Multivariate calibration techniques applied to the spectrophotometric analysis of one-to-four component systems

The UV spectrophotometric analysis of a multicomponent mixture containing paracetamol, caffeine, tripelenamine and salicylamide by using multivariate calibration methods, such as principal component regression (PCR) and partial least-squares regression (PLS), was described. The calibration set was based on 47 reference samples, consisting of quaternary, ternary, binary and single-component mixtures, with the aim to develop models able to predict the concentrations of unknown samples containing as many as one-to-four components. The calibration models were optimized by an appropriate selection of the number of factors as well as wavelength ranges to be used for building up the data matrix and excluding any information about the interfering excipients included in pharmaceutics. The PCR and PLS models were compared and their predictive performance was inferred by a successful application to the assays of synthetic mixtures and pharmaceutical formulations.     

A multidisciplinary approach to the mortars characterization from the Town Walls of Gubbio (Perugia,Italy)

Journal of Thermal Analysis and Calorimetry - In the frame of the HERACLES (HEritage Resilience Against CLimate Events on Site) project, a set of cultural heritage sites was studied to improve...     

Chemical fingerprinting of Equisetum arvense L. using HPTLC densitometry and HPLC

Equisetum arvense L. is a herbaceous medicinal plant, commonly known as horsetail, whose extracts have been reported to possess diuretic and haemostatic properties. The aim of this study was to evaluate the use of fingerprint chromatographic methods on commercially available raw materials or preparations of E. arvense L. in order to ascertain their quality and identify possible adulterants using HPLC and HPTLC densitometry. Two chromatographic methods were used to determine the chemical fingerprints of E. arvense and other allied species. The first was based on HPTLC identification followed by densitometric measurement at 350?nm. The second was based on HPLC separation. The ease of sample preparation and the possibility of simultaneous analysis of several samples in a short time make HPTLC a method of choice for the comprehensive quality evaluation of herbal products.     

Hydrolytic and photoinduced degradation of tribenuron methyl studied by HPLC-DAD-MS/MS

The paper studies, with the help of HPLC-DAD-MS/MS technique, the hydrolytic and photoinduced degradation processes that take place in aqueous solutions of tribenuron methyl, both when preserved in the dark and when undergoing solar box irradiation under conditions that simulate sun light. The results indicate that the degradation products formed by hydrolysis alone and by photoirradiation are the same, but kinetics of the hydrolysis reaction is much slower. The degradation products are identified as 2-methoxy-4-methylamino-6-methyl-1,3,5-triazine (P1), methyl 2-aminosulfonylbenzoate (P2), and saccharin (P3) and quantified. Ecotoxicological biotests performed on 0.1 microg L(-1) photoirradiated solutions of the herbicide give a border line toxicity situation comparable to that of the precursor and indicate that the herbicide is characterized by low persistence in the environment, as required. Its degradation, however, does not lead to mineralization but to the formation of products of comparable toxicity. To evaluate the matrix effects, the photodegradation of the herbicide is also studied in the presence of rice paddy waters: the process is slower than in ultrapure water but leads to the same products. Experiments performed for comparison by irradiating ultrapure water solutions with UV lamp (254 nm) show that the degradation process is not only faster with respect to sunlight, but gives a different pathway, without in anyway leading to mineralization.     

Solvent effects on the complexation of 1-alkanols by parent and modified cyclodextrins. Calorimetric studies at 298 K

The formation of complexes of parent and alkylated cyclodextrins (CDs) with 1-heptanol and 1-octanol has been studied calorimetrically at 298 K in water and in concentrated aqueous solutions of urea. The forces involved in the association process are discussed in the light of the signs and values of the thermodynamic parameters obtained: association enthalpy, binding constant, Gibbs free energy, and entropy. It was inferred that: (i) in water, the formation of complexes for parent and substituted α-cyclodextrins (αCDs) is determined by enthalpy. For parent and substituted β-cyclodextrins (βCDs), instead, hydrophobic interactions are the prevailing forces determining complexation, as indicated by the small and negative or positive enthalpies and by the high and positive entropies. (ii) In urea, hydrophilic interactions are attenuated. The formation of complexes with alkylated CDs does not occur. (iii) The analysis of the thermodynamic properties confirms that inclusion is a process dominated by hydration phenomena. Modifications experienced by the solvent water in the hydration shells of the interacting substances upon association determine the formation of the complexes.     

Effects of thermal history in the ring opening polymerization of CBT and its mixtures with montmorillonite on the crystallization of the resulting poly(butylene terephthalate)

Differential scanning calorimetry was used to study the thermal characteristics and morphological structure of species produced during the ring opening polymerization of cyclic butylene terephthalate (CBT). Thermal programs consisting of a first ramp heating scan and an isothermal step, followed by cooling and a second ramp heating step, were used to study the effects of thermal history, catalyst (butyl chlorotin dihydroxide) at concentrations between 0.1 and 1.3% (w/w), and the presence of a layered silicate nanofiller (montmorillonite at 4.0%, w/w) on the structure of the resulting polymer (poly(butylene terephthalate), pCBT). Wide angle X-ray diffraction was used to monitor the degree of exfoliation of the nanocomposites.It was found that pCBT is formed in the amorphous state, and crystallizes during the heating step or during the isothermal step at temperatures lower than the equilibrium melting temperature of the polymer (). When premixed with the nanofiller, irrespective of whether this was previously intercalated with a tallow surfactant or used in its pristine form, polymerization took place at higher temperatures and most of the crystallization was found to occur during the cooling stage. In those cases where crystallization took place during either the first heating scan, or during a prolonged isothermal step below the of the polymer, the resulting crystals were found to have a higher lamellar thickness, as compared with the same polymer crystallized from the melt during the cooling step from temperatures above the polymer .     

Identification of phosphoproteins and determination of phosphorylation sites by zirconium dioxide enrichment and SELDI-MS/MS

Reversible protein phosphorylation mediated by protein kinases and phosphatases is the most studied post-translational modification. Efficient characterization of phosphoproteomes is hampered by (1) low stoechiometry, (2) the dynamic nature of the phosphorylation process and (3) the difficulties of mass spectrometry to identify phosphoproteins from complex mixtures and to determine their sites of phosphorylation. Combination of the phosphopeptide enrichment method with MALDI-TOFMS, or alternatively, with HPLC-ESI-MS/MS and MS(3) analysis was shown to be a step forward for the successful application of MS in the study of protein phosphorylation. In our study we used phosphopeptide enrichment performed in a simple single-tube experiment using zirconium dioxide (ZrO(2)). A simple protein mixture containing precipitated bovine milk caseins was enzymatically digested and the mixture of tryptic fragments was analysed before and after enrichment using nanoflow HPLC-ESI-MS/MS and surface-enhanced laser desorption/ionization (SELDI)-MS/MS on QqTOF instruments to compare the efficiency of the two methods in the determination of phosphorylation sites. Both approaches confirm the high selectivity obtained by the use of batch-wise, ZrO(2)-based protocol using di-ammonium phosphate as the eluting buffer. More phosphorylation sites (five for beta-casein and three for alpha(S1)-casein) were characterized by SELDI-MS/MS than by nanoflow HPLC-ESI-MS/MS. Therefore, ZrO(2)-based phosphopeptide enrichment combined with SELDI-MS/MS is an attractive alternative to previously reported approaches for the study of protein phosphorylation in mixtures of low complexity with the advance of fast in situ peptide purification. The method was limited to successful analysis of high-abundance proteins. Only one phosphorylation site was determined for the minor casein component alpha(S2)-casein by ESI-MS/MS and none for kappa-casein. Therefore an improvement in enrichment efficiency, especially for successful phosphoproteomic applications, is needed.     

Replicated observations in metrology and testing: modelling repeated and non-repeated measurements

In order to choose the right statistical tool, a basic issue for an accurate analysis of each specific problem is to understand whether the set of replicated measurement results under examination is to be considered as pertaining to repeated measurements or not. This issue is particularly important, since most of the traditional tools are valid only for repeated measurements, but, in many cases, such as laboratory comparisons (in metrology and in testing), the measurements necessary to assess correctly the measurand value and the associated uncertainty do not represent repeated measurements. The analysis performed in this paper aims to shine some light on these issues, starting with a review of the basic concepts, such as repeatability, reproducibility, accuracy, systematic error and bias, as defined in international documents and as used in the literature. The paper shows that, currently, a full consensus on a common language and understanding has not yet been achieved, and then shows how this fact reflects on the basic data models, especially those concerning inter-comparison data.