María del Carmen Barciela-Alonso

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.

Evaluation of an in vitro method to estimate trace elements bioavailability in edible seaweeds

Raw edible seaweed harvested in the Galician coast (Northwestern Spain), including two red seaweed types (Dulse and Nori), three brown seaweed (Kombu, Wakame and Sea Spaghetti), one green seaweed (Sea Lettuce) and one microalgae (Spirulina platensis) were studied to assess trace elements bioavailability using an in vitro method (simulated gastric and intestinal digestion/dialysis). Similarly, a cooked seaweed sample (canned in brine) consisting of a mixture of two brown seaweed (Sea Spaghetti and Furbelows) and a derived product (Agar-Agar) from the red seaweed Gelidiumm sesquipedale, were also included in the study. The total trace element content as well as the non-dialyzable fractions was carried out after a microwave acid digestion of the seaweed samples by inductively coupled plasma-mass spectrometry (ICP-MS). The dialyzable fraction was determined without any pre-treatment by ICP-MS. PIPES buffer solution at a pH of 7.0 and dialysis membranes of 10kDa molecular weight cut off (MWCO) were used for intestinal digestion. Accuracy of the method was assessed by analyzing a NIES-09 certified reference material (Sargasso seaweed). The accuracy of the in vitro procedure was established by a mass balance study which led to good accuracy of the whole in vitro process, after statistical evaluation (95% confidence interval). The highest dialyzability percentages (100±0.2%) were obtained for Dulse in Mn and V.

Characterization of estuarine sediments by near infrared diffuse reflectance spectroscopy

It has been developed a partial least squares near infrared (PLS-NIR) method for the determination of estuarine sediment physicochemical parameters. The method was based on the chemometric treatment of first order derivative reflectance spectra obtained from samples previously lyophilized and sieved through a lower than 63 microm grid. Spectra were scanned from 833 to 2976 nm, averaging 36 scans per spectrum at a resolution of 8 cm(-1), using chromatographic glass vials of 9.5 mm internal diameter as measurement cells. Models were built using reference data of 31 samples selected through the use of a hierarchical cluster analysis of NIR spectra of sediments obtained from the Ria de Arousa estuary and prediction parameters were established from a validation set of 50 samples of the same area. pH, redox potential (Eh), carbon (C), nitrogen (N) and hydrogen (H) content together with Sn, Pb, Cd, As, Sb and total Cr and also acid soluble, reducible and oxidable Cr fractions were employed as characteristic parameters of the studied sediments. Standard error of prediction values for C and N content were of the order of 4 and 1.3 mg g(-1) for H. Prediction errors for pH and Eh were 0.15 units and 37 mV, respectively, thus indicating the good prediction capabilities of the method. Regarding trace metal concentrations PLS-NIR provided prediction error levels for unknown samples around 20% for Sn, Pb, As and Sb and root mean square errors of prediction around 40% for concentration levels of 400 ng g(-1) Cd and 100 microg g(-1) Cr. For the different extractable fractions of Cr the residual prediction deviation varied from 1.3 to 1.7 but relative errors found for samples of the validation set were only useful for screening purposes.

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.

Matrix solid phase dispersion-assisted BCR sequential extraction method for metal partitioning in surface estuarine sediments.

The BCR (the Community Bureau of Reference) of the European Union sequential extraction scheme for metal partitioning in estuarine sediments has been accelerated by using a matrix solid phase dispersion (MSPD) approach. The MSPD assisted BCR procedure consists of passing the extractants proposed by conventional BCR protocol (0.11 M acetic acid, 0.1M hydroxylammonium chloride and 8.8M hydrogen peroxide plus 1M ammonium acetate) through the dispersed sample packaged inside a disposable syringe. Different silica-, magnesium- and aluminium-based materials were tested as dispersing agents and sea sand was found to offer the best performances. Variables for assisting the three stages of the BCR protocol were optimized, and accurate results were obtained when assisting the first and the third stages (exchangeable and oxidizable fractions, respectively). However, lack of accuracy was observed when assisting the second step (reducible fraction) and this result agrees with most of the assisted BCR procedures for which extracting the reducible fraction is the most troublesome stage. The organic matter oxidation (third stage) was successfully assisted by passing hydrogen peroxide at 50°C through the dispersed sample inside de syringe just before passing ammonium acetate. Therefore, the time-consuming and unsafe conventional organic matter oxidation processes, commonly performed even for microwave/ultrasounds assisted BCR procedures, are totally avoided. Inductively coupled plasma-mass spectrometry (ICP-MS) was used as a selective detector. The target elements were Cd, Co, Cr, Mn, Ni, Sr and Zn (first stage), Cd, Co and Ni (second stage), and Co, Cr, Mn, Ni, Sr and Zn (third stage). Repeatability of the method (n=7) was good, and RSDs values of 9, 10, 10, 8, 8, 3 and 8% was obtained for Cd, Co, Cr, Mn, Ni, Sr and Zn, respectively (first stage); 10, 9 and 9% for Cd, Co and Ni, respectively (second stage); and 6, 2, 3, 4, 7 and 9% Co, Cr, Mn, Ni, Sr and Zn, respectively (third stage). The procedure was also validated by analysing two certified reference materials (CRM 601 and CRM 701). Good accuracy was obtained for the target elements extracted at the first stage: Cd (4.0 ± 0.1 and 7.3 ± 0.09 μg g(-1) in CRM 601 and CRM 701, respectively), Cr (0.36 ± 0.008 and 2.21 ± 0.08 μg g(-1) in CRM 601 and CRM 701, respectively), Ni (8.0 ± 0.3 and 15.4 ± 0.3 μg g(-1) in CRM 601 and CRM 701, respectively) and Zn (262 ± 3 and 203 ± 3 μg g(-1) in CRM 601 and CRM 701, respectively). Also, good accuracy was observed for elements extracted at the third step: Cd (1.8 ± 0.09 and 0.29 ± 0.03 μg g(-1) in CRM 601 and CRM 701, respectively), Cr (145 ± 4 μg g(-1) in CRM 701), Ni (8.2 ± 0.7 and 15.1 ± 0.5 μg g(-1) in CRM 601 and CRM 701, respectively) and Zn (45 ± 0.7 μg g(-1) in CRM 701).

Characterization of Edible Seaweed Harvested on the Galician Coast (Northwestern Spain) Using Pattern Recognition Techniques and Major and Trace Element Data

Major and trace elements in North Atlantic seaweed originating from Galicia (northwestern Spain) were determined by using inductively coupled plasma-optical emission spectrometry (ICP-OES) (Ba, Ca, Cu, K, Mg, Mn, Na, Sr, and Zn), inductively coupled plasma-mass spectrometry (ICP-MS) (Br and I) and hydride generation-atomic fluorescence spectrometry (HG-AFS) (As). Pattern recognition techniques were then used to classify the edible seaweed according to their type (red, brown, and green seaweed) and also their variety (Wakame, Fucus, Sea Spaghetti, Kombu, Dulse, Nori, and Sea Lettuce). Principal component analysis (PCA) and cluster analysis (CA) were used as exploratory techniques, and linear discriminant analysis (LDA) and soft independent modeling of class analogy (SIMCA) were used as classification procedures. In total, t12 elements were determined in a range of 35 edible seaweed samples (20 brown seaweed, 10 red seaweed, 4 green seaweed, and 1 canned seaweed). Natural groupings of the samples (brown, red, and green types) were observed using PCA and CA (squared Euclidean distance between objects and Ward method as clustering procedure). The application of LDA gave correct assignation percentages of 100% for brown, red, and green types at a significance level of 5%. However, a satisfactory classification (recognition and prediction) using SIMCA was obtained only for red seaweed (100% of cases correctly classified), whereas percentages of 89 and 80% were obtained for brown seaweed for recognition (training set) and prediction (testing set), respectively.

Two-Dimensional Isoelectric Focusing OFFGEL and Microfluidic Lab- on-Chip Electrophoresis for Assessing Dissolved Proteins in Seawater

Dissolved proteins were assessed in surface and deep seawater by two-dimensional isoelectric focusing (IEF) OFFGEL-lab-on-chip (LOC) electrophoresis after tangential flow ultrafiltration followed by centrifugal ultrafiltration (preconcentration factor of 3000). Dissolved protein isolation was performed by treating the ultrafiltrated retentate with cold acetone and also with chloroform as precipitating reagents. The best electrophoretic behavior of the isolated proteins was obtained after protein precipitation with chloroform before different rinsing stages for removing methanol and water interferences. Metals bound to proteins in the different OFFGEL fractions were assessed by inductively coupled plasma-optical emission spectrometry and electrothermal atomic absorption spectrometry, under optimized operating conditions. Experiments regarding stability of the metal-binding proteins [superoxide dismutase (SOD) and alcohol dehydrogenase (ADH) as protein models] showed the integrity of the Zn-binding SOD/ADH under the OFFGEL electrophoretic conditions. However, stability of Cu bound to SOD is not guaranteed. The first electrophoretic dimension (IEF OFFGEL) showed that dissolved proteins in surface seawater exhibit alkaline isoelectric points (pIs of 8.10 and 8.37) and also acid Ips (4.82, 5.13, 5.43, and 5.73), while LOC showed that the isolated proteins exhibit a spread molecular weight range (within 15 - 63 kDa); although, high molecular weights were the most commonly found. Regarding deep seawater, isolated proteins were of acid Ips (from 3.30 to 4.22) and low molecular weight (within the 21-24 kDa range). Elements such as Cd, Cu, Mn, and Ni were mainly associated with dissolved proteins of alkaline pIs in surface seawater, while Zn was mainly associated to proteins of acid pIs. However, only Cu and Mn were found to be bound to dissolved proteins of higher Ips in deep seawater, and the amount of Mn (from 68 to 84 μg L(-1)) was higher than that found in dissolved proteins in surface seawater (22.4 μg L(-1)).