Specific Refractive Index Increment (∂n/∂c) of Polymers at 660 nm and 690 nm

Abstract

The specific refractive index increment (∂n/∂c) is an essential datum for the accurate quantitation of molar mass averages and distributions (inter alia) of macromolecules when refractometry, static light scattering, and/or viscometry detection are coupled on-line to size-based separation techniques. The latter include methods such as size-exclusion and hydrodynamic chromatography, and asymmetric and hollow-fiber flow field-flow fractionation. The ∂n/∂c is also needed for accurate determination of the weight-average molar mass of polymers by off-line, batch-mode multi-angle static light scattering. However, not only does ∂n/∂c differ among chemical species, it also depends on experimental conditions such as solvent, temperature, and wavelength. For the last seventeen years, the author’s laboratories have measured the ∂n/∂c of a variety of natural and synthetic polymers, at both 690 nm and, more recently, 660 nm, under a variety of solvent and temperature conditions. In all cases, this has been done by off-line, batch-mode differential refractometry, not by assuming 100% analyte column recovery and 100% accurate peak integration. Results of these determinations are presented here, along with the relevant experimental data.

Getting Closer to Absolute Molar Masses of Technical Lignins

“…This leads to just a few‐percent difference (1–3 %) between the values measured with lasers operating in red and infrared regions. In the case of online MALS measurements, small changes of x  % in dn / dc cause the same x  % error in the calculated molar masses 44, 45. Therefore, the possible errors in a calculated M w originating from the dn / dc inaccuracy in this study are considered to be non‐significant.…”

“…In the case of online MALS measurements, small changes of x %i ndn/dc cause the same x %e rror in the calculated molarm asses. [44,45] Therefore, the possible errors in ac alculated M w originating from the dn/dc inaccuracy in this study are considered to be non-significant.…”

Introducing the Inaugural Chromatographia Virtual Issue: Macromolecular Separations

“…Highlighted therein are reviews and original papers published in the journal during the last 2 calendar years. Should you have missed this e-mail, or should our e-mailing have (unforgivably) missed you, our readers can still find out about some of the diverse work published in Chromatographia in 2016 and 2017 in the area of polymer chromatography through the eight papers constituting the virtual issue [1][2][3][4][5][6][7][8].…”

“…These publications exemplify the range of analytical techniques applicable to macromolecular separations, via original papers dealing with inverse gas chromatography [1], high-temperature multi-detector size-exclusion chromatography (SEC) [4], mass spectrometry and ion mobility separation [3], and asymmetric flow field-flow fractionation [5]; and in reviews dealing with off-line refractometry [7] and with SEC with on-line viscometry, in particular [2], and also covering hyphenated liquid chromatographic polymer analysis methods, in general [6].…”

“…The range of analytes studied employing these separation methods is also shown, in applications ranging from block copolymers [1,3], to polyethylene [4], to nanoparticles [5], to polysaccharides [2,7,8], to a variety of synthetic polymers [2,6,7].…”