A. Bermejo-Barrera

Determination of trace metals in natural waters by flame atomic absorption spectrometry following on-line ion-exchange preconcentration

An on-line column preconcentration technique for flow-injection flame atomic absorption spectrometry has been developed for the determination of trace metals in natural waters. A minicolumn (20 mm × 2 mm i.d.) filled with a poly(aminophosphonic acid) chelating resin (PAPhA, 20–30 mesh) was used for the preconcentration 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 μg 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).

Determination of trace metals (As, Cd, Hg, Pb and Sn) in marine sediment slurry samples by electrothermal atomic absorption spectrometry using palladium as a chemical modifier☆

Abstract Methods for the determination of As, Cd, Pb, Hg and Sn by electrothermal atomic absorption spectrometry in marine sediment slurry samples were developed. Triton X-100 was used as surfactant to stabilize the marine sediment slurry. Palladium or a mixture of palladium and magnesium nitrates was used as a chemical modifier. With the use of these modifiers it was possible to stabilize As, Cd, Pb, Hg and Sn to temperatures of 1200, 700, 900, 200 and 1300°C respectively, and the optimum atomization temperatures were 2300, 2500, 2500, 1450 and 1900°C. Precision and accuracy of the method were investigated using the marine sediment reference material PACS-1 (National Research Council Canada). The detection limits were 44, 0.08, 60, 70 and 57 μg kg −1 for As, Cd, Pb, Hg and Sn respectively.

Chromium available fractions in arousa sediments using a modified microwave BCR protocol based on microwave assisted extraction.

In a research of chromium availability, the three-stage sequential extraction procedure, proposed by European Community Bureau of Reference (BCR), has been applied for the metal fractionation in marine sediment samples. The procedure has been modified, evaluating the effect of microwave energy to perform the sequential method. Results achieved a substantial reduction in time in comparison to the traditional shaking technique. The time of the first and the second extractions were reduced to 30s in both steps using microwave heating and working at 66W of power. To the third extraction, higher power was necessary so it was chosen to work at 198W. In the last step investigated, time was reduced to 1min, being a great improvement respect to the conventional BCR sequential extraction protocol. Chromium determinations in these extracts were carried out by Electrothermal Atomic Absorption Spectrometry (ETAAS). The developed method was applied for chromium determination in marine sediment samples from Ria de Arousa (Galicia, NW of Spain). The values obtained by our laboratory ranged from 0.10 to 1.02mugg(-1) for soluble and reducible fractions, and from 5.5 to 60.0mugg(-1) for the oxidisable fraction. The higher concentrations obtained were the chromium associated with the organic fraction of the marine sediments.

Palladium as a chemical modifier for the determination of mercury in marine sediment slurries by electrothermal atomization atomic absorption spectrometry

A method for the determination of mercury in marine sediment slurries by electrothermal atomization atomic absorption spectrometry was optimized. It was found that a particle size < 20 μm is sufficient to achieve total atomization of the mercury content in the solid particles of the slurry. This particle size was achieved with simple mechanical grinding, using zirconia beads. The use of different thickening agents, viz., Triton X-100, Viscalex HV30 and glycerol, during the slurry preparation was studied. In addition, an acid predigestion was applied to verify the efficiency of the slurry sampling. The use of palladium at a concentration of 15 mg l−1 was found satisfactory for stabilizing mercury at 200°C. Three charring steps, two involving an oxidative process, were studied. The optimum atomization temperature was 1450°C. A limit of detection of 70 μg kg−1 was achieved. The standard additions method was used for the determination of mercury in marine sediment samples from the Galician coast, the levels being between 2.2 and 3.2 mg kg−1.

Separation of Cr(III) and Cr(VI) using complexation of Cr(III) with 8-hydroxyquinoline and determination of both species in waters by ETA-AAS

SummaryA method for the determination of chromium(III) and (VI) species has been studied and applied to mineral water samples. The chromium(III) was chelated with 0.1 mol/l 8-hydroxyquinoline in methyl alcohol, extracted in isobutyl methyl ketone and determined by ETA-AAS. The effects of the pH, extraction and heating time and amounts of the reagents required for the extraction were studied. A method for the determination of total chromium was optimized too, and the chromium(VI) can be calculated. The precision, sensibility, accuracy, graphite furnace program and interferences for both methods were also investigated.

Optimization of a microwave-pseudo-digestion procedure by experimental designs for the determination of trace elements in seafood products by atomic absorption spectrometry

Abstract A Plackett–Burman 2 7 ×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 1.2–2.2 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.

Study of chemical modifiers for direct determination of silver in sea water by ETA-AAS with deuterium background correction

Methods for the direct determination of silver in sea water samples by ETA-AAS using different chemical modifiers were studied. The effect of salinity was studied using synthetic sea water of high (72.8 per thousand) and low (34.2 per thousand) salinity, and the results were compared with aqueous standard solutions. The charring temperatures achieved were 800 and 900 degrees C for magnesium nitrate and ammonium dihydrogen phosphate respectively, being 1100 degrees C for palladium nitrate and their mixtures. The best sensitivity obtained in the peak-height measurement mode was achieved by using reduced palladium (limit of detection (LOD) between 0.5 and 1.1 mug l(-1) for an injection volume of 20 mu1) with analytical recoveries close to 100% for synthetic and real sea water samples. The use of ammonium dihydrogen phosphate (LOD of 1.3 mug l(-1) for an injection volume of 20 mu1) produced good recoveries for low salinity; at high salinity an increase of around 25% was obtained, the method being unsuitable for sea water analysis. Finally, an interference study of the major components of sea water was carried out and applied to the analysis of surface sea water from the Galicia coast.

Preconcentration of trace amounts of manganese from natural waters by means of a macroreticular poly(dithiocarbamate) resin

A chelating poly(dithiocarbamate) resin (PDTC) with macroreticular support is characterized as effective collector for traces of manganese from natural waters. Using small PDTC columns preconcentration of manganese can be achieved even at high flow-rates (5-6 ml/min) and sample volumes (1500 ml). Accordingly, PDTC resin is used for the preconcentration of manganese from water samples prior to its determination by flame atomic-absorption spectrometry. A series of ions abundant in natural waters do not interfere. The sensitivity and detection limit were 2.5 and 0.5 mug/l., respectively. The relative standard deviations of the results for a manganese concentration of 40-400 mug/l. are in the range 1.1-6.2%. In mineral and tap waters analysed, the manganese concentration range was between 2.9 and 30.8 mug/l.

Speciation of arsenic by the determination of total arsenic and arsenic(III) in marine sediment samples by electrothermal atomic absorption spectrometry

A method for the determination of arsenic(III) and total arsenic was studied. Arsenic(III) was chelated with 2% sodium diethyldithiocarbamate in water, extracted with isobutyl methyl ketone and determined by electrothermal atomic absorption spectrometry, using palladium as chemical modifier. The effects of pH, extraction time and amounts of reagents required for the extraction were studied. The detection limit of this method was 25 µg kg–1. Different modifiers [LaCl3–HNO3, Pd–Mg(NO3)2] for the total arsenic determination in slurries of marine sediment samples were also investigated; LaCl3–HNO3 was avoided because a double peak was observed. The detection limit for the determination of total arsenic using Pd–Mg(NO3)2 as modifier was 44 µg kg–1. The precisions obtained for the different amounts of arsenic(III) and total arsenic were 0.57–2.99 and 0.83–0.45%, respectively. The graphite furnace programmes, accuracy and interferences for both procedures were also studied. The method has been applied to the determination of arsenic(III) and total arsenic in sediment samples from Galicia (North West of Spain).

Direct speciation analysis of Cr(VI) by electrothermal atomic absorption spectrometry, based on the volatilization of Cr(III)–thenoyltrifluoracetonate from the graphite furnace☆

A new method for the direct determination of Cr(VI) by electrothermal atomic absorption spectrometry has been developed. The formation of a volatile complex between Cr(III) and thenoyltrifluoracetonate was used to separate both species. The optimum conditions for complex formation were: pH range 5–6 (using HAc/NaAc as a buffer solution), sonication time of 5 s at 40 °C with a reaction time of 3 h and 30 min before measurement. At temperatures above 700 °C the complex formed was completely volatilized, making Cr(VI) determination possible, independent from Cr(III). The optimum temperature program for Cr(VI) determination was 1600 and 2400 °C for pyrolysis and atomization, respectively. Better separation of the species was obtained when 5 mg l−1 of palladium was added as a modifier. The developed method was precise (with R.S.D.<10%), with a detection limit of 0.7 μg l−1 Cr. CRM 544 (lyophilized chromium) was used to demonstrate the accuracy of the method.