16 votes
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Typesetting of the retardation factor (Rf)

According to Nomenclature for Chromatography (IUPAC Recommendations 1993) [1, pp. 843, 845] (also listed in IUPAC Gold Book), retardation factor is denoted as follows: Column chromatography: $R$ (...
andselisk's user avatar
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13 votes
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What would a (gas) chromatogram look like if two compounds have the same retention times?

] Complete overlap (= identical retention) is a regular feature of experimental chromatography with very different compounds and complex mixtures. It just happens when the selectivity happens to be ...
AChem's user avatar
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12 votes
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Does molten metal liquid chromatography exist?

An obstacle of implementation is that the blend of metals has to be kept liquid all the time the chromatography runs, top to bottom of the column, while the equipment around has to sustain the ...
Buttonwood's user avatar
11 votes
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HPLC: peak area vs concentration

However, in my opinion, there should be a proportionality between the concentration and the peak intensity, not the peak area. There is a proportionality between both peak area vs. concentration and ...
Curt F.'s user avatar
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10 votes

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

I wish we would stop teaching chromatography in terms of "polar" and "nonpolar." The aspirin will interact fairly strongly with the silica due to hydrogen bonding/electrostatic interactions of the ...
SendersReagent's user avatar
9 votes

Normal phase vs reverse phase HPLC

Normal phase Normal phase HPLC systems are similar to the flash-column chromatography that you might be familiar with. A silica stationary phase is eluted with a non-polar solvent such as hexane, ...
NotEvans.'s user avatar
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9 votes

Does molten metal liquid chromatography exist?

Molten liquid chromatography does not exist currently. However the problems you mentioned for purifying metals is very conveniently done using ion-exchange chromatography. A lot of difficult to ...
AChem's user avatar
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8 votes

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

Since aspirin has a carboxylic acid group on it, it would be considered polar. Silica gel, consisting of $\ce{SiO2}$, is also polar. Since polar molecules attract other polar molecules, the aspirin ...
ringo's user avatar
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8 votes
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What inference can be made from the fact that there is no reversal in how three components eluate?

Question 1 Yes, of course! Something that is "relatively" non-polar would travel further with a non-polar mobile phase because it would have less attraction to the stationary phase. While a ...
Bob's user avatar
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8 votes
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What is the purpose of trimming the bottom corners of TLC plates?

Yes, your question contains the answer. Think about capillarity. Without the little cuts the eluant would be "sucked" and flow from both the bottom and the left ( and right) edges of the thin plate, ...
Alchimista's user avatar
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8 votes
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ELSD detection principle

ELSD is an acronym for Evaporative Light Scattering Detector. It is used as a quasi-universal detector for HPLC. The first step is the nebulization of the column effluents with a dry gas as you have ...
S R Maiti's user avatar
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7 votes
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Is paper or water the stationary phase in paper chromatography?

The stationary phase in chromatography is the one that doesn’t move according to the eyes of a macroscopic (i.e. human researcher) observer. (That complicated way to put it was to prevent anybody ...
Jan's user avatar
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7 votes

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

Not sure if I can fulfill Ed's "real answer". I like the word you used for tuning solvent polarity- a knob. Modern students may understand this better. There is no theoretical restriction in ...
AChem's user avatar
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7 votes
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How to read a chromatography calibration curve?

I assume your teacher explained the HPLC separation. If injected a mixture of four ions you will get four peaks. Each peak has an area, which is proportional to the concentration of the substance. ...
AChem's user avatar
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7 votes
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What is the correct unit of a RI detector used for HPLC analysis?

Good question. Now that you have mentioned the instrument name (Agilent 1260 LC), it is easy to locate Agilent's "Refractive Index Detector Agilent InfinityLab LC Series User Manual." It is ...
AChem's user avatar
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7 votes
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Why will changing the solvent crack the column for column chromatography?

The fundamental reason for cracks in packed beds is that all chromatography columns (used in organic labs or even HPLC) do not have particles packed in a regular crystalline manner. This means that ...
AChem's user avatar
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6 votes

Removal of tetrabutylammonium from an organic reaction

I know it is a relative old issue but I had the same problem with nucleosides during my PhD. I tried a wide range of reagents but all of them lead to the decomposition of compounds or no reaction ...
Guillermo Bañuelos Sanchez's user avatar
6 votes
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Does every solute spend at least $t_M$ in the mobile phase?

Dead time ($t_{\bf M}$, also called holdup time) is the time it takes for the mobile phase (eluent) to traverse one length of the column, for a given flow rate. Because moieties in the eluent do not ...
Todd Minehardt's user avatar
6 votes
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Gas chromatography flame ionization detector (FID) - why hydrogen gas?

The key to the answer is understanding how FID works. The hydrogen flame has a minimal flame ionisation, what is needed for the low signal baseline. Incoming organic molecules from the HPGC column ...
Poutnik's user avatar
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6 votes
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What dictates cathode vs anode nomenclature use?

Who was responsible for this naming system and how can we change it? Michael Faraday was responsible for the terms anode and cathode more than hundred years ago. All the confusion regarding the ...
AChem's user avatar
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6 votes

Has anyone added dyes to a mixture about to separated by chromatography in order to visualize where the desired product lies?

the idea is good for academic purposes and good for a lecture hall demo. One may also try a UV lamp, if your compound fluoresces in the column. Caution UV is very harmful for the eyes (protective ...
AChem's user avatar
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5 votes

Reasoning retention factor of benzoic acid

The answer is the dimer formation of the benzoic acid. This is why higher concentrations lead to more extended dimer formation, thus higher $\mathrm{R_f}$ values as the carboxyl group "gets shielded." ...
logical x 2's user avatar
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5 votes
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Monitoring reaction progress?

Slightly askew of what was asked, but still relevant. TLC is not dependent on conjugation. That reasoning suggests to me You are using UV light to visualize the TLC. UV light is used because it is ...
Lighthart's user avatar
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5 votes

How to separate two diastereomeric amines?

When you mentioned column chromatography I had to assume you meant flash chromatography or biotage, which by implication is normal phase. When people mention HPLC they are normally defaulting to ...
Beerhunter's user avatar
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5 votes

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

Mixture of solvents is used for 2 main reasons: Elution time For given HPLC column and set of analytes, the mobile phase must have the proper degree of general polarity, what is often called "...
Poutnik's user avatar
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5 votes

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

Although natural rubber and synthetic rubber display a poor chemical resistance to alkanes among others, they do not dissolve in alkanes. Your GC/MS traces (I believe that so because of alkane/alkene ...
Mathew Mahindaratne's user avatar
5 votes
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Types of chromatogram shapes

Good to know that someone is working in DSP and chromatography but there are many software out there like PeakFit, why a new one? Your first test could be peak detection as function of resolution as ...
AChem's user avatar
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5 votes

How to read a chromatography calibration curve?

Suppose it is a calibration curve of high performance liquid chromatography (HPLC) to determine concentration of chloride ion in unknown solutions. The detector is sensitive to charge ions, which gave ...
Mathew Mahindaratne's user avatar
5 votes

HPLC: Peak height calculation

Height in HPLC simply refers to the height of the peak (= maximum value of the peak) above the baseline. The point by z1273 is right in the sense that this voltage to height conversion factor is ...
AChem's user avatar
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5 votes

Source for UV cut-off values of buffers

Snyder cites an article by Li [1] as the primary source for UV cutoff values ("Ref 7" below) for various buffers [2, p. 299]: TABLE 7.1 Buffers for Use in HPLC Separation $$\begin{array}{...
andselisk's user avatar
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