Insight into the aggregation of coal derived material in solvent — an observation by size exclusion chromatography

Chen, C.; Iino, Masashi

doi:10.1016/s0016-2361(00)00201-5

Cited by 25 publications

(13 citation statements)

References 28 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…These shifts have been attributed to the dissipation of noncovalent binding forces, causing disaggregation of polar clusters, which would otherwise have appeared at retention times appropriate to larger molecular masses. 35,36 More recently, similar claims have been made for tetrabutylammonium acetate 37 (TBAA).…”

Section: Mixed-mentioning

confidence: 74%

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

et al. 2004

View full text Add to dashboard Cite

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.

show abstract

Section: Mixed-mentioning

confidence: 74%

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

et al. 2004

View full text Add to dashboard Cite

show abstract

“…In one set of experiments, lithium bromide (LiBr) was added to the eluent NMP and found to shift the SEC chromatograms to longer retention times (smaller apparent masses). These shifts have been attributed to the dissipation of ionic binding forces, causing disaggregation of polar clusters, which would otherwise have appeared at retention times appropriate to larger molecular masses. , More recently, similar claims have been made for tetrabutylammonium acetate (TBAA); , their results were interpreted to show the aggregation of coal molecules on changing the eluent from NMP to NMP/CS 2 or to NMP with anionic additives. The material eluting near the exclusion limit corresponded to material presumed to be strongly aggregated, which disappeared when the eluent was changed.…”

Section: Introductionmentioning

confidence: 84%

Effect of Salts on the SEC Profiles of Heavy Hydrocarbon Liquids: New Approach with Salts Dissolved in Solvents Used for Planar Chromatography

et al. 2004

View full text Add to dashboard Cite

Two related propositions addressing the interpretation of size-exclusion chromatograms of heavy hydrocarbon liquids have been examined. First, that peaks observed at the exclusion (short retention time) limits of size exclusion chromatography (SEC) columns, when using 1-methyl-2-pyrrolidinone (NMP) as eluent, are due to aggregation brought about by sample polarity. Second, that the addition of salts such as LiBr to the NMP eluent dissipates ionic binding forces and causes the disaggregation of polar clusters. The resulting shift to longer elution times (smaller masses) is then interpreted as representing those of the disaggregated sample molecules. However, in earlier work, we observed that the addition of this salt shifted chromatograms to retention times later than the permeation limits of the analytical columns. The salt appeared to have increased surface interactions between the sample and column packing. Thus, the addition of the salt directly to the SEC eluent did not allow distinguishing between any possible disaggregation effect and its adverse effect on the size mechanism. In this work, we have attempted to separate the two effects. The samples were fractionated by planar chromatography (PC) using solvents with dissolved salts: LiBr or tetrabutylammonium acetate (TBAA). Any presumed disaggregation would be expected to take place during the planar chromatographic separation. The fractions were then recovered from the plates and characterized by SEC. Three coal-derived liquids were investigated. The results indicated that the salty solvents were able to mobilize more large-mass material than the solvent alone because the increased polarity of the salty solvent was better able to displace larger molecules from the polar sites of the silica. SEC showed these fractions to be of larger apparent MM than those recovered in PC using untreated solvents. No evidence of disaggregation was found due to the use of salts.

show abstract

“…The problem was most obvious in samples with a high propor- tion of excluded material; after hydrocracking to smaller molecules, the proportion in the excluded region decreased [11,12,14,15] and the signal in the valley approached zero intensity. Chromatograms showing significant intensity between excluded and retained peaks have also been found when using NMP as eluent and refractive index detection [20]. However, Lafleur and Nakagawa [2] appear to have avoided overloading their column while examining the pyridine extracts of coals.…”

Section: Uv-fluorescence Spectrometrymentioning

confidence: 98%

Matching average masses of pitch fractions of narrow polydispersity, derived from matrix‐assisted laser desorption ionisation time‐of‐flight mass spectrometry, with the polystyrene calibration of SEC

Islas

Suelves

Millán

et al. 2003

J of Separation Science

View full text Add to dashboard Cite

Matching average masses of pitch fractions of narrow polydispersity, derived from matrix-assisted laser desorption ionisation time-of-flight mass spectrometry, with the polystyrene calibration of SEC A coal tar pitch has been fractionated by preparative and analytical size exclusion chromatography (SEC) to provide narrow time-elution fractions, expected to have relatively low molecular dispersities. The fractions were characterised by analytical SEC, by UV-fluorescence spectroscopy, and by laser-desorption MS and by MALDI-MS using sinapinic acid as matrix. The MALDI spectra were evaluated by measuring the peak-intensity mass, M p , and by calculating number (M n ) and weight (M w ) average masses. The high mass limits of the spectra were determined by three methods based on (i) truncating the spectrum when the signal fell below 5 times the standard deviation of signal at the instrument limit, (ii) taking the upper mass as defined by a minimum slope of the spectrum from baseline, and (iii) taking all of the high mass signal as from sample. The laser desorption spectra were evaluated by M p values only; the results below m/z 1,000 were in excellent agreement with the polymer calibration. The MALDI mass spectra gave a good fit between M p values below m/z 3,000 and the calibration of SEC by polymers. Working with M p gave better results than the M n and M w values from Method (i). Results from Methods (ii) and (iii) were significantly worse. Reasons for the lack of agreement between results above m/z 3,000 by MALDI and above m/z 1,000 by LD-MS have been discussed.

show abstract

Insight into the aggregation of coal derived material in solvent — an observation by size exclusion chromatography

Cited by 25 publications

References 28 publications

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

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

Effect of Salts on the SEC Profiles of Heavy Hydrocarbon Liquids: New Approach with Salts Dissolved in Solvents Used for Planar Chromatography

Matching average masses of pitch fractions of narrow polydispersity, derived from matrix‐assisted laser desorption ionisation time‐of‐flight mass spectrometry, with the polystyrene calibration of SEC

Contact Info

Product

Resources

About