed reference material, NASS-4, after pre-reduction of As(v) with L-cysteine 0.25% (m/v). © The Royal Society of Chemistry 2005.

"Determination Of Selenium In Infant Formulas Whey Fractions By SEC-HPLC-HG-ETAAS"
J. Anal. At. Spectrom. 2001 Volume 16, Issue 2 Pages 188-193
Pilar Bermejo, Julia Barciela, Elena M. Peña, Adela Bermejo, José M. Fraga and José A. Cocho

Abstract: A method to determine the selenium distribution in milk whey fractions was developed. After milk whey pre-concentration by ultrafiltration, selenium in the protein fractions was separated by size exclusion chromatography (SEC) and determined by electrothermal atomic absorption spectroscopy (ETAAS) using a sampling procedure based on fraction collection, fraction pre-concentration by ultrafiltration and introduction into the furnace after digestion, hydride generation and hydride pre-concentration. The digestion and reduction conditions of the milk whey fractions obtained by SEC were studied. The hydride generation parameters and pre-concentration into an iridium coated graphite tube using ETAAS with a Zeeman background correction were optimized. The method was applied to six infant formula milks and selenium was found in three fractions of cow-based infant formulas: 40 kDa, > 160 kDa and mostly in the < 10 kDa fraction.

"Factorial Designs For Cd, Cr, Hg, Pb And Se Ultrasound-assisted Acid Leaching From Human Hair Followed By Atomic Absorption Spectrometric Determination"
J. Anal. At. Spectrom. 2000 Volume 15, Issue 2 Pages 121-130
Pilar Bermejo-Barrera, Antonio Moreda-Pi&ntilde;eiro and Adela Bermejo-Barrera

Abstract: An acid leaching procedure, for use as a sample pre-treatment, was developed for Cd, Cr, Hg, Pb and Se determination in human hair. A Plackett-Burman experimental design was used as a multivariate strategy for the evaluation of the effects of varying several variables at once. The effects on acid leaching of metals of nitric acid, hydrochloric acid and hydrogen peroxide concentrations, acid solution volume, exposure time to ultrasound, temperature of the ultrasonic bath, and hair particle size, have been investigated. From these studies, certain variables showed up as significant, and they were optimized by a 2(3) + star central composite design, which involved 16 experiments. Optimum values of the variables were selected for the development of acid leaching procedures to extract trace metals from human hair. Electrothermal atomic absorption spectrometry (ETAAS) was used to determine Cd, Cr, Pb and Se, while cold vapor-atomic absorption spectrometry (CVAAS) was used for Hg measurements. An acid digestion induced by microwave energy was used to obtain the total metal concentration and also for comparative purposes. IAEA-085 and NIES No. 13 certified reference materials, which offer certified values for some elements, were used in order to verify the accuracy of the methods.
Extraction

"Use Of Flow Injection Cold Vapor Generation And Preconcentration On Coated Graphite Tubes For The Determination Of Mercury In Polluted Sea Waters By Electrothermal Atomic Absorption Spectrometry"
J. Anal. At. Spectrom. 1997 Volume 12, Issue 3 Pages 317-321
Pilar Bermejo-Barrera, Jorge Moreda-Pi&ntilde;eiro, Antonio Moreda-Pi&ntilde;eiro and Adela Bermejo-Barrera

Abstract: Methods have been developed for the trace determination of total and inorganic mercury in natural waters by cold vapor generation-trapping and atomization in a graphite furnace by selective reduction with NaBH4 and SnCl2. Iridium, tungstate and zirconium coated graphite tubes were investigated for the pre-concentration of the mercury vapor, The carrier solution was 0.4 M of HCl, and 0.2% NaBH4 and 1.0% SnCl2 were used as reducing solutions for total and inorganic mercury, respectively, Using iridium coated graphite tubes characteristic masses of 300 and 240 pg for total and inorganic mercury, respectively, and detection limits of 90 and 60 ng L-1 for total and inorganic mercury were obtained for a 1500 µl sample volume. The precision was between 0.7 and 2.1%, Accuracy of method was confirmed by the analysis of IAEA/W-4 fresh water reference material. 34 References
Mercury Methylmercury ion Sea IAEA W-4 Spectrophotometry Preconcentration Volatile generation Reference material Volatile generation

"Tin Determination In Seawater By Flow Injection Hydride Generation Atomic Absorption Spectroscopy"
Atom. Spectrosc. 1999 Volume 20, Issue 3 Pages 120-125
Bermejo Barrera, P.;Ferron Novais, M.;Gonzalez Campos, G.;Bermejo Barrera, A.

Abstract: A method for the trace determination of tin in seawater samples by a hydride generation technique using a flow injection system coupled with AAS was investigated. Tin hydride was generated using 0.4% NaBH4 in 0.2% NaOH as the reductant. The carrier solution was 5.6 * 10^-2 M HCl. The tin hydride generated was carried to the quartz cell by an :argon stream flow of 100 mL/min, where it was atomized at 900°C. Peak height was used for measurement of the analytical signal. a detection limit of 130 ng/L was obtained for a 500 µL sample volume. The precision was between 2.0 and 9.0%, and analytical recovery was close to 100%.
Preconcentration

"The Multivariate Optimisation Of Ultrasonic Bath-induced Acid Leaching For The Determination Of Trace Elements In Seafood Products By Atomic Absorption Spectrometry"
Anal. Chim. Acta 2001 Volume 439, Issue 2 Pages 211-227
Pilar Bermejo-Barrera, &Oacute;scar Mu&ntilde;iz-Naveiro, Antonio Moreda-Pi&ntilde;eiro and Adela Bermejo-Barrera

Abstract: The effects of several variables on the As, Ca, Cd, Co, Cr, Cu, Fe, Hg, Mg, Mn, Pb, Se and Zn ultrasonic bath induced-acid leaching from lyophilised seafood samples have been studied by experimental designs. The determinations were carried out by electrothermal atomic absorption spectrometry (As, Cd, Co, Cr, Mn, Pb and Se), flame atomic absorption spectrometry (Ca, Cu, Fe, Mg and Zn) and by cold vapor-atomic absorption spectrometry (Hg), A Plackett-Burman experimental design was used to select the most significant variables that affect to the acid leaching process, while central composite designs were used to found optimum values for the variables involved in the acid leaching. The optimum conditions found for each variable and each element were tabulated. Accurate results were obtained by measuring DORM-1, DOLT-1 and TORT-1 certified reference materials, and the procedure was finally applied to mussel, clam and tuna samples.

"Direct Trace Determination Of Lead In Estuarine Water Using In-situ Preconcentration Of Lead Hydride On Ir, Zr And W-coated Graphite Tubes"
Anal. Chim. Acta 1998 Volume 368, Issue 3 Pages 281-289
Pilar Bermejo-Barrera*, Jorge Moreda-Pi&ntilde;eiro, Antonio Moreda-Pi&ntilde;eiro and Adela Bermejo-Barrera

Abstract: Methods for the direct trace determination of lead in sea water involving hydride generation, trapping and the atomization of the hydride generated in a graphite furnace has been developed. Different permanent coated graphite tubes: iridium, tungstate and zirconium coated graphite tubes were investigated for the in situ pre-concentration of lead hydride. The results obtained were compared with the ones achieved by the conventional HG-AAS. Trapping on Ir-coated graphite tubes offers the best analytical performances, with detection limits of 60 ng 1-1. The accuracy was studied using IAEA/W-4 and SLRS-2 reference materials, and the method was applied to several sea water samples. The number of samples analyzed in an hour was 40. 41 References.
Lead Estuarine Sea IAEA W-4 NRCC SLRS-2 Spectrophotometry Volatile generation Reference material

"Determination Of Trace Metals In Natural Waters By Flame Atomic Absorption Spectrometry Following On-line Ion-exchange Preconcentration"
Anal. Chim. Acta 1995 Volume 303, Issue 2-3 Pages 341-345
M. C. Yebra-Biurrun, A. Bermejo-Barrera, M. P. Bermejo-Barrera* and M. C. Barciela-Alonso

Abstract: An on-line column pre-concentration technique for flow-injection flame atomic absorption spectrometry has been developed for the determination of trace metals in natural waters. A minicolumn (20 mm x 2 mm i.d.) filled with a poly(aminophosphonic acid) chelating resin (PAPhA, 20-30 mesh) was used for the pre-concentration procedure. For 2 mL samples, detection limits of 0.5, 5.0, 1.5, 1.6, 3.5, 0.6, 3.2, 3.1 and 0.4 g 1-1 for Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn, respectively, were achieved. The precision (coefficient of variation) obtained was in the range between 1.1 (Cd and Cu) and 3.3% (Co). Accuracy was also investigated and results agreed with the certified values of the reference material. The sampling rate was 48 h-1. The method was applied to the determination of trace metals in natural waters samples from Galicia (Spain).
Cadmium Cobalt Chromium Copper Iron Manganese Nickel Lead Zinc Environmental Ion exchange Spectrophotometry Preconcentration Column Resin Reference material

"Determination Of Total Selenium And Selenium Distribution In The Milk Phases In Commercial Cow’s Milk By HG-AAS"
Anal. Bioanal. Chem. 2005 Volume 381, Issue 6 Pages 1145-1151
&Oacute;scar Mu&ntilde;iz-Naveiro1, Raquel Dom&iacute;nguez-Gonz&aacute;lez1, Adela Bermejo-Barrera1, Jos&eacute; A. Cocho2, Jos&eacute; M. Fraga3 and Pilar Bermejo-Barrera

Abstract: A procedure has been developed for determining the selenium in cow's milk using hydride generation-atomic absorption spectrometry (HG-AAS) following microwave-assisted acid digestion. The selenium distributions in milk whey, fat and micellar casein phases were studied after separating the different phases by ultracentrifugation and determining the selenium in all of them. The detection limits obtained by HG-AAS for the whole milk, milk whey and micellar casein were 0.074, 0.065 and 0.075 µg l-1, respectively. The accuracy for the whole milk was checked by using a Certified Reference Material CRM 8435 whole milk powder from NIST, and the analytical recoveries for the milk whey and casein micelles were 100.9 and 96.9%, respectively. A mass balance study of the determination of selenium in the different milk phases was carried out, obtaining values of 95.5-100.8%. The total content of selenium was determined in 37 milk samples from 15 different manufacturers, 19 whole milk samples and 18 skimmed milk samples. The selenium levels found were within the 8.5-21 µg l-1 range. The selenium distributions in the different milk phases were studied in 14 whole milk samples, and the highest selenium levels were found in milk whey (47.2-73.6%), while the lowest level was found for the fat phase (4.8-16.2%). A strong correlation was found between the selenium levels in whole milk and the selenium levels in the milk components.