The Role of Electrochemical Impedance Spectroscopy in the Characterization of Electrodes and Devices for Energy Conversion and Storage

U ovom su članku opisani osnovni principi elektrokemijske impedancijske spektroskopije, EIS, i mogućnosti njezine primjene u karakterizaciji elektroda i elektrokemijskih uređaja za pretvorbu i skladištenje energije. Objašnjen je koncept impedancije, opisani nužni stupnjevi analize mjerenih impedancijskih spektara i dane osnovne relacije za impedanciju pojedinih elektrokemijskih procesa u sustavu. Prikazani su električni ekvivalentni krugovi kao impedancijski analozi jediničnih članka elektrokemijskog (super)kondenzatora, galvanskog članka (baterije) i gorivnog članka, opisane pojedine komponente i parametri koji definiraju sustav. Navedene su prednosti i problemi pri primjeni ove tehnike u procjeni stanja i pogrešaka pri radu ovih elektrokemijskih uređaja.This article describes the basic principles of the Electrochemical Impedance Spectroscopy, EIS, technique and its application in the characterization of electrode materials and electrochemical devices for energy conversion and storage. The concept of impedance and the necessary steps of impedance spectra analysis are explained. Basic relations for impedance of particular electro- chemical processes occurring in the system(s) are derived. Electrical equivalent circuits as impedance analogues for single-cell units of electrochemical (super)capacitors, galvanic cells (batteries) and fuel cells, as well as separate impedance components and parameters describing the system(s) are presented and discussed. The advantages and problems in application of the EIS technique for evaluation of operating states and possible failures of these electrochemical devices are described

ZNAČAJ VISOKOMOLEKULARNIH PODJEDINICA GLUTENINA U PROCJENI KAKVOĆE PŠENICE

High-molecular-weight glutenin subunits (HMW-GS) composition was analyzed by sodium-dodecyl-sulfat-polyacrilamid-gel electrophoresis (SDS-PAGE), while the quantitative determination of total HMW-GS was obtained by reversed phase- high performance liquid chromatography (RP-HPLC). Considering HMW-GS composition, the most frequent subunits at Glu-A1 locus were N, at Glu-B1 locus 7+9 and at Glu-D1 locus 2+12. The cultivars with the GS 5+10 at Glu-D1 locus have shown better technological characteristics in contrast to cultivars with the GS 2+12. The cultivars Žitarka, Srpanjka, Barbara, Klara and Golubica in spite of presence HMW-GS 2+12 have shown very good and good technological properties because they had optimal proportions (>10%) of total HMW-GS. The results of the linear correlation analysis between quality parameters and HMW-GS composition have shown significant (P10%) ukupnih HMW-GS. Rezultati linearne korelacije između parametara kakvoće i sastava HMW-GS pokazali su značajan (p<0,05) pozitivan utjecaj HMW-GS (Glu-1 bodovi) na sedimentacijsku vrijednost (r=0,55), gluten indeks (r=0,72), energiju tijesta (r=0,61), maksimalni otpor (r=0,64), te omjera otpora i rastezljivosti tijesta (r=0,58). U odnosu na sastav HMW-GS, njihovi udjeli pokazuju značajniji utjecaj na udio proteina (r=0,82), vrijeme razvoja tijesta (r=0,70), stupanj omekšanja (r=-0,90), energiju tijesta (r=0,74) i na volumen kruha (r=0,65)

Prediction of the genetic similarity of wheat and wheat quality by reversed-phase high-performance liquid chromatography and lab-on-chip methods

The aim of this study was to compare efficiency of RP-HPLC (Reversed-Phase High-Performance Liquid Chromatography) and LOC (Lab-on-Chip) methods for wheat gluten protein quantification regarding clustering of wheat cultivars according to the genetic similarity (HMW-GS combinations), as well as to explore relations of these two methods to wheat quality parameters. For that purpose, wheat quality parameters (protein content, falling number, wet gluten content, gluten index, Farinograph, Extensograph, and Amylograph), as well as amounts of gliadin and glutenin fractions by RP-HPLC and LOC methods were determined in two different sets of wheat cultivars (Croatian and Serbian). The percentages of gluten proteins and the values of quality parameters were used to characterize the samples by principal component analysis (PCA). Gluten protein quantification performed by method based on the protein fraction separation by molecular weights (LOC) was better for grouping of genetically similar wheat cultivars than quantification of proteins separated by their different solubility in specified solvent gradient (RP-HPLC). LOC method showed higher potential in wheat quality prediction

THE IMPORTANCE OF HIGH-MOLECULAR-WEIGHT GLUTENIN SUBUNITS FOR WHEAT QUALITY EVALUATION

High-molecular-weight glutenin subunits (HMW-GS) composition was analyzed by sodium-dodecyl-sulfat-polyacrilamid-gel electrophoresis (SDS-PAGE), while the quantitative determination of total HMW-GS was obtained by reversed phase- high performance liquid chromatography (RP-HPLC). Considering HMW-GS composition, the most frequent subunits at Glu-A1 locus were N, at Glu-B1 locus 7+9 and at Glu-D1 locus 2+12. The cultivars with the GS 5+10 at Glu-D1 locus have shown better technological characteristics in contrast to cultivars with the GS 2+12. The cultivars Žitarka, Srpanjka, Barbara, Klara and Golubica in spite of presence HMW-GS 2+12 have shown very good and good technological properties because they had optimal proportions (>10%) of total HMW-GS. The results of the linear correlation analysis between quality parameters and HMW-GS composition have shown significant (P<0.05) positive influence of HMW-GS (Glu-1 score) on sedimentation value (r=0.55), Gluten Index (r=0.72), dough energy (r=0.61), maximum resistance (r=0.64) and resistance to extensibility ratio (r=0.58). The influence of HMW GS proportions on technological parameters, compared to HMW-GS composition, was more pronounced on protein content (r=0.82), dough development time (r=0.70), degree of softening (r=-0.90), dough energy (r=0.74) and loaf volume (r=0.65)

Sullivan au solstice. Les Saisons Sullivan, de Françoise Sullivan et Marion Landry avec une postface de Louise Déry. Galerie de l’UQAM, 91 p.

The influence of monomeric and micellar concentrations of the cationic monomeric, dodecyltrimethylammonium bromide (DTAB), and the corresponding dimeric, bis(N, N-dimethyl-N-dodecyl) ethylene-1,2-diammonium dibromide (12-2-12), surfactants on the formation and transformation of amorphous calcium phosphate (ACP) was investigated. The combination of microscopy (AFM and TEM) and light scattering techniques (size and zeta potential measurements) enabled, for the first time, the simultaneous monitoring of the effect that additives exert on different length scales during CaP formation in solution - from prenucleation clusters and ACP particles to the crystalline phase. Depending on their aggregation state (monomers or micelles) and the geometry of the aggregate (spherical or elongated micelles), DTAB and 12-2-12 have exhibited different effects on the rate of ACP transformation, as well as on the morphology of the amorphous and crystalline phases. It was shown that the effect of surfactants on the precipitation process observed on the microscale could be a result of different pathways on the nanoscale. The obtained results may have implications for the understanding of the general mechanism of inorganic-organic interactions underlying the biomineralization processes, as well as for materials science