A quantitative approach to the analysis of supermicron dispersions by field-flow fractionation with UV-vis detectors. The application of an absolute method

Abstract

SummaryQuantitative analysis in field-flow fractionation is becoming a necessary requirement for routine applications, instrumental optimization and scale-up to preparative separations. The use of detection systems which show complex dependence on sample characteristics (i.e. UV spectrometry) has hindered the application of quantitative methods of analysis in fieldflow fr actionation. A standardless model, shown valid in flow-through, homogeneous systems, is applied here to a heterogeneous system (dispersed supermicron particles) in field-flow fractionation by single peak area measurements. Absolute analysis in the fractionation of spherical silica particles for high-performance liquid chromatography column packing by gravitational fieldflow fractionation with UV-Vis detectors is presented. It has been shown that for such samples extinction coefficients are independent of sample concentration and are determined by the size and density of the particles. The accuracy of such an approach to absolute analysis is discussed.

Standardless method for quantitative particle-size distribution studies by gravitational field-flow fractionation. Application to silica particles

“…According to the well-known L.-B. law (already applied to heterogeneous flow-through systems [4,6]) signal A can be converted into the concentration of the eluting sam-…”

“…The standardless method for quantitative analysis of particles requires calculation of the extinction coefficient from sample specifications and from the extinction efficiency [4,12]. For large spherical particles, estimation of the actual value of the effective extinction efficiency Q'ext with conventional UV-Vis detectors is possible by applying a derivation of van de Hulst' s expression given by Walstra [13][14][15].…”

“…Linear regression of the data (c, A) was performed and the experimental extinction coefficient was calculated from the slope of the best fitting line. The experimental value of extinction efficiency was finally obtained as described in [4]. The van de Hulst-Walstra model was, then, applied and Q'ext was determined.…”

“…GrFFF channels were built up as described elsewhere [3,4,6,7,11,12]: two mirror-polished glass plates were clamped together over a Mylar sheet from which the channel volume had been removed. Two channels (Channels 1 and 2) were employed, the dimensions of which were 0.0197 or 0.0202 cm thick, 2 cm wide and 30 or 50 cm tip-to-tip long, respectively.…”

“…On the other hand, in a more recent paper [4], a derivation of the Lambert-Beer (L.-B.) law, already described for standardless determination of the sample quantity in homogeneous flow-through systems [5], was applied to heterogeneous samples for quantitative analysis in field-flow fractionation (FFF) coupled with UV-Vis detection.…”