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A C Olivieri

Publications and source records attributed to A C Olivieri.

17 recordsLinked to original sources
PubMed2006

Second-order calibration of excitation-emission matrix fluorescence spectra for the determination of N-phenylanthranilic acid derivatives.

A spectrofluorimetric method has been developed for the quantitative determination of mefenamic, flufenamic, and meclofenamic acids in urine samples. The method is based on second-order data multivariate calibration (unfolded partial least squares (unfolded-PLS), multi-way PLS (N-PLS), parallel factor analysis (PARAFAC), self-weighted alternating trilinear decomposition (SWATLD), and bilinear least squares (BLLS)). The analytes were extracted from the urine samples in chloroform prior to the determination. The chloroform extraction was optimized for each analyte, studying the agitation time and the extraction pH, and the optimum values were 10 minutes and pH 3.5, respectively. The concentration ranges in chloroform solution of each of the analytes, used to construct the calibration matrix, were selected in the ranges from 0.15 to 0.8 microg mL-1 for flufenamic and meclofenamic acids and from 0.25 to 3.0 microg mL-1 for mefenamic acid. The combination of chloroform extraction and second-order calibration methods, using the excitation-emission matrices (EEMs) of the three analytes as analytical signals, allowed their simultaneous determination in human urine samples, in the range of approximately 80 mg L-1 to 250 mg L-1, with satisfactory results for all the assayed methods. Improved results over unfolded-PLS and N-PLS were found with PARAFAC, SWATLD, and BLLS, methods that exploit the second-order advantage.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2001

Sustained prediction ability of net analyte preprocessing methods using reduced calibration sets. Theoretical and experimental study involving the spectrophotometric analysis of multicomponent mixtures.

A newly developed multivariate method involving net analyte preprocessing (NAP) was tested using central composite calibration designs of progressively decreasing size regarding the multivariate simultaneous spectrophotometric determination of three active components (phenylephrine, diphenhydramine and naphazoline) and one excipient (methylparaben) in nasal solutions. Its performance was evaluated and compared with that of partial least-squares (PLS-1). Minimisation of the calibration predicted error sum of squares (PRESS) as a function of a moving spectral window helped to select appropriate working spectral ranges for both methods. The comparison of NAP and PLS results was carried out using two tests: (1) the elliptical joint confidence region for the slope and intercept of a predicted versus actual concentrations plot for a large validation set of samples and (2) the D-optimality criterion concerning the information content of the calibration data matrix. Extensive simulations and experimental validation showed that, unlike PLS, the NAP method is able to furnish highly satisfactory results when the calibration set is reduced from a full four-component central composite to a fractional central composite, as expected from the modelling requirements of net analyte based methods.

Calibration↗
PubMed2000

Determination of the minor component bromhexine in cotrimoxazole-containing tablets by absorption spectrophotometry and partial least-squares (PLS-1) multivariate calibration.

The mucolitic bromhexine [N-(2-amino-3,5-dibromobenzyl)-N-methylcyclohexylamine] has been determined in cotrimoxazole-containing tablets by partial least-squares (PLS-1) multivariate of spectrophotometric calibration data in the spectral range 310-350 nm. In the studied commercial tablets, cotrimoxazole is present in large excess (ca. 100:1 in weight) with respect to bromhexine, and a high degree of spectral overlapping exists among bromhexine and cotrimoxazole components. However, the obtained recoveries are reasonably good with the presently discussed technique.

Bromhexine↗
PubMed1999

Enhanced synchronous spectrofluorometric determination of tetracycline in blood serum by chemometric analysis. Comparison of partial least-squares and hybrid linear analysis calibrations.

Tetracycline has been determined in human serum samples by a combination of: (1) synchronous fluorescence spectra of whole sera treated with Mg2+, and (2) the multivariate calibration methods of partial least-squares (PLS-1) and a variant of the recently introduced hybrid linear analysis (HLA), which does not require the knowledge of pure-component spectra. The calibration set was designed with 50 sera spiked with concentrations of tetracycline in the range 0.0-4.0 micrograms mL-1'. Studies concerning validation, precision, accuracy and figures of merit (selectivity, sensitivity and limit of determination) were also carried out. A novel wavelength-selection procedure was applied to minimize the effect of nonmodeled interferents present in serum samples containing bilirubin, triglycerides, and salicylate. Overall, the performance of the newly developed HLA approach seems to be better than that of PLS-1.

Calibration↗
PubMed1999

Simultaneous multivariate spectrophotometric analysis of paracetamol and minor components (diphenhydramine or phenylpropanolamine) in tablet preparations.

The use of multivariate spectrophotometric calibration is reported for the analysis of two decongestant tablets, where paracetamol is the principal component and diphenhydramine or phenylpropanolamine are the minor components. The resolution of these mixtures has been accomplished without prior separation or derivatisation, by using partial least-squares (PLS-1) regression analysis of electronic absorption spectral data. Although the molar ratios of paracetamol to the minor components were 38:1 and 25:1 respectively, the latter have been determined with high accuracy and precision, and with no interference from tablet excipients. PLS is able to take into account small deviations of paracetamol from linearity in the studied concentration range. The application of classical least-squares (CLS) analysis yields unsatisfactory results, due to the low absorbances of the minor components within the range where all components obey Beer's law.

Acetaminophen↗
PubMed1999

Simultaneous determination of rifampicin, isoniazid and pyrazinamide in tablet preparations by multivariate spectrophotometric calibration.

The use of multivariate spectrophotometric calibration is presented for the simultaneous determination of the active components of tablets used in the treatment of pulmonary tuberculosis. The resolution of ternary mixtures of rifampicin, isoniazid and pyrazinamide has been accomplished by using partial least squares (PLS-1) regression analysis. Although the components show an important degree of spectral overlap, they have been simultaneously determined with high accuracy and precision, rapidly and with no need of nonaqueous solvents for dissolving the samples. No interference has been observed from the tablet excipients. A comparison is presented with the related multivariate method of classical least squares (CLS) analysis, which is shown to yield less reliable results due to the severe spectral overlap among the studied compounds. This is highlighted in the case of isoniazid, due to the small absorbances measured for this component.

Antitubercular Agents↗
PubMed1998

Spectrofluorometric determination of piroxicam.

The spectrofluorometric determination of piroxicam [4-hydroxy-2-methyl-N-(2-pyridyl)-2II-1,2-benzothiazine-3-carboxam ide-1, 1-dioxide] in pharmaceutical tablets is described. It involves excitation at 330 nm of an acid solution (HNO3 0.5 M) of the drug, and measurement of the fluorescence intensity at 440 nm. The linear range is 0.01-1.25 micrograms ml-1.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1998

Errors in chemical shift tensor components and orientation in the molecular frame as obtained from MAS NMR spinning sideband analysis.

It is shown how to calculate random errors in chemical shift tensor components and in the Euler angles which fix the orientation of the sigma tensor in the molecular frame, as obtained from spinning sideband analysis of MAS NMR spectra of powdered solids, when heteronuclear dipolar coupling interactions occur in a two spin system. The procedure was applied to experimental data corresponding to the chemical shift tensor of a carbon-13 bonded to a phosphorus-31 nucleus. Clues are given concerning the experimental variables to be set in order to obtain the desired accuracy in the orientation angles.

Humans↗
PubMed1997

63Cu-31P coupling constants and 63Cu quadrupole couplings from 31P CP/MAS spectra of copper (I)--phosphine complexes with aryldithiocarboxylates or benzoate.

Magic-angle spinning 31P NMR spectra of solid [CuS2C-Ph(PPh3)2] 1, [{CuS2C-pT}4(PPh3)2] 2, [{CuS2C-Ph}4(PPh3)2] 3. [CuS2C-Ph(dppm)]2 4 and [CuO2C-Ph(dppm)]2 5, (T = tolyl, dppm = bis(diphenylphosphino)methane) were obtained at 109.6 MH2. They consist of distorted quartets from non-equivalent phosphorus atoms and provide approximate values of the indirect spin-spin coupling constant J[63Cu,31P], that are indicative of the covalency of the dithiocarboxylate-copper bonding. The spacing distortions are related to a number of molecular and structural parameters and thereby allow an estimation of the copper quadrupole coupling constant e2qQ/h which, as expected, is smaller for tetra-coordinated (1, 2, 3 and 4) than for tri-coordinated (5) copper sites. The spectrum of 2 has been successfully simulated (including the isotope effects from the less abundant 65Cu isotope) using the full theory for calculation of the spin eigenfunctions of the quadrupolar nucleus.

Benzoates↗
PubMed1997

Solid state NMR sideband shape simulations for any spinning angle and speed. First order calculation of residual dipolar coupling to quadrupolar nuclei.

A simple procedure is described which can be used to simulate solid state NMR sideband shapes for samples rotating at any angle and speed, when a combination of chemical shift anisotropy and dipolar coupling between spin-1/2 and quadrupolar nuclei occurs. The use of Herzfeld-Berger equations for computing individual sideband intensities is coupled to first order perturbation calculation of dipolar coupling effects. The present method can be easily and efficiently implemented on a desktop computer (source code is provided).

Chemical Phenomena↗
PubMed1996

13C CP/MAS NMR of a 13C-2H residual dipolar coupled pair.

When a spin-1/2 nucleus is dipolar coupled to a spin-1 nucleus, the spectrum of the spin-1/2 nucleus can be split into an asymmetric doublet in magic-angle spinning experiments. When the spin-1/2 nucleus is 13C and the spin-1 nucleus is 2H there is also the possibility of this splitting being modified by the indirect (J) coupling. 13C-2H residual dipolar couplings are seen because of the large full dipolar coupling of the nucleus pair. However, this has implications on the spinning speed used in the CP/MAS NMR experiment and the intensities of the isotropic 13C dipolar coupled to 2H. The calculation of side band intensities for slow spinning when the dipolar, quadrupolar and chemical shift tensors are axially symmetric and coaxial is discussed.

Anisotropy↗
PubMed1994

Retrieval of solid-state 31P nuclear magnetic resonance (NMR) chemical shielding parameters: proposal of an approach concerning variable-temperature 31P NMR mass spectra of urea phosphate and comparison of different methods.

Several methods are used to retrieve the principal components of the 31P chemical shielding tensor from variable-temperature 31P NMR spectra of urea phosphate (both static and spinning at the magic angle at low speeds). A complementary approach is proposed for the study of small changes in these parameters, based on the measurement of selected side-band intensities which are most sensitive to changes in sigma.

Magnetic Resonance Spectroscopy↗
PubMed1993

Quadrupole effects of spin-3/2 nuclei on the solid-state magic-angle spinning nuclear magnetic resonance spectra of spin-1/2 nuclei. Deviations from first-order theory and implications concerning the sign of the indirect coupling constant.

The effect of the interaction between spin-3/2 and spin-1/2 nuclei on solid-state magic-angle spinning nuclear magnetic resonance (MAS NMR) spectra of the latter is studied in cases where deviations from first-order theory are expected. A comparison is made between the exact and first-order perturbation approaches. Both dipolar and indirect (iso- and anisotropic) coupling interactions are considered. Implications regarding 13C,35,37Cl, 31P,63,65Cu and 119Sn,35,37Cl cases are discussed. It is shown that in the latter two cases the sign of the indirect coupling constant J can be derived.

Magnetic Resonance Spectroscopy↗
PubMed1993

A simple theoretical treatment of quadrupolar effects on magic-angle-spinning solid-state NMR spectra of spin-1/2 nuclei in the limit of large quadrupole coupling constants.

A simple approach is discussed for studying the effect of quadrupolar nuclei on the magic-angle-spinning solid-state NMR lines of spin-1/2 nuclei in the limit of large quadrupole coupling constants. Equations are derived both for the isotropic shifts and the Pake-like powder patterns for any quadrupolar spin and for arbitrary orientations of the internuclear vector with respect to the unique axis of an axially symmetric quadrupole tensor. First-order effects due to a small Zeeman perturbation on these lines are explored, as well as deviations from axial symmetry in the electric field gradient when S = 3/2 quadrupolar nuclei are involved. Spectral parameters likely to be observed in the case of coupling between 31P and 201Hg are also discussed.

Magnetic Resonance Spectroscopy↗
PubMed1992

Magic-angle-spinning 31P NMR spectra of solid dihydrogen phosphates. Comparison of ordered and dynamically disordered compounds.

High-resolution 31P NMR spectra are reported for several dihydrogen phosphates in the solid state. Shielding tensor components were retrieved by analysis of the sideband intensities. The results, together with previously published data, can be grouped according to the presence and type of proton exchange occurring in the crystals. Static MH2PO4 samples (M = Na, Li) show a shielding anisotropy delta sigma of approximately 120 ppm. In the case of M = Cs (one static P-OH bond and two oxygens attached to "half" hydrogens on the average) delta sigma is smaller (approximately 75 ppm) and can be understood in terms of the accepted, proton-exchange model. For highly disordered samples (M = K, NH4, Rb), where all four oxygens have nearby hydrogens with 50% occupancy, delta sigma is even smaller (approximately 30 ppm) but not zero. In the last-mentioned cases, 31P NMR information suggests that local PO4 environments may not have the symmetry that could be expected on the basis of the known crystal structures.

Crystallization↗