Jorge Moreda-Piñeiro

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.

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.

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.

Simultaneous pressurized enzymatic hydrolysis extraction and clean up for arsenic speciation in seafood samples before high performance liquid chromatography–inductively coupled plasma-mass spectrometry determination

The feasibility of pressurized conditions to assist enzymatic hydrolysis of seafood tissues for arsenic speciation was novelty studied. A simultaneous in situ (in cell) clean-up procedure was also optimized, which speeds up the whole sample treatment. Arsenic species (As(III), MMA, DMA, As(V), AsB and AsC) were released from dried seafood tissues using pepsin as a protease, and the arsenic species were separated/quantified by anion exchange high performance liquid chromatography (HPLC) coupled to inductively coupled plasma-mass spectrometry (ICP-MS). Variables inherent to the enzymatic activity (pH, temperature and ionic strength), the amount of enzyme (pepsin), and factors affecting pressurization (pressure, static time, number of cycles and amount of dispersing agent, C-18) were fully evaluated. Pressurized assisted enzymatic hydrolysis (PAEH) with pepsin can be finished after few minutes (two cycles of 2 min each one plus 3 min to reach the hydrolysis temperature of 50 °C). A total sample solubilisation is not achieved after the procedure, however it is efficient enough for breaking down certain bonds of bio-molecules and for releasing arsenic species. The developed method has been found to be precise (RSDs lower than 6% for As(III), DMA and As(V); and 3% for AsB) and sensitive (LOQs of 18.1, 36.2, 35.7, 28.6, 20.6 and 22.5 ng/g for As(III), MMA, DMA, As(V), AsB and AsC, respectively). The optimized methodology was successfully applied to different certified reference materials (DORM-2 and BCR 627) which offer certified AsB and DMA contents, and also to different seafood products (mollusks, white fishes and cold water fishes).

Direct determination of dissolved selenium (vi) and selenium (vi) in sea-water by continuous flow hydride generation atomic fluorescence spectrometry

Highly sensitive and simple methods were developed for the direct determination of trace amounts of selenite and selenate in sea-water. For SeIV determination, sea-water samples and reagent blank in 1.5 mol l–1 HCl containing 2.0% m/v KH2PO4, as an interference eliminating reagent, are merged with 1.5% m/v NaBH4 in 0.5% m/v NaOH using flow rates of 22 and 2.0 ml min–1, respectively. The selenium hydride produced is passed through a gas–liquid separator and a dryer tube using an argon carrier flow of 0.45 l min–1, and Se is determined with a mini-hydrogen diffusion flame by a non-dispersive atomic fluorescence spectrometer equipped with a Se boosted discharge hollow cathode lamp. For total Se determination, samples are acidified (1.5 mol l–1) and treated with NaBr (4.0% m/v) by heating at 70 °C for 60 min to reduce selenate. The determination of total Se by atomic fluorescence is then carried out as described above. SeVI is calculated as the difference between total Se and SeIV. The detection limits (3σ of blank) of the methods were reached with 0.96–1.3 ng l–1 of Se. The calibration graph was rectilinear up to 80 ng l–1. The recoveries of 20 ng l–1 SeIV added into sea-water were 99.3–100 (s±8.4) %, and those of SeVI were 98.9–104 (s±4.0) %. The method is suitable for the direct analysis of natural samples and the results obtained for a certified reference material were in good agreement with the reported value.

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.

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.

Matrix solid-phase dispersion as a sample pretreatment for the speciation of arsenic in seafood products.

Matrix solid-phase dispersion (MSPD) has been applied to extract arsenical species (arsenite, As(III); arsenate, As(V); monomethylarsonic acid; dimethylarsinic acid, DMA; arsenobetaine, AsB; and arsenocholine) from seafood products. High-performance liquid chromatography coupled to inductively coupled plasma-mass spectrometry was used to separate and detect all arsenic species. Variables affecting MSPD, such as the solid support material (dispersing agent), solid support mass/sample mass ratio, elution solvent composition, and elution solvent volume, have been fully evaluated. Quantitative recoveries for inorganic and organic arsenic species have been obtained when using diatomaceous earth or octadecyl-functionalized silica gel (C18) as a solid support material, with a solid support mass/sample mass ratio of 7.0. Elution of arsenical compounds has been assessed using 10 mL of 50/50 methanol/ultrapure water as an elution solvent. The MSPD method has been found precise, with RSDs of approximately 9% for As(III), DMA, and As(V) and 3% for AsB. The developed procedure has been tested by analyzing different certified reference materials of marine origin such as DORM-2 and BCR 627, which offer certified contents for some arsenic species. The method has been also applied to assess arsenic speciation in different mollusks, cold water fishes, and white fishes.

Application of fast ultrasound water-bath assisted enzymatic hydrolysis--high performance liquid chromatography-inductively coupled plasma-mass spectrometry procedures for arsenic speciation in seafood materials.

Enzymatic hydrolysis of seafood materials for isolating arsenic species (As(III), As(V), DMA and AsB) has been successfully performed by assisting the procedure with ultrasound energy (35 kHz) supplied by an ultrasound water-bath. The use of pepsin, as a proteolytic enzyme, under optimized operating conditions (pH 3.0, temperature 40°C, enzyme to sample ratio of 0.3) led to an efficient assistance of the enzymatic process in a short period of time (from 4.0 to 30 min). The enzymatic extract was then subjected to a clean-up procedure based on ENVI-Carb™ solid phase extraction (SPE). An optimized anion exchange high performance liquid chromatography (HPLC) coupled to inductively coupled plasma-mass spectrometry (ICP-MS) permitted the fast separation (less than 15 min) of six different arsenic species (arsenite, As(III); arsenate, As(V); dimethylarsinic acid, DMA; and arsenobetaine, AsB; as well as monomethylarsonic acid, MMA; and arsenocholine, AsC) in a single run. Relative standard deviations (n=11) of the over-all procedure were 7% for AsB and DMA, 11% for As(III) and 9% for MMA. HPLC-ICP-MS determinations were performed using aqueous calibrations covering arsenic concentrations of 0, 5, 10, 25, 100 and 200 μg L(-1) (expressed as arsenic) for As(III), As(V), MMA, DMA and AsC; and 0, 125, 250, 500, 750, 1000 and 2000 μg L(-1) (expressed as arsenic) for AsB. Germanium (5 μg L(-1)) was used as an internal standard. Analytical recoveries from the anion exchange column varied from 96 to 105% (enzymatic digests spiked with low target concentrations), from 97 to 104% (enzymatic digests spiked with intermediate target concentrations), and from 98 to 103% (enzymatic digests spiked with high target concentrations). The developed method was successfully applied to two certified reference materials (CRMs), DORM-2 and BCR 627, which offer certified AsB and DMA contents, and also to different seafood samples (mollusks, white fish and cold water fish). Good agreement between certified and found AsB concentrations was achieved when analyzing both CRMs; and also, between certified and found DMA concentrations in BCR 627. In addition, the sum of the different arsenic species concentrations found in most of the analyzed samples was statistically similar to the assessed total arsenic concentrations after a total sample matrix decomposition treatment.

Determination of aluminium and manganese in human scalp hair by electrothermal atomic absorption spectrometry using slurry sampling.

Methods for the determination of aluminium and manganese in human scalp hair samples by electrothermal atomic absorption spectrometry using the slurry sampling technique were developed. Palladium and magnesium nitrate were used as chemical modifiers. Hair samples were pulverized using a zirconia vibrational mill ball, and were prepared as aqueous slurries. Determinations can be performed in the linear ranges of 1.9-150 mug l(-1) Al(3+) and 0.03-10.0 mug l(-1) Mn(2+). Limits of detection of 0.9 mg kg(-1) and 27.6 mug kg(-1) were obtained for aluminium and manganese, respectively. The analytical recoveries were between 99.6 and 101.8% for aluminium and in the 98.3-101.3% range for manganese. The repeatability of the methods (n=11), slurry preparation procedure and ETAAS measurement, was 16.0 and 7.9% for aluminium and manganese, respectively. The methods were finally applied to the aluminium and manganese determination in 25 scalp hair samples from healthy adults. The levels for aluminium were between 8.21 and 74.08 mg kg(-1), while concentrations between 0.03 and 1.20 mg kg(-1) were found for manganese.