Antonio Moreda-Piñeiro

The classification of tea according to region of origin using pattern recognition techniques and trace metal data

Trace metals in tea originating from various Asian and African countries were determined by using inductively coupled plasma-atomic emission spectrometry and inductively coupled plasma-mass spectrometry. Pattern recognition techniques were then used to classify the tea according to its geographical origin. Principal component analysis (PCA) and cluster analysis (CA), as exploratory techniques, and linear discriminant analysis (LDA) and soft independent modelling of class analogy (SIMCA), were used as classification procedures. In total, 17 elements (Al, Ba, Ca, Cd, Co, Cr, Cu, Cs, Mg, Mn, Ni, Pb, Rb, Sr, Ti, V, Zn) were determined in a range of 85 tea samples (36 samples from Asian countries, 18 samples from African countries, 24 commercial blends and seven samples of unknown origin). Natural groupings of the samples (Asian and African teas) were observed using PCA and CA (squared Euclidean distance between objects and Wards method as clustering procedure). The application of LDA gave correct assignation percentages of 100.0% and 94.4% for the African and Asian teas, respectively, at a significance level of 5%. SIMCA offered percentages of 100.0% and 91.7% for African and Asian groups, respectively, at the same significance level. LDA, also at a significance level of 5%, allowed a 100% of correct case identification for the three classes China, India and Sri Lanka. However, a satisfactory classification using SIMCA was only obtained for the Chinese teas (100% of cases correctly classified), while teas from India and Sri Lanka appear to form the same class.

Inductively coupled plasma–optical emission spectrometry/mass spectrometry for the determination of Cu, Ni, Pb and Zn in seawater after ionic imprinted polymer based solid phase extraction

The capabilities of a synthesized ionic imprinted polymer (IIP), originally prepared for Ni recognition/pre-concentration from seawater, have been evaluated for other trace elements pre-concentration. The polymer has been synthesized by the precipitation polymerization technique using a ternary pre-polymerization complex formed by the template (Ni), the monomer (2-(diethylamino) ethyl methacrylate, DEM) and a non-vinylated chelating agent (8-hydroxyquinoline, 8-HQ). Since the complexing agent (8-HQ) is trapped into the polymeric matrix, but is not linked to the polymer chains, specific interactions between the functional groups (present in the monomer and the complexing agent) and other trace elements rather than Ni may occur. Results have shown that the IIP offers imprinting properties for the template (Ni(II)) and also for Cu(II), Pb(II), Zn(II), As(V) and Cd(II), with analytical recoveries close to 100% for all elements except for As(V) and Cd(II) (around 70%), whereas the non-imprinted polymer (NIP) did not show affinity for any trace element. In addition, the polymer does not interact with alkaline or alkaline-earth metals, so Na, K, Mg and Ca from the seawater salt matrix could be effectively removed. Variables affecting the IIP-solid phase extraction (SPE) process (pH, load flow rate and concentration and volume of the eluting solution) were completely studied. Inductively coupled plasma-optical emission spectrometry (ICP-OES) and inductively coupled plasma-mass spectrometry (ICP-MS) have been used as multi-element detectors. Acidified seawater samples must only be treated to fix an alkaline pH (8.5+/-0.5) and passed through IIP-SPE cartridges. After seawater sample loading (250 mL), analytes were eluted with 2.5 mL of 2.0M nitric acid, offering a pre-concentration factor of 100. Therefore, the limits of detection (LODs) of the method were 0.14, 0.15, 0.18 and 0.03 microg L(-1), for Ni, Cu, Pb and Zn, respectively, when using ICP-OES detection and 0.0022, 0.0065, 0.0040 and 0.009 microg L(-1), for Ni, Cu, Pb and Zn, respectively, for ICP-MS detection. Accuracy of the method was assessed by analyzing SLEW-3 (estuarine water), and TM-23.3 and TM-24 (lake water) certified reference materials.

A review on iodine speciation for environmental, biological and nutrition fields

A review of recent literature focused on iodine determination/speciation in environmental, biological and clinical materials is provided. The review covers the different sample pre-treatments to extract total iodine, as well as specific iodinated forms, and the most used analytical techniques for assessing total iodine (cathodic stripping voltammetry, differential pulse voltammetry, neutron activation analysis, catalytic spectrophotometry, and atomic spectrometric techniques, mainly inductively coupled plasma-mass spectrometry) and iodine speciation (nonchromatographic methods, and mainly high performance liquid chromatography, gas chromatography and capillary electrophoresis coupled to electrochemical, UV spectrophotometric and mass spectrometric detection).

Microwave assisted extraction of iodine and bromine from edible seaweed for inductively coupled plasma-mass spectrometry determination.

The feasibility of microwave energy to assist the solubilisation of edible seaweed samples by tetramethylammonium hydroxide (TMAH) has been investigated to extract iodine and bromine. Inductively coupled plasma-mass spectrometry (ICP-MS) has been used as a multi-element detector. Variables affecting the microwave assisted extraction/solubilisation (temperature, TMAH volume, ramp time and hold time) were firstly screened by applying a fractional factorial design (2(5-1)+2), resolution V and 2 centre points. When extracting both halogens, results showed statistical significance (confidence interval of 95%) for TMAH volume and temperature, and also for the two order interaction between both variables. Therefore, these two variables were finally optimized by a 2(2)+star orthogonal central composite design with 5 centre points and 2 replicates, and optimum values of 200 degrees C and 10 mL for temperature and TMAH volume, respectively, were found. The extraction time (ramp and hold times) was found statistically non-significant, and values of 10 and 5 min were chosen for the ramp time and the hold time, respectively. This means a fast microwave heating cycle. Repeatability of the over-all procedure has been found to be 6% for both elements, while iodine and bromine concentrations of 24.6 and 19.9 ng g(-1), respectively, were established for the limit of detection. Accuracy of the method was assessed by analyzing the NIES-09 (Sargasso, Sargassum fulvellum) certified reference material (CRM) and the iodine and bromine concentrations found have been in good agreement with the indicative values for this CRM. Finally, the method was applied to several edible dried and canned seaweed samples.

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.

Evaluation of the effect of data pre-treatment procedures on classical pattern recognition and principal components analysis: a case study for the geographical classification of tea

A simple transformation that uses the half-range and central value has been used as a data pre-treatment procedure for principal component analysis (PCA) and pattern recognition techniques. The results obtained have been compared with the results from classical normalisation of data (mean normalisation, maximum normalisation and range normalisation), autoscaling and the minimum-maximum transformation. Three data sets were used in the study. The first was formed by determining 17 elements in 53 tea samples (901 pieces of data). The second and third data sets arose from two long-term drift studies performed to examine instrumental stability at standard and robust conditions. The instruments used were an inductively coupled plasma atomic emission spectrometer and an inductively coupled plasma mass spectrometer. Each drift diagnosis experiment consisted of replicate determinations of a test solution containing 15 analytes at 10 mg l-1 over 8 h without recalibration. Twenty-nine emission lines were determined 99 times, thus, each data set was formed by 2881 pieces of data. Data pre-treatment was applied to the three data sets prior to the use of principal component analysis, cluster analysis, linear discrimination analysis and soft independent modelling of class analogy. The study revealed that the half-range and central value transformation resulted in a better classification of the tea samples than that achieved using the classical normalisation. The loadings in the PCA for the long-term stability study, under both standard and robust conditions, were found to be similar to the drift trends only when the minimum-maximum transformation and the mean or maximum normalizations were used as data pre-treatments.