1,721,188 research outputs found
Determination of Carnosine in Feed and Meat by High-pH Anion-Exchange Chromatography with Integrated Pulsed Amperometric Detection
No full textCamosine (beta-alanyl-L-histidine) is a dipeptide regarded as an important molecular marker of the presence of processed animal proteins including meat and bone meal in animal feed. For its identification and quantification a sensitive and selective method by high-performance anion-exchange chromatography coupled with integrated pulsed amperometric detection (HPAEC-IPAD) was developed. The assay is based on isocratic elution with 100 mM NaOH as the mobile phase. Interferences of real matrices were efficiently removed; carnosine could be determined at the concentration ranges 0.1-100 muM with a rather low detection limit of 0.23 ng. Unlike feeds for dogs and cats, no carnosine peak was observed in all examined feeds for ruminants. The good analytical characteristics allowed carnosine determination down to 5 mug/g of feed
The safeguard of natural resources from persistent organic micropollutants. Principles and aspects of photochemical oxidation using titanium dioxide immobilized on inert support: the case of norfloxacin in wastewater. La salvaguardia delle risorse naturali dai microinquinanti organici persistenti. Principi ed aspetti dell'ossidazione fotochimica mediante biossido di titanio immobilizzato su supporto inerte: il caso del norfloxacin nelle acque reflue.
Full text linkThis thesis work reconstructs, in its first section, the reasons that led to the emergence in public opinion of a new sensitivity towards the problem of the exhaustion of mineral resources and, out of sympathy, also towards natural ones despite apparently inexhaustible ones.
This sensitivity has led States to adopt mandatory legislative measures aimed at safeguarding the environment and to promote research aimed at identifying sources of pollution due not only to substances of which the evidence is known but also to those included in the grouping of pharmaceutical products. and for personal care (PPCP) for their subtle environmental danger.
Many researchers, examining the processes conventionally adopted for the purification of wastewater, have found that some PPCPs have a particular chemical inertness that prevents the transformation into harmless compounds for natural ecosystems.
In a second section, the scientific literature is reported which identifies, among others, the class of fluoroquinolones among the compounds which, due to their metabolic inertness, are excreted as such by man after having carried out their therapeutic action, thus expressing their ability to dangerously interfere with natural aquatic ecosystems.
Having these compounds with antibiotic properties, they pass undisturbed the civil purification plants to be released in the natural accepting water bodies.
Among the most damaging environmental effects, we recognize the modification of the composition of the new microbes naturally present in those environments, the alteration of the balance existing between them, the entry into the food chain and the onset of resistant microbial strains, including pathogens, and the consequent proliferation of new molecules for therapeutic use with unknown environmental effects.
In the following sections, to propose suitable methods to remove these substances from secondary wastewater, the theoretical foundations on which the photochemical process is based and the modes of action of the photocatalytic substances were discussed.
Then, taking into consideration the structure and properties and the zwitterionic nature of norfloxacin, a fluoroquinolone antibiotic, the thesis evaluates its photochemical degradability by focusing on the reaction pH, and the catalytic efficacy of the TiO2 immobilized on the glass in comparison. with what happens using the catalyst dispersed in suspension in the reaction mixture, employing a solar simulator in which the irradiation is obtained using a xenon arc lamp emitting in the UV–Vis regions of the electromagnetic spectrum.
Furthermore, the initial and residual toxicity of the reaction mixtures was evaluated by the Microtox method.Questo lavoro di tesi ricostruisce, nella sua prima sezione, i motivi che hanno portato all’insorgenza nell'opinione pubblica di una nuova sensibilità rivolta verso il problema dell’esauribilità delle risorse minerarie e, per simpatia, anche verso quelle naturali malgrado apparentemente inesauribili.
Questa sensibilità ha indotto gli Stati ad adottare misure legislative obbligatorie volte alla salvaguardia dell'ambiente e a promuovere la ricerca tesa a individuare fonti di inquinamento dovute non solo a sostanze delle quali è nota l’evidenza, ma anche a quelle incluse nel raggruppamento dei prodotti farmaceutici e per la cura della persona (PPCP) per la loro subdola pericolosità ambientale.
Molti ricercatori, esaminando i processi convenzionalmente adottati per la depurazione delle acque reflue, hanno rilevato che alcuni PPCP sono dotati di una particolare inerzia chimica che ne impedisce la trasformazione in composti innocui per gli ecosistemi naturali.
In una seconda sezione, si riporta la letteratura scientifica che individua, tra altre, la classe dei fluorochinoloni tra i composti che, per la loro inerzia metabolica, vengono escreti tal quali dall'uomo dopo aver svolto la loro azione terapeutica esprimendo in tal modo la loro capacità di interferire pericolosamente con gli ecosistemi acquatici naturali.
Infatti, avendo questi composti proprietà antibiotiche, superano indisturbati gli impianti di depurazione civile per essere rilasciati nei corpi idrici naturali accettori.
Tra gli effetti ambientali più dannosi si riconosce la modifica della composizione delle popolazioni microbiche naturalmente presenti in quegli ambienti, l’alterazione degli equilibri esistenti tra queste, l’ingresso nella catena alimentare e l'insorgenza di ceppi microbici, anche patogeni, resistenti e la conseguente proliferazione di nuove molecole ad uso terapeutico con effetti ambientali sconosciuti.
Nelle sezioni successive, al fine di proporre metodi adeguati a rimuovere queste sostanze dalle acque reflue secondarie, sono stati discussi i fondamenti teorici su cui si basa il processo fotochimico e le modalità di azione delle sostanze fotocatalitiche.
In seguito, prendendo in considerazione la struttura e le proprietà e la natura zwitterionica della norfloxacina, un antibiotico fluorochinolonico, la tesi valuta la sua degradabilità fotochimica focalizzando l'attenzione sul pH di reazione, e l'efficacia catalitica del TiO2 immobilizzato sul vetro in confronto con quanto avviene utilizzando il catalizzatore disperso in sospensione nella miscela di reazione, mediante un simulatore solare nel quale l’irraggiamento è ottenuto mediante una lampada ad arco allo xeno emittente nelle regioni dell’ UV−Vis dello spettro elettromagnetico.
Inoltre, delle miscele di reazione è stata valutata la tossicità iniziale e residua, mediante il metodo Microtox
Electron-Transfer Secondary Reaction Matrices for MALDI MS Analysis of Bacteriochlorophyll a in Rhodobacter sphaeroides and Its Zinc and Copper Analogue Pigments
No full textBacteriochlorophyll a (BChl a), a photosynthetic pigment performing the same functions of chlorophylls in plants, features a bacteriochlorin macrocycle ring (18 π electrons) with two reduced pyrrole rings along with a hydrophobic terpenoid side chain (i.e., the phytol residue). Chlorophylls analysis by matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) is not so straightforward since pheophytinization (i.e., release of the central metal ion) and cleavage of the phytol-ester linkage are invariably observed by employing protonating matrices such as 2,5-dihydroxybenzoic acid, sinapinic acid, and α-cyano-4-hydroxycinnamic acid. Using BChl a from Rhodobacter sphaeroides R26 strain as a model system, different electron-transfer (ET) secondary reaction matrices, leading to the formation of almost stable radical ions in both positive ([M](+•)) and negative ([M](-•)) ionization modes at m/z 910.55, were evaluated. Compared with ET matrices such as trans-2-[3-(4-t-butyl-phenyl)-2-methyl-2-propenylidene]malononitrile (DCTB), 2,2':5',2''-terthiophene (TER), anthracene (ANT), and 9,10-diphenylanthracene (DP-ANT), 1,5-diaminonaphthalene (DAN) was found to provide the highest ionization yield with a negligible fragmentation. DAN also displayed excellent ionization properties for two metal ion-substituted bacteriochlorophylls, (i.e., Zn- and Cu-BChl a at m/z 950.49 and 949.49), respectively. MALDI MS/MS of both radical charged molecular species provide complementary information, thus making analyte identification more straightforward. Graphical Abstract ᅟ
Separation and pulsed amperometric detection of alditols and carbohydrates by anion exchange chromatography using alkaline mobile phases modified with Ba(II), Sr(II), and Ca(II) ions
No full textEffect of Ca(II), Sr(II), and Ba(II) on the pulsed amperometric detection of alditols and carbohydrates at a gold electrode in alkaline solutions
No full textThe kinetic and analytical behaviours of an l-lysine amperometric biosensor based on lysine oxidase immobilised onto a platinum electrode by co-crosslinking
No full textAn improved L-lysine amperometric biosensor based on lysine oxidase immobilised onto a platinum electrode by glutaraldehyde co-crosslinking with bovine serum albumin is described. A thoroughly optimization of the enzyme immobilization procedure permitted the fabrication of a fast-response biosensor with high sensitivity and improved stability. Moreover, the relevant electrochemical study showed the possibility to tune the overall kinetic control of biosensor from merely diffusive to enzymatic or mixed by switching the pH from weakly alkaline to weakly acid values, respectively, as well as by controlling its hydrodynamic behaviour. The response time, t(0.95), evaluated in batch addition experiments, was lower than 6 s. Linear lysine responses up to 0.6 M were observed with a sensitivity of 4.4 mu A mM(-1), while detection limit at S/N = 3 was 1 mu M. The sensor has been tested for lysine determination of a pharmaceutical sample obtaining a good agreement with the expected values
Accurate Mass Analysis of N-Acyl-Homoserine-Lactones and Cognate Lactone-Opened Compounds in Bacterial Isolates of Pseudomonas aeruginosa PA01 by LC-ESI-LTQ-FTMS
No full textN-acyl-homoserine-lactones (AHSLs) are widely conserved signal molecules present in quorum sensing systems of Gram-negative bacteria such as Pseudomonas aeruginosa. We present here the results obtained with a hybrid linear trap/Fourier transform ion cyclotron resonance (LTQ-FTICR) mass spectrometer used to investigate the occurrence of AHSLs and cognate N-acyl-homoserines (AHSs) in bacterial isolates of P. aeruginosa (strain PAO1). Two hydrolysed AHSs were found in significant amounts, most likely formed through the lactone opening of N-3-oxo-decanoyl-L-homoserine-lactone (3OC(10)-HSL) and N-3-oxo-dodecanoyl-L-homoserine-lactone (3OC(12)-HSL). Structure elucidation of these ring-opened molecules, i.e. N-3-oxo-decanoyl-L-homoserine (3OC(10)-HS), and N-3-oxo-dodecanoyl-L-homoserine (3OC(12)-HS), which are not detected by bacterial biosensors, was performed by high-resolution and accurate mass measurements upon liquid chromatography (LC) and confirmed by tandem MS in the LTQ analyser. Assignment of chemical formula, with mass spectra in the form of [M + H](+), was significantly expedited by extracted ion chromatograms (XICs) because the number of potentially plausible formulae for each protonated signalling molecule was considerably reduced a priori by the LC behaviour, the high mass measurement accuracy available in FTICR mass spectra and the isotopic patterns. At least two concentration levels were observed in spent culture supernatants of P. aeruginosa: compounds at a relatively high content (5-15 mu M) that is C(4)-HSL, 3OC(10)-HS, and 3OC(12)-HS and those occurring at a lower content (<0.2 mu m) that is C(6)-HSL and C(8)-HSL. The implications of this work extend to a great variety of Gram-negative bacteria
Amperometric Determination of Underivatised Amino Acids at a Nickel-Modified Gold Electrode
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