Questions tagged [analytical-chemistry]
The branch of chemistry concerned with identifying and quantifying the chemical constituents of matter.
960
questions
3
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Wave Dispersive X-ray Fluoresence and Bragg's Law
Thermo Fisher website explains that "WDXRF uses crystals to disperse the fluorescence spectrum into individual wavelengths of each element, providing high resolution and low background spectra ...
2
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0answers
31 views
How would I find what specific wavelength I need to measure for a specific chemical in spectrophotometry (calcium perchlorate)?
I am currently doing a research project, and for it, I would like to use a photospectrometer to find the concentration of Calcium Perchlorate in my sample solutions. My current method of data ...
0
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32 views
Applied potential to Saturated silver electrode
I recently did my first cyclic voltammetry. I used a saturated silver reference electrode and two platinum working and counter electrode. This was done with an IKA electrasyn 2.0 device, my parameters ...
3
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0answers
22 views
How to adjust selectivity of gas-permeable PDMS membranes for environmental applications?
I have an idea about making an environmental sensor that uses a gas-permeable membrane (GMP) and how its probe could be submerged in a water source with an off the shelf gas sensor.
So far, my ...
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0answers
54 views
Mass Spectrometry
I am struggling with the problem below :
"When a sample containing a mixture of
isotopes is introduced into a mass spectrometer, the
ratio of the peaks observed reflects the ratio of the
percent ...
-4
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0answers
38 views
What is the structure of this molecule given its NMR and IR data? [closed]
The formula of the molecule is C7H6O3. According to its IR spectrum, it is a carboxylic acid. Its C NMR spectrum consists of 5 peaks, so there are 5 different carbons. Its H NMR spectrum consists of 4 ...
0
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0answers
51 views
Testing for lead in alcohol
I want to test for lead in alcohol rather than water. The reason for this is that I have many antique crystal decanters and flasks. Crystal is made with lead oxide (PbO) added to the glass.
Normally ...
0
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2answers
46 views
Precipitation of equimolar amounts of chloride and bromide [duplicate]
I was just wondering about the following situation; if we had a solution containing 0.1M bromide and 0.1M chloride ions, and treated it with excess silver nitrate, what would happen and would ...
2
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0answers
25 views
Chemical analysis of campholene nitrile
I have a problem. I am synthesizing an organic compound called campholene nitrile (2,2,3-trimethylcyclopent-3-en-1-ylacetonitrile).
I need to analyze it. But there's a problem. I do not work for a ...
1
vote
1answer
57 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 ...
5
votes
1answer
55 views
The relationship of the osmotic pressure of a polymeric solution and its the molecular mass
Why is the osmotic pressure of a polymeric solution decreases when the molecular mass is increasing?
I am honestly unsure if the above statement is true, at least it seems to me to be true. When I ...
1
vote
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 ...
0
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1answer
50 views
Finding the percent of light absorbed by a sample [closed]
I have an absorbance of $0.266$ and need to find the percent of light absorbed by the sample. Is it found by just turning it back into transmittence% and subtracting 1? So by that, would it be $(1 - 0....
2
votes
0answers
44 views
Why do the splitting pattern on my NMR differ from those stated in literature?
I attempt the synthesis of p-toluic acid using the Grignard reagent (prepared from 4-bromotoluene and Mg) and dry ice. The NMR of the raw product was recorded using $\ce{CDCl3}$ and a peak showing ...
-1
votes
1answer
32 views
Why in calculating 25 mM of Tris HCl the answer in gram is automatically refer to the gram in 1000 ml [closed]
In the lab class,my teacher told me that the answer i get in grams is automatically the grams in 1000 ml.
Why is it possible without we doing anything the grams i get automatically the grams in 1000 ...
1
vote
1answer
44 views
Understanding weak acid-strong base titration
Today I stumbled across a website which defined the titration of weak acid and strong base as the following:
"The titration of a weak acid with a strong base involves the direct transfer of ...
1
vote
1answer
83 views
How Does Differential Scanning Calorimetry (DSC) Differentiate Between Exothermic and Endothermic Changes?
In DSC, heat flux difference between sample and reference is measured as function of temperature while temperature of sample and reference are maintained the same. DSC is often used for polymer ...
10
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3answers
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What is the English translation of the German term "Aufschluss", a method to get insoluble analytes into solution?
In the analysis of solids, often the first step is to get the analyte into solution in some form. Sometimes, solids are heated in the presence of acids (acid digestion) or molten salts (sample ...
0
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1answer
45 views
Displacement of salts due to higher solubility
I was wondering why mixtures of salts in the same solution precipitate excactly in order of their solubilities. Imagine a solution with NaCl, NaBr, NaI in equal moles. If AgNO₃ solution is now added ...
0
votes
1answer
27 views
Approximation for pH calculation with diluted acids in weak-strong titration curve
I was wondering how one could calculate small pH changes in titrations with dilute acids.
As we know, usually we approximate the pH by saying that the conversion is quantitative. For example, when we ...
0
votes
1answer
35 views
How do I quantify a mix of SiO2 (amorphous), silicon (amorphous, polycrystal), graphite (dust) in a solid sample?
I collected solid samples from a plugged tube-side of a heat exchanger. These deposits include compounds such as hexachlorodisilane, hexachlorodisiloxane, pentachlorodisilane, graphite dust and ...
2
votes
2answers
117 views
Elucidating an unknown compound using 1H- and 13C-NMR spectral data [closed]
I am currently struggling with the following NMR spectrum for this compound:
I know for sure that we should multiply the integrals of the hydrogen atoms by four, and that the compound contains at ...
3
votes
1answer
78 views
Is absorbance from HPLC UV detector comparable between runs?
Suppose that I have an HPLC with a variable wavelength UV detector, as well as two pure protein samples that differ by a point mutation (otherwise same concentration, extinction coefficient, buffer ...
3
votes
0answers
33 views
Characteristics of cations with KCN and excess KCN
How many cations from $\ce{Ag+,Pb^2+,Cu^2+,Cd^2+,Fe^2+,Fe^3+}$ form precipitate with $\ce{KCN}$ but also get dissolved in excess $\ce{KCN}$?
I have just been introduced to Qualitative Analysis of a ...
2
votes
1answer
49 views
Determining ppm concentrations from food label information for ICP-OES analysis?
Overview: I am looking to determine what ppm values of trace metals are present in a particular formula while considering digestion, dilution, and detection limits for ICP-OES. For example, one ...
0
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0answers
12 views
Quantifying Residual Chlorine content in ppm in a Hydrocarbon
I have a process troubleshooting application where we need to quantify the amount of residual chlorine content in a liquid Hydrocarbon sample since this chlorine is a poison for the downstream ...
0
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1answer
40 views
Mass spectrometer Ions with same mass/charge ratio but different charges [closed]
The mass spectrometer identifies ions based on mass/charge ratio. What happens when two ions have the same mass/charge ratio but different charges or masses?
0
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0answers
21 views
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 ...
0
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0answers
96 views
How much Na2O (from NaOH) do I add to sodium silicate with a weight ratio of SiO2/Na2O = 2.34 to get the solution to a weight ratio SiO2/Na2O = 1.9?
There is some confusion in industry as sodium silicate is made with NaOH but given a ratio with respect to Na2O (i.e. SiO2/Na2O not SiO2/NaOH). I presume it follows from this equation:
2NaOH -> ...
0
votes
1answer
30 views
In electrophoresis of amino acids and dipeptides, how can I rationalize the observed mobilities?
For part b(i) why is the spot tyrosine? I know tyrosine has an overall -2 charge while phenylalanine has an overall -1 charge. However, phenylalanine has a smaller Mr so shouldn't it travel faster? ...
4
votes
1answer
146 views
Relative abundance of mixture in mass spectra
In MS, as far as I know, the $y$-axis, relative abundance means the number of ions detected. Then does ratio of heights of two peaks stand for molar ratio, not mass ratio
For example, given that I ...
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1answer
62 views
Fields of Study in Chemistry [closed]
Is there a standard classification scheme for different areas of study and research for chemistry like mathematics has Mathematics Classification Scheme (MSC)?
5
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2answers
437 views
Is there a simple way to distinguish grades of purity for copper metal?
Is there a simple way to distinguish different grades of fine copper purity (on a trace metal basis) that can be carried out in a small lab?
Specifically, I would like to be able to differentiate 4N, ...
2
votes
1answer
51 views
In cation analysis, can reagents of higher group precipitate lower group cations?
My teacher told me that Al$^{3+}$ and Zn$^{2+}$ hydroxides are frequently precipitated together and that is why we have to be careful about the concentration of base (NH4OH) added.
Does this mean that ...
0
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0answers
48 views
Calculating the weight of a chemical within a liquid mixture
I want to know the weight of ethylene glycol in a mixture of Shellzone 50/50 Antifreeze. I have taken the mid-range of 40-60% from the safety data sheet(SDS) for the amount of ethylene glycol in the ...
2
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0answers
43 views
Preparation of isotopic CO2 standards from Sn-encapsulated CaCO3
I wish to prepare isotopic CO2 gas standards for highly 13C enriched CO2. The CO2 concentrations will be ~1000 ppm, with the balance either N2 or zero air.
My plan is as follows:
Encapsulate labeled ...
3
votes
2answers
85 views
Hydrogen concentration measurement without gas chromatography
Please suggest ways to measure $\ce{H2}$ concentration in a sample of gas containing $\ce{HCl},$ $\ce{CH4},$ $\ce{N2},$ $\ce{CO2}$ and trace amounts of chlorosilanes without GC.
The problem is that I ...
1
vote
1answer
38 views
Association constant calculation in 3:1 complexes
I have a question about calculating the association constant related to 3:1 host-guest complexes. I am using the UV-vis titration method, I know the stoichiometry from the molar fraction method which ...
4
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0answers
61 views
Why wouldn't a standard addition fluorometric method return the same starting concentration of a solution used to make the standards?
I am trying out a new standard addition method and having some very basic problems. I am hoping someone could point me in the right direction.
I am using a fluorometric method to quantify ammonium in ...
2
votes
1answer
60 views
How would I go about developing a linker molecule that binds SiO2?
I'm trying to develop a molecule that acts as a bridge between a protein and surface of SiO2 lattice. The end that binds the protein is simple and easy but I can't figure out a way to draft up how I ...
3
votes
1answer
61 views
pH meter mechanism - connecting potential differences
This question was asked here: pH probe bulb - what is happening within the glass? and How does a pH glass electrode work?.
But, the mechanism remains unanswered. How does a potential difference ...
2
votes
1answer
47 views
How to account for dilution in the sample solution when reading calibration standards?
I have been provided the following table of calibration standards from an ICP-MS experiment.
(Some text is in German, I am operating in a location where DIN standardization is ubiquitous)
I ...
1
vote
0answers
135 views
Does formaldehyde and ethylene glycol give positive Fehling's test?
Fehling's test follows a single electron transfer mechanism, with electron transfer form the substrate to $\ce{Cu^2+}$, which forms $\ce{Cu^1+}$finally giving reddish brown precipitate of $\ce{Cu2O}$. ...
2
votes
0answers
99 views
UV-spectra of benzene
I measured the UV-absorption-spectrum of benzene vapor as well as solved in methanol and cyclohexane. The absorption of the vapor was much stronger than in solution. I also noticed that the peaks get ...
3
votes
1answer
78 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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1answer
77 views
Finding out the composition of a sample in analytical chemistry without knowing what to test for [closed]
I am little new to analytical chemistry, but after reading up on it, I realised that most analytical procedures need you to know what to test for beforehand.
May I know, given a sample of material G, ...
0
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0answers
27 views
Can ethanol and heat during distillation cause degradation/dissolution of vinyl tubing leading hot vapors of the distillate to the condenser?
I'm a chemist and a qa lab, and we occasionally test herbal remedy products from one of our customers for alcohol content using a distillation, then using the specific gravity of the distillate to ...
3
votes
0answers
42 views
Why neglecting Bradford Solution Volume in the assay?
I would like to know why do we not need to take account of Bradford agent solution in dilution calculation?
For example, $\pu{2.5 \mu g mL-1}$ BSA will calculate from $\pu{0.4 \mu L}$ of $\pu{1 mg mL-...
5
votes
1answer
203 views
Calculate Michaelis-Menten constant of enzyme catalyzed reaction
I have:
$$\begin{array}{c|c}
\dfrac{v }{ [S]}/\pu{s^{-1}} & v \cdot 10^2/\pu{mol dm^-3 s^-1} \\ \hline
0.257\ & 5.15\\
0.895 & 4.48\\
2.00\ & 3.35\\
3.59\ & 1.8\\
4.82\ & 0....
2
votes
1answer
56 views
Why is the silver salt ammoniated to form the Tollen's reagent? [duplicate]
When doing a distinguishing test between aldehydes and ketones using Tollen's reagent, is it necessary to convert $\ce{Ag+}$ ions into $\ce{Ag(NH3)2+}$ in order to oxidize the aldehyde?
