Questions tagged [chromatography]
collective term for a set of laboratory techniques for the separation of mixtures
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chromatographic interactions with methanol, acidic or basic?
How can I describe the interaction between methanol and thiophene in a chromatographic separation in an acid media?
I'm confused with the different concepts:
Methanol present a hydrogen acceptor ...
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22 views
Dark smudge at the TLC solvent front
I have recently started using TLC in my graduate work to test for the cleavage of a cyclic oligo-adenylate in an enzymatic reaction. The sample I'm spotting on my plate is in an aqueous solution ...
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Has anyone added dyes to a mixture about to separated by chromatography in order to visualize where the desired product lies?
Usually in preparative chromatography one needs to know when the desired substance to be separated is coming down the pike. Often this required some sophisticated instrumentation. But, it occurred to ...
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44 views
Gas chromatography of samples containg water
I have read a few articles where it is stated that samples containing water are detrimental for a GC experimental results and equipment.
For example, in the paper Identification of essential oil ...
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49 views
Why is Ion Exchange Chromatography done in a column?
It seems like the idea of Ion Exchange Chromatography is to get a maximum amount of exposure of your gel to your solution. It seems like overhead stirring and a gel bed would be more likely to be ...
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1answer
59 views
Optimal lipophilic solvent for washing PEEK-lined reversed-phase HPLC columns
What would be the reasonable strategy for washing a reversed-phase (RP) octadecylsilyl (ODS) C18 HPLC columns from lipids and other non-polar residues? The columns are used for biochemical analysis of ...
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1answer
85 views
What is the function of thin layer in thin layer chromatography?
I just learned about the thin layer chromatography, which I think is basically the same as the paper chromatography.
I am wondering what is the function of the thin layer? I mean, what's special about ...
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1answer
102 views
Impact of flow rate on peak areas in Mass Spectrometry
As a follow up to the discussion in comments: it's now clear that UV peaks will have larger area if flow rate is decreased, because the same portion of molecules are measured again and again.
With ...
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Why are cations detected in capillary gel electrophoresis with a positive applied voltage and a coated fused silica capillary?
In capillary gel electrophoresis, when a positive voltage is applied to a coated fused silica capillary, why are positively charged ions (among positive, negative and neutral) detected first?
What is ...
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Does triethylamine affect all materials in TLC?
In TLC, I heard that if I treat acid-sensitive materials such as amines, then I can add some triethylamine. The principle of TLC is interaction between materials and polar silanol group of silica. ...
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60 views
Analysis of reaction mixture by TLC and finding column chromatography condition
I am conducting an organic synthesis. Below is the TLC image.
I used dichloromethane:methanol:triethylamine=10:1:0.15 as eluent, but I stored it during 3 days, so it may be a little bit concentrated.
...
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Is it possible to run column chromatography in reversed phase?
I'm conducting a synthesis involving aza-crown-ether.
Whether aza-crown-ether acts as a base or not is unclear, but when I do TLC using dichloromethane/methanol, it is hardly drawn up with the mobile ...
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Reason for GC peak splited
I ran GCMS and one of the peak of GC appears:
The peak shows some tailing, but there seems to be another peak at right-hand end of the signal. I have already checked the MS and confirmed that there ...
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1answer
56 views
Can the paper in thin layer chromatography be any type of paper?
I'm doing a chemistry chromatography lab that wants me to recreate anything I want. I decided to measure how far a pigment goes in each color for the same brand, but I'm stuck at the paper part. I ...
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1answer
87 views
Normal phase dead time marker
In reverse-phase HPLC, Thiourea, Uracil, Nitromethane or $\ce{KNO3}$ are used as dead time markers because of their polarity and therefore weak interactions with the stationary phase. However, I could ...
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Why is Retention factor for Iodide greater than Bromide?
I did a separation of Bromide and Iodide ions using paper chromatography technique for 0.3% solutions of Bromide and Iodide of sodium. I got the Retention factor equal to ~0.71 for Iodide and ~0.47 ...
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1answer
58 views
Is it possible to functionalize silica gel as Activated Carbon can be? How?
Activated carbon and Silica gel both have a high surface area.
If I understand correctly it is possible to trap stuff inside activated charcoal pores to give it specific retention properties (by ...
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How does a lipid such as PC, with N(CH)3+ bind to a silica gel with many OH groups?
I'm trying to determine the polarity of two lipids(phosphatidylcholine (PC) and phophatidylglycerol (PG)) and my experimental results indicate that that PC is the most polar, yet when I look at their ...
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Comparing retention time of acetic acid, salicylic acid and acetylsalicylic acid in HPLC
I want to compare retention time of acetic acid(AA), salicylic acid(SA) and acetylsalicylic acid(ASA) in HPLC. What are the factors do I have to consider when comparing? Considering dipole moment only,...
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37 views
Can acetone be used as a GC–MS solvent for a sample containing ammonia?
Сan acetone be used as a GC–MS solvent/diluent for a sample containing ammonia? Will there be a reaction between these two species?
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1answer
183 views
Source for UV cut-off values of buffers
When I want to check a $\mathrm{p}K_\mathrm{a}$ value I look it up in CRC Handbook. Is there such source for UV cut-off values of various buffers?
Usually books in chromatography contain tables with ...
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3answers
195 views
Why do I see two peaks for methyl salicylate in my GC–MS spectrum?
I ran a neat sample of methyl salicylate (CAS: 119-36-8) on the GC–MS and used $m/z~120$ as the quantifier and $m/z~92$ and $152$ as qualifiers. Below is the SIM spectrum for these ions, with two ...
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Bad repeatability of GC-FID meassurements
I am new to GC-FID and I am struggling with calibration curve. And I am strugling with the repeatability of measurements. One vial measured 5× in a row provides results which differs even 2 orders of ...
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2answers
140 views
How the plate height is assumed to be the standard deviation?
Fundamentals of Analytical Chemistry book states that the plate height can be thought of as the length of column that contains a fraction of the analyte that lies between $L$ ...
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Can I use silica gel to perform column chromatography at home?
While this question has been asked and answered, it may indicate that a column chromatography qualitatively is possible. At home, is it possible after collecting silica gels from small bags of them ...
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1answer
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What are quantifier and qualifier ions in mass spectrometry data for GC-MS or LC-MS?
I've read that one should pick an ion peak that is unique to an analyte for quantification purposes and then pick at least 2 qualifier peaks and use their ratios to identify the analyte (or avoid ...
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1answer
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Retention Time Change in Reversed Phase Chromatography (revised)
I previously learned in books that in reversed phase chromatography, retention time changes depending on the content in mobile phase, which means as the polarity of mobile phase increases, retention ...
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3answers
788 views
What would a (gas) chromatogram look like if two compounds have the same retention times? [closed]
In gas chromatography, the number of peaks represents the number of compounds in an unknown sample, as retention times for each component differ.
But what would happen if two components have the same ...
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1answer
44 views
How do I interpret the results of this chromatogram and does it tell me about the compounds' polarities?
I am reading this journal article which discusses using high-performance liquid chromatography (HPLC) to separate dyes from wine. Here are the relevant facts about the experimental setup:
Two mobile ...
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1answer
238 views
ELSD detection principle
While documenting myself on the detectors used in HPLC, I came across one that I did not know: ELSD.
I understood that the sample with the mobile phase was nebulized at the column outlet but I do not ...
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1answer
55 views
What are the benefits of using zero capillary voltage for discarding fractions in LC–ESI–MS/MS?
In the second episode of The Association for
Mass Spectrometry & Advances in the Clinical Lab (MSACL) podcast, namely Getting going with mass spectrometry : Josh learns chromatography (aired 2021-...
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1answer
43 views
How can over grinding lead to reduced API extraction in HPLC analysis?
I am looking for some advice regarding particle size distribution (PSD) & how this can be affected by grinding a tablet.
During an assay by HPLC, the method requires grinding of a tablet before ...
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Right conductivity of protein sample for Protein A purification of human IgG?
A sample from a cell culture has some IgG and this is to be purified using protein A chromatography. Based on the chromatography handbook from GE-Healthcare/Cytiva, the protein sample should have &...
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2answers
719 views
HPLC: Peak height calculation
I am trying to implement a small python script to detect peaks and calculate the corresponding area. The y-values are in mAU and x-values in minutes but there are some unit conversions in most HPLC ...
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1answer
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Chromatography- why tM is separated from other peaks? [closed]
tM in Chromatography is the time of exist mobile phase. But, the mobile phase exist together with all the compunds that tasted in the process. So, why in the graph of signal to time we can see a peak ...
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1answer
221 views
What is "silanol activity"?
In a previous post about how pyridine failed to move much from the baseline of a TLC, I was told to look into "silanol activity". However, I was unable to find a textbook-style description. ...
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Salting out worsens extraction efficiency
I'm currently writing a thesis about using dispersive liquid-liquid microextraction DLLME for extracting nitramines from aqueous solutions. We've been using octan-1-ol as the extractant and HPLC for ...
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1answer
72 views
Does using same calibration curve for chemical analysis introduce correlation in sample error/uncertainty values?
I am using a hypothetical case to explain my question
Let us consider a chemical analysis method A (using a certain instrument), which is used to quantify the value of a particular species b. ...
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1answer
47 views
Compound Polarity Lookup
I know from the literature that the following compounds have decreasing polarity: Rosmarinic Acid -> TMF -> Sinensetin and I guess comparing compounds of ...
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1answer
361 views
Determining the mass of a substance using calibration curve produced by HPLC
I hope everyone is doing well and safe! Yesterday, I was fortunate enough to be taught about how to read a chromatography calibration curve through this stackexchange! Special thanks to those who ...
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How to read a chromatography calibration curve?
I am a high school student who has been studying a bit of chromatography. I came across calibration curve during class and I trying to figure how to read it and use it? I have no clue how to read off ...
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1answer
218 views
Modifying a TLC mobile phase in order to increase the RF values [closed]
You are running a TLC using 50% ethyl acetate in hexane and find the resulting $R_f$ values are too low. How would you modify the TLC mobile phase in order to increase the $R_f$ values?
Would the ...
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1answer
377 views
Calculating the concentration of product in a solution based on the peak area of HPLC [closed]
Please help me resolving the following:
A sample solution, $\pu{0.24mg/mL}$ Compound A, is exposed to heat to form Compound B. From HPLC data report I have peak area for Compound A and Compound B. ...
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2answers
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The best chromatographic technique to analyse a solution of benzene, toluene, and ethylbenzene in n-hexane
What is the best chromatographic technique to analyse a solution containing benzene, toluene, and ethylbenzene in n-hexane?
Is gas chromatography (GC) the best way to analyse this solution? Or is ...
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1answer
151 views
Types of chromatogram shapes [closed]
I'm trying to generate a testing set of different chromatograms to check peak detection (whether peak boundaries are detected correctly) and smoothing algorithms. Currently I'm figuring out which ...
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37 views
Column Dispersive Mass Balance analytical / numerical solution
Is there any analytical solution for the most common expression of column mass balance:
$\dfrac{\partial C}{\partial t} + \left(\dfrac{1+\varepsilon}{\varepsilon}\right)\dfrac{\partial q} {\partial t} ...
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1answer
175 views
Stronger ESI signal for deuterated substances
I observe a constant phenomenon in my ESI measurements, which indicates that deuterated substances give a stronger signal than the same substance in non-deuterated form. Unfortunately I can't make any ...
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1answer
410 views
Is there any database, or reference, for retardation factors (Rf)? [closed]
I'll like to compare the Rf of myrcene, obtained in Thin Layer Chromathography, for different species. Toluene:Ethyl Acetate (97:3) would be fine, but is not a necessity.
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1answer
210 views
Theoretical plates in Plate theory of chromatography
In "Chromatography theory" by Scott and Cazes,
The plate volume is given as ($v_m+Kv_s$) where $v_m$ and $v_s$ are the volume of stationary and mobile phase in the column and $K$ is the ...
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1answer
95 views
How do I analyze 17 different gases from a sample?
I am designing a test setup in which I heat a battery until it releases its gases, and I need to analyze the composition of the fumes. Below is the list of gases that are believed to be present in the ...
