Questions tagged [chromatography]
collective term for a set of laboratory techniques for the separation of mixtures
277
questions
2
votes
0
answers
65
views
When is chromatography regarded as a viable industrial purification strategy?
I understand the basics that chromatography is a fairly slow and expensive process compared to direct synthesis. When a synthesis route is not feasible, the economics become favorable. Not being in ...
-2
votes
0
answers
26
views
Would decreasing the percentage of ethyl acetate increase the polarity? [closed]
I was doing practice problems to prepare for an upcoming test and I came across the problem above. I wrote that the answer was C since that would increase the polarity of the hexane, thereby making it ...
3
votes
1
answer
112
views
Are there LCMS compatible buffer systems available for the high pH range 12-14?
I want to perform chemical stability studies for different pH Values. To achieve pH Values from 1 to 6 I can prepare solutions with trifluoric acid and formic acid and ammonium formate and acetate. I ...
1
vote
0
answers
36
views
"Is there any library in Python or software for analyzing raw chromatography data?"
I have taken the data directly from the FID sensor using a DAQ, so I have the chromatography data in this format:
(2 data colummns in a txt file) (18000 rows)
Time (s) Intensity (V)
0.00367___0.0008
...
2
votes
0
answers
44
views
How do I calculate the masses of compounds in a mixture from a GC?
I'm supposed to analyse the two GC graphs in the attached picture (I quickly drew them instead of taking a picture). The question states ths "A mixture contains 3-Methylhexane. To determine the ...
2
votes
0
answers
59
views
Regression equation for peak fronting/tailing in chromatography
Background
I would like to have a sum of functions $$\sum_{i=1}^k f_i(x)$$ which approximates my chromatogram. The variable $x$ would be my retention time, although I don't mind if answers change it ...
1
vote
1
answer
38
views
Term for one chromatography sample affecting the next?
Suppose I am running a collection of samples on a chromatograph (gas or liquid) in some order. Some of the sample molecules have large retention times due to their size and/or interactions with each ...
0
votes
0
answers
53
views
When creating a separation method in gas chromatography, calibration with compounds mixture or for each separate component?
When creating a separation method in gas chromatography, is there any difference between the calibration with the compounds mixture and the calibration for each separate component? I have 5 components....
5
votes
1
answer
198
views
How to effectively replace DMSO with LC–MS-compatible solvent for the samples from a well plate?
I want to do LC–MS analysis of the samples from a 384-well plate where each compound (at around 1–10 μM) is dissolved in 10–15 μL of DMSO. I am worried about the DMSO dwarfing the analyte’s signal, as ...
1
vote
1
answer
116
views
Is there any reason why KMnO4 for TLC is stored under basic condition?
my mentor told me that the KMnO4 solution specifically for TLC has added some bases like sodium hydroxide but we don't know why. I try to search on google, and found that the bases are usually by-...
1
vote
1
answer
106
views
How to interpret gas chromatography results?
I am having trouble interpreting gas chromatography (GC) results for the production of ethyl acetate from acetic acid and ethanol. I am trying to find the reaction order from these results, as well as ...
0
votes
0
answers
23
views
HPTLC Densitogram - Not Showing Other Secondary Metabolites
I have run a HPTLC analysis of methanolic extract of Gymnema Sylvestre R.Br. plant in order to determine the concentration of active ingredient (Gymnemic acid using Gymnemagenin as standard). Sample ...
4
votes
1
answer
103
views
How can I approximate the actual HPLC gradient?
In High Performance Liquid Chromatography (HPLC), the actual gradient is a bit different from the true gradient programmed because of dwell volume and other effects. For example, in the figure added, ...
2
votes
0
answers
115
views
How to choose the solvent gradient for the flash column chromatography of a complex mixture?
When performing a flash column chromatography, it is advised to select an eluent in which the desired compound has an $R_\mathrm{F}$ of about $0.25$ in TLC.
However, if I want to separate and isolate ...
1
vote
2
answers
175
views
How does industry separate glucose from fructose using liquid chromatography when producing high-fructose corn syrup?
Can someone explain how the separation of glucose and fructose is achieved using liquid chromatography in the industrial production of high-fructose corn syrup?
I've seen references to ion-exchange ...
1
vote
0
answers
60
views
Trouble analyzing amine using GC-FID
I am trying to analyze a sample containing hexamethylenediamine (HMD) dissolved in ethanol using GC-FID for an undergraduate chemical engineering project. The column used is Agilent DB-FFAP (high ...
2
votes
0
answers
57
views
Dynamic equilibrium of Girard T-derivatized oxysterols
This is a question relating to organic chemistry, moreso than chromatography.
I am running LC-MS on various hydroxycholesterols (HC) and dihydroxycholesterols (diHC). To increase ionization efficiency ...
0
votes
1
answer
67
views
Why I am unable to detect nystose & kestose using hplc and refractive index detector while could see peaks of glucose,sucrose,fructose, and raffinose [closed]
Mobile phase is 60% acetonitrile and temperature of the column is 25 degrees (supercosil amino from sigma). RID is also set up at 25.
3
votes
1
answer
49
views
Mystery GC peak appearing between 1H2 and various molecular combinations of 1H, 2H and 3H?
The following gas chromatograph, taken from "Review of the different techniques to analyse tritium", labels all but the largest peak. Given that the analyte is likely to be from some source ...
5
votes
3
answers
1k
views
Why will changing the solvent crack the column for column chromatography?
When we perform column chromatography with silica to purify the reaction crude product, we sometimes need to change the solvent system to better extract our target product.
For example, changing from ...
1
vote
0
answers
35
views
Using Hydrogen as a carrier gas for a GC; consideration of reactivity with analytes
In many cases people use H2 as a carrier gas for a GC. But does this exclude analysis of (say) systems with unsaturation or aromatic compounds etc. If a analysis uses a temperature program say up to ...
1
vote
2
answers
77
views
Determining volume of hydrogen gas evolved in water splitting reaction
I want to carry out a photocatalytic water spliting reaction. This reaction will generate Hydrogen and Oxygen gas in 2:1 ratio according to the following reaction -
2H2O + energy (light) → 2H2 + O2
So,...
6
votes
1
answer
524
views
What is the correct unit of a RI detector used for HPLC analysis?
I analyze sugar compounds in soft drinks with HPLC using refractive index detection (RID) on Agilent 1260 Infinity Binary LC (System User Guide (PDF)). I am not sure which unit to put next to the $y$-...
0
votes
2
answers
811
views
Finding unknown concentration using HPLC standard curve
I calculated a standard curve equation from a given concentration and peak area, which gave me $y=1994.6x+218.4$. I made the graph with the $x$-axis μg/mL and $y$-axis peak area.
The question is, a ...
3
votes
1
answer
320
views
Chromatography and Height Equivalent to a Theoretical Plate (HETP)
HETP can be expressed in two ways:
HETP = L/N
HETP = A + B/u + Cu
where:
L: lenght of the coloumn
N: Number of theoretical plates
A: Eddy-diffusion parameter, related to channeling through a non-...
1
vote
0
answers
42
views
How to change the counterion of a nucleotide salt?
I need to take the sodium nucleotide salts I have available in my lab and modify them to instead contain some more exotic counterions. Can I do this by binding my nucleotides to a strong anion ...
-1
votes
1
answer
148
views
Synthetic resin method to remove permanent hardness of water [closed]
Why is $\ce{R-SO3H}$ first treated with NaCl and then the RNa form i.e., the sodium form of resin is used for treating hard water? Why cannot we directly treat hard water with $\ce{R-SO3H}$? What is ...
2
votes
1
answer
113
views
How does having a basic stationary phase help the separation of acidic/basic compounds from non acidic/basic ones?
I have to reason whether silica or alumina would be a better choice of stationary phase for separating a mixture of pyridine and cyclohexanone with column chromatography.
I would expect both pyridine ...
1
vote
0
answers
13
views
How to minimize sample dispersion during spotting for paper electrophoresis?
I am separating highly polar amino acids and their derivatives using paper electrophoresis. This requires pre-wetting a piece of filter paper with electrophoresis buffer (in this case, carbonate-...
0
votes
1
answer
103
views
What matters for ion exchange: net or local charge?
I am interested in separating two small organic molecules by ion exchange chromatography.
Following the example set by several old papers for these molecules, I want to use a cation exchanger. Both ...
2
votes
1
answer
49
views
What's a good high precision analysis technique (after GC) to measure trace isopropanol in water samples?
Looking to measure trace IPA content in water samples.
Only GC I have access to doesn't take samples with water. Different columns not an option.
2
votes
0
answers
53
views
Mixture is eluted too early from alumina in flash column chromatography
I have recently tried to purify my reaction mixture by column chromatography. Because my reaction mixture had poor resolution in silica-based TLC, I used neutral alumina-based TLC plate. After I ...
3
votes
0
answers
90
views
Why does column chromatography not work like it's supposed to?
I'm a few months into working in an organic synthesis lab and I consider myself to have a solid intuition for, well, how chemistry works. I have ran at least 50 columns at this point but no matter ...
1
vote
1
answer
64
views
Decomposable solvent identification in GC-FID
How can a gas chromatography with flame ionization detection (GC-FID) be used to identify a liquid solvent that decomposes at its boiling point like DMSO? In a solution with other higher boiling ...
1
vote
0
answers
222
views
Activating alumina before column chromatography
Recently I synthesized some amine compounds, and because it showed better separation in the neutral alumina TLC plates than silica plates, I am planning to purify the reaction mixture using neutral ...
2
votes
0
answers
55
views
How much analyte should I use for paper chromatography?
I am looking into using paper chromatography to distinguish between standard drugs and counterfeit drugs for my high school research project. I have decided on using aspirin as the "standard"...
1
vote
0
answers
114
views
Solvent for Terephthalic Acid TLC
We're trying to do thin layer chromatography to assess the purity of Terephthalic Acid. So far we have tried DMF, and Water of different pH values. Does anybody know a better solvent or combination?
0
votes
0
answers
235
views
Triethylamine is detected by ninhydrin during TLC
Continued from this question. I purchased new triethylamine from Sigma Aldrich, spotted freshly opened triethylamine to the TLC plate, dipped into ninhydrin solution, and heated it. Again the purple ...
2
votes
1
answer
567
views
Does ninhydrin staining detect triethylamine?
My reaction mixture has amine compounds, so it shows tailing in bare silica plates. Therefore I decided to add small amount of triethylamine in the eluent. Because my amine compound is not detected by ...
1
vote
0
answers
63
views
Corruption of TLC plates or solvent
I have been conducting TLC experiments, and sometimes I observed some lines when I use mixture of eluents.
And I found that some lines are observed after I develop the TLC plates with some eluents. ...
1
vote
0
answers
64
views
Fragmentation behavior of spots in TLC
I tested multiple development using eluent condition hexane + 1% of ethyl acetate. Then I observed kind of fragmentation of spot.
I'm not sure, but I guess that successive spots are from the skyblue ...
1
vote
0
answers
40
views
Ion Exchange chromatography [closed]
Suppose that Anion exchanger is used in the stationary phase
normally -ve charge A.A will be eluted first as it will not attach
but my question is does the zwitter ion(have net charge 0 will be the ...
2
votes
0
answers
562
views
Using neutral or basic alumina in column chromatography for purification of amines
I am conducting a synthesis involving amines, and it is found that some spots still hardly moves from the starting point in spite of the dichloromethane 9:methanol 1 eluent condition. Addition of ...
3
votes
2
answers
120
views
Can I expect the same (or very close) peak areas from herbal extracts prepared with the same plant/solvent ratio?
I prepared an extract by using 100 mg of plant and 2 mL of ethanol, filtered and injected 20 μl into the HPLC system equipped with Waters® XSelect (150 mm × 4.6 mm, 5 μm) column. If I prepare an ...
1
vote
0
answers
43
views
Can I scrape off compounds from normal TLC like in prep TLC for MS analysis?
As far as I know, the limit of detection of mass spectrometry is very low compared to other analysis. In principle, so I think I can scrape off some compounds from normal TLC plate after development ...
3
votes
0
answers
155
views
TLC monitoring of Buchwald-Hartwig coupling reaction using ninhydrin stain
I am conducting a synthesis involving Buchwald-Hartwig coupling reaction. The reagents are 2,3,5-tribromothiophene, 1-aza-18-crown-6, NaOtBu as base, $\ce{Pd_2(dba)_3}$ as palladium source, DavePhos ...
1
vote
0
answers
79
views
Separation of very nonpolar mixtures using column chromatography
I am conducting a synthesis using Buchwald-Hartwig coupling. Below is the TLC result after nearly all consumption of limiting starting material. Th is 2,3,5-tribromothiophene, which is the limiting ...
1
vote
0
answers
17
views
How can I determine the purity of an oligonucleotide solution?
After desalting an oligonucleotide via gel chromatography, I am left with (presumably) an oligonucleotide substance suspended in a buffer. What is the simplest way to verify the oligonucleotide's ...
3
votes
1
answer
110
views
Why can I extract all metabolites from blood plasma with one solvent, but to extract only fatty acids I must use many solvents?
I want to do a metabolite study using GC- without derivatization and UPLC-MS (RP and NP) on samples of plasma and urine. My hypothesis is agnostic about which metabolite will correlate with the ...
3
votes
1
answer
949
views
Interpretation of permanganate-stained TLC spots
When I stain TLC spots with $\ce{KMnO4}$, I found that some spots appear differently as time goes by. Here is the example:
The leftmost one is the plate right after staining, and the others are ...