Maria Itria Pilo

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).

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.

Electrochemical and spectroelectrochemical study of copper complexes with 1,10-phenanthrolines

The redox behaviour of a series of copper(II) complexes with different phenanthrolines (1:2 metal to ligand) in dimethylformamide solvent is reported. Cyclic voltammetry, controlled potential coulometry and spectroelectrochemistry in the visible region have been used. Accurate values for the formal potential of the copper(II)/ copper(I) couples could be computed by spectroelectrochemistry, also in those cases in which the systems are poorly reversible. Two further reductions lead to neutral and anionic copper species, respectively. The nature of the substituents on the phenanthroline ligands has been found to affect strongly the redox potential of the former couples, while a less marked influence on the latter ones has been evidenced. On the other hand, differences in the ligands induce very different kinetic stability of the copper complexes formed in the more cathodic processes.

Electrochemical behaviour of cyclometallated gold(III) complexes. Evidence of transcyclometallation in the fate of electroreduced species

Abstract The electrochemical behaviour of a series of neutral and cationic N–C and N–N–C cyclometallated gold(III) species: ([Au(py1)(Cl)2], Hpy1=2-benzylpyridine; [Au(bipyn)(Cl)][PF6], Hbipy1=6-benzyl-2,2′-bipyridine, Hbipy2=6-(1-methylbenzyl)-2,2′-bipyridine, Hbipy3=6-(1,1-dimethylbenzyl)-2,2′-bipyridine, Hbipy4=6-phenyl-2,2′-bipyridine) has been investigated in different solvent systems using cyclic voltammetry and controlled-potential coulometry. All the species considered show, in cyclic voltammetry, an irreversible one-electron reduction in the potential range −0.9/−1.2 V versus Fc+/0, using a Pt electrode. On the other hand, exhaustive coulometries have shown the consumption of a number of Faraday per mole within the range 1–2. The very complex decomposition of the electrogenerated species affords elemental gold and significant amounts of different gold by-products. In some situations (e.g. reduction of [Au(bipy4)(Cl)][PF6]), working with 0.1 mol dm−3 Na[PF6], CH3CN solvent system, it has been possible to characterise the most abundant gold(III) compound, by NMR, FAB-MS, and elemental analysis. The analytical and spectroscopic data provide evidence for the N–C bis-cyclometallated gold(III) derivative (e.g. [Au(bipy4)2][PF6]); the result entails quite an unusual transcyclometallation process. The same compound can also be obtained, albeit in very minor yield, by chemical reduction of [Au(bipy4)(Cl)][PF6].

Recent Advances in the Analysis of Phenolic Compounds in Unifloral Honeys

Honey is one of the most renowned natural foods. Its composition is extremely variable, depending on its botanical and geographical origins, and the abundant presence of functional compounds has contributed to the increased worldwide interest is this foodstuff. In particular, great attention has been paid by the scientific community towards classes of compounds like phenolic compounds, due to their capability to act as markers of unifloral honey origin. In this contribution the most recent progress in the assessment of new analytical procedures aimed at the definition of the qualitative and quantitative profile of phenolic compounds of honey have been highlighted. A special emphasis has been placed on the innovative aspects concerning the extraction procedures, along with the most recent strategies proposed for the analysis of phenolic compounds. Moreover, the centrality of validation procedures has been claimed and extensively discussed in order to ensure the fitness-for-purpose of the proposed analytical methods. In addition, the exploitation of the phenolic profile as a tool for the classification of the botanical and geographical origin has been described, pointing out the usefulness of chemometrics in the interpretation of data sets originating from the analysis of polyphenols. Finally, recent results in concerning the evaluation of the antioxidant properties of unifloral honeys and the development of new analytical approaches aimed at measuring this parameter have been reviewed.

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.

Platinum complexes with NNC ligands. Syntheses, electrochemical and spectroscopic characterisations of platinum(II) and relevant electroreduced species

Abstract A series of cyclometallated platinum(II) species with NNC ligands (NNC= ortho -C-deprotonated form of 6-benzyl-substituted 2,2′-bipyridines) and different fourth monodentate ligands (Cl − , I − , CN − , CO, PPh 3 , Py, MeCN) has been investigated electrochemically, with particular emphasis to the analysis of the relatively stable one-electron reduced species. EPR spectra have been recorded at different temperatures on the electroreduced solutions. The analyses were supported by a systematic comparison with simulated spectra and allowed a definition of the interaction of the additional unpaired electron with the 195 Pt, 14 N, and 1 H nuclei present in the molecule. Attention has been also paid to the effects of the ligands on the thermodynamics ( E 1/2,r ) of the reduction, as well as to some reactivity aspects of the substrates that could be shown by voltammetric tests. A number of these compounds have been synthesised for the first time, so that a full characterisation has been performed.

Electrochemical properties of copper complexes with unsubstituted and substituted 1,10-o-phenanthrolines in N,N-dimethylformamide solvent

Abstract The electrochemical reduction of a series of copper(II) complexes with 1,10- o -phenanthrolines, namely the 1:1 and 1:2 metal:ligand complexes with 2,9-dimethylphenanthroline, 4,7-dimethylphenanthroline and unsubstituted phenanthroline, respectively, has been studied in N,N -dimethylformamide using platinum electrodes. As to the 1:2 complexes, the effect of the presence of substituents with different electronic and steric effects on the phenanthroline ligands has been studied with the aim of rationalizing the different values of the standard potentials which have been measured. Furthermore, the possibility of electrogenerating neutral species, with a formally zerovalent copper centre, exhibiting different stability depending on the nature of the ligands, has been ascertained. In out solvent medium, 1:1 complexes have been found to be in equilibrium with the corresponding 1:2 complexes. A scheme for the reduction of solutions of these compounds, including the different equilibria associated to the electrode charge transfers, has been outlined.

Ru2+ complexes comprising terpyridine ligands appended with terthiophene chromophores: energy transfer and energy reservoir effect.

Two Ru(2+) complexes containing terpyridine ligands appended with terthiophene units connected by a methyleneoxy or an alkynyl bridge show very different luminescent behaviours: the former is non-luminescent at 298 K owing to a photoinduced energy transfer process to the terthiophene moiety, while the latter exhibits an extraordinary long excited state lifetime because of an energy reservoir effect.