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Questions tagged [analytical-chemistry]

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

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Iodine/iodide electrochemistry help

I have an electrochemistry experiment with iodine in solution. I am initially wanting to quantify the iodide in solution and extrapolate the concentration of I2(aq) and I3-(aq) in solution from this ...
ChemStudent24's user avatar
7 votes
1 answer
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Why are amber bottles used to store Water for HPLC?

Image Source: https://www.calpaclab.com/water-hplc-spectro-grade-4-liter-bottles-case-4/ted-ws2211-001 When ordering HPLC/Spectro grade Water for HPLC from certain vendors(not all), it comes in an ...
Ronith's user avatar
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What test would give me a qualitative recognition of the presence of benzene in methylphenidate?

I need a couple of tests to recognize the presence of benzene in my compound (methyphenidate). I've looked into tests with bromide or Freidel-Crafts reactions but I'm not sure if both or neither would ...
Lucy's user avatar
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6 votes
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How to draw complex speciation diagram?

Given complexation reactions for a specific Metal $X$ and Ligand $L$: $$ XL_i + L \rightleftharpoons XL_{i+1}, k_i = \frac{XL_{i+1}}{XL_i \cdot L} $$ It's usual to draw a speciation diagram such those:...
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Why does my EBT indicator not turn pink in EDTA titration?

I am working on finding the calcium content lost upon cooking kale, using complexometric titration. For my indicator, I am using Eriochrome Black T indicator (EBT; solid form, not the liquid). ...
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1 vote
1 answer
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Experimental determination of ring strain energy

For my thesis I am looking to expand a part of it to include experimental means of calculating ring strain, thus far I have calorimetry covering heats of combustion and hydrogenation as well as ...
nking1390's user avatar
3 votes
1 answer
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Why is there a [M-1]+ in lieu of a parent signal in the Mass Spectrometry of Primary Alcohol Chains?

I have looked virtually everywhere for an explanation of why alcohols EI GC-MS always have a more prominent M-1 signal over a Parent chain signal--sometimes no parent signal at all. One site says http:...
James Perrin's user avatar
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How to dissolve a powdered drug once it has been mixed with water

For a biological experiment I have acquired $\pu{10 mg}$ of CHIR 99021 (laduviglusib). In order to obtain a $\pu{10 mM}$ stock solution, I had to dissolve the powder in $\pu{2.15 mL}$ of dimethyl ...
felbamato's user avatar
4 votes
1 answer
356 views

Meaning for chromatography terms linear velocity and volume flow rate

I am learning about chromatography and there are two terms that confuse me a lot: linear velocity and volume flow rate. These terms are defined in Daniel Harris's Qualitative Chemical Analysis: ...
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Does catechol give Tollens’ test?

Do hydroquinones like catechol or p-hydroxyphenol give Tollens’ test? I know that β-diketones can reduce Tollens’ reagent to give a “silver mirror”, so I would guess that due to tautomerization ...
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Quantify below detection limit

If I want to detect a substance which is below the detection limit of my instrument, can I just add a known quantity and then quantify it?
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2 answers
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Atomization and excitation in AES

AES (atomic emission spectroscopy) is often mentioned as both quantitative and qualitative analyzing method. From this site Atomic Emission Spectroscopy the sources such as flame and ICP are used. ...
Shira's user avatar
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An investigation on the rate of degradation (in %) of Chrysoidine-Y dye, as measured by UV-Vis spectrophotometry

Planning to do an investigation on the rate of degradation (in %) of Chrysoidine-Y dye, using UV-Vis spectrophotometry. I am planning to take an approach of increasing the concentration of Hydrogen ...
Ronith's user avatar
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16 votes
3 answers
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How can I identify the material of this mystery gear?

I have this small gear which has sat on my desk for a couple years. I can't remember where it originally came from or what material it's made out of, so I'm hoping you can help me solve this mystery. ...
hifkanotiks's user avatar
2 votes
1 answer
185 views

Examples of compounds that are hard to ionise or which decompose easily upon ionisation in mass-spectrometer

From Chemistry LibreTexts — 4.11: Mass Spectrometry: Limitations of MS generally stem from compounds that are not easily ionizable, or which decompose upon ionization. Geometric isomers can generally ...
Percival the caterpillar's user avatar
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1 answer
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Minimum volume of benzene with percentage yield

The overall yield for the synthesis of N-phenylethanamide from benzene was found to be $35.2\%$. Calculate the minimum volume of benzene, in $\mathrm{cm}^3$, required to make $10.0\, \mathrm{g}$ of N-...
Jane902's user avatar
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How did early chemists work out the number of protons in the nucleus?

I was reading about the history of the periodic table and the description of an element’s atomic number as its proton number. I couldn’t find the source again but it was stated that they figured out ...
powerful_bob's user avatar
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What is the best alternative to dialysis?

What is the best alternative to dialysis? I want to "design" at a purely theoretical level an industrial installation for the purification of a recombinant protein and dialysis is not ...
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What is the industrial alternative to dialysis?

I want to separate a recombinant protein from imidazole. Both of them are in a solution of pH 8. I was thinking of using ion exchange chromatography with cationite: the imidazole being positively ...
MathEnthusiast's user avatar
2 votes
1 answer
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Weird jumps in DSC measurements between scans

I have multiple DSC measurements with multiple up- and down-scans and some of the time, seemingly at random, the inflection points will show massive jumps in the heat flow. I have no idea where they ...
J.Doe's user avatar
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Trends in pKb for both acetic acid and water

I am trying to rationalise a result that I have recently measured in the lab. I'm measuring the pKb of different compounds in anhydrous acetic acid, using the procedure outlined in this paper (https://...
Stephen's user avatar
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2 votes
1 answer
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The formula of ammonium phosphomolybdate

It is written in my qualitative chemistry textbook that phosphate could be tested by introducing phosphate, nitric acid and ammonium molybdate which gives (NH4)3H4[P(Mo2O7)6]. I found out in the ...
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1 answer
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Aliphatic alcohol analysis in capillary gas chromatography

4.5. Standard solutions of trimethylsilyl ethers of aliphatic alcohols from C20 to C28. They may be prepared from mixtures of pure alcohols at the time they are required for use. Reference solution ...
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Analysis of a sample with several Na compounds

I have a sample that is composed of NaOH, NaNO3 and NaCl in unknown proportions and I would like to determine the approximate proportions. I can determine the melting point of the combination. I was ...
Chemnewbie's user avatar
-4 votes
1 answer
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Determination of Calcium from a mixture of calcium and magnesium using Back Titration [closed]

I've some confusions in the experiment. Step 7 gives us the concentration of both calcium and magnesium (Ca+Mg combined), right? How do we find the concentration of magnesium only from back titration ...
Bilal Malik's user avatar
1 vote
0 answers
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I analyzed samples for arsenic with ICP-MS, my calibration standards are off. Any suggestions?

I used a multi-element calibration standard (10 ppm, with As,Fe,Mg etc.) from a vendor. I then diluted this down to get calibration standards of 0, 1, 2, 5, 10, 20, and 100 ppb. I analyzed these ...
Stefg7's user avatar
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1 answer
112 views

Testing whether an unknown powder is wheat gluten (at home)?

Last week, I ordered wheat gluten to make seitan. I received some powder and attempted a recipe, which mixes 100g of water with 100g of gluten to form a sticky dough. However in my case, I only got a ...
Alduno's user avatar
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1 answer
161 views

Would ferrous ion give the flame test?

My question to ask is "Does $\ce{Fe^2+}$ ion give flame test?" Background: Last month, I gave the JEE exam and a question was as follow: Number of metal ions characterized by flame test ...
Aryan Sinha's user avatar
3 votes
1 answer
133 views

Hydrogen sulfide in acetone?

In the lecture slides for Analytical Chemistry I am going through right now, for the qualitative analysis of metal cations, in the hydrogen sulfide separation group, there is something that wonders me....
Selenimoon's user avatar
4 votes
2 answers
235 views

Can glycerol slow down the kinetics of an inhibitor going to a binding pocket of a target enzyme?

I am currently doing enzymatic inhibition assays and in my current setup I observe that a commercial inhibitor is showing inhibition as expected. Still, the inhibition is not as strong as the ...
raptorlane's user avatar
2 votes
0 answers
69 views

Stability of n-Dodecyl-beta-D-maltoside in buffer solutions for assay experiments

I have a buffer system which contains multiple salts and in addition DTT and n-Dodecyl-beta-D-maltoside. I understand that DTT is hydrolysing quite fast and this component must be used always fresh ...
raptorlane's user avatar
2 votes
0 answers
58 views

How can I refine my method of determining iron content in spinach?

I have begun a chemistry experiment that attempts to determine how iron content in spinach is affected by the length of time it is cooked. Through research, I learned that iron content is often ...
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What does it mean for a substance to be "sparingly soluble"?

I have trouble understanding what solubility means. Merriam-Webster defines it as follows: 1 the quality or state of being soluble 2 the amount of a substance that will dissolve in a given amount of ...
odin98's user avatar
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0 answers
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Does nitroprusside test only work for ketones and not aldehydes?

Since the Brady test will be positive for both aldehydes and ketones, we need a way to distinguish between the two. The Tollen's test is only positive for aldehydes (and $\alpha$-hydroxyketones). I ...
AVS's user avatar
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0 answers
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What is the most accurate way to determine the amount of water in a material from XRF and LOD-105 results?

this might seem like a silly question but I want to be sure. I have the results from an external laboratory for the bulk chemical composition (by XRF) and moisture (by Loss on Drying to 105 degrees ...
Hendrix13's user avatar
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3 votes
0 answers
56 views

Can Schiff's reagent respond to hemiacetal?

Glucose responds with both Tollens' reagent $(\ce{AgNO3})$ and Fehling's solution $(\ce{CuSO4}).$ But it doesn't respond when treated with Schiff's reagent (p-rosaniline hydrochloride), the reason ...
znerd's user avatar
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5 votes
2 answers
901 views

False positive test for chloride ions during lab practical

In my highschool practical examination yesterday, I was given an inorganic salt to identify using chemical tests. The test I performed for the presence of chloride was to heat salt in a test tube with ...
Gaurav Sai Maddipati's user avatar
5 votes
1 answer
333 views

How can the double-layer capacitance be constant in the Helmholtz model?

The differential capacitance of ideal electrochemical double layers is constant, as the surface charge $\sigma$ linearily increases with the applied surface potential $\Psi$ relative to the point of ...
Mäßige's user avatar
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2 votes
2 answers
131 views

Multiple equilibria

I was reading about multiple equilibria reactions and can't quite comprehend some things. Suppose we have two reactions: \begin{align} \ce{A + B &<=> C + D},& K_\mathrm{eq} &= 10^{20}...
Mäßige's user avatar
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2 votes
1 answer
88 views

What can I do if a peptide won't go in solution in a biological assay?

I have working on the realisation of on assay, that is intended to examine the activity of a protein. The assay works in a way, in which the product of the target enzyme is transfered by a support ...
raptorlane's user avatar
3 votes
1 answer
195 views

How and when do redox indicators work?

In redox titrations, for example cerimetry, cerium(IV) is reduced to cerium(III) with a reducing analyte. The Ce(IV)/Ce(III) redox potential is around $\pu{1.76 V}$. We keep track of the solutions' ...
Mäßige's user avatar
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-4 votes
1 answer
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The log K value for Cr-EDTA complex is 23, still Cr(III) cannot be titrated directly [closed]

It's related to stability constants. I don't get the question and where is it taking and wanting to answer.
Akshita's user avatar
-1 votes
1 answer
64 views

What precipitate forms when adding aqueous sodium sulfate solution to an unknown white solid?

I don't understand why there aren't two solutions to the following problem: You are presented with a white solid and told that due to careless labeling it is not clear if the substance is barium ...
Spi-Phi Quotes's user avatar
4 votes
0 answers
99 views

I can't understand a fragment in the Mass-Spectrum of Benzophenone

Summary: Took multiple Mass spectra of Benzophenone; There always is a peak at $\pu{152.2}$ that I don't understand. I made some Measurements of Benzophenone with a GC-MS. Always using EI (electron ...
Franz Emanuel Rüger's user avatar
1 vote
0 answers
82 views

How do you calculate the pH range for which one metal precipitates but the other stays in solution?

The problem I have been asked to solve is: $\ce{Cd^2+}$ and $\ce{Fe^2+}$ (starting concentration $\pu{E-3 mol/L}$) should be separated by precipitation using $\ce{H2S}$. Does a pH range exist ...
andrej's user avatar
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2 votes
1 answer
50 views

Identifying analytes in Gas Chromatography

Since the retention time of a sample tested using GC will necessarily depend on the column parameters (stationary phase material, oven temperature, flow rate, etc), it follows that the chromatograph ...
student1's user avatar
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4 votes
1 answer
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Does reduction occur well above the reduction potential?

I was reading the voltammetry section of Analytical Chemistry 2.1 (Harvey), and it says that for the reduction of $\ce{[Fe(CN)^{III}6]^3-}$ to $\ce{[Fe^{II}(CN)6]^4-}$, which has a standard reduction ...
mertvy's user avatar
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0 answers
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Is the amine nitrogen of methylglycinediacetic acid (MGDA) protonated?

MGDA is a tertiary amine with 3 acetic acid groups. I would like to know whether the amine Nitrogen of MGDA is protonated or not for a given pH value. I could not find any literature data which ...
VKM's user avatar
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3 votes
1 answer
179 views

Role of MnSO4 in permanganometric titration

This might sound like a stupid question, but I have been unable to wrap my head around it. Recently in a lab I had to titrate H2C2O4 with KMnO4 in acidic medium (H2SO4). However, in the work, it ...
confusionfromarizona's user avatar
-1 votes
1 answer
274 views

Differences in UV/vis absorbance spectrum of tap water and distilled water

In my lecture, I was told that the absorbance of a substance can be measured by a colorimeter. By connecting the device to a computer, a graph showing the wavelengths and absorbance values can be ...
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