Questions tagged [analytical-chemistry]

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

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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 ...
Mike's user avatar
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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
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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 ...
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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://...
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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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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
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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
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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 ...
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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 ...
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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
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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
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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
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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
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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 ...
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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 ...
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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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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 ...
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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
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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 ...
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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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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
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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' ...
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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
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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
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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
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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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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 ...
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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 ...
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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 ...
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1 answer
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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
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1 answer
174 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 ...
Elizabeth's user avatar
-1 votes
1 answer
36 views

Quantitative Method Comparison & Experimental Error [closed]

I'm a Y1 Chem Undergrad and I standardised hydrogen peroxide using two different methods (both redox titrations) in the lab. This was done to compare the 2 different methods and their reliability. I ...
Joseph's user avatar
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1 vote
1 answer
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What does it mean if a calibration curve regression doesn't cross (0,0)

I have been taking many lab courses in my second year of university and I have come across the technique of creating a calibration curve quite a bit. One thing I noticed in a lot of my plots is that ...
user139281's user avatar
3 votes
1 answer
166 views

Why is there a yellow solution formed upon reaction of silicon tetrachloride with water?

I've read somewhere that reacting the two will give a white solid and a yellow solution. I'm assuming the white solid is the silicon dioxide, but what is the chemical origins of the yellow colour of ...
Quimbinator's user avatar
2 votes
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Student Teaching of RP and NP HPLC - Labor practise

I am teaching pharmacy students in the instrumental analytics course and my main topic is HPLC. currently we have a (in my opinion) boring students experiment were the student determine impurities in ...
Louis S's user avatar
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-2 votes
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ppm of CaCo3 of an unknown sample [closed]

A 1g impure solid sample of CaCO3 was dissolved in 100ml of water. After titration the hardness of the solution was determined to be 900ppm - now, how do I calculate the amount of CaCO3 in the impure ...
Jess's user avatar
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How to calculate the resolution of a GC-FID peak using only peak area and height

I think the title pretty much says it all. I'm trying to calculate the resolution of my GC-FID peaks, but the software doesn't report the width of the peaks. Do I need to manually do this by ...
inwales's user avatar
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2 votes
1 answer
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pKa and pKb in solvents other than water

I know that when you have aqueous solutions, then the pKa and the pKb are linked to each other (pKa + pKb = 14). Is there an equivalent relationship between pKa and pKb in non aqueous environments? I'...
Jack's user avatar
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2 votes
1 answer
648 views

How do I interpret the results of this DNA gel electrophoresis performed with potentially mislabeled samples?

Here is the cropped image I am working with: It doesn't really matter for my question, but this was performed with 0.8% agarose gel in 1xTBE buffer using ethidium bromide and a TriDye 1kb DNA ladder, ...
Sidereus's user avatar
2 votes
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51 views

What methods are there for drying oils?

I am trying to generate thin films of sample for TXRF testing, but my samples contain a significant amount of oil in them. My slides are analyzed vertically, so the oil simply drips off. I have access ...
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Voltammogram during calibration is not smooth

During calibration for differential pulse voltammetry, the voltammogram obtained has two distinct peaks. I am not sure why I am getting two peaks in the range from $\pu{-0.6 V}$ to $\pu{-0.9 V}.$ I ...
AvG's user avatar
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4 votes
1 answer
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LC-MS/MS analysis of rosuvastatin in rat plasma two peaks

I am trying to analyse samples of Rosuvastatin in rat plasma using LC-MS/MS and ran into the problem that I get two peaks for Rosuvastatin, one after a retention time of around 7 mins and one around ...
Ratpricker's user avatar
1 vote
1 answer
136 views

Does dilution of titrant gives a more accurate result?

When I see demonstrations of titration of acid solutions of unknown concentration with phenolphthalein as the indicator, when the last drop of NaOH went in the analyte solution became permanently pink....
sfbk's user avatar
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1 vote
1 answer
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Using a sulfate test to determine % sulfuric acid

I work as an amino acid lab technician in a production facility, and we've been tasked with figuring out how to determine the amount of sulfuric acid remaining in a solution made in our plant. ...
Joe's user avatar
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2 votes
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How do I calculate the masses of compounds in a mixture from a GC?

I'm supposed to analyse the two GC graphs in the attached picture (I quickly drew them instead of taking a picture). The question states ths "A mixture contains 3-Methylhexane. To determine the ...
Ladan's user avatar
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3 votes
1 answer
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Methanol Ethanol butanol mixture assay via spectrophotometer

I have a mixture of Ethanol / Methanol and Butanol that I wanted to assay. Would it be possible to develop a spectrophotometeric method for this? (Currently a GC is being used) The analysis does not ...
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6 votes
4 answers
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How to distinguish silver chloride, bromide and iodide?

When we test for chloride, bromide and iodide ions we use the obvious silver nitrate and dilute nitric acid test. However distinguishing between the precipitates is often quite tricky. How can we tell ...
Goffried Leibniz's user avatar
4 votes
2 answers
112 views

Why would my pH meter have changed its voltage setpoints?

I'm using a Thermo Scientific Orion Dual Star pH/ISE Dual Channel Benchtop Meter. The manual says that a $\mathrm{pH}~7$ buffer should read about $\pu{0 mV},$ and a $\mathrm{pH}~4$ buffer should read ...
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