Paulo Rogério Miranda Correia

Reconhecimento de padrões por métodos não supervisionados: explorando procedimentos quimiométricos para tratamento de dados analíticos

An activity for introducing hierarchical cluster analysis (HCA) and principal component analysis (PCA) during the Instrumental Analytical Chemistry course is presented. The posed problem involves the discrimination of mineral water samples according to their geographical origin. Thirty-seven samples of 9 different brands were considered and the results from the determination of Na, K, Mg, Ca, Sr and Ba were taken into account. Non-supervised methods for pattern recognition were explored to construct a dendrogram, score and loading plots. The devised activity can be adopted for introducing Chemometrics devoted to data handling, stressing its importance in the context of modern Analytical Chemistry.

Simultaneous determination of manganese and selenium in serum by electrothermal atomic absorption spectrometry

A method for determination of manganese and selenium in serum by simultaneous atomic absorption spectrometry (SIMAAS) is proposed. The samples (30 mul) were diluted (1+3) to 1.0% v/v HNO(3)+0.10% w/v Triton X-100 directly in the autosampler cups. A total of 20 mug Pd+10 mug Mg(NO(3))(2) was used as chemical modifier. The pyrolysis and atomization temperatures for the simultaneous heating program were 1200 and 2300 degrees C, respectively. The addition of an oxidant mixture (15% w/w H(2)O(2)+1.0% v/v HNO(3)) and the inclusion of a low temperature pyrolysis step (400 degrees C) attenuated the build-up of carbonaceous residues onto the integrated platform. An aliquot of 15 mul of the reference or sample solution was introduced into the graphite tube and heated at 80 degrees C; subsequently, 10 mul of oxidant mixture+10 mul of chemical modifier was introduced over that aliquot and the remaining heating program steps were executed. This strategy allowed at least 250 heating cycles for each THGA tube without analytical signal deterioration. The characteristic masses for manganese (6 pg) and selenium (46 pg) were estimated from the analytical curves. The detection limits were 6.5 pg (n=20, 3delta) for manganese and 50 pg (n=20, 3delta) for selenium. The reliability of the entire procedure was checked with the analysis of serum from Seronormtrade mark Trace Elements in Serum (Sero AS) and by addition and recovery tests (97+/-9% for manganese and 96+/-7% for selenium) using five serum samples.

Silver as internal standard for simultaneous determination of Cd and Pb in whole blood by electrothermal atomic absorption spectrometry

The use of internal standardization for simultaneous atomic absorption spectrometry (SIMAAS) was investigated for Cd and Pb determination in whole blood. The comparison of thermochemical and physico-chemical parameters allowed the selection of Ag, Bi, and Tl as internal standard candidates. Correlation graphs, plotted from the normalized absorbance signals (n = 20) of internal standard (axis y) versus analyte (axis x), precision and accuracy were used to select Ag as the most appropriate internal standard. Blood samples were diluted (1 + 9) with 0.11% (m/v) Triton X-100 + 1.1% (v/v) HNO3 + 0.28% (m/v) NH4H2PO4 + 10 µg L−1 Ag+. Pyrolysis and atomization temperatures for the optimized heating program were 550 and 1700 °C, respectively. Characteristic masses based on integrated absorbance were 1.68 ± 0.01 pg for Cd and 30.3 ± 0.1 pg for Pb. The detection limits (DL) were 0.095 ± 0.001 µg L−1 and 0.86 ± 0.01 µg L−1 for Cd and Pb, respectively. The mean RSD for all determinations was the same for Cd (13 ± 9%) with or without Ag as internal standard (IS). On the other hand, the use of Ag as IS improved the RSD for Pb from 3.6 ± 4.0% to 2.2 ± 2.0%. An effective contribution of the internal standard Ag was verified in the recoveries of spiked samples (0.5 µg L−1 Cd2+ and 5.0 µg L−1 Pb2+). The mean recoveries were 81 ± 8% and 91 ± 4% for Cd, and 80 ± 11% and 93 ± 6% for Pb without and with IS correction, respectively. This is the first application of IS for a simultaneous determination by SIMAAS.

The use of concept maps for knowledge management: from classrooms to research labs

Our contemporary society asks for new strategies to manage knowledge. The main activities developed by academics involve knowledge transmission (teaching) and production (research). Creativity and collaboration are valuable assets for establishing learning organizations in classrooms and research labs. Concept mapping is a useful graphical technique to foster some of the disciplines required to create and develop high-performance teams. The need for a linking phrase to clearly state conceptual relationships makes concept maps (Cmaps) very useful for organizing our own ideas (externalization), as well as, sharing them with other people (elicitation and consensus building). The collaborative knowledge construction (CKC) is supported by Cmaps because they improve the communication signal-to-noise ratio among participants with high information asymmetry. In other words, we can identify knowledge gaps and insightful ideas in our own Cmaps when discussing them with our counterparts. Collaboration involving low and high information asymmetry can also be explored through peer review and student-professor/advisor interactions, respectively. In conclusion, when it is used properly, concept mapping can provide a competitive advantage to produce and share knowledge in our contemporary society. To map is to know, as stated by Wandersee in 1990.

Cobalt as internal standard for arsenic and selenium determination in urine by simultaneous atomic absorption spectrometry

The effectiveness of internal standardization for simultaneous atomic absorption spectrometry (SIMAAS) was investigated for As and Se determination in urine. Co and Sn were selected as internal standard (IS) candidates based on the evaluation of some physico-chemical parameters related to the atomization. Correlation graphs, plotted from the normalized absorbance signals (n=20) of internal standard (axis y) versus analyte (axis x), precision, and accuracy of the analytical results were the supportive parameters to choose Co as the most appropriate IS. The urine samples were diluted 1+2 to 1.0% (v/v) HNO(3)+80mugL(-1) Co(2+). The mixture 20mug Pd+3mug Mg was used as chemical modifier and the optimized temperatures for pyrolysis and atomization steps were 1400 and 2300 degrees C, respectively. The characteristic masses for As (47+/-1pg) and Se (72+/-2pg) were estimated from the analytical curves. The detection limits (n=20, 3delta) were 1.8+/-0.1 and 2.6+/-0.1mugL(-1) for As and Se, respectively. The reliability of the entire procedure was checked with the analysis of certified reference material from Sero AS(Seronormtrade mark Trace Elements in Urine). The obtained results showed the matrix interference disallowed the instrument calibration with aqueous standards. The best analytical condition was achieved when matrix-matched standards were used in combination with Co as IS, which improved the recoveries obtained for As. Under this experimental condition, eight urine samples were analysed and spiked with 10 and 25mugL(-1) As and Se. The mean recoveries were 96+/-6% (10mugL(-1) As), 95+/-6% (25mugL(-1) As), 101+/-7% (10mugL(-1) Se), and 97+/-4% (25mugL(-1) Se).

Avaliação da padronização interna em espectrometria de absorção atômica utilizando gráficos de correlação

The use of an internal standard (IS) in ET AAS can be considered a new trend after the commercial introduction of a simultaneous spectrometer. The evaluation of experimental data to choose the most appropriate IS can be done by comparing correlation graphs. They were used to verify the resemblance among the simultaneous measurements obtained for the analyte(s) and the IS by inductively coupled plasma optical emission spectrometry (ICPOES). The judicious selection of IS by using correlation graphs for determinations by ET AAS can be exploited to improve the precision and accuracy of the analytical results. Therefore, a new approach for studying the use of IS in ET AAS is presented.

Exploring the emission intensities of ICP OES aided by chemometrics in the geographical discrimination of mineral waters

A rapid method for classification of mineral waters is proposed. The discrimination power was evaluated by a novel combination of chemometric data analysis and qualitative multi-elemental fingerprints of mineral water samples acquired from different regions of the Brazilian territory. The classification of mineral waters was assessed using only the wavelength emission intensities obtained by inductively coupled plasma optical emission spectrometry (ICP OES), monitoring different lines of Al, B, Ba, Ca, Cl, Cu, Co, Cr, Fe, K, Mg, Mn, Na, Ni, P, Pb, S, Sb, Si, Sr, Ti, V, and Zn, and Be, Dy, Gd, In, La, Sc and Y as internal standards. Data acquisition was done under robust (RC) and non-robust (NRC) conditions. Also, the combination of signal intensities of two or more emission lines for each element were evaluated instead of the individual lines. The performance of two classification—k-nearest neighbor (kNN) and soft independent modeling of class analogy (SIMCA)—and preprocessing algorithms, autoscaling and Pareto scaling, were evaluated for the ability to differentiate between the various samples in each approach tested (combination of robust or non-robust conditions with use of individual lines or sum of the intensities of emission lines). It was shown that qualitative ICP OES fingerprinting in combination with multivariate analysis is a promising analytical tool that has potential to become a recognized procedure for rapid authenticity and adulteration testing of mineral water samples or other material whose physicochemical properties (or origin) are directly related to mineral content.

Charles Darwin goes to school: the role of cartoons and narrative in setting science in an historical context

Science education is under revision. Recent changes in society require changes in education to respond to new demands. Scientific literacy can be considered a new goal of science education and the epistemological gap between natural sciences and literacy disciplines must be overcome. The history of science is a possible bridge to link these ‘two cultures’ and to foster an interdisciplinary approach in the classroom. This paper acknowledges Darwins legacy and proposes the use of cartoons and narrative expositions to put this interesting chapter of science into its historical context. A five-lesson didactic sequence was developed to tell part of the story of Darwins expedition through South America for students from 10 to 12 years of age. Beyond geological and biological perspectives, the inclusion of historical, social and geographical facts demonstrated the beauty and complexity of the findings that Darwin employed to propose the theory of evolution.

Mapas conceituais como ferramenta de avaliação na sala de aula

A utilizacao dos mapas conceituais (MCs) como ferramenta de avaliacao da aprendizagem foi explorada na disciplina Ciencias da Natureza, oferecida aos alunos ingressantes da Escola de Artes, Ciencias e Humanidades (EACH). Devido a riqueza e a diversidade das estruturas proposicionais elaboradas pelos alunos, o desafio de corrigir MCs e mais complexo do que a correcao de testes de multipla escolha ou de questoes dissertativas. Um procedimento comparativo envolvendo o professor (P), tres especialistas em mapeamento conceitual (E) e os alunos (A) foi utilizado para avaliar MCs (n = 109). A pergunta focal dos MCs explorou as relacoes conceituais entre as observacoes astronomicas do seculo XVI, o nascimento da ciencia moderna e a ampliacao da nossa compreensao sobre o universo. Graficos de correlacao foram elaborados para comparar as avaliacoes (PxE, PxA e ExA). Os resultados obtidos confirmaram a complexidade do processo de avaliacao dos MCs, impondo uma mudanca nos procedimentos usualmente adotados na sala de aula. A possibilidade dos alunos serem incluidos no processo avaliativo e confirmada pela correlacao verificada entre as avaliacoes feitas pelo professor e pelos alunos.

Using Novakian Concept Maps to Foster Peer Collaboration in Higher Education

Novakian Concept maps (N-Cmaps) and the hierarchical reductionism method are combined to create a new pedagogic architecture to address high-complexity issues in classrooms. This strategy considers the epistemological challenge of managing a substantial amount of information from diverse disciplinary fields and the need to engage students in productive, collaborative work sessions to generate the synergistic effect of combining many informed individuals’ perspectives. Discussions through peer collaboration can be organised to achieve the creation of a knowledge model (KW), i.e. a hypertext structure containing a collection of N-Cmaps with any digital resources about the field under study. Students create their own hypertext and use it as visual resource of information to navigate through the complexity they are learning. After discussing the theoretical foundations that underlie our instructional design, we present a case study involving the collaborative creation of a KM to characterise the interdisciplinary connections among six undergraduate courses offered at the School of Arts, Sciences and Humanities (University of Sao Paulo, Brazil). Fifty-two students worked collaboratively to map the connections among these courses and the results revealed an interesting perspective. The structured approach adopted to organise the collaborative knowledge construction process allowed students to make explicit several latent information about the courses they were enrolled. The possibility of reducing cognitive overload explains why the combination of N-Cmaps and the hierarchical reductionism method is useful to grasp complexity in classrooms.