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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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How can one remove crystalline water from an inorganic salt such as borax? [on hold]

The borax formula is $\ce{Na2B4O7·10H2O}$. Can I remove 10 water molecules without affecting its specification?
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1answer
11 views

Taking a procedure for ICP and adapting it to use with AAS

I was reading a paper regarding metal detection and they gave their procedure for an acid digest of a soil sample which was then analysed by ICP-OES. They used nitric acid, hydrogen peroxide and ...
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1answer
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Metal Evaporation in GFAAS?

Our lab is doing aqua regia digestion of an ore matrix for the determination of PGE. We're getting white smoke when we run it through a GFAAS. Smoke forms above 1000 C, so we think it's some metal ...
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1answer
14 views

Why are original solutions in the systematic inorganic analysis of cations not prepared in conc. HNO3 or H2SO4 [closed]

The first step in the wet tests (tests involving aqueous solutions) for systematic inorganic analysis of cations is the preparation of “original solutions” - clear, transparent solutions of the given ...
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1answer
20 views

Identifying food, quick and cheap? [closed]

I’m asking this question in the most technical perspective of identifying substances, so I’m not considering the use of chemical tests like Benedict’s solution, biuret solution, Sudan III stain, or ...
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14 views

Conversion from absorption cross section to absorption coefficient

I am currently trying to convert values from the absorption cross section (ACS) $\sigma$ in $\pu{cm2//molecule}$ into absorption coefficient (AC) $\alpha$ in $\pu{cm^{-1}}$. The data is from HITRAN. I ...
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1answer
20 views

Mole fraction concept

In a certain titration experiment, 1) when $\ce{KIO3}$ solution is added to $\ce{KI}$, the $\ce{I-}$ ion is oxidised to the triiodide complex, $\ce{I3-} $ $\ce{IO3- + 8 I- -> 3 I3- + 3H2O}\tag{1}...
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2answers
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Will number of moles (amount of substance) of a chemical change when I dissolve it’s solid state in a solvent so it becomes a solution

Let’s say if I have a known mass (10g) of an inorganic compound (NaCl) in its solid form and I dissolve it in water to form an NaCl solution and the total mass of the solution, let’s say 100g. if I ...
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Pressure in Skoog Instrumental Analysis Problem 27-22b (gas chromatography)

Problem 27-22b in: Skoog; Holler; Crouch. Principles of Instrumental Analysis. Thomson Brooks/Cole (publisher varies by country) asks for corrected retention volumes. A compressibility factor, $j$ ...
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32 views

Is it possible to use too much precipitant? Or precipitant that is too pure?

When carrying out a precipitation in the laboratory, is it possible to either use too much precipitant? Or perhaps a precipitant that is too pure? For example, when using ammonium hydroxide, is it ...
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1answer
26 views

Conceptual understanding of solution / solute in a question [closed]

6.853g of sodium cyanide was dissolved in water and brought to volume in a 100ml volumetric flask. The final mass of the solution was found to be 107.166g My understanding - A solution is ...
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48 views

Photometric titration with EDTA

The $\ce{Bi^{III+}-EDTA}$ complex absorbs at $\pu{265nm}$. The $\ce{Bi^{III+}-TU}$ complex absorbs at $\pu{470nm}$. I have to make the ''theoritical'' titration curves for the following occasions: ...
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1answer
33 views

How do we know cyclopentadienylmolybdenum tricarbonyl occurs as a dimer?

Cyclopentadienylmolybdenum tricarbonyl, $\ce{MoC8H5O3}$, dimerizes to form the cyclopentadienylmolybednum tricarbonyl dimer, $\ce{(MoC8H5O3)2}$. $\hspace{3cm}$ How was it discovered that it does ...
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1answer
23 views

Determination of Urea and Hydrogen Peroxide in Cow Milk by ATR-FTIR(Attenuated total reflection-Fourier Transform Infrared Spectroscopy) [closed]

I am doing a research on cow milk adulteration. I am checking Urea and Hydrogen Peroxide content in milk by ATR-FTIR(Attenuated total reflection-Fourier Transform Infrared Spectroscopy). I am using $\...
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1answer
108 views

What are some example of the use of argentometric titration?

Like, we use alkalimetric titration to calculate the real concentration of table vinegar. What about argentometric titration?
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20 views

What happens to chromium (as Cr2O7-) in the plasma of the ICP?

I have recently been analyzing some biological samples for chromium using a standard Cr(VI) solution for external calibration. Cr standards are typically supplied in a 2% nitric acid matrix. That ...
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1answer
54 views

Artificial nose sensors

I'm am doing research in creating an artificial nose. I need to know how this process works by someone with domain expertise; essentially, what technologies are available currently to detect a broader ...
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1answer
28 views

How many samples would be worth when following a desorption? How to relate with limit of detection?

I am following the desorption of a compound from a polymer. Let's imagine that it occurs at a certain rate and most of the compound is desorbed after 5 days (as in the figure). Then, I could use many ...
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1answer
73 views

How do we know that we have isolated a substance?

In The Historical Background of Chemistry by Henry M. Leicester page 131, the author says: Carl Wilhelm Scheele (1742-1786) [...] isolated many organic compounds, including hydrogen cyanide, lactic,...
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1answer
68 views

Dissolving cast iron in nitric acid

Decades ago my job was to find the silicon content in cast iron gravimetrically. The first step was dissolving the sample in hot Nitric acid. Did this turn all of the constituents in the sample, ...
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1answer
28 views

Bromides limit test

I have a question in the monograph of sodium chloride. In the limit test of bromides the limit is 100 ppm but the concentration of the standard is much lower than the limit. So I want to know why. ...
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41 views

Stoichiometry based on chemical equations

A $\ce{21.1 mg}$ sample of a mixture of glycine $\ce{CH2NH2COOH}$ and benzoic acid $\ce{C7H6O2}$ yields $\ce{N_2}$ at $\ce{730 torr}$ at $\ce{21°C}$. This $\ce{N_2}$ displaces $\ce{5.235g}$ of mercury ...
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15 views

Isoprene standard preparation dilution Nitrogen

My concern is dealing with Isoprene. I am from a pure electronic background and my research includes dealing with organic vapor. From the literature I came to know that Isoprene commercial form is ...
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1answer
56 views

Normalized standard calibration curve

I have a dynamic assay whose absorbance changes with time. I recorded it’s spectrum initially after preparing it. Then I added my analyte and mixed the contents. Then I waited for 2 min and recorded ...
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3answers
397 views

Why does 2,4 DNP give orange colour crystals?

Why does 2,4 DNP give orange crystals on reacting with solution of aldehydic or ketonic group? Why does this test give orange crystals? Is this related to the electron emissions? This is just a ...
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29 views

How to divide the peaks of two anion ions using ion chromatography?

I used an ion chromatography system (Dionex IC-2000) to determine the inorganic ions and acid from the samples collected in the atmosphere. For measuring $\ce{SO4^2-, NO3, Cl-}$, and low molecular ...
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3answers
104 views

What is the proof of complete ionic dissociation in water?

Is there any way to prove that ionic compounds, for instance $\ce{NaCl}$, completely dissociate into singular $\ce{Na+}$ and $\ce{Cl-}$ ions within water by hard experimental evidence? Besides ...
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2answers
37 views

Does ICP-OES detect molecules in suspension?

I'm curious whether ICP-OES has the ability to detect molecules in suspension?
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1answer
130 views

Mathematical explanation of blank titration in Mohr method for argentometry

In my book it is written that in order to minimize systematic error in Mohr method for argentometry it is a common procedure to conduct a blank titration with $ \mathrm{Ag^+} $ against a $\mathrm{CrO_{...
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0answers
25 views

Internal standard calibration in GC/MS

The experiment is about quantification of di-n-octyl phthalate(DNOP) in PVC flooring material using fluoranthene-d10 as internal standard, and TA sent me this data and asked me to draw standard curve ...
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1answer
52 views

Is the pressure in an HPLC system the same throughout?

I'm not sure if I'm articulating myself well enough, but here's my problem: I have a current HPLC system, where we typically have backpressure readouts of around 15 MPa. We are looking to get a new ...
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36 views

Capacity of buffer

I want to dissolve 23 mg of EDC (N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride) in MES buffer with pH=6. How can I know the amount and concentration of MES buffer which can keep the pH=...
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Why are signals broadened in polarography?

In the attached polarogram from Heyvrovsky's 1959 Nobel lecture, transitions from one plateau to the next are smoothened out rather than sharp and abrupt. Why is that? I understand that currents were ...
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36 views

How does the “sample type” selection on the MassHunter software for Agilent 7900 ICP-MS affect the quantitative results?

I'm new to using the instrument, and recently I have tried to measure Cr in both the eluent(1% nitric acid) and a method blank (also 1% nitric acid, but after it has gone through the entire analytical ...
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1answer
55 views

marijuana testing process [closed]

Does anyone know a bit about how costly and accurate are the current THC measurement techniques? Please speculate what drives cost chemicals, consumables or instrument time.
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1answer
42 views

What's the identity of the crystalline solid in the following reaction? [closed]

A mixture of toluene, benzoic acid, aniline and phenol was dissolved in diethyl ether and extracted with 5% $\ce{NaHCO3}$ solution? This extract was acidified until a white crystalline compound ...
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23 views

How does activated carbon catalyse oxidation?

Context: I am doing an experiment on the quantitative analysis of ascorbic acid in a blackcurrent syrup using fluorescence spectroscopy. In order to do so, ascorbic acid was first oxidised into ...
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33 views

Why are the results of two methods different for calculation LOD and LOQ?

I calculated the Limit of Detection (LOD) and Limit of Quantification (LOQ) with results (Table 1) obtained from HPLC (spiked muscle sample). For this purpose, I used regression analysis and two ...
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1answer
50 views

Collision rates between two molecules in a liquid

How would I calculate the collision rate between kaolinite and amylopectin particles in a liquid with a density of ($\pu{1.01g/m^3}$) and a viscosity of ($\pu{0.000434 Pa s}$)? I know this is related ...
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34 views

Calculation of Molar Mass

What is the molar mass of whey protein isolate? I already know that whey protein consists 70% of β-lactoglobulin (18.3 kDa) and (30%) of α-lactalbumin (14.2 kDa), however, as their molecular weights ...
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1answer
3k views

What is number of 1H NMR signals for toluene?

I am searching the web for the number of 1H NMR signals of toluene and I find two different results. Some say there are two signals while others say there are four (According to me, it should be 4). ...
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1answer
119 views

Obtaining values for electrical mobility from ion transport numbers in a Hittorf cell

I am following the experiments detailed in the links below in order to find the electrical mobility of a variety of ionic species: Wikipedia article on ion transport numbers and Hittorf method PHYWE ...
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1answer
42 views

How to interpret detection limits

I am learning about different analytical methods such as Atomic Absorption Spectrscopy and Atomic Emission Spectroscopy and I'm having a difficult time understand how to interpret the detection limits ...
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1answer
91 views

Could thin layer chromatography separate enantiomers? [duplicate]

My textbook states the thin layer chromatography could separate enantiomers only if both/or the mobile and solid phases are chiral? Why so?
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5answers
373 views

Utility of proton vs carbon NMR

I've just learnt about both types of NMR, and I haven't ever used NMR in real life, so anything I say may be wrong. The crux of this question is that, in my own opinion, proton NMR gives you more ...
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1answer
73 views

Detection limits

I am given this question: A study showed that over 2000 children in China have been poisoned by lead. Blood samples have been taken and show that there is 10 times as much as the acceptable amount of ...
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38 views

Is endpoint pH concentration dependent? Choosing an acid/base indicator

We use titrations to determine analyte concentrations with a standardized titrant and an acid/base indicator, BUT how do we choose the indicator? It is my understanding that indicators are supposed to ...
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0answers
27 views

How does a glass pH electrode measure potential difference? [duplicate]

I think I have a basic understanding of how an ion-selective electrode (in particular the pH electrode) works. I've read that section of Harris's Quantitative Chemical Analysis many times. The gap ...
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1answer
419 views

Which compound is responsible for the borax bead test?

When borax is heated, the reaction that takes place is : $$\ce{Na_2B_4O_7.10H_2O \ce{->} 2NaBO_2 + B_2O_3 + 10H_2O}$$ And the compounds that are responsible for the colors are $\ce{M_x(BO_2)_y}$ ...
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1answer
220 views

What does “the magnesium salt of EDTA” mean?

I am attempting to prepare an ammonium chloride/ammonium hydroxide buffer solution ($\ce{pH}=10 \pm 0.1$) for titrating water hardness with calgamite and EDTA. In the 17th Edition of the Standard ...