The Experts below are selected from a list of 174 Experts worldwide ranked by ideXlab platform
G R Meira - One of the best experts on this subject based on the ideXlab platform.
-
size exclusion chromatography of polymers with molar mass detection computer simulation study on Instrumental Broadening biases and proposed correction method
Polymer, 1999Co-Authors: P I Prougenes, Dusan Berek, G R MeiraAbstract:Abstract This theoretical work evaluates the errors in average molecular weights due to Instrumental Broadening when a size exclusion chromatograph is fitted with ideal on-line M n or M W sensors, and a correction method is proposed to compensate for such errors. The basic assumptions are that linear homopolymers are analyzed, and that the Instrumental Broadening is uniform. It was verified that an ideal molar mass detector systematically underestimates the polydispersity and that such bias may be simply obtained from the spreading function polydispersity. The correction method uses an estimate of the instantaneous polydispersity. Such function can be directly obtained from the spreading function alone, since it is proven to be little dependent on the shape of the analyzed MWD.
-
Distributions of functionality and of molecular weights in an hydroxyl-terminated polybutadiene by dual-detection size exclusion chromatography
Journal of Applied Polymer Science, 1994Co-Authors: R O Bielsa, M. C. Brandolini, Leni Akcelrud, G R MeiraAbstract:The article deals with data treatment problems associated with the estimation (via dualdetection size exclusion chromatography) of the independent distributions of molecular weight and functionality in a derivatized hydroxyl-terminated polybutadiene. Calculations are based on an approach originally developed for linear copolymers and include corrections for (a) effect of functional groups on instantaneous mass and molecular weights, (b) dependence of refractive index with molecular weight, and (c) Instrumental Broadening. Compared to other more laborious analytical methods, the proposed technique is simple and provides accurate results. © 1994 John Wiley & Sons, Inc.
-
linear copolymer analysis with dual detection size exclusion chromatography correction for Instrumental Broadening
Journal of Applied Polymer Science, 1992Co-Authors: R O Bielsa, G R MeiraAbstract:This article deals with data treatment problems associated with the estimation of the combined distribution of molecular weights and chemical composition in linear copolymers by size exclusion chromatography, when correction for Instrumental Broadening is considered. Standard dual detection is assumed, i.e., the chromatograph is fitted with a “universal” detector (a differential refractometer) and a specific sensor to one comonomer only (a UV spectrophotometer). A real and a “synthetic” example (involving the analysis of a diblock styrene–butadiene rubber) are presented. Also, a propagation of errors study associated with the deconvolution operations is developed. It is concluded that the best calculation procedure is to first compute the combined distributions from the raw chromatograms and then correct such distributions for Instrumental Broadening. © 1992 John Wiley & Sons, Inc.
-
Linear copolymer analysis with dual‐detection size exclusion chromatography: Correction for Instrumental Broadening
Journal of Applied Polymer Science, 1992Co-Authors: R O Bielsa, G R MeiraAbstract:This article deals with data treatment problems associated with the estimation of the combined distribution of molecular weights and chemical composition in linear copolymers by size exclusion chromatography, when correction for Instrumental Broadening is considered. Standard dual detection is assumed, i.e., the chromatograph is fitted with a “universal” detector (a differential refractometer) and a specific sensor to one comonomer only (a UV spectrophotometer). A real and a “synthetic” example (involving the analysis of a diblock styrene–butadiene rubber) are presented. Also, a propagation of errors study associated with the deconvolution operations is developed. It is concluded that the best calculation procedure is to first compute the combined distributions from the raw chromatograms and then correct such distributions for Instrumental Broadening. © 1992 John Wiley & Sons, Inc.
-
Instrumental Broadening correction in size exclusion chromatography comparison of several deconvolution techniques
Journal of Liquid Chromatography & Related Technologies, 1990Co-Authors: Luis Marcelino Gugliotta, Jorge Ruben Vega, G R MeiraAbstract:Abstract Several deconvolution techniques (1–7) and a novel method herein presented, are compared in relation to their ability for correcting size exclusion chromatograms for the undesirable effect of Instrumental Broadening. Such methods are evaluated on the same computer, and through a “synthetic” example of known solution. Methods based on the frequency domain are only applicable to uniform deconvolution problems with stationary statistics. However, in the herein presented heuristic method (based on the Wiener filter in the frequency domain), it is possible to relax this last restriction, and generate solutions that are equivalent to considering signals with time-varying statistics. The evaluated techniques are compared on the basis of quality of results, computational considerations and adjustment facility. Stochastic techniques provide the best (and nearly identical) numerical solutions. This is mainly due to their increased facility to introduce “a priori” information about the expected solution. As...
P I Prougenes - One of the best experts on this subject based on the ideXlab platform.
-
size exclusion chromatography of polymers with molar mass detection computer simulation study on Instrumental Broadening biases and proposed correction method
Polymer, 1999Co-Authors: P I Prougenes, Dusan Berek, G R MeiraAbstract:Abstract This theoretical work evaluates the errors in average molecular weights due to Instrumental Broadening when a size exclusion chromatograph is fitted with ideal on-line M n or M W sensors, and a correction method is proposed to compensate for such errors. The basic assumptions are that linear homopolymers are analyzed, and that the Instrumental Broadening is uniform. It was verified that an ideal molar mass detector systematically underestimates the polydispersity and that such bias may be simply obtained from the spreading function polydispersity. The correction method uses an estimate of the instantaneous polydispersity. Such function can be directly obtained from the spreading function alone, since it is proven to be little dependent on the shape of the analyzed MWD.
Philip J Wyatt - One of the best experts on this subject based on the ideXlab platform.
-
mean square radius of molecules and secondary Instrumental Broadening
Journal of Chromatography A, 1993Co-Authors: Philip J WyattAbstract:Abstract In a chromatographic separation such as size-exclusion chromatography, the concentrations of the injected molecules are generally so low by the time they reach the light-scattering (LS) detector that terms involving the second virial coefficient may be neglected in the equations which relate the measured Rayleigh excess ratio to the derived molecular weights and sizes. For sufficiently large molecules (root mean square radius greater than about 10 nm for 633 nm incident light wavelength), the root mean square radius may be calculated independently of the molecular concentration from the Rayleigh ratios measured as a function of scattering angle. Precise measurements of the root mean square radius are presented for some nearly monodisperse polystyrene standards. These measurements confirm that the eluting molecules have a nearly constant size over a relatively broad range of elution volumes, yet the corresponding mass values are not constant. This inconsistency is shown to be due to a secondary Instrumental Broadening (IB) of the sample which occurs primarily in the refractive index detector which follows the LS detector. This secondary IB, which may be calculated from the distorted mass versus elution volume curves, is shown to vary with molecular mass.
R O Bielsa - One of the best experts on this subject based on the ideXlab platform.
-
Distributions of functionality and of molecular weights in an hydroxyl-terminated polybutadiene by dual-detection size exclusion chromatography
Journal of Applied Polymer Science, 1994Co-Authors: R O Bielsa, M. C. Brandolini, Leni Akcelrud, G R MeiraAbstract:The article deals with data treatment problems associated with the estimation (via dualdetection size exclusion chromatography) of the independent distributions of molecular weight and functionality in a derivatized hydroxyl-terminated polybutadiene. Calculations are based on an approach originally developed for linear copolymers and include corrections for (a) effect of functional groups on instantaneous mass and molecular weights, (b) dependence of refractive index with molecular weight, and (c) Instrumental Broadening. Compared to other more laborious analytical methods, the proposed technique is simple and provides accurate results. © 1994 John Wiley & Sons, Inc.
-
linear copolymer analysis with dual detection size exclusion chromatography correction for Instrumental Broadening
Journal of Applied Polymer Science, 1992Co-Authors: R O Bielsa, G R MeiraAbstract:This article deals with data treatment problems associated with the estimation of the combined distribution of molecular weights and chemical composition in linear copolymers by size exclusion chromatography, when correction for Instrumental Broadening is considered. Standard dual detection is assumed, i.e., the chromatograph is fitted with a “universal” detector (a differential refractometer) and a specific sensor to one comonomer only (a UV spectrophotometer). A real and a “synthetic” example (involving the analysis of a diblock styrene–butadiene rubber) are presented. Also, a propagation of errors study associated with the deconvolution operations is developed. It is concluded that the best calculation procedure is to first compute the combined distributions from the raw chromatograms and then correct such distributions for Instrumental Broadening. © 1992 John Wiley & Sons, Inc.
-
Linear copolymer analysis with dual‐detection size exclusion chromatography: Correction for Instrumental Broadening
Journal of Applied Polymer Science, 1992Co-Authors: R O Bielsa, G R MeiraAbstract:This article deals with data treatment problems associated with the estimation of the combined distribution of molecular weights and chemical composition in linear copolymers by size exclusion chromatography, when correction for Instrumental Broadening is considered. Standard dual detection is assumed, i.e., the chromatograph is fitted with a “universal” detector (a differential refractometer) and a specific sensor to one comonomer only (a UV spectrophotometer). A real and a “synthetic” example (involving the analysis of a diblock styrene–butadiene rubber) are presented. Also, a propagation of errors study associated with the deconvolution operations is developed. It is concluded that the best calculation procedure is to first compute the combined distributions from the raw chromatograms and then correct such distributions for Instrumental Broadening. © 1992 John Wiley & Sons, Inc.
Dusan Berek - One of the best experts on this subject based on the ideXlab platform.
-
size exclusion chromatography of polymers with molar mass detection computer simulation study on Instrumental Broadening biases and proposed correction method
Polymer, 1999Co-Authors: P I Prougenes, Dusan Berek, G R MeiraAbstract:Abstract This theoretical work evaluates the errors in average molecular weights due to Instrumental Broadening when a size exclusion chromatograph is fitted with ideal on-line M n or M W sensors, and a correction method is proposed to compensate for such errors. The basic assumptions are that linear homopolymers are analyzed, and that the Instrumental Broadening is uniform. It was verified that an ideal molar mass detector systematically underestimates the polydispersity and that such bias may be simply obtained from the spreading function polydispersity. The correction method uses an estimate of the instantaneous polydispersity. Such function can be directly obtained from the spreading function alone, since it is proven to be little dependent on the shape of the analyzed MWD.