P. Piu

RP-HPLC determination of water-soluble vitamins in honey

The assessment and validation of reliable analytical methods for the determination of vitamins in sugar-based matrices (e.g. honey) are still scarcely explored fields of research. This study proposes and fully validates a simple and fast RP-HPLC method for the simultaneous determination of five water-soluble vitamins (vitamin B(2), riboflavin; vitamin B(3), nicotinic acid; vitamin B(5), pantothenic acid; vitamin B(9), folic acid; and vitamin C, ascorbic acid) in honey. The method provides low detection and quantification limits, very good linearity in a large concentration interval, very good precision, and the absence of any bias. It has been successfully applied to 28 honey samples (mainly from Sardinia, Italy) of 12 different botanical origins. While the overall amount of the analytes in the samples is quite low (always below 40 mg kg(-1)), we have observed a marked dependence of some of their concentrations (i.e. vitamin B(3) and vitamin B(5)) and the botanical origin of the honey. This insight might lead to important characterization features for this food item.

An RP-HPLC determination of 5-hydroxymethylfurfural in honey The case of strawberry tree honey.

The use of the RP-HPLC official method of the International Honey Commission (IHC) for the determination of 5-hydroxymethylfurfural (HMF) in strawberry tree honey (Arbutus unedo, a typical Sardinian honey) has brought to light a specific and heavy chromatographic interference that prevents accurate quantification. The interference has been identified as homogentisic acid (HA), i.e. the marker of the botanical origin of the honey. For this reason, an alternative RP-HPLC method is proposed. The bias-free method allows a complete separation of HMF from HA to the baseline level and is faster and more precise than the RP-HPLC official method: the detection and quantification limits are 1.9 and 4.0mgkg(-1), respectively, whereas the repeatability is ca. 2% in the HMF concentration range of 5-140mgkg(-1).

Coordination of transition-metal ions by polygalacturonic acid: A spectroscopic study

The interaction between polygalacturonic acid with Cu(II), VO(IV), Mn(II), Ni(II) and Co(II) has been studied with the aid of ESR, electronic and IR spectra. The results show that in fully hydrated gels Cu(II) and VO(IV) ions form inner-sphere carboxylate complexes, whereas [Mn(H2O)6]2+ retains its inner hydration sphere. On dehydration, all the ions are bound to carboxyl groups, whose binding mode is dependent on the nature of the ion. The changes observed in spectral parameters upon dehydration suggest the substitution of water molecules by sugar oxygen atoms in order to preserve the stereogeometry of the ions.

A direct RP-HPLC method for the determination of furanic aldehydes and acids in honey.

In this study 5-hydroxymethyl-2-furaldehyde (HMF), 2-furaldehyde, 3-furaldehyde, 2-furoic acid and 3-furoic acid are contemporarily determined in honey using a swift and direct RP-HPLC approach. The validation protocol was performed in terms of detection and quantification limits, precision (by repeatability and reproducibility), linearity and accuracy (by recovery tests); the acceptability of the precision and accuracy results was positively verified using Horwitzs model and AOAC guidelines, respectively. The method was tested on 18 honey samples of different ages, and botanical and geographical origin. HMF and 2-furaldehyde correlated highly with the age of the samples, whereas no correlation was observed with regards to 2-furaldehyde and 2-furoic acid. Hypotheses relating to the formation of minority furanic compounds are also proposed.

Interaction of metal ions with humic-like models. Part VII. Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) complexes of 2,5-dihydroxybenzoic acid

Abstract Complexes of formula M(2,5-DHB) 2 4H 2 O (M = Mn, Co, Ni, Zn, Cu and Cd; 2,5-DHB = 2,5-dihydroxybenzoate) were prepared and characterized by means of infrared and electronic spectroscopy, and by electron spin resonance. For the Zn complex the crystal and molecular structure was also determined by single-crystal X-ray diffraction analysis. The crystal is orthorhombic, space group Pbca (No. 61), with a = 18.503(4), b = 13.536(3), c = 6.900(2) A, and Z = 4. The final refinement used 877 reflections and gave a residual R value of 0.041. The complex has slightly compressed octahedral coordination, with the zinc atom bound to two monodentate carboxylate groups lying in trans positions and four water molecules. X-ray data and infrared spectra show the Mn, Co, Ni, Zn and Cd complexes to be isostructural with the Zn compound. The electronic, infrared and ESR spectra of the copper(II) complex are consistent with a CuO 4− based chromophore involving two water molecules and two monodentate carboxylate groups in the metal plane, and long axial contacts.

SPECTROSCOPIC ANALYSIS OF BINARY AND TERNARY COPPER(II) COMPLEXES FORMED BY HISTIDINE AND GLUTAMIC ACID

Abstract Ternary copper(II) complexes of the type [Cu(His)A] (HisH=L-histidine, A=glycinato, L-valinato, L-alaninato, L-threoninato, L-serinato, or L-asparaginato) and [Cu(Glu)B]n- (GluH2=L-glutamic acid, B=glycinato, L-alaninato, L-valinato (n=1) or an amino-acid with positively charged protonated side chain such as L-asparagine, L-lysine, or L-ornithine (n=0)) have been investigated in aqueous solution by means of ESR and absorption spectra. It is suggested that in the ternary species the histidinate ion adopts a histamine-like bonding mode giving rise to CuN3O chromophores in the metal plane. Coordination in the bis-(glycine)-like mode is detected in the Glu-containing species. The spectral results have been used to postulate plausible structures for the bis-(histidinato)copper(II) complexes.

Study of the short-term release of the ionic fraction of heavy metals from dental amalgam into synthetic saliva, using anodic stripping voltammetry with microelectrodes.

The present paper describes a fast and reproducible procedure, employing differential pulse stripping analysis technique with graphite microelectrodes, for the quantitative evaluation of the ionic fraction of heavy metals (namely Hg, Cu, and Zn) released from dental amalgams into synthetic saliva during 6-90 h contact between amalgam and saliva, after completion of the dental restoration (short-term release). The Zn(2+) concentration was evaluated by linear calibration, whereas Cu(2+) and Hg(2+) contents were estimated by the standard additions method. While the concentration of Zn(2+) ion does not increase significantly anymore after a 6-h contact (values from 288+/-12 to 346+/-12 mugdm(-3) at time of contact from 6 to 90 h, respectively), in the same time interval the concentration of both Cu(2+) and Hg(2+) ions progressively increases (from 38+/-6 to 197+/-4 mugdm(-3) and from 15+/-3 to 101+/-2 mugdm(-3), respectively). The results of the release tests reveal that Hg concentration is at the highest level of risk (HBM III), as identified by the three human biomonitoring categories suggested by the Institut für Wasser-, Boden- und Lufthygiene des Umweltbundesamtes (Germany) for the estimation of potential harmful effects on health due to exposure to heavy metals.

Analytical study of the reduction of chromium(VI) by D- galacturonic acid

Abstract The reduction of chromium (VI) to chromium(III) by d -galacturonic acid takes place to a significant extent only in the presence of metal ions such as copper(II) or chromium(III) itself. These metals can form stable complexes in which the opening of the sugar ring leads to a reducing free aldehydic group. The stoichiometry of the reaction, the dependence of the yield on the nature of the metal ion and the pH of the solution and the products formed, were studied. Stoichiometries and stability constants of the complexes present in the system chromium(III)- d -galacturonic acid were evaluated.

Complexing and redox properties of the system D-galacturonic acid-iron(III)

Abstract The stoichiometry of the reduction reaction and D -galacturonic acid with iron(III) has been determined, leading to a 4:1 ratio between the quantities of reduced iron and oxidized D -galacturonic acid, respectively. This last molecule is oxidized to formic acid, and the residue is thought to present a further terminal carboxylic group. The reducing predominant species appears to be the FeGal 3 complex.

Spectroscopic investigation on the presence of OH in natural barrerite and in its collapsed phases

Barrerite, a zeolite with a stilbite-type framework, transforms on heating at 200–380° C and at 380–450° C into two new phases, called barrerite B and D respectively. After a few days barrerite B rehydrates to barrerite C. In the B and C heat-collapsed phases the aluminosilicate framework is interrupted by the statistical breaking of an oxygen bridge, giving rise to two partially occupied face-sharing tetrahedra. Near infrared (NIR) diffuse reflectance spectra show the absence of hydroxyls in natural barrerite and the presence of hydroxyls in its heat-collapsed phases. These results confirm the hypothesis that the fourth vertex of the tetrahedra generated from the breaking of the oxygen bridge is a hydroxyl. The presence of OH-bands in phase D suggests for this phase, as in the B and C phases, the presence of interrupted oxygen bridges.