Questions tagged [chromatography]

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

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19 views

How to determin the order of elution? [closed]

the following compounds are separated by liquid / solid chromatography on silica gel: CH3COOCH3, CH3CH2CH3, CH3CH2COOH. determine the order of elution?
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40 views

Why can DAP be used to elute a protein in affinity chromatography?

A little background: as part of my bioinformatics degree I have to take Protein Chemistry course, but I miss chemistry basics (have CS background), so that's why I'm asking the following question. We ...
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1answer
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Can we use HPLC to purify an organic reaction product?

I know HPLC is a form of column chromatography that uses high pressure to pump a sample mixture/eluent through a column. However, I'm not sure if this technique is being used to purify and isolate ...
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62 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-...
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Software platforms with integration of multi vendor mass spectrometer device data?

I know about ACD/Spectrus Processor which is a software platform to integrate analytical chemistry data from multiple mass spectrometer device vendors (e.g. Agilent Technologies, Bruker, Waters) to ...
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1answer
31 views

Organic solvent for cleaning autosampler syringe

I work in a laboratory where gas chromatography is used extensively. We handle phthalates. What are the possible wash solvent for autosampler syringe? I've been using acetone.
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1answer
65 views

Why n-alkanes can be found in organic solvent extract of rubber?

Sorry for the confusing title, I didn't know how to describe this better. So, if we douse rubber, say, a bicycle tire or a certain type of rubber glove, with organic solvent (n-heptane), we can find n-...
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1answer
35 views

When to use chromatographic separation vs vacuum-assisted rectification distillation?

I'm trying to understand a bit more about industrial scale separation processes. One particular element I'm interested in is the question as to when chromatography (HPLC or Simulated Moving Bed) may ...
6
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1answer
760 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 ...
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2answers
398 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
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1answer
33 views

Why mustn't the sample be dipped in the mobile phase in paper chromatography?

As the title says it, I am curious about why the sample (ie, an extract of plant's chlorphyl transferred onto paper) must not be dipped into the mobile phase (ie, the solvent which goes up the paper)? ...
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484 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?
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82 views

How to pool fractions after chromatography?

I used chromatography to purify my protein and now I have fractions with different concentrations ranging from 1-16 mg/ml. Should I pool all these fractions or just the ones with high concentration (...
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1answer
95 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 ...
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2answers
57 views

Can I normalize my data in order to compare it?

I have three chromatograms of the same eluted protein but at different concentrations, since it got diluted during purification process) and hence peak maximums at very different absorbances. The ...
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1answer
2k views

Single Point vs. 5 Point Calibration in HPLC

Single-Point calibrations aren't that useful for quantitative analysis and there is more room for error in result readings as compared to a 5-Point calibration. Is this why a 5-Point calibration is ...
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I am having difficulties with analysing steroids in GC/MS [closed]

Is there anyone here that has already analysed estrone and 17beta-estradiol on GC/MS (HP5-MS column and MSTFA as derivatizing agent)? Is it necessary to make a mixture of other reagents with MSTFA or ...
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1answer
38 views

How appropriate/adaptable is HPLC for in situ sample analysis on Titan?

I have a limited background in chemistry (nothing beyond general Chem 2), so I am asking for help with a group project. We have two chemists on our team, but communication is limited at the time and I ...
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31 views

Protein purification pressure limits confusion, about the X-MPa limit for FPLC?

I have always been a bit confused about column pressure limits. I have to elaborate a bit on the problem to get to my question: In protein purification we use the äkta purification machines (e.g. ...
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Do I have to change my sample buffer before IEX chromatography?

I will use IEX chromatography to purify a protein and will then use a equilibration buffer Tris-HCl, pH 8 to set the start conditions for my column and optimize the binding of my protein. Then inject ...
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Change buffer in dialysis?

I have a protein that I purified in PBS buffer, pH 7. I will do dialysis to remove salt and will then further purify the protein with ion exchange chromatography. I will need to use another buffer (...
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1answer
70 views

Column length for baseline separation

I have a GC-chromatogram with 4 retention times and peak widths and a column length. How can I calculate the column length that I need in order to get baseline separation for all components in the ...
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30 views

Acid and base separation on an anion exchange column [closed]

I'm new with this concept and so I would need some advice. I want to separate an acid and a base in a water solution. The acid has $\mathrm{p}K_\mathrm{a}(\ce{HA}) = 5$ and the corresponding acid of ...
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3answers
62 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 ...
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1answer
14k views

How to determine the order of elution in silica gel column chromatography?

Benzofuranoids ustusoranes A (1), B (2), and E (3) were isolated from Aspergillus ustus 094102. If these compounds were separated by column chromatography on silica gel, what would be the elution ...
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1answer
58 views

Physical meaning of tm

The definition of dead time ($t_\mathrm m$) is mentioned as the time taken for elution of an unretained species. It is also mentioned that the retention time ($t_\mathrm r$) is sum of the time analyte ...
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1answer
96 views

In HPLC, how does column diameter affect the retention time?

I am using a smaller diameter column than my previous one keeping all other factors such as stationary phase, solvent, solvent gradient constant. (Obviously, flow rate will be less in smaller column). ...
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2answers
931 views

Retention time and dead time

Why does ts start just after tm ? Does the analyte starts spending time in the stationary phase only after the mobile phase has passed and reached the detector ? Wouldn't there be an overlap between ...
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1answer
367 views

Concept of Adjusted Retention Time in Chromatography

Why is the relation between the adjusted retention time, retention time and dead time as follows : tR' = tR - tM ? To find the time that the sample spends in stationary phase (adjusted retention ...
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2answers
206 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 ...
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104 views

Chromatography types and techniques

Are HPLC and GC comparable in term to size exclusion, ion exchange, sequential injection chromatography? Or they are two different terms, HPLC and GC refers to the equipment and phase of the analyte, ...
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1answer
75 views

How to determine polarity of components in TLC

Estimate how a TLC-analysis would look like for the following reaction when you take a TLC at: a) the start of the reaction, b) after 65% conversion and c) after full conversion of A. (You may assume ...
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1answer
77 views

Use a solid or liquid stationary phase in gas chromatography

In my textbook, they mention that the stationary phase used in gas chromatography is a solid, such as silica or an adsorbed high-boiling-point liquid. My question is that what is the advantage of ...
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ApexTrack: peak tail looks like a shoulder

I'm trying to implement ApexTrack algorithm in my software by following the description written by Waters. But many chromatograms that I see have noticeable tailing of peaks: . No matter what ...
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1answer
591 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 ...
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2answers
56 views

In Ion Chromatography instrument, Does the specific conductivity (peak area) of an analyte depends upon background conductivity?

In Ion Chromatography instrument, Does the specific conductivity (peak area) of an analyte depends upon background conductivity ? Assume Specific Conductivity (peak area) of fluoride ion is 4 unit ...
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2answers
231 views

Pre-Hydrogen Feature On the Output Of a Gas Chromatography Thermal Conductivity Detector

A candidate for "dark matter", predicted and now apparently detected to have both a higher thermal conductivity and higher diffusion rate than H2 is purported in this PowerPoint Presentation file. ...
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Monitoring amino acid esterification

I am trying to monitor the esterification of a non UV active amino acid.I used thionyl chloride and Methanol as reagents. As amino group is unprotected, Ninhydrin should give positive result for both ...
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1answer
403 views

What does it mean to equilibrate a column in size exclusion chromatography and why is a buffer used?

I'm reading a procedure on size exclusion chromatography and it says that the first step is to equilibrate the column with buffer. What does this mean?
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Impediments to GC-MS characterization of petroleum products

In an attempt to characterize, and sometimes to 'match' oil on feathers of birds, a laboratory utilize gas chromatographic - mass spectrometry. Persons likely to encounter oiled birds are advise to ...
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1answer
210 views

How can I use a solvent gradient in column chromatography? [closed]

I am working to use the column, there are a lot of videos which explain it, but I don't understand this statement in the procedure. The residue was finally purified by column chromatography using ...
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1answer
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Separation of sugar and fat in a column chromatography [closed]

I am chemist at organic and bioorganic chemistry,I want to know if we are separating sugar and fat in a column chromatography who will be down first ? and why ? Thank you.
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how could I make a file conversion from .spc (thermo fisher) in .cdf (Shimadzu) format file?

how could I make a file conversion from .spc (thermo fisher) in .cdf (Shimadzu) format file?
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1answer
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Can I get feedback on assignment? (chromatography)

HW question asks me why samples can be separated into their components by chromatography. My answer is that each component in the mixture will have different affinity for the solvent (mobile) phase as ...
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Pressure in Skoog Instrumental Analysis Problem 27-22b (gas chromatography)

Problem 27-22b in: Skoog; Holler; Crouch. Principles of Instrumental Analysis. Thomson Brooks/Cole (publisher varies by country) asks for corrected retention volumes. A compressibility factor, $j$ ...
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1answer
780 views

Free Open Source Gas Chromatography Software

Collecting data is one thing, however sometimes one needs to plot or analyse data at a later date when access to the original software may no longer be feasible or possible. Open Source software is ...
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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. ...
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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 (...
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573 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 ...
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1answer
59 views

Is the pressure in an HPLC system the same throughout?

I'm not sure if I'm articulating myself well enough, but here's my problem: I have a current HPLC system, where we typically have backpressure readouts of around 15 MPa. We are looking to get a new ...