Adela Bermejo-Barrera

Slurry sampling electrothermal atomic absorption spectrometric determination of lead, cadmium and manganese in human hair samples using rapid atomizer programs

Rapid methods for the determination of lead, cadmium and manganese in human scalp hair by ETAAS using rapid atomizer programs and deuterium arc background correction have been developed. Samples were powdered by means of a zirconia vibrating ball mill over a period of 20 min (mean particle size less than 1 µm). Then 0.1 g of the powder was suspended in a few ml of water and diluted to 25 ml. An optimum drying temperature of 250 °C was found for lead, cadmium and manganese. Optimum atomization temperatures of 2200 and 1900 °C were found for cadmium and manganese, and for lead, respectively. The program cycles were 38 s for cadmium and lead, and 37 s for manganese. Glycerol, at an optimum concentration of 0.4% m/v, was used as a stabilizing agent. Simple aqueous calibration was used for all analytes. The limits of detection were 0.03, 0.05 and 0.04 mg kg -1 for cadmium, lead and manganese, respectively. Accuracy was studied by analysing CRM 397 human hair, and the cadmium and lead levels were found to be in accordance with the certified accuracy values. The levels of metals obtained were in agreement with those previously reported for healthy people in Europe, i.e. , less than 3.0 and 0.3 mg kg -1 for lead and cadmium, respectively.

Usefulness of the chemical modification and the multi-injection technique approaches in the electrothermal atomic absorption spectrometric determination of silver, arsenic, cadmium, chromium, mercury, nickel and lead in sea-water

A critical study of the use of chemical modification and background correction systems was carried out for the direct determination of several high and medium volatility and refractory metals (Ag, As, Cd, Cr, Hg, Ni and Pb) in sea-water samples by ETAAS. The influence of increasing sea-water inorganic matrix on the atomic signals, by the introduction of a large injection volume, was evaluated for different chemical modifiers [mainly Pd(NO3)2 , Mg(NO3)2 and also reduced palladium, which was done by using different reducing agents, viz., ascorbic acid, hydroxylamine hydrochloride and citric acid] and with two background correction systems [deuterium arc background correction (DABC) and Zeeman effect background correction (ZEBC)]. The influence of the salt matrix from sea-water was found to be very important for medium volatility metals such as Ag, As and Pb (charring temperatures between 1100 and 1400 °C), whereas for refractory (Cr and Ni, with charring temperatures of 1500 and 1600 °C, respectively) and high volatility metals such as Cd and Hg (charring temperature of 500 and 300 °C, respectively) this influence was insignificant. By using chemical modification and background correction, the interferences from the saline matrix were lowered for all metals studied (except Pb) and their direct determination in sea-water samples became possible. For high and medium volatility metals the use of reduced palladium offers better analytical performance than the use of palladium nitrate, while the addition of reducing agents does not improve the analytical performance for refractory metals.

The multivariate optimisation of ultrasonic bath-induced acid leaching for the determination of trace elements in seafood products by atomic absorption spectrometry

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 vapour-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.

Sample pre-treatment methods for the trace elements determination in seafood products by atomic absorption spectrometry

Different sample pre-treatments for seafood products have been compared with determine trace elements (As, Cd, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Se and Zn) by flame atomic absorption spectrometry (FAAS) and electrothermal atomic absorption spectrometry (ETAAS). Classic pre-treatments as microwave assisted-acid digestion and the slurry sampling technique were compared with new procedures such as microwave energy or ultrasound energy assisted-acid leaching process and enzymatic hydrolysis methodologies based on the use of pronase E. The methods were applied to DORM-1 and DOLT-1 reference materials with certified contents for the studied elements. The Student-Newman-Keuls (SNK) method was used to compare with element concentration means obtained with each sample pre-treatment and also the certified concentration means in both reference materials. Multivariate techniques such as principal components analysis (PCA) was also applied to comparative purposes.

Experimental designs in the optimisation of ultrasonic bath-acid-leaching procedures for the determination of trace elements in human hair samples by atomic absorption spectrometry

Experimental designs were used for the optimisation of acid-leaching procedures assisted by ultrasonic energy for the extraction of Ca, Cu, Fe, Mg, Mn and Zn from human hair samples. A Plackett-Burman 2(7) x 3/32 design for seven factors ([HNO3], [HCl], [H2O2], acid/oxidant solution volume, exposure time to ultrasounds, temperature of the ultrasonic bath and hair particle size) was used in order to choose the variables affecting the acid-leaching process. The variables [HNO3], [HCl] and temperature of the ultrasonic bath were found to be the most important parameters for the acid-leaching procedure, and these variables were optimised by a response surface design (central composite design 2(3) + star) which involved 16 experiments. Optimum values in the 3.7-4.2 M range were found for [HNO3], while optimum values between 3.0 and 3.5 M were found for [HCl]. The optimum temperature of the ultrasonic bath was between 80 and 90 degrees C. An acid digestion induced by microwave energy (details given) was used to obtain the total metal concentration and also for comparative purposes. Ca, Cu, Fe, Mg and Zn were measured by flame atomic absorption spectrometry (FAAS) using a conventional air/acetylene flame, while Mn was determined by electrothermal atomic absorption spectrometry (ETAAS) under optimised conditions. Two different reference materials, IAEA-085 International Atomic Energy Agency, Monaco) and NIES No. 13 (National Institute for Environmental Studies, Japan), with certified metal contents for some of the elements investigated, were used in order to verify the accuracy of the methods.

Selenium speciation in cow milk obtained after supplementation with different selenium forms to the cow feed using liquid chromatography coupled with hydride generation-atomic fluorescence spectrometry

The purpose of this paper is to develop an easy and quick on-line selenium speciation method (LC-UV-HG-AFS) in cow milk obtained after different supplementation to cow feed. This study focuses on selenium speciation in cow milk after the use of different selenium species (organic selenium as selenised yeast and inorganic selenium as sodium selenite) in the supplementation of forages. Separation was carried out on a muBondapack C(18) column with the positively charged ion-pairing agent tetraethylammonium chloride in the mobile phase. The optimization of pre-reduction conditions was carried out; this step was done with UV irradiation and a heating block to improve the reduction of the different Se-compounds. Variables such as exposure time, hydrochloric acid concentration and temperature were studied. The detection limits for SeCyst(2), Se(IV), SeMet and Se(VI) were 0.4, 0.5, 0.9 and 1.0mugl(-1), respectively. The proposed method was applied to cow milk samples. The milk samples obtained after an organic supplementation of feeding as selenised yeast present three species of selenium, SeCyst2, Se(IV) and SeMet, while only SeCyst2 and Se(IV) are present in milk samples obtained after an inorganic supplementation of feeding.

SEGMENTAL HAIR ANALYSIS FOR COCAINE AND HEROIN ABUSE DETERMINATION

Segmental hair analysis was performed to obtain information about the history of drug abuse of subjects in a rehabilitation programme. The analytical data from hair samples were correlated, when possible, with urine analysis and to toxicological anamnesis. Toxicological analysis of hair seems to be a valid tool in this specific field.

Slurry sampling for the determination of lead in marine sediments by electrothermal atomic absorption spectrometry using palladium–magnesium nitrate as a chemical modifier

A method for the determination of lead in slurries of marine sediment using palladium–magnesium nitrate as a chemical modifier has been optimized. To stabilize the marine sediment slurry, different thickening agents were studied. The grinding time and the particle size were also studied. To achieve complete pyrolysis of the slurry sample, two charring steps were used: the first one at a low temperature, 480 °C, and the second at 900 °C. The precision of the method was studied as within-run and within-batch precision; the relative standard deviations obtained in both cases were less than 3%. The relative standard deviation for the repeatability of the over-all procedure was 5.0%. The accuracy of the method was studied using a Certified Reference Material PACS-1 (Marine Sediment) from the National Research Council of Canada, which has a certified lead content of 404 ± 20 mg kg–1; the result obtained was 418 ± 11 mg kg–1. The detection limit for lead was 0.22 µg l–1. Calibrations using aqueous standards and the reference material were compared. This method has been applied to the determination of lead in marine sediment samples from the Galicia Coast and the results were compared with a sample digestion method using nitric and hydrochloric acids in a high pressure poly(tetrafluoroethylene) bomb and microwave energy. No significant differences were found between the two procedures.

Usefulness of enzymatic hydrolysis procedures based on the use of pronase E as sample pre-treatment for multi-element determination in biological materials

Several minor (Cu, Fe, Mg and Zn) and trace (Ag, As, Cd and Pb) elements were extracted from biological materials, such as human hair and mussel, using an enzymatic hydrolysis procedure based on pronase E. The reaction conditions, viz., pH and temperature, were fixed at optimum values of 7.4 and 37 °C, respectively. Other variables affecting the enzymatic hydrolysis procedure, such as enzymatic hydrolysis time, enzyme concentration, volume of enzyme solution and sample mass, were studied and optimized. The pH value was adjusted with a TRIS–HCl solution as buffer system. The minor elements were measured by FAAS while trace elements were determined by ETAAS under optimum conditions. In order to determine the total element concentration in samples, a microwave-induced acid digestion procedure in laboratory-made low pressure PTFE bombs was optimized. The enzymatic hydrolysis was effective for mussel samples (recoveries of about 100% were obtained for As, Cd, Cu and Mg); however, it was poor for human hair (recoveries were lower than 70%).

Application of ultrasound-assisted acid leaching procedures for major and trace elements determination in edible seaweed by inductively coupled plasma-optical emission spectrometry

A new method using diluted reagents (nitric and hydrochloric acids and oxygen peroxide) and ultrasound energy to assist metals acid leaching with from edible seaweed was optimized. The method uses a first sonication at high temperature with hydrochloric acid as a previous stage to an ultrasound-assisted acid leaching with 7ml of an acid solution containing nitric acid, hydrochloric acid and hydrogen peroxide at concentrations of 3.7, 3.0 and 3.0M, respectively. Optimum conditions for the first sonication step were ultrasound energy at 17kHz, sonication temperature at 65 degrees C, an acid volume of 2ml, an hydrochloric acid concentration of 6.0M and a sonication time of 10min. It has been found that the first sonication stage at high temperature with hydrochloric acid is necessary to obtain quantitative recoveries for As, Ba, Fe and V. Otherwise quantitative recoveries were reached for the other elements investigated (Ca, K, Na, Mg, Cd, Cr, Cu, Mn, Ni, Pb and Zn). The repeatability of the ultrasound-assisted acid leaching method was around 10% for all elements. Adequate limit of detection and limit of quantification were reached by using inductively coupled plasma-optical emission spectrometry (ICP-OES) for measurements. The method resulted accurate after analysing several seaweed certified reference materials (IAEA-140/TM, NIES-03 and NIES-09). The method was finally applied to the multi-element determination in edible seaweed samples.