Questions tagged [analytical-chemistry]

The branch of chemistry concerned with identifying and quantifying the chemical constituents of matter.

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1answer
119 views

Plotting the data using Beer-Lambert law [closed]

For the spectroscopy lab we had a stock dye ($\pu{1.00E-4 M}$ Erioglaucine Blue) that we had to dilute. We had to dilute $\pu{1 mL},$ $\pu{3 mL},$ $\pu{5 mL},$ $\pu{8 mL},$ and $\pu{10 mL}$ in $\pu{...
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2answers
1k views

How to differentiate between iron and sodium flames?

According to my textbook, when a flame test of an iron salt is performed, it produces an orange, mostly yellow flame. Sodium salts also produce a yellow flame. As the colours of these two flames are ...
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0answers
17 views

Performing a Redox Titration on a Vitamin C Sample Solution Containing Cellulase enzymes

I was wanting to performing an Iodometric Redox Titration on a Vitamin C sample solution created from allowing diced citrus fruits to sit in a water + cellulase solution. Because vitamin c is water ...
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0answers
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How does Mars rover Curiosity's ChemCam's infrared laser produce a 100,000 K plasma plume (kT = 8.6 eV)?

Mars rover Curiosity's ChemCam uses a pulsed diode-pumped solid-state laser (DPSS) at 1064 nm to excite material on the surfaces of rocks up to 7 meters away, and a large aperture telescope to collect ...
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1answer
58 views

% coefficient of variation (%CV) for log-linear and log-log regression (calibrations)

I have a data set comprising the peak areas of an analyte measured in spiked calibration samples at 'known' and different concentrations levels. For each concentration level I have 5 replicates. My ...
4
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2answers
261 views

Do both iodine and potassium iodide turn dark in the presence of starch?

I will do a titration to standardise a solution of sodium thiosulfate with potassium permanganate solution and potassium iodide solution. My book says that when the potassium permanganate solution ...
0
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1answer
37 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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4answers
338 views

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
41 views

Confused on the peak intensities in this mass spectrometry problem

A problem from Introduction to Spectroscopy by Pavia et al. [1, p. 137]: *4. An unknown hydrocarbon has a molecular ion peak at $m/z = 84,$ with a relative intensity of $31.3.$ The $\ce{M + 1}$ peak ...
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1answer
26 views

Is Cu stable as Cu(H2O)2+ for determination on MP-AES?

I have an unknown sample of mineral which I need to dissolve in nitric acid. I need to analyze $\ce{Cu}$ from it on MP-AES. Do I need to add $\pu{1ml}$ of $\ce{HCl}$ to stabilize $\ce{Cu}$, or it is ...
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1answer
67 views

How to oxidise iron in spinach to iron(III)

I'm planning an experiment to test the iron content of spinach. I plan to ash spinach, grind it, then dilute it in a solution which would hopefully oxidise the iron ions in it to $\ce{Fe^3+}.$ This is ...
6
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1answer
114 views

Behavior of Natural Abundance and Mass Spec Ratios

The presence of sulfur in a mass spec is 96% and 4%. I believe this to be because the natural occurrence of sulfur isotopes are within these proportions. However, chlorine behaves in a 66%/33% ratio ...
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1answer
68 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
115 views

Are there methods for iron content determination in spinach that do not require thiocyanate?

I am looking for a way to measure the iron content of spinach for a chemistry experiment. Unfortunately I am not sure that thiocyanate will be available and I'm therefore trying to find an alternate ...
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0answers
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How to calculate volume of sample needed given an endpoint?

I did an EDTA titration where I poured $\pu{5mL}$ of hard water, $\pu{25mL}$ of deionized water, $\mathrm{pH}$ buffer, and an indicator into a flask. My endpoint was $\pu{10.77mL}$. However, how ...
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1answer
178 views

Why is the test for sodium as dihydrogen antimonate so specific?

I have been attending lectures of salt analysis in my college. We are at group 6 cations or also known as group zero cations, namely $\ce{NH4^+}$, $\ce{K^+}$, $\ce{Na^+}$, $\ce{Mg^2+}$. The lecturer ...
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1answer
120 views

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
46 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
44 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
53 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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0answers
30 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 ...
4
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1answer
57 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
47 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
87 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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0answers
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
28 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
64 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 — that is to say I have virtually zero ...
1
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1answer
59 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
84 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
42 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
45 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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0answers
189 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
60 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
66 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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0answers
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
167 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
49 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
179 views

Identify the structure of compound with C₉H₁₀ 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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0answers
35 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, ...
1
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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
67 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
30 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 $(\pu{0.020 mol dm-3}$ ...
6
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1answer
96 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 $\ce{Na_{2−x}Fe[Fe(CN)6]}$...
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0answers
64 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?
1
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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
45 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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