Questions tagged [chromatography]

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

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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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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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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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30 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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49 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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2answers
56 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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39 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
144 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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33 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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42 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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538 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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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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179 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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28 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 ...
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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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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 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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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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157 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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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
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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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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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47 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 ...
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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 ...
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1answer
59 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 ?
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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 ...
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1answer
654 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 ...
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62 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.
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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 ...
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1answer
188 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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406 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 ...
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1answer
50 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 ...
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2answers
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Is it possible to calculate the concentration percentage using chromatography paper?

I'm trying to calculate the concentrations of specific compounds using paper chromatography. Would I be able to calculate a rough estimate by comparing the size of each concentrated spot? If not is ...
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381 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 ...
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107 views

can you separate inorganic ions with chromatography?

For example, if you run a solution of sodium and potassium chloride through a colum? I am just wondering if i can get pure potassium chloride from a mixture of sodium and potassium chloride.
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248 views

Difference between batch and column mode?

I have heard Ion-exchange chromatography can be used in batch or column mode, have you got any idea how are those modes? I have looked descriptions all over books and web (Skoog for example, both ...
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Can I use chromatography to compare the amounts of chlorophyll in different leaves?

I have been unable to find a clear answer online about the effect that concentration of a solute has on the retention factor. If it is as I suspect, I should see plants with more chlorophyll having ...
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Can I use a 1:1 mixture of isopentyl alcohol and water as mobile phase to carry out paper chromatography of a mixture of red and blue ink?

Can I use a 1:1 mixture of isopentyl alcohol and water as mobile phase to carry out paper chromatography of a mixture of red and blue ink? We generally use ethanol water mixture as mobile phase for ...
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307 views

Predict polarity (TLC, column) using ChemSketch (-Draw)

I'm currently working on a project where I have to make and isolate often quite similar molecules. But, as I change the functional groups the overall electronic situation and polarity of the product ...
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136 views

Process Chromatography vs Solid Phase Extraction techniques

Process Chromatography is typically performed by flowing eluent from the top to the bottom of the column. The standard method of solid phase extraction at industrial scale e.g. to extract natural ...
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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
304 views

Affinity to mobile or stationary phase during column chromatography [closed]

I have carried a column chromatography and obtained two compounds. The first one is liquid (ester) and the second one is solid (nitro) yet I know that the second compound is less polar than the first ...
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2answers
13k views

Normal phase vs reverse phase HPLC

What is the difference between normal phase and reverse phase high-performance liquid chromatography?
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432 views

Purification of polar NHS esters

What are the options that I might be missing for the purification of a molecule with the following characteristic: Contains an activated ester that reacts with water (NHS) Reacts readily with ...
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1answer
365 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 ...
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1answer
86 views

Compare concentrations using LC/MS

Suppose I run a reaction and then pass the results through LC/MS to find the conversion. One idea could be to compare the peaks of the reactants to the peak of the product. But: MS peak will depend ...
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0answers
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Dibenzoyl-L-tartaric acid won't show up on HPLC chromatogram

I'm trying to develop a method for HPLC to detect dibenzoyl-L-tartaric acid. Concentration doesn't matter at this point; I'm only concerned with detection. The problem I'm having is the compound won't ...
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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 ...
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240 views

If I mix an aqueous solution of hydrogen chloride with an organic solvent, will the organic solvent contain hydrogen ions?

For example, let's say I mix $36\ \text{cm}^3$ 2-propanol, $9\ \text{cm}^3$ methyl ethyl ketone and $15\ \text{cm}^3$ hydrochloric acid with a concentration of $1,0\ \text{mol}/\text{dm}^3$. The ...