Gas chromatography, liquid chromatography, mass spectrometry, capillary electrophoresis. How good are they?

Suppose I had an unholy mixture of organic chemicals such as a heavy crude oil with high sulphur content. How many different chemicals could I identify from the mixture using any combination of the above four methods? 100 chemicals? 1,000? 10,000? 100,000? More?

PS, I’m not too fussed about separating isomers accurately, but am fussy about picking up the correct number of double bonds.

mollwollfumble said:

Gas chromatography, liquid chromatography, mass spectrometry, capillary electrophoresis. How good are they?

Suppose I had an unholy mixture of organic chemicals such as a heavy crude oil with high sulphur content. How many different chemicals could I identify from the mixture using any combination of the above four methods? 100 chemicals? 1,000? 10,000? 100,000? More?

PS, I’m not too fussed about separating isomers accurately, but am fussy about picking up the correct number of double bonds.

A typical crude oil assay using chromatography on boiling point fractions finds only about 100 chemicals. Up to n-pentane and iso-pentane. And up to C12 without details. No attempt at all to look for compounds containing either nitrogen or oxygen, and only a token look for sulphur and asphaltenes (organics insoluble in hexane). Possibly only looks for 4 or 5 aromatic chemicals.

That’s nowhere near good enough.

Such an assay doesn’t include mass spectrometry.

mollwollfumble said:

mollwollfumble said:

Gas chromatography, liquid chromatography, mass spectrometry, capillary electrophoresis. How good are they?

Suppose I had an unholy mixture of organic chemicals such as a heavy crude oil with high sulphur content. How many different chemicals could I identify from the mixture using any combination of the above four methods? 100 chemicals? 1,000? 10,000? 100,000? More?

PS, I’m not too fussed about separating isomers accurately, but am fussy about picking up the correct number of double bonds.

A typical crude oil assay using chromatography on boiling point fractions finds only about 100 chemicals. Up to n-pentane and isopentane. And up to C12 without details. No attempt at all to look for compounds containing either nitrogen or oxygen, and only a token look for sulphur and asphaltenes (organics insoluble in hexane). Possibly only looks for 4 or 5 aromatic chemicals.

That’s nowhere near good enough.

Such an assay doesn’t include mass spectrometry.

Slowly delving into the scientific literature.

The paper “Characterization of naphthenic acids in oil sands wastewaters by gas chromatography-mass spectrometry” finds 56 chemicals using a single scan of GC-MS, all naphthenic acids (-COOH) or other chemicals with the same C:H:O ratios.

The paper “Analysis and characterization of naphthenic acids by gas chromatography–electron impact mass spectrometry of tert.-butyldimethylsilyl derivatives” finds 91 chemicals using a single scan of CG-MS, mostly naphthenic acids but with other chemicals such as phenols.

Now I’m starting to read “Fractionation of a Light Crude Oil and Identification and Quantitation of Aliphatic, Aromatic, and Biomarker Compounds by GC-FID and GC-MS”. 281 compounds comprising “102 aliphatic, 126 aromatic, and 53 biomarker hydrocarbons … n-alkanes (n-C8 to n-C40), selected isoprenoids, total petroleum hydrocarbons, target polycyclic aromatic hydrocarbons (PAHs), alkyl PAH homologues, and biomarker compounds”.

281 is still really pissweak compared to the number of chemicals that are actually in there.

mollwollfumble said:

Gas chromatography (GC), liquid chromatography, mass spectrometry (MS), capillary electrophoresis. How good are they?

Suppose I had an unholy mixture of organic chemicals such as a heavy crude oil with high sulphur content. How many different chemicals could I identify from the mixture using any combination of the above four methods? 100 chemicals? 1,000? 10,000? 100,000? More?

PS, I’m not too fussed about separating isomers accurately, but am fussy about picking up the correct number of double bonds.

OK, I have a definitive answer on this now.

First paper found 52 naphthenic acids.

Next paper found 91. That seems to be about the limit for a single GC-MS run, after chemical modification. Mostly naphthenic acids.

Next paper found 281. That’s aliphatics, aromatics, terpanes & steranes from a single light crude oil. No chemical modification. Separation first, then multiple GC-MS runs.

Next paper found 681. “Chemical Analysis of a Miller-Type Complex Prebiotic Broth”. Most come from a two dimensional GCxGC-MS. But they also use a whole suite of other techniques including NMR spectroscopy, FTICR-MS and, in a follow-up paper, coherent anti-Stokes Raman scattering.

So it seems that 1,000 chemicals from a top of the line analysis is about the limit. There are several different factors that set this limit.

• Mass spectrometry fragmentation seems to set an upper limit of about 33 carbon atoms. The larger the molecule, the worse the fragmentation.
• Non-n-paraffin aliphatics and all aromatics are limited to 18 to 20 carbon atoms.
• n-Hexane solubility also seems to set an upper limit near 33 carbon atoms. Other similar solvents, ditto.
• Finding the closest match between observed gas chromatograph peaks and the database NIST/W9N08.
• Chemical modification of aliphatics containing COOH groups can push that 20 carbon atoms up to 33.

mollwollfumble said:

mollwollfumble said:

Gas chromatography (GC), liquid chromatography, mass spectrometry (MS), capillary electrophoresis. How good are they?

Suppose I had an unholy mixture of organic chemicals such as a heavy crude oil with high sulphur content. How many different chemicals could I identify from the mixture using any combination of the above four methods? 100 chemicals? 1,000? 10,000? 100,000? More?

PS, I’m not too fussed about separating isomers accurately, but am fussy about picking up the correct number of double bonds.

OK, I have a definitive answer on this now.

First paper found 52 naphthenic acids.

Next paper found 91. That seems to be about the limit for a single GC-MS run, after chemical modification. Mostly naphthenic acids.

Next paper found 281. That’s aliphatics, aromatics, terpanes & steranes from a single light crude oil. No chemical modification. Separation first, then multiple GC-MS runs.

Next paper found 681. “Chemical Analysis of a Miller-Type Complex Prebiotic Broth”. Most come from a two dimensional GCxGC-MS. But they also use a whole suite of other techniques including NMR spectroscopy, FTICR-MS and, in a follow-up paper, coherent anti-Stokes Raman scattering.

So it seems that 1,000 chemicals from a top of the line analysis is about the limit. There are several different factors that set this limit.

• Mass spectrometry fragmentation seems to set an upper limit of about 33 carbon atoms. The larger the molecule, the worse the fragmentation.
• Non-n-paraffin aliphatics and all aromatics are limited to 18 to 20 carbon atoms.
• n-Hexane solubility also seems to set an upper limit near 33 carbon atoms. Other similar solvents, ditto.
• Finding the closest match between observed gas chromatograph peaks and the database NIST/W9N08.
• Chemical modification of aliphatics containing COOH groups can push that 20 carbon atoms up to 33.

This link claims 200 chemicals for GC-MS on diesel oil.
And 5000 chemicals for GCxGC-MS on diesel oil

http://www.chem.wilkes.edu/~mencer/pdf_docs/2D_Gas_Chrom.ppt&ved=2ahUKEwiy2f3suMDiAhUK7nMBHcA8ChkQFjAAegQIARAB&usg=AOvVaw24s1-hS_ReF9_z9J8tGzFO&cshid=1559124392858

I suspect this is “salesman’s claims for performance” not actually achievable in practice.

At least now I know how the heck two-dimensional chromatography actually works. It’s not a physical separation into two dimensions but a time-based separation, with a first (mass) column having peaks with width > 3 sec, during which time a second column separates further on the basis of polarity.