Retention in Field-Flow Fractionation with a Moderate Nonuniformity in the Field Force

Martin, Michel; Batten, and Charles Van; Hoyos, Mauricio

doi:10.1021/ac9605307

Cited by 19 publications

(19 citation statements)

References 23 publications

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“…(c) Perhaps there are experimental errors of unknown origin which cause systematic errors resulting in the gradient of the calibration line log Sλ vs log M to deviate from b. Alternatively Martin et al 29 have suggested that the deviations in b can be explained by simplifications made in the theoretical calculations.…”

Section: Resultsmentioning

confidence: 99%

Determination of Thermal Diffusion Coefficients for Polydisperse Polymers and Microgels by ThFFF and SEC−MALLS

Nguyen¹,

Beckett²,

Pille³

1998

Macromolecules

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A new method combining thermal field-flow fractionation (ThFFF) and SEC−MALLS is proposed for the measurement of the thermal diffusion coefficient D T for polydisperse polymeric samples. This method should greatly increase the range of applicability of ThFFF for characterization of block copolymers and also for studies of thermal diffusion, an interesting phenomenon not yet well understood. ThFFF is one of only a few techniques (e.g., thermal diffusion forced Rayleigh scattering) that can determine D T values of polymers. The values of D T can be used to reflect the surface composition of block copolymer molecules as reported in recent studies. Currently, the value has been measured with ThFFF based on the sample peak maximum method, which can introduce errors when the sample has a broad MW distribution. The method proposed here measures D T by taking all digitized points in the entire sample peak into consideration, and has been tested with polystyrene, poly(tert-butylstyrene), and some copolymer microgels. Preliminary results are presented and discussed.

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Section: Resultsmentioning

confidence: 99%

Determination of Thermal Diffusion Coefficients for Polydisperse Polymers and Microgels by ThFFF and SEC−MALLS

Nguyen¹,

Beckett²,

Pille³

1998

Macromolecules

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“…It is also the elution time of an unretained compound. In thermal FFF, it has been shown that 2 can be expressed as [12,13]:…”

Section: Theorymentioning

confidence: 99%

“…The 2-value which is determined from the experimental measurement of the retention time in thermal FFF is thus an apparent value, )Lapp. Assuming that the rate of variation of 2 with x is approximately constant, at least in the vicinity of the accumulation wall, it has been shown that the position, Xeq, at which this apparent value is equal to the actual value of 2 is given by [14]:…”

Section: Theorymentioning

confidence: 99%

Experimental study of the concentration dependence of the soret coefficient by thermal field-flow fractionation: the case of polystyrene in decalin

et al. 2002

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SummaryThermal field-flow fractionation separates poJymers with high selectivity according to their Soret coefficient, ST, hence, according to their molar mass, and therefore consitutes an efficient physicochemical tool for the determination of the Sorer coefficient of a given polymer in the carrier liquid from its retention time. However, the polymer concentration in the sample influences the retention time and, hence, the value of ST derived from it. An experimental study of the influence of sample concentration on retention, ST, and peak shape was performed for the polystyrene-decahn system over a relatively large temperature domain and for various molar masses.It is found that the retention time and the value of ST increase with increasing sample concentration, the more so as the cold wall temperature is lower. This appears to be in contradiction with the general non-equilibrium thermodynamic expression derived for polymer-solvent systems with positive second virial coefficients, such as the present system over the temperature range investigated. There seems to be a temperature for which the dependence of S T on sample concentration vanishes. This temperature is about 375 K for the polysb, rene-decalin system.As the sample concentration increases, the peak barycentre and the standard deviation increases. As the peaks are fronting, the skewness is negative and becomes more negative as the sample concentration increases. The peak skewness appears to be a good indicator of the onset of sample concentration effects. The threshold concentration, forwhich these effects begin to become significant, decreases with increasing molar mass.

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“…(6) and (7) and determined by solving Eq. (13), is associated with a welldefined value of x, the so-called equivalent position x eq , where the quantities (D/D T ), the local temperature T, and the local gradient (dT/dx) assume well-defined values, (D/D T ) eq , T eq , and (dT/dx) eq , respectively [11,14,21]. Moreover, this k quantity is linked to the quantities DT, T c , h c , and M according to Eq.…”

Section: General Aspects Of Thfffmentioning

confidence: 99%

Determination of calibration function in thermal field flow fractionation under thermal field programming

Pasti

Ventosa

Mingozzi³

et al. 2006

J of Separation Science

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A new procedure for determining the calibration function able to relate retention and operative parameters to molecular weight of the species in thermal field flow (ThFFF) under thermal field programming (TFP) conditions is presented. The procedure involves determining the average values of retention parameters under TFP and determining a numerical function related to the temperature variations that occur during TFP. The calibration parameters are obtained by a procedure fitting the retention and operative parameters that hold true at the beginning of the TFP. The procedure is closely related to the one previously developed to calibrate the retention time axis under TFP ThFFF and, together, they constitute a full calibration procedure. Experimental validation was performed with reference to polystyrene (PS)-decalin and PS-THF systems. The calibration functions here obtained were compared to those derived by the classical procedure at constant thermal field ThFFF to obtain the calibration function at variable cold wall temperatures. Excellent agreement was found in all cases proving "universality" of the ThFFF calibration concept, i.e. it is independent of the particular system on which it was determined and can thus be extended to ThFFF operating under TFP. The new procedure is simpler than the classical one since it requires less precision in setting the instrumentation and can be obtained with fewer experiments. The potential applications for the method are discussed.

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Retention in Field-Flow Fractionation with a Moderate Nonuniformity in the Field Force

Cited by 19 publications

References 23 publications

Determination of Thermal Diffusion Coefficients for Polydisperse Polymers and Microgels by ThFFF and SEC−MALLS

Determination of Thermal Diffusion Coefficients for Polydisperse Polymers and Microgels by ThFFF and SEC−MALLS

Experimental study of the concentration dependence of the soret coefficient by thermal field-flow fractionation: the case of polystyrene in decalin

Determination of calibration function in thermal field flow fractionation under thermal field programming

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