The Calibration of Size Exclusion Chromatography Columns:  Molecular Mass Distributions of Heavy Hydrocarbon Liquids

Abstract

The aim of the study was to obtain calibration curves for a pair of size exclusion chromatography (SEC) columns operating with 1-methyl-2-pyrrolidinone (NMP) as eluent. The dependence of the calibrations on sample chemical structures has been examined. The calibrations have been compared with elution times of several sets of standards. The level of agreement between SEC and MALDI-mass spectrometry has been evaluated. Molecular mass distributions of several complex samples have been examined in terms of these calibrations. The polystyrene (PS) and poly(methyl methacrylate) (PMMA) calibration curves were close, while a set of polysaccharides (PSAC) and other oxygenates eluted much earlier. However, numerous other samples eluted closer to the PS-PMMA line. To a first approximation, deviations between the PSAC and PS-PMMA lines may be treated as an upper limit to errors arising from structure-dependent variations in this SEC system. Below 15 000 u, MMs of oxygenated samples could be estimated to within a factor of ∼2-2.5. Other structural features gave rise to smaller deviations. Good agreement was observed up to about m/z 3000, between SEC and MALDI and LD-MS. The techniques are independent, suggesting that up to this limit, SEC may be considered as a quantitative tool. The accuracy of the measurement is subject to greater uncertainty with increasing molecular mass. The often-made assumption that high-mass materials are composed of aggregates has been examined. Furthermore, evidence from several analytical techniques provides indications of entirely different structural makeup (e.g., nature of fragments in mass spectrometry; trace element concentration) between fractions with different apparent molecular massessas determined by SEC. It is possible that some molecules adopt 3-dimensional conformations and show up as larger than they really are. While the "aggregates" assumption did not explain our experimental observations, structures of material appearing under the excluded peak in SEC require further careful study.

The Pentane- and Toluene-Soluble Fractions of a Petroleum Residue and three Coal Tars by Size Exclusion Chromatography and UV-Fluorescence Spectroscopy

“…The mass spectrum in Figure 5 shows the complexity of the low temperature tar in the minor peak at 30 min of the 2nd pentane fraction. We note that the polystyrene calibration for the Mixed-D column closely matched [19] the measured peak intensity masses (from LDand MALDI-MS) up to a little over m/z 3000 in the pitch sample. That range far exceeds the mass limits observed by GC-MS of the three coal tars used here.…”

“…SEC using NMP as eluent has been described in detail elsewhere [1,19]. The column chromatography fractions of the petroleum residue and the coal liquids were examined using the Mixed-D column (Polymer Laboratories, Church Stretton, UK) at 80°C with NMP as eluent to examine aromatics in the different fractions.…”

Separation and measurement of flame‐formed high molecular weight polycyclic aromatic hydrocarbons by size‐exclusion chromatography and laser desorption/ionization time‐of‐flight mass spectrometry

“…16,[31][32][33] In the SEC system using NMP as eluent, fullerene mixed [C60 and C70] eluted in the excluded region of two SEC columns. 33 Moreover, ethylene flames at atmospheric pressure are considered unfavorable for fullerene formation in the gas phase, because the temperature is too low and the hydrogen concentration too high. 34 The possibility of fullerene formation in the TOF mass spectrometer in a plasma produced by laser irradiation of the flame-formed samples appears unlikely under the experimental conditions used in the present work.…”

Mechanisms of Catalytic Activity in Heavily Coated Hydrocracking Catalysts

“…The size exclusion chromatography (SEC) system and its calibrations have been described elsewhere [20,21]. Briefly, a polystyrene/polydivinylbenzene SEC "Mixed-A" column from Polymer Laboratories Ltd was used in this work.…”