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Thu Sep 24, 2020, 03:57 PM

Utilizing the 21 Tesla Magnet at the National High Magnetic Field Lab to Characterize Asphaltenes.

The papers I'll discuss in this post are the two parts of papers appearing recently in the scientific journal Energy and Fuels.

They are: Probing Aggregation Tendencies in Asphaltenes by Gel Permeation Chromatography. Part 1: Online Inductively Coupled Plasma Mass Spectrometry and Offline Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (Marshall et al., Energy and Fuels, Energy Fuels 2020, 34, 7, 8308–8315)...

...and...

Probing Aggregation Tendencies in Asphaltenes by Gel Permeation Chromatography. Part 2: Online Detection by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry and Inductively Coupled Plasma Mass Spectrometry (Marshall et al., Energy and Fuels, Energy Fuels 2020, 34, 9, 10915–10925).

This journal's papers are generally overwhelmingly about dangerous fossil fuels. Anyone with a passive knowledge of my often turgid writings will be aware that I oppose the use of all dangerous fossil fuels and believe they must be phased out as quickly as possible on an emergency basis. I nonetheless regularly read this journal for several reasons. One is that while I favor largely doing away with the car CULTure - something of a hard sell I freely admit - there are certain materials, including to be perfectly honest, fuels, that cannot be ethically banned while respecting human development goals, that are obtained from dangerous fossil fuels. Thus to maintain access to these materials while simultaneously banning the mining of dangerous fossil fuels, we must understand what these materials are and how they can be either manufactured or replaced without the use of dangerous fossil fuels themselves. Of particular importance are "cokes" which are carbonaceous materials used widely in the reduction of metal ores, either in thermal settings (as in Bessamer furnaces in the steel industry) or as electrodes in Hall Heroult and FFC processes. The second reason is that many papers, especially those in the (generally smaller) section related to biomass offer insights to the now necessary goal of removing carbon dioxide from the air. A third reason is that there is generally a section in this journal connected with the capture of carbon dioxide. Although these are largely addressed to the quixotic idea of giant underground dangerous fossil fuel waste dumps (aka "sequestering" ) they are also relevant to more sane means of addressing climate change. A final reason is that often these papers just contain good science.

The papers under discussion here are largely directed to problems in the dangerous fossil fuel industry, in particular, the dangerous petroleum industry, but they are relevant actually to many of the reasons I gave above. For example, in the case of removing carbon dioxide from the air: In the high temperature reformation of biomass, it is often the case that "tars" are formed; these are in fact, asphaltenes, close to those found in dangerous crude petroleum. Although asphaltenes are problematic - very problematic - in industrial equipment, they are widely used as the familiar product asphalt, generally an aggregate of sand and asphaltenes. Thus, were we to pave roads, bicycle paths and walkways with asphaltenes obtained from the reformation of biomass, we would be removing carbon dioxide from the air and effectively sequestering in an economically viable manner. Indeed, as we will see below, asphaltenes can be regarded, in part, as fragmented graphene, and a deeper understanding of their chemistry can lead to new insights in materials science. Finally this paper utilizes one of the tremendous resources built in an era when the US government was more committed to science rather than racism, corruption, lies, hypocrisy, the subjugation and denigration of women, power grabbing and the spreading of diseases as it is today in the Senate and Administration. The National High Magnetic Field Laboratory at Florida State University is a tremendous scientific resource.

The introduction of Part 1 of the two part series:

Asphaltenes are one of the most complex and problematic components of petroleum crude oils. Across(1) the entire production chain, asphaltenes pose potential complications.(2) Upstream, on the oil recovery side, asphaltene deposits can block pipelines, often requiring production shutdowns to remedy, resulting in massive losses. Downstream, on the upgrading and refining side, crude oils with high asphaltene concentrations typically have lower yields and higher maintenance costs. Defined purely on the basis of insolubility in an n-alkane solution (typically n-pentane or n-heptane), asphaltenes are not a well-defined (or well-understood) chemical compound class.(3) Compared to their parent crude oils, asphaltenes are typically more aromatic with greater heteroatom content.(4−6) Thus, historically it has long been hypothesized that π–π stacking and hydrogen bonding between polar compounds drive asphaltene nanoaggregation, which leads to precipitation and eventual deposition. However, asphaltenes are extremely difficult to analyze due to their tendency to aggregate, resulting in very poor ionization efficiency in mass spectrometry analysis.
Linking molecular structure to aggregation potential requires detailed molecular level information. On a bulk scale, asphaltenes are more aromatic and contain more polar compounds than their parent crude oils. However, recent works have started to illuminate the importance of wax-like interactions between more aliphatic compounds that may contribute to asphaltene aggregation. Unstable asphaltenes have also been shown to have higher binding capacities for alkanes and waxes.(7) Berrueco et al. observed a correlation between decreases in fluorescence intensity and UV absorbance in the largest, excluded molecular weight regime of GPC fractions from asphaltenes, petroleum pitch, and coal-derived materials.(8−10) They hypothesized that compounds in the largest, excluded GPC peak may be larger and more aliphatic.(10) Characterization by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) for GPC aggregate fractions collected from a typical atmospheric residue revealed a surprisingly strong correlation between nanoaggregation potential and decreased aromaticity.(11) Large, very aliphatic compounds with extremely low ionization efficiencies comprised the largest, most aggregated fractions...

... Trace metals present in crude oils also complicate refinery processes by potentially deactivating hydrotreatment and hydrocracking catalysts. Vanadium, nickel, and iron are typically the most abundant metals found in petroleum products. Structurally, these metals are incorporated into heterocyclic macrocycles with four modified pyrrole subunits, known as porphyrins.(17,18) The forces driving asphaltene aggregation are not well understood: although metal-containing petroporphyrins are greatly enriched in precipitated asphaltenes, the nature of their involvement is unknown.(19) To probe the forces driving asphaltene aggregation in a laboratory, gel permeation chromatography (GPC) acts as a proxy for real-world aggregation. However, it is not entirely clear how well on-column nanoaggregation mimics that of asphaltene aggregation in the field.

Inductively coupled plasma mass spectrometry (ICP-MS) coupled with GPC yields quantitative chromatograms, commonly called size distributions or size profiles, for individual elements. For porphyrinic metals like vanadium and nickel, GPC chromatograms generally yield trimodal/multimodal aggregate size profiles sufficiently unique to act as “fingerprints” for petroleum samples.(20,21)...


Two of the most important analytical tools in chemistry, NMR and mass spectrometry, depend on magnetic fields. The absolute most sensitive mass spectrometers in the world, those with the highest mass resolution, are Fourier Transform Ion Cyclotron Resonance Mass Spectrometers, and a major manufacturer of these is Bruker, which is the company that built the 21 Tesla magnet at the Lab. The use of this magnet in mass spectrometry allows for the most sensitive analysis ever conducted anywhere.

The authors continue:

Four GPC fractions corresponding to various aggregate sizes were collected from an Arabian heavy crude oil and its corresponding purified asphaltenes for further analysis by 9.4 T Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). For petroleum product and complex mixtures, differences in ionization efficiency and aggregation tendency between compounds result in the preferential detection of the most easily ionized species. Although ionization bias can be partially overcome by chromatographic separations,(27,28) the choice of ionization method is still critical. Here, we chose positive-ion atmospheric pressure photoionization ((+)APPI), which is believed to be the most suitable method for characterization of asphaltenes.(29−31) Although APPI is well known to preferentially ionize aromatic compounds, ionization is more uniform than electrospray.(29,32) This work is the first part of a two-part study investigating the molecular composition of the PetroPhase 2017 asphaltene sample across a GPC elution profile. Here, we focus on the results from offline fraction collection and direct infusion and highlight some of the challenges we faced with that approach. In part 2, we shall examine the benefits of coupling the GPC method with online detection by 21T FT-ICR-MS, which reveals a more comprehensive molecular characterization.


Aromaticity in chemistry refers to a quantum chemical effect in which a ring system contains (2n+2) "pi" electrons where n is an integer including zero. Aromatic rings are stabilized when compared to non aromatic systems of carbon atoms, the latter being termed "aliphatic" above. (The size of the ring also contributes to aromaticity: An eight membered ring with 2 pi electrons is not aromatic, a three membered ring with two pi electrons is aromatic.) The degree to which a ring system is aromatic can be crudely examined (for very complex systems like asphaltenes) by considering "double bond equivalents" herein called "DBEs."

Besides carbon, asphaltenes also contain quantities of sulfur, nitrogen and oxygen. Under certain circumstances these atoms can donate electrons to a ring system, inducing a degree of aromaticity. For instance, furan, a five membered ring containing an oxygen, derivatives of which has been the subject of considerable attention in connection with biofuels made from non-food biomaterials, has a measurable degree aromaticity.

The asphaltenes were solvated in xylene, aromatic molecules which are a mixture of dimethylbenzenes, and subject to gel permeation chromatography (GPC) a chromatographic technique which separates molecules (somewhat crudely) on the basis of their molecular size, which generally correlates closely with molecular weight. The elution through the chromatograph columns utilized THF, tetrahydrofuran, which is made by hydrogenating furan, mentioned above, or by condensation of a product of the dangerous fossil fuel industry, butadiene. A small portion of the eluted asphaltenes were diverted to a commercial high resolution inductively coupled plasma (ICP) high resolution mass spectrometer designed to measure "heteroatoms," those atoms which are not carbon or hydrogen. These were used to monitor sulfur, using the isotope with a mass of 32, the most common sulfur isotope, presumably in such a way as to break up interfering O2 molecules, vanadium-51, the only stable isotope of this element, (natural vanadium is very slightly radioactive owing to the very rare radioactive isotope vanadium-50), and Nickel-58. It does not seem iron was monitored.

A word on why these metals are important in studying aggregation: Metals are known to complex with certain aromatic rings, in particular cyclopentadiene anions, but also with the molecules described above as porphyrins. The presence of porphyrins is definitely an artifact of the fact that the origin of most dangerous fossil fuels was from biomass; dangerous fossil fuels are stored solar energy. Porphyrins are very common in biological systems, two metal coordinating porphyrins are generally known by the general public. Chlorophyll contains a porphyrin structure coordinating magnesium, and hemoglobulin a porphyrin coordinating iron. (There are many other examples.) The authors remark that the fractions that are highly aggregated often contain metals, and part of their effort is to explore why this is.

Some pictures from the text of Part 1:

Sulfur, Vanadium and Nickel:



The caption:

Figure 1. Sulfur (top), vanadium (middle), and nickel (bottom) GPC ICP mass chromatograms. Intensities for the Petrophase 2017 purified asphaltenes are plotted in blue, and parent whole crude oil’s intensities are in red. High, medium, and low molecular weight (HMW, MMW, and LMW) and tailing fraction elution ranges are indicated at the top.


In general, the heaviest molecules elute first in GCP.

The distribution and ratios of hetero atoms, sulfur, nitrogen and oxygen in the various fractions:



The caption:

Figure 2. Heteroatom class distributions from (+) APPI 9.4 T FT-ICR mass spectral analysis for the PetroPhase 2017 purified asphaltenes and its corresponding GPC fractions. Heteroatom classes represent the most abundant heteroatom classes for the purified asphaltenes prior to fractionation.


The lower the ratio of hydrogen to carbon, the more aromatic character a molecule is likely to have:



The caption:

Figure 3. Average H/C ratios for the heteroatom class groups from the purified asphaltenes and its corresponding GPC aggregate fractions.


In general, asphaltenes, especially given their aromatic character, are difficult to ionize. A typical ionization technique - for which a Nobel Prize was awarded, is ESI - electrospray ionization - but in this case, another method, more suitable to the ionization of aromatics, APPI - atmospheric pressure photoionization by which the ionization is achieved by the use of very high energy ultraviolet radiation was utilized, owing the expected aromatic nature of asphaltenes. The ionization efficiency was obtained by recording the number of ions collected as a function of time:



The caption:

Figure 4. (Right) Monomer ion yields for the Arabian whole crude oil and its fractions. (Left) Monomer ion yields for the purified asphaltenes and its fractions. Ionization efficiencies were calculated from the inverse of the ion accumulation periods used to collect the FT-ICR mass spectra (see text). Those values were then normalized to the tailing fraction from the whole crude oil. Both the whole crude oil and the purified asphaltenes show an inverse relationship between ionization efficiency and aggregate size.


It is important to note the different scales on the y axes in the graphic above.

In the next series of graphics, the double bond equivalents within molecules within the fractions are represented. The closer this distribution - these in effect a three dimensional graphics where the third dimension is represented by color - lies to the red line in each graphic, the more highly aromatic these asphaltenes are:



The caption:

Figure 5. Positive-ion APPI-derived isoabundance-contoured plots of double-bond equivalents vs carbon number for the S1 class (top) and S2 class (bottom) for the asphaltenes and its corresponding GPC fractions. Red dashed lines represent the polycyclic aromatic hydrocarbon planar limit.(47,48)




The caption:

Figure 6. Positive ion APPI-derived isoabundance-contoured plots of double-bond equivalents vs carbon number for the O1S1 class (top) and O1S2 class (bottom) for the asphaltenes and its corresponding GPC fractions. Red dashed lines represent the polycyclic aromatic hydrocarbon planar limit.


To some extent, this data is a function of the analytical method.

The authors write:

The high-MW fraction has the lowest average DBE and the greatest average carbon number for both classes. The compositional range corresponds to compounds that are the most aliphatic, and the distribution becomes less aromatic as aggregate size increases. The most abundant species likely have ∼2–4 aromatic rings, as nonaromatics ionize very poorly by APPI, and likely contain very long alkyl chains. It is interesting to note that compounds with DBE 6 and 50 carbons are likely entrained material that coprecipitated with the purified asphaltenes, because they should be soluble in heptane on their own. As shown in Figure 6, the same observations discussed above were also made for the O1S1 and O1S2 heteroatom classes, which were among the most abundant heteroatom classes in the whole asphaltene prior to fractionation. The average composition shifts to larger, more aliphatic compounds as aggregate size increases.


In this case, the samples were collected by fractionation and analyzed by direct infusion. In part 2, the limitations of this procedure are addressed by the use of in line LC/MS/MS using the 21 Tesla magnet.

The conclusion of part 1:

Monomer ion yield and aggregation state were strongly correlated in both the crude oil and the asphaltenes. The monomer ion yields of the two largest aggregate GPC fractions (high MW and medium MW) from the asphaltenes were ∼1000 times lower than that of the least aggregated, tailing fraction from the whole crude. Due to the extremely low monomer ion yields in these fractions, analysis was limited to only the most abundant heteroatom classes in the asphaltenes. Note that it is difficult, if not impossible, to determine the extent to which the observed heteroatom classes represent the actual composition of the high- and medium-MW GPC fractions; it is entirely possible that additional heteroatom classes are present but ionize so poorly due to their aggregation state that they are not observed. However, for all of the heteroatom classes that we were able to characterize, both in the whole crude oil and in the purified asphaltenes, we observed a strong correlation between aggregation tendency and more aliphatic compounds. As aggregate size decreased, the composition shifted toward more condensed aromatics. No clear evidence of polar functionalities driving aggregation during the GPC separation was observed. A follow-up study will utilize online GPC with detection by 21 T FT-ICR-MS to overcome the limitations associated with fraction collection and direct infusion experiments.


Part 2 begins thus:

Notoriously one of the most problematic components of crude oils—asphaltenes—can complicate every stage of the production chain.(1) On the recovery side, asphaltene deposition in pipelines can require production shutdowns to remove the blockage. On the refinery side, high asphaltene concentrations typically decrease a crude oil’s yield and, simultaneously, increase maintenance costs. Asphaltenes are also possibly the most polydisperse and compositionally complex mixture in the world.(2−6) Unfortunately, asphaltenes are not a well-understood chemical compound class partly due to their poor definition: insolubility in an n-alkane solution, typically n-pentane or n-heptane.(7) Based on bulk properties, asphaltenes typically contain higher concentrations of polar heteroatoms and are more aromatic than their parent crude oils.(8−10) On the basis of these typical characteristics, it has long been believed that asphaltene nanoaggregation is driven primarily by π–π stacking and hydrogen bonding between polar compounds. However, linking chemical functionalities to aggregation potential requires detailed molecular-level information, and the tendency of asphaltenes to aggregate results in very poor ionization efficiency and makes them extremely difficult to analyze.
Despite the challenges associated with the analysis of asphaltenes, recent work has begun to reveal that waxlike interactions between more aliphatic compounds may play a more important role in asphaltene aggregation than previously known...

...Gel permeation chromatography (GPC) can help probe the forces driving asphaltene aggregation by acting as a proxy for studying aggregation in a laboratory. GPC is often coupled online with detection by inductively coupled plasma mass spectrometry (ICP MS), thereby enabling the quantitative determination of individual elements. GPC ICP MS chromatograms are commonly termed size distributions or size profiles. Most commonly, sulfur is monitored along with the most abundant heavy metals in petroleum products (vanadium, nickel, and iron). Heavy metals are of interest due to their potential to deactivate hydrotreatment and hydrocracking catalysts during upgrading and refinery processes. Vanadium, nickel, and iron exist structurally in petroleum as porphyrins (heterocyclic macrocycles with four modified pyrrole subunits).(20,21) Metal-containing petroporphyrins are enriched in precipitated asphaltenes, but their exact role in asphaltene aggregation is unknown.(22) GPC ICP MS chromatograms for porphyrinic metals typically exhibit multimodal/trimodal aggregate size distributions that provide “fingerprints” for petroleum samples.(23,24)...

...In the analysis of complex mixtures, especially asphaltenes, ionization biases arise from differences in ionization efficiencies and aggregation tendencies, resulting in the preferential detection of the species that ionize most efficiently. Chromatographic separations help to overcome ionization biases by simplifying the sample matrix,(2,30) but just as important is the choice of ionization method. Positive-ion atmospheric pressure photoionization ((+)APPI) is widely thought to be the most compatible method for asphaltenes.(5,31,32) Despite the well-known ionization biases of aromatic compounds, APPI ionizes more uniformly compared to electrospray, which is why it was selected for this study,(5,33) which is the second installment of a study that investigates the aggregation tendencies and molecular composition of the PetroPhase 2017 asphaltene sample by use of GPC. In part 1, GPC aggregate fractions were collected from the PetroPhase 2017 asphaltene sample and analyzed by direct infusion.(34) Monomer ion yields and aggregation state were strongly correlated. The asphaltene fractions that were most aggregated ionized ∼1000 times less efficiently than the least aggregated fractions in the whole crude oil...


And a rationale for the improvement at 21 Tesla:

...Very few previous reports have combined chromatographic methods with online detection by FT-ICR MS to characterize petroleum products and/or asphaltenes.(36) Several close mass differences are critical to resolve in the analysis of petroleum products. Two particularly important mass differences are the 3.4 mDa (S1H4 vs C3) and 1.1 mDa (13C1H332S1 vs C4). These close mass differences make online detection by high-resolution MS difficult on a chromatographic time scale. Often, long transients are required to obtain high mass resolving power, and coaddition of time-domain transients is required to increase signal-to-noise ratio to maintain sufficient dynamic range. For that reason, many studies with online detection by high-resolution MS resemble fraction collection and analysis by direct infusion...


From the experimental section, the mass resolution that would make any mass spectrometrist weep with envy:

The APPI source (ThermoFisher Scientific, San Jose, CA) was set to a vaporization temperature of 350 °C, and N2 was used for the sheath gas (50 psi) and the auxiliary gas (32 mL/min) to avoid sample oxidation. Experiments were performed with a custom-built hybrid dual ion-trap 21 T FT-ICR mass spectrometer described previously.(41,42) Excitation and detection were performed with a Predator data station.(43) Online detection by 21 T FT-ICR MS yields a mass resolving power of 3400000 at m/z 400 for an adsorption-mode mass spectrum (6.2 s transient duration), yielding 6451 unique assigned molecular formulas (120 ppb RMS error).(36) A 3.1 s transient often maximizes sensitivity and improves scan rate, while maintaining sufficient resolving power to separate the 1.1 mDa mass split out to ∼m/z 700. In this study we expected to observe species with molecular weights as great as ∼1000 Da, so we chose a 4.5 s transient to maintain resolution of the 1.1 mDa mass split. All spectra were phase-corrected for a mass resolving power of ∼2500000 at m/z 400


Resolution envy is a terrible vice.

This mass resolution is basically an order of magnitude greater than the very best common commercial instruments.

Some pictures from the text:



The caption:

Figure 1. GPC total ion chromatogram (TIC) from (+)APPI 21 T FT-ICR mass spectral analysis of the PetroPhase 2017 asphaltenes plotted in black on the primary axis. Sulfur (blue) and vanadium (red) GPC ICP-MS chromatograms are plotted on the secondary axis on the right.




The caption:

Figure 2. GPC TIC (black) and extracted ion chromatogram (XIC) for the N4O151V1 heteroatom class (blue) from the (+)APPI mass spectral analysis of purified Athabasca Bitumen asphaltenes plotted on the left axes. The vanadium (red) GPC ICP-MS chromatogram is plotted on the secondary axis on the right.


TIC is "total ion current" a measure of the number of ions being recorded in a unit of elution time. The N4 focus is particularly important to represent porphyrins, which are macrocyclic rings with 4 internal rings, each of which contains one nitrogen.

More N4 related stuff:



The caption:

Figure 3. XIC and (+)APPI derived isoabundance color-contoured plots of double-bond equivalents (DBE) vs carbon number shown in order of elution from left to right for the N4O151V1 heteroatom class (top) from the analysis of the PetroPhase 2017 asphaltenes. The inverted chromatogram shows the XIC’s average H/C ratio (bottom).


Some data on the presence of sulfur, and an unexpected finding with respect to π–π stacking:



The caption:

Figure 4. GPC FT-ICR MS extracted ion chromatograms for the hydrocarbon and sulfur heteroatom classes (center). Positive APPI-derived isoabundance contour plots of DBE vs carbon number for the HC class (top), S1 class (middle), and S2 class (bottom) with short retention times (left) and long retention times (right). As aggregation decreases, the compositional range for each class moves from more aliphatic species on the left toward condensed polycyclic aromatics on the right.


Some more along these lines:



The caption:

Figure 5. Extracted ion chromatograms and plots of DBE vs carbon number shown in order of elution from left to right for the N1O2S1 (top) and N1O2S2 (bottom) heteroatom classes from the PetroPhase 2017 asphaltenes. As aggregation decreases, the compositional range shifts toward more condensed aromatics in the high DBE range, and the abundance of lower DBE species increases, possibly indicating a shift in structural motifs (i.e., from thiophenic to sulfidic sulfur).




The caption:

Figure 6. Extracted ion chromatograms and plots of DBE vs carbon number shown in order of elution from left to right for the O1S1 (top) and O1S2 (bottom) heteroatom classes from the PetroPhase 2017 asphaltenes.




The caption:

Figure 7. Extracted ion chromatograms and plots of DBE vs carbon number shown in order of elution from left to right for the O1S1 (top) and O2S1 (bottom) heteroatom classes from the PetroPhase 2017 asphaltenes.


Some commentary from the paper in connection with figure 8:

The first major advantage with online detection is the ability to track compositional changes for heteroatom classes not observable by direct infusion, making it well suited for analysis of samples with low ionization efficiencies. The second major advantage is the increased chromatographic resolution afforded by online detection. For the N1O1S1 and N1O1S2 heteroatom classes shown in Figure 8, we observe the same global trends as previously discussed. The XICs for the N1O1S1 (black) and N1O1S2 (red) heteroatom exhibit a bimodal distribution with a smaller, narrow peak eluting near the total exclusion limit from ∼25–30 min and a second, broader, later-eluting hump from ∼34–55 min. The isoabundance-contoured plots of DBE vs carbon number on the top correspond to the N1O1S1 class, whereas those on the bottom correspond to the N1O1S2 heteroatom class. The plots of DBE vs carbon number directly above and below the XICs show the composition of large elution periods of ∼7 min. The longer elution periods reveal the same global trends discussed previously at length. If we were able to successfully track compositional changes for those heteroatom classes by direct infusion (which we were not able to do), we would expect to observe similar global trends. The most aliphatic species elute earliest in the largest aggregates, and aromaticity increases as aggregation lessens at longer elution times.


This suggests that the bigger asphaltenes are not actually graphene like fragments.

Figure 8:



The caption:

Figure 8. Extracted ion chromatograms and plots of DBE vs carbon number for the PetroPhase 2017 asphaltenes shown in order of elution from left to right for the N1O1S1 (top) and N1O1S2 (bottom) heteroatom classes. The composition for the most aggregated species exhibits a bimodal distribution. Online detection enables the small overlaid plots to show three discrete segments of that region. The shorter time windows reveal that the first species to elute are actually more aromatic, with DBE ≈ 20–25. Those species are followed closely by more alkylated compounds in much higher relative abundance.




The caption:

Figure 9. Extracted ion chromatograms and plots of DBE vs carbon number for the PetroPhase 2017 asphaltenes shown in order of elution from left to right for the N1 (top) and N2 (bottom) heteroatom classes.




The caption:

Figure 10. Extracted ion chromatograms and plots of DBE vs carbon number for the PetroPhase 2017 asphaltenes shown in order of elution from left to right for the N1O1 (top) and N1O2 (bottom) heteroatom classes.


The following is the cartoon from the abstract page that kind of "rubs it in" about the incredible mass resolution observed with this instrument.



The overall conclusion from this two part work:

GPC coupled with online detection successfully overcomes the challenges associated with fraction collection and analysis by direct infusion and reveals that for all heteroatom classes in the PetroPhase 2017 asphaltene sample aggregate size and aromaticity are inversely correlated. The largest aggregate region is composed of the most alkylated species, and the composition shifts toward more aromatic compounds as aggregation decreases. In addition to the ability to characterize samples with extremely low ionization efficiencies, online coupling improves the chromatographic resolution, which enables a closer examination of the most aggregated region. Smaller time segments revealed a local trend in the largest aggregates that opposed the global trend. The very first species to elute in the largest aggregates are actually more aromatic, and more alkylated compounds eluted shortly thereafter in greater relative abundance. Even disregarding the limitations associated with fraction collection and direct infusion, it would be difficult (and certainly impractical) to collect a sufficient number of fractions with short enough time intervals to reveal this local trend in the largest aggregates.


Sigh...

I have to admit that as much as I hate dangerous fuels and want them banned as quickly as is humanly and humanely possible, I certainly took pleasure in reading this paper about a problem in the dangerous fossil fuel industry, and, in any case, as noted in the turgid and highly esoteric text above, I see asphaltenes as a potential means to sequester carbon dioxide removed from the air via biomass.

It is important to note that this very powerful instrument can do many incredible things other than to address problems in the dangerous fossil fuel industry. The National High Magnetic Field Laboratory can serve to solve many intractable biological problems, in particular those associated with human disease, as well as addressing many severe environmental problems.

In these times of public insanity, it is wonderful to take a break and recognize that great scientific tools still exist and have yet to be wrecked along with our Constitution and our Country.

Have a nice evening.

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