Questions tagged [chromatography]

collective term for a set of laboratory techniques for the separation of mixtures

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12
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1answer
555 views

Typesetting of the retardation factor (Rf)

What should be the typesetting for the symbol of the retardation factor as used in thin-layer chromatography? These are the possibilities: Rf - only f in italics Rf - both R and f in italics Rf - ...
10
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2answers
8k views

Gas chromatography/mass spectrometry: Can I use peak ratios and molecular mass to derive quantity?

Can derive the quantity of a substance from a GC/MS report if I know: the ratio to another substance in the data, the quantity of that second substance, and the molecular mass of both substances. ...
9
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2answers
650 views

How to separate two diastereomeric amines?

I am developing a method to synthesize amines using organometallic catalysts and my reaction yield these two diastereomeric amines ($\ce{R2N}$ is, in this case, a morpholine group). With both being ...
9
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1answer
897 views

Silica turning transparent during column chromatography with chloroform

Initially, my column had been loaded with n-hexane and ethyl acetate, however I ended up having to use a more polar solvent to elute my product. It was my first time running chloroform through a ...
8
votes
1answer
9k views

What is the Kovat's Index used for?

As mentioned in the title, why do we use the Kovat's Index in gas phase chromatography? It seems a little arbitrary to compare everything to the order that n-alkanes (such as n-pentane, n-hexane, and ...
8
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2answers
380 views

How to translate the mobile phase from thin layer chromatography to column?

I recently was told that once you find a good solvent mixture for separation on thin layer chromatography (TLC), you should only use 10% of the more polar solvent (for silica) when you run your column....
7
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2answers
47k views

If the polarity of the solvent increases, will the Rf value increase or decrease?

True or False: A sample of aspirin has an $R_f$ value of 0.20 when measured on a silica gel TLC plate with a certain solvent mixture. If the polarity of the solvent is increased, the $R_f$ value of ...
7
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1answer
634 views

What is the purpose of trimming the bottom corners of TLC plates?

During my chemistry lab course, I was told by my instructor to make 2 small cuts on the bottom corners of the TLC (Thin-Layer Chromatography) plate. Does this make the solvent rise uniformly on the ...
7
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2answers
3k views

Removal of tetrabutylammonium from an organic reaction

I need to synthesize some organic compound for my Ph.D. research. Everything went OK during the synthetic route but got messed up at the very end. In my final step (once the final compound has been ...
7
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1answer
1k views

What is the behavior of a Zwitterion during ion exchange chromatography?

We're interested in purifying a protein that has an azide moiety using ion exchange chromatography. Due to its unique structure, the moiety is a Zwitterion with a novel chemical behavior. My question ...
6
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3answers
546 views

In High Performance Liquid Chromatography, why are ratios of solvents used?

How do they allow for better separation? For example, why isn't 100% hexane used?
6
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1answer
702 views

How to choose a proper chromatography way to separate substrates?

I'm a freshman and I recently learned how to do TLC and column chromatography. I also know a little about other ways to separate things by chromatography, such as affinity chromatography, gel ...
6
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1answer
802 views

Different elution profiles of carvacrol and thymol

I have identified carvacrol and thymol via thin-layer-chromatography and via gas chromatography On a normal silica plate the thymol has a higher Rf-value then carvacrol. The explanation for this would ...
6
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0answers
56 views

Can you convert smells to variables? [closed]

Is there a way to map smells to numerical values of different variables? I.e. With RGB colours, each colour is made up of numerical values from 0-255. For example, red is (255,0,0), and yellow is (...
5
votes
2answers
28k views

Normal phase vs reverse phase HPLC

What is the difference between normal phase and reverse phase high-performance liquid chromatography?
5
votes
1answer
4k views

What is 'Retention period' in chromatography and what is its importance?

I heard people quite often speak about retention time/retention period in Chromatography and Mass Spectrometry. I see somewhere that it is the time duration between the injection time and the target ...
5
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1answer
6k views

What does 'preconcentration techniques' mean?

In the scope of the analysis of organic compounds in column-switching liquid chromatography, what does the following statement mean? sample preconcentration techniques with high enrichment factor(...
5
votes
1answer
80 views

How to recover C18 column after prolonged exposure to phosphate buffer?

A colleague of mine who occasionally does HPLC in a biochemistry lab discovered that a C18 column was not properly flushed after the previous experiment. It appears that the column was stored for ...
5
votes
1answer
152 views

How to quantify amount of pigments in plant leaves?

Using thin-layer chromatography, it is possible to see what pigments plant leaves contain. For example, I can test whether there are chlorophyll a or b, carotenoids, or anthocyanins. What kind of ...
5
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1answer
2k views

Analytical Chemistry predicting the order of elution of compounds in a reverse phase HPLC

Predict the order of elution for a mixture containing caffeine and benzoic acid, using a reverse phase HPLC. Explain your answer. My try: Since benzoic acid is more acidic that caffeine, which means ...
5
votes
2answers
202 views

Is is possible to do mass spectrometry without coupled liquid chromatography?

It's possible to identify a solution with several compounds* without the coupled liquid chromatography (LC) before to isolate the compounds? On the university where I study, the LC is broken, so all ...
5
votes
1answer
91 views

What mechanisms might make a substance travel different distances on the same TLC plate?

When doing TLCs to monitor reactions, it is considered good common practice to not only spot the reactants and the reaction mixture (likely after some mini-workup), but also to include a ‘cross-spot’: ...
5
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2answers
16k views

How does the Rf value change when changing the eluent composition?

A non-polar molecule X is analyzed by TLC chromatography on silica to determine its $R_f$ value. The first eluent was hexane:EtOAc = $9:1$ and the $R_f$ value was $0.5$. In the second run, the eluent ...
5
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1answer
588 views

A good book for learning paper and thin-layer chromatography

What book would you recommend for learning paper and thin-layer chromatography? I don't have access to fancy equipment (just to these two basic techniques that are relatively cheap), so it would be ...
4
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2answers
226 views

Gas chromatography flame ionization detector (FID) - why hydrogen gas?

Why is $\ce{H2}$ used in an FID, apart from the fact its combustion does not contaminate the flame? In other words, is the temperature of the flame important or critical? Is the stability of the ...
4
votes
1answer
374 views

What inference can be made from the fact that there is no reversal in how three components eluate?

I gave an answer this question about TLC. I now realize that I am blundering my way through this question. The problem statement doesn't specify if the compounds to be eluted are polar or non-polar. ...
4
votes
1answer
1k views

Reasoning retention factor of benzoic acid

In my organic chemistry lab, we ran a TLC plate on silica to determine the identity of an unknown compound. The two possibilities were benzoic acid and acetanilide. I know that the general rule is, ...
4
votes
1answer
163 views

Stronger ESI signal for deuterated substances

I observe a constant phenomenon in my ESI measurements, which indicates that deuterated substances give a stronger signal than the same substance in non-deuterated form. Unfortunately I can't make any ...
4
votes
1answer
52 views

What happens to the “leftover” Ions in the Mass Analyzer

I am very intrigued by what happens to the ions which do not make it to the detector in mass spectrometers, do they just pile up? I have never seen anyone clean our quadrupole, is this done? or do ...
4
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1answer
14k views

HPLC: peak area vs concentration

Many text books say that there is a proportionality between the peak area of the chromatogram and the concentration. However, in my opinion, there should be a proportionality between the concentration ...
4
votes
1answer
86 views

Could chromatography induce a conformational change?

We'd been studying chromatography in our instrumental analysis course and I was wondering if chromatography could induce a conformational change. For example, you have a straight chain with a ...
4
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1answer
253 views

Reverse Phase Chromatography

Please help me figuring out what is going on with my RP-HPLC protocol. I am purifying a small peptide out of E.coli Culture, heat stable enterotoxin, its amino acid sequence is: N-T-F-Y-C-C-E-L-C-...
4
votes
1answer
1k views

What does the pressure in the HPLC(High performance liquid chromatography) do?

Well I have to do research about the HPLC. It says, that because of the pressure the stationary phase can be made out of smaller particles and the pillars can be shorter. Also the seperation of the ...
4
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2answers
661 views

What is the relationship between the molecular weight of a polymer and that of polystyrene?

So, I read in a similar chemistry thread that you can get Mn and Mw of the polymer of the interest by comparing the result of the sample obtained from GPC/SEC with the standard known molecule weight ...
4
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1answer
1k views

How do I find Rf values & length size of paper in chromatography?

A student is designing an experiment using paper chromatography. From previous results, she knows that the Rf values for two dyes that she wishes to investigate are 0.72 and 0.80. It is proposed that ...
4
votes
1answer
447 views

HPLC method for salicylic acid

Salicylic acid is a relatively polar compound hence I thought that normal phase would be preferred as the stationary phase of normal phase is polar. However, it is said that reverse phase would be the ...
4
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1answer
84 views

Protein purification with Cobalt

Cobalt exhibits a more specific interaction with histidine tags, resulting in less nonspecific interaction than nickel. For this reason, cobalt is the preferred divalent cation for purifying His-...
4
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0answers
125 views

How to make a sephadex slurry

I want to purify crude alpha-amylase with column chromatography. I am using a spehadex 75, But for some reason I can't find any information on how to make the slurry. I can quickly find tons of ...
4
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0answers
433 views

Difference between neutral and basic activated alumina

Sigma Aldrich sells two different types of activated alumina for column chromatography: neutral and basic. Apparently basic alumina is more active and better at adsorbing anions. Why is this the ...
3
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1answer
1k views

Why note the solvent level on chromatography paper when it is removed from the chamber?

Why is it important to mark solvent level on chromatography paper when you remove it from the chamber?
3
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2answers
508 views

What dictates cathode vs anode nomenclature use?

what was the justification for the use the cathode and anode terminology in IEF? There is no redox taking place in IEF, just proteins interacting with an electric field
3
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1answer
129 views

Does every solute spend at least $t_M$ in the mobile phase?

In 'Fundamentals of Analytical Chemistry' 9th edition by Skoog, West, Holler and Crouch, there is the following passage (page 865). The dead time (void time), $t_M$, is the time it takes for an ...
3
votes
3answers
94 views

Applying vacuum at the end of a flash chromatography column

I know that flash chromatography uses a positive or pushing pressure to achieve the goal which is separation. Would the same goal be achieved if you had a vacuum on the other end instead of a ...
3
votes
1answer
124 views

Choosing LC-MS modifier - why only acids?

During method selection our chromatographists have options like NH4, TFA, Formic Acid. What's the point of choosing only between acid? Why not use the strongest that guarantees ionization? The sample ...
3
votes
1answer
2k views

How do I perform thin-layer chromatography to identify alkaloid content in fruits?

Fruits and as well as other plant parts usually contain alkaloids, which are nitrogenous compounds. I'd like to know how the Thin-Layer Chromatography method can be used to determine the alkaloid ...
3
votes
1answer
479 views

Chromatography: Why does the insoluble compound get pulled along?

In paper chromatography, we see that a paper with an ink spot on it get dissolved in the liquid and travels up with water due to capillary action. Then the compounds with more affinity to the paper ...
3
votes
1answer
1k views

What's the difference between Carvacrol and Thymol?

What is the difference when it comes to separating Carvacrol and Thymol on HPPLC with reverse phase - C18 column? Carvacrol elutes first, is that because it is ortho?
3
votes
2answers
1k views

Plotting a calibration curve for Gas-Liquid Chromatography

Question: The given graph of abundance of different samples of butanol with respect to time is- Textbook solution: But why aren't the points like this: $(20,5);(40,10);(60,15);(a,7)$ after which, ...
3
votes
1answer
66 views

How do I import CSVs to OpenChrom?

My end objective is to compare GC outputs of samples in two groups using PCA. I have bene given the data in Excel format but have saved to CSV. Whilst I can locate CSV files through OpenChrom, they ...
3
votes
1answer
514 views

Diffusion/Streaky bands on TLC plate

These days I am working on a research project where I am supposed to run TLC for samples which are wax extracts from coconut butten nuts using chloroform as the solvent. All the samples have been ...