Questions tagged [analytical-chemistry]
The branch of chemistry concerned with identifying and quantifying the chemical constituents of matter.
813
questions
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Methods used to compare two spectra in order to determine the effects of irradiation of sample
I would like to compare two absorption spectra (or interferograms) and conclude whether between these two there are statistically significant differences at particular wavelength intervals. At the ...
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2answers
45 views
A Spectrophotometric technique to evaluate Vitamin C concentration in Citrus Fruit
Is there a visible spectrophotometric technique that can gage the concentration of vitamin C in solution? I plan on boiling different citrus fruit in water, and taking aliquotes of the boiled solution ...
2
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1answer
81 views
Detectable elements using flame AES
I've been looking for extra information concerning flame atomic emission spectroscopy. I need a clear overview of which elements are detectable with this technique, but I can't find anything because ...
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0answers
15 views
antibody-drug conjugation calculation [closed]
Can you please tell me how to calculate the number of moles of drug needed if I want to react 20 molar excess, mol wt known of the drug to an antibody whose volume and concentration is known ?
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40 views
Why cupric ion oxidises iodide to iodine
I have learnt in the qualitative analysis of cupric ions that upon treating its aqueous solution with excess $\ce{KI}$, triiodide ions are formed which can be further tested using starch.
The ...
2
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1answer
52 views
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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23 views
XPS Analysis: How do they identify oxidation states based on electronic levels? [closed]
I am doing an XPS analysis of some nanoparticles and I have read that in order to understand the analysis it is necessary to understand all the chemistry around an atom, which is what I am doing.
In ...
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0answers
29 views
Reason for no change in electrode potential in reference electrodes
Reference electrodes such as the saturated calomel electrode and silver chloride electrode have a constant potential because the $\ce{Cl-}$ concentration (or, to be more precise, the activity) is ...
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34 views
Stubborn CuAAC reaction as derivatization for ESI-MS
Problem description
I have a substance that is extremely non-polar and therefore does not ionize in the ESI source, which makes it impossible to quantify small amounts. The substance contains only two ...
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1answer
44 views
Conductometric titrations: dilution effect
Since the conductivity of a solution changes linearly with the electrolyte concentration, during a conductometric titration the volume increases with each addition of the titrant aliquot. For this ...
4
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1answer
66 views
Tollen's Test with Salicylaldehyde
I have read that Tollens' test is given by aldehydes. The aldehyde is oxidised to a carboxylate ion and silver is deposited.
My teacher had given me notes which pointed that salicylaldehyde does not ...
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39 views
Estimating amount of Hydrogen Sulfide released into the air? and how fast does gas expand when it is produced?
I unknowingly exposed myself to hydrogen sulfide gas and am trying to figure out how much Hydrogen Sulfide gas i may have been exposed to.
I mixed .5 grams of Sodium Sulfide Nonahydrate into a ...
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1answer
25 views
is there any single non toxic compound/chemical which can give direct color change by react with pure ethanol? [closed]
I want single compound/reagent/chemical/paper/dye which gives colored reaction with pure ethanol and it should be non toxic as well.
By simply adding/diping it to pure ethanol it should give color ...
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1answer
63 views
Caustic and Toxicological Determination [closed]
I need to determine whether or not a product that I am importing is "toxic" and or "corrosive" as defined below. But I am a chemistry n00b ā that is to say I have virtually zero ...
1
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1answer
58 views
What is peak identification? [closed]
I am sorry if this question is too vague, but what is peak identification? I am working with a chemistry professor to program an autosampler and he says he would like to "program the robot for a ...
3
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1answer
80 views
What is the purpose of subtracting the blank when constructing an analytical calibration curve?
When building a calibration curve for quantification of some analyte using any spectroscopic technique, what is the purpose of subtracting the intensity of the blank from the intensity of each point ...
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1answer
41 views
Do pipettes always outclass glass syringes?
I was previously working in a lab preparing lots of samples for gas chromatography that exclusively used glass pipettes and was able to get really high precision between replicates. Now I'm working on ...
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0answers
41 views
Protonated forms of EDTA and their constants of formation with metal ions
It is widely known that the fully deprotonated form of EDTA (usually written as Y4-) is the only form that is significantly involved in complexation reactions. From what I have read, this accounts for ...
2
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1answer
71 views
Is reverse osmosis a fancy term for filtration?
In Reverse Osmosis (RO) systems, the water to be purified is pushed against a semipermeable membrane and comes cleaner the other side, the path of water is the reverse of regular osmosis, hence the ...
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125 views
Differences in Novichok agent mass spectra
As we have all heard, in 2018, a series of poisonings with a nerve agent alleged to be of the Novichok series was carried out on British soil. It is claimed that the agent used was A-234. However, a ...
2
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1answer
58 views
Make very accurate solutions without weighing
I am currently facing a hen-egg problem. For a LC-MS method development I need to prepare reference solutions which are used to calibrate the method. Since the method is to be used for quantification ...
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1answer
52 views
Lewis acidity order of Aluminum Halides [closed]
There is a similar question already on StackExchange which was not satisfactorily answered. So I am asking it again. I am unable to find this information in any book.
Link to the other question:
...
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66 views
How do scientists know they have discovered an element? [duplicate]
I have a background in math not chemistry and perhaps this question is inappropriate but I will try. I read that after pitchblende was discovered Martin Klaproth in 1879 a latter date discovered that ...
4
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1answer
165 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
48 views
How much NaOH I have to add to increase pH?
I'm stuck in solving this problem. I have two solution of $\pu{5 M}$ $\ce{H2SO4}$ that needs two consequential $\mathrm{pH}$ increasing: the first from the natural $\mathrm{pH}$ of $\pu{5 M}$ $\ce{...
3
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1answer
170 views
Identify the structure of compound with CāHāā formula using IR and NMR data [closed]
Use IR and NMR data to define the structure of the molecule, the formula of the given structure $\ce{C9H10}.$
On what basis do we conclude that its structure is that (the answer) only? On what points ...
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33 views
By what mechanism is ammonia liberated in the Kjeldahl Method of protein determination?
I was looking at the Kjeldahl digestion of proteins, and I very much do not understand the mechanism by which it works. The reaction scheme is as follows:
$$\ce{Protein-N + H_2SO_4 ->[K_2SO_4, ...
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1answer
52 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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0answers
51 views
Can analytical precision be finer than a lower detection limit?
Can analytical precision be finer than a lower detection limit?
For example, if the lower detection limit of an analytical method is reported as 0.010 ppm. Is it possible to have an analytical ...
3
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0answers
66 views
Peak broadness and artifact peaks in intact antibody MS?
I am having an issue where the MS for my antibody (intact/nonreduced, deglycosylated by PNGase) shows multiple clusters of what appear to be ghost peaks after deconvolution, and the main peak is ...
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0answers
22 views
Free refined value in Rietveld
I have a question about Rietveld refinement
The author of this paper claimed that the free refined CN ligand is 1.081.
However, they does not show how they got that number. They stated it was based ...
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1answer
28 views
Elution and void volumes in a gel chromatography experiment
I was using gel-filtration for separation Hb from xylene cyanol FF with Blue Dextran to determine the void volume. Sephadex G-25 is stationary phase, and mobile phase was buffer $(\pu{0.020 mol dm-3}$ ...
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1answer
94 views
Determining stoichiometry in ICP-OES data analysis
I have questions regarding data analysis for an inductively coupled plasma (ICP) experiment from a paper by Wang et al. [1].
The generic formula for the chemical compound is $\ce{Na_{2āx}Fe[Fe(CN)6]}$...
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63 views
Is there a reason why we add (CH3CSNH2) but not H2S in qualitative group analysis? [closed]
Brief question: In $\ce{Cu}$-$\ce{As}$ group analysis we are expected to add thinoacetamide to make a precipitate with sulfide. Can we use $\ce{H2S}$ instead?
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1answer
67 views
Qualitative Analysis- Distinguishing between two ions or two salts [duplicate]
I know my question is going to be quite below the level of this site but I am 1st grade in university and I can't understand anything.
I am going to give an example from the book: distinguish ...
1
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1answer
42 views
Can I make UV-Vis calibrant in the lab?
I have a Thermo Nanodrop 1000 spectrometer that I have reason to believe is out of calibration. After consulting the manual, it appears as though there is a way to check the calibration of the ...
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36 views
How much glucose oxidase is usually deposited on a glucometer strip?
The concentration of serum glucose is on average roughly around 5 mmol/L and let's say a typical blood droplet applied to a glucometer is 1Ī¼L. We are therefore depositing 5 nmol of glucose on the test ...
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1answer
49 views
Creating a 10 ppb Lead Nitrate Solution
Iām trying to make a 10 ppb Lead Nitrate solution as part of a concentration calibration step for a Beer Lambertās Law experiment. I plan on performing a dilution in three steps. The calculations have ...
2
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0answers
27 views
Dissolving hydrated vs non-hydrated salts
in chemical catalogs, salts are often sold in hydrated and non-hydrated versions. Like sodium sulfate anhydrous and sodium sulfate decahydrate. I tried dissolving the anhydrous and it didn't ...
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0answers
19 views
How does the purification until analytical grade work? [closed]
What are some industrial methods used for puryfing organic solutions, like toluen, until it is analytical grade? Im not looking for details just some names and somewhere to keep reading
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48 views
The IR/ H-NMR analysis of benzophenone?
I think I have figured out the IR spectrum for benzophenone. Would it be that the sharp peak in the middle (1700 cm^-1) is for the ketone and the little peaks pass 2900 cm^-1 rang are the sp2/sp3 ...
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0answers
23 views
Disadvantages of SIM vs TIC in GC-MS [closed]
In GC-MS what are the relative advantages/disadvantages of using Selected-Ion Monitoring (SIM) vs using Total Ion Chromatograms (TIC)?
I know that SIM offers a better S/N ratio, however if the S/N is ...
0
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1answer
119 views
The H NMR analysis of the hydrogens in salicylic acid
I am currently working with an unknown and from the IR spectrum I was able to figure out that the compound I am working with is salicylic acid.
I am looking at the H NMR, but I am a bit confused on ...
3
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1answer
39 views
Why there is no need for reference standards in High Resolution Mass Spectrometry (HRMS)
I have a question about HRMS (High Resolution Mass spectrometry). HRMS is a powerful technique that can discriminate between possible target compounds without the need of reference standards, unlike ...
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0answers
22 views
Why is a current in capillary electrophoresis unstable?
Why can be a current unstable in CE and how can I fix it? I changed a buffer, changed a capillary, cleaned electrodes. I sometimes hear a crackling noise inside the CE. The method and buffer which I ...
0
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2answers
98 views
How to determine the iron content of a screw?
In Analytical Chemistry, I was asked to determine the iron content of a screw.
I thought it could be solved in the following way:
Treat the screw with a solution of sulfuric acid or hydrochloric ...
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Explanation of Specific Chemical Shifts on an H-NMR Spectrum
Recently, I've been looking into chemical shifts on H-NMR Spectrums and I came across a graph I didn't quite understand...
As you can see from the spectrum attached, the signal emitted from the ...
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2answers
58 views
Can one exclude calibration points using a combination of permutation testing and a non-parametric test statistic?
I work in bioanalytical chemistry. I have used an analytical instrument (LC-MS) to measure the response (peak area) of several compounds spiked in to equivalent samples at known concentrations. Each ...
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2answers
66 views
Titrating iodine starch solution with sodium thiosulphate - Colour change
I investigated two mixtures with different solvents, one with water and one with n-heptane. Both contained iodine $\ce{I2}$ as a solute. To both solutions I added a bit of starch.
As I remember this ...
2
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1answer
102 views
How to test for and remove lead(II) sulfate from a sample of 1 M sulfuric acid?
If you had a clear, colourless sample of dilute sulfuric acid and suspected lead contamination, probably lead sulfate, how would you test for this? It's solubility is low in sulfuric acid solutions, ...
