Questions tagged [chromatography]
collective term for a set of laboratory techniques for the separation of mixtures
170
questions
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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?
2
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1answer
48 views
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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0answers
57 views
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 ...
2
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1answer
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 ...
2
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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-...
3
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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
0
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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 ...
0
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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)?
...
6
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3answers
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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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.
3
votes
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 ...
1
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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 ...
0
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1answer
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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0answers
17 views
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 ...
3
votes
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 ...
2
votes
0answers
19 views
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 ...
1
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0answers
19 views
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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0answers
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. ...
1
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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 ...
1
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0answers
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 ...
3
votes
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 ...
1
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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). ...
1
vote
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 ...
0
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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 ...
0
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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 ...
4
votes
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 ...
2
votes
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 ...
2
votes
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 ...
2
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0answers
69 views
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 ...
7
votes
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 ...
1
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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 ...
-3
votes
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. ...
0
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0answers
33 views
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 ...
1
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0answers
37 views
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
40 views
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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votes
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 ...
0
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0answers
28 views
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?
1
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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?
2
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0answers
179 views
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, $j$ ...
-1
votes
1answer
68 views
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 ...
6
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0answers
54 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 (...
0
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0answers
62 views
How to divide the peaks of two anion ions using ion chromatography?
I used an ion chromatography system (Dionex IC-2000) to determine the inorganic ions and acid from the samples collected in the atmosphere.
For measuring $\ce{SO4^2-, NO3, Cl-}$, and low molecular ...
2
votes
0answers
67 views
Visualization of TLC plates
I'd like to know what exactly happens when various agents are used after developing a TLC plate, during the visualization phase, of sugars with anisaldehyde for example.
I know that those compounds ...
1
vote
1answer
72 views
Sephadex and purification of products [closed]
Sephadex is useful for the separation and purification of many natural products.
Is it also useful for the separation and purification of artificial chemicals (in organic synthesis ) or not and why ?
3
votes
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 ...
3
votes
1answer
1k views
Why is Rf called Retardation Factor?
I understand that $$R_\mathrm{f} = \frac{\text{distance traveled by center of analyte spot } (b)}{\text{ distance travelled by solvent front } (a)}$$ What I do not understand is why this is called ...
0
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1answer
64 views
marijuana testing process [closed]
Does anyone know a bit about how costly and accurate are the current THC measurement techniques?
Please speculate what drives cost chemicals, consumables or instrument time.
-1
votes
1answer
19 views
What is the relation between the speed of various components of a mixture, and their respective Retardation Factors in adsorption chromatography? [closed]
Consider two components, I and II, of a mixture which is subject to adsorption column chromatography. Let I have higher adsorption than II.
I know that Retardation Factor ($R_f$) of component II will ...
0
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1answer
551 views
Could thin layer chromatography separate enantiomers? [duplicate]
My textbook states the thin layer chromatography could separate enantiomers only if both/or the mobile and solid phases are chiral?
Why so?
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0answers
549 views
Why is methamphetamine less polar then amphetamine? [closed]
The question is as stated in the title. Is there a general way to determine relative polarity of organic compounds?
This question is for use in the context of the manner in which polarity of the ...
