Questions tagged [analytical-chemistry]
The branch of chemistry concerned with identifying and quantifying the chemical constituents of matter.
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Making a solution of 3.2M NH4OAc in HNO3
I'm working on a method for analyzing metal concentrations in soil samples. I'm going to use a sequential extraction process to find the proportion of easily exchangeable metals, those bound to ...
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Fragmentation Pathway for 4'-Aminoacetophenone in Mass Spec
I was wondering if anyone would be able to help me draw the fragmentation pathway for this disubstituted benzene, I have never really encountered fragmentation in anything but very simple molecules ...
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What does one mean by “Contact Interaction” in EPR (hyperfine splitting)? An intuitive picture would be helpful
While studying hyperfine interactions in EPR, I came across a term contact interaction, which roughly means interaction between nuclear and electronic spin angular moment. I don't know what does it ...
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1answer
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Methods to quantify lead(II) concentration in water on the ppm/ppb level
While there are several ways to quantify metal concentrations in water, a lot of them are only specific to select metals. For example, there is the orthophenanthroline method for quantification of Fe(...
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1answer
18 views
Can o-phenanthroline be used as a complexing agent for lead(II)?
I’ve been trying to find a method to perform a spectrophotometric analysis to determine lead concentration (on the ppm level). This would require some chelator capable of forming a coloured complex ...
2
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2answers
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Chemicals that form coloured complexes with Pb2+
I’m currently conducting a photo-spectrometric analysis of lead concentration in water and was looking into using Eriochrome Black t as an indicator for Pb2+ (due to the complex forming a reddish ...
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1answer
24 views
Should I relate the number of moles between substances when converting weight units?
Good day! I graduated from an undergrad degree of chemistry almost 3 years ago but I'm frustrated that I fail to reconcile these things:
In gravimetric analysis, to get the correct amount for the ...
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25,0 ml HNO3 with titration 0,006128 g/ml + 0,25 ml 0.1105H. NaOH. pH-? [closed]
25,0 ml HNO3 with titration 0,006128 g/ml + 0,25 ml 0.1105H. NaOH. Find pH
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43 views
Concentration of gas above aqueous ammonia
I am a physicist who has run into some chemistry in the lab (and unfortunately, I've completely evaded any formal training in chemistry). I have exposed some samples (I think details of the sample are ...
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2answers
25 views
Checking how chemically plausible a molecular structure is? [closed]
I was working on a project, which dealt with the plausibility of a chemical structure. So i wanted to know on what basis can i check it?
It would be nice if someone could list down all the features ...
2
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1answer
39 views
Can I use an acid other than sulfuric for hydrogen peroxide determination?
I would like to perform a permanganometric titration of hydrogen peroxide at home following a procedure similar to http://www.titrations.info/permanganate-titration-hydrogen-peroxide, i.e. the ...
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1answer
26 views
How do I extract pure lactic acid from the mixture shown below? [closed]
How do I extract pure lactic acid from the mixture shown below?
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1answer
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How to recalibrate qpCR reading when incorrect qty of solution is added during DNA elution step?
I have 20 viral DNA samples collected for 6 time points. The DNA content varies over time
My DNA extraction protocol step suggests that in the last step of the protocol during elution I had 100uL of ...
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36 views
Spectrophotometry: shifting absorbance curves vertically so isosbestic points match
We're measuring reaction kinetic parameters of a hydration reaction (Co complex) by measuring the absorption spectrum a different time intervals, and calculating the ratio of product to reactant by ...
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0answers
25 views
SPE recovery greater than 100%?
I am evaluating a paper Gan et. al. 2013 (https://doi.org/10.1016/j.chroma.2012.11.081) Table S4 (see image below) and I am focusing on evaluating the percent recovery for using different solid-phase ...
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3answers
79 views
Is it possible to measure light absorbance for analysis of lead concentration without photospectrophotmeter
I’m designing an experiment which requires I measure final and initial lead concentrations for the determination of aqueous lead uptake by different mediums. Because lead concentrations would be ...
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1answer
89 views
What is “dithreitol”?
The article by Hu et al. [1] mentions a compound "dithreitol" in the Saliva Proteome Analysis section (emphasis mine):
For the "shotgun" approach, saliva samples (1 mL) were pre-fractionated with ...
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2answers
51 views
Effect of the counterion on the colour emitted by a metalic salt
Could someone please enlighten me on what would be the theoretical effect of a counter ion on the colour of the flame emitted by a metallic salt in a flame test?
Eg. NaCl - what would be the effect of ...
2
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1answer
28 views
How concentrated does the analyte solution need to be in order to perform a (chelatometric) titration
I’m currently investigating a method to chemically pretreat cellulosic waste as bisorbents for enhanced uptake of lead in water. I intend to measure the initial and final concentration of water to ...
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1answer
40 views
Cause of m/z = 56 peak in 4-methyl-1-pentanol
This is the mass spectrum for 4-methylpentan-1-ol:
From its structural formula, what could be the fragmentation which results in a peak at $m/z = 56?$
I was considering a few possibilities; could it ...
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1answer
27 views
Problem with determining the mass value of a soil sample for gravimetric calculations [closed]
I'm having some trouble with how to determine the representative mass value of a prepared soil sample for calculating its $\ce{Cl-}$ concentration in ppm (mg/kg).
Recently I carried out a gravimetric ...
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18 views
When an electron is excited to a singlet state, must it flip its spin state to enter the triplet state and flip once more to the ground state?
I understand the Jablonski diagram in that it has intersystem crossing from the singlet state to the triplet state, but how many spin switches are necessary to complete to phosphores? When an electron ...
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Application of ISO/DIS 18219 Leather - Determination of chlorinated hydrocarbons in leather?
The following norm is for the analysis of leather:
ISO/DIS 18219 Leather - Determination of chlorinated hydrocarbons in leather
This regulation allows to measure short-chain chlorinated paraffins (...
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34 views
Writing mass balance equations of solution containing EDTA, metal, and other ligand
I am a first-year undergraduate student so my knowledge of analytical chemistry is limited but we are given a homework question that seems too difficult to me. Here is the question.
EDTA is a ...
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1answer
82 views
Why is absorbance in UV-VIS spectrometer negative even after calibration?
I was collecting data to plot a calibration curve using pure beta-carotene sample. Prepared 5 different concentrations of beta-carotene dissolved in methanol. Pure methanol was used as blank. However, ...
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1answer
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Why can zwitterions be difficult detect by HPLC-MS?
I understand that to separate molecules by HPLC (or SFC) you commonly adjust the pH of the mobile phase to get preferable charges (i.e. negative charges) on the molecules - so that they interact with ...
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2answers
51 views
Where do the percents in empirical formula questions come from?
A typical empirical formula problem reads something like this:
Determine the empirical formula for a compound that contains 35.98% aluminum and 64.02% sulfur. source
How would those percentages be ...
3
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1answer
78 views
Is there a list of must-have columns for LC-MS/MS used in biochemistry/clinical lab setting?
Considering a wide variety of chromatographic columns used for (U)HPLC based on
phase type (normal or reverse);
column dimensions (geometry, length, inner diameter);
particle material $(\ce{SiO2},$ $\...
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1answer
44 views
Why does the concentration of the acid equals that of the base at the mid-point of titration? [closed]
Consider this graph of the titration of a weak acid and a strong base:
The buffering region is strongest at the midpoint of titration because there is equal concentrations of acetic acid and its ...
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2answers
89 views
Why is H⁺ ion considered the source of acidity, and OH⁻ considered the source of basicity? [closed]
As the title implies, what caused the association between $\ce{H+}$ and acidity, and between $\ce{OH-}$ and basicity?
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0answers
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What are common solvent removal methods?
In a laboratory setting, the most common solvent removal method is rotary vacuum distillation. This is something I have performed many times, starting in organic chemistry labs. However, I am ...
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1answer
51 views
Spectrum Of Metals [closed]
Recently, I've read that when metals are exposed to a high voltage source, metals produce a spectrum. I am curious on what is the minimum value of that 'high voltage'? Is the spectrum due to the high ...
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1answer
42 views
Setup for Sensing change in concentration of NaCl
I am making a sensor to sense the change in concentration of NaCl. My background is in electronics and chemistry is not my strong area. I got some screen printed electrodes, with Silver (Working ...
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26 views
UV-spectrophotometer analytical method for doxycycline hyclate and tylosin tartrate powder [closed]
I am trying to detect tylosin tartrate from the mixture of doxycycline hyclate using $\pu{0.01 M}$ $\ce{HCl}$ as solvent, and waveleghth of $\pu{290 nm}$ for detecting tylosin tartrate in UV-...
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2answers
36 views
Solubility and wetting of substances in water [closed]
We have seen that, when we pour salt in water then it gets dissolved, that means it is soluble in water. But when we pour sand into water then it doesn't dissolve in water, that means it is insoluble, ...
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1answer
33 views
What causes the differences in price in home testing kits for lead in water? [closed]
The price differences between home testing kits to test tap-water for lead are huge.
20 dollar will either buy 1 test kit or 100 test strips. Both are intended to test drinking-water safety.
What ...
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Extraction of Chitosan
Does the temperature and duration during oven drying will affect the chemical properties and the quality of the chitosan that will be yield after deacetylation? Any help is highly appreciated. Thank ...
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1answer
66 views
Is it safe to touch salts given to you for analysis? [closed]
In our chemistry practical paper (High school level), Inorganic salt analysis is one of the questions asked. We are given a petri dish with a sample of salt and are asked to find the cation and anion ...
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Risks of using organic mercury compounds in analytical chemistry
I'm interested in speciation analysis. Hearing of fatal accidents with organic mercury compounds made me wonder about the risks for the analytical chemist trying to determine Hg species in foodstuff. ...
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How to account for the common ion effect on osmolarity quantitatively?
In adjusting the osmolarity of a solution of Benzalknonium Cl, Disodium Editate, and Disodium borate/boric acid buffer to be isotonic (about 290 mOsm), the addition of NaCl showed unexpected behavior, ...
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2answers
84 views
What is the principle of RP-HPLC? [duplicate]
Is the following statement the correct way to explain principle of RP-HPLC?
It works on the principle of hydrophobic interactions hence the more nonpolar the material is, the longer it will be ...
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0answers
32 views
How can a DPPH assay to measure antioxidant activity of beta carotene be conducted?
I am currently doing some research regarding beta-carotene. With reference to other sources and their methodoloy for DPPH assay, I conducted my experiment but failed to find any significant peak in ...
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23 views
Ideal characterization technique to study behavior of heated metal nitrates
I have 3-4 metal nitrates as precursors for my coprecipitation reaction. I need to study the behavior of each individual nitrate and also of various combinations at 60 degrees Celsius, which is my ...
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LIF spectrum with laser-coupled levels lines as the strongest
Why, if I excited the OH molecule Q-branch transition, my LIF spectrum (recorded during and after the laser pulse) does not result in only Q line being the most prominent, but also P and R lines with $...
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1answer
49 views
Is it possible to obtain the amount of air required for a combustion analysis?
I'm not very sure if the required amount of oxygen (I assume) can be found by only knowing the amounts of the produced subtances after a combustion.
To illustrate this I found this problem:
$1.14\,...
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1answer
83 views
Conditions for choosing quantifying and qualifying ion in LC-MS/MS
In my PhD-work, we are trying to develop LC-MS/MS methods for targeted analysis. Usually, I determine my quantifying ion/fragment based on a few different criteria:
If there is a 13C internal ...
3
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1answer
80 views
Why is high molar molar mass a requirement of good primary standards for volumetric analysis? [closed]
I have been taught that using primary standards with a relatively high molar mass will reduce the error between the equivalence point and the end point during titration. However, I am unsure as to why ...
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Separation and qualitative identification of cations
A liquid problem may contain the following cations: $\ce{Pb^{2+}}$, $\ce{Cr^{3+}}$, $\ce{Fe^{2+}}$, $\ce{Ca^{2+}}$, $\ce{Fe^{3+}}$, $\ce{Ag^{+}}$, $\ce{Au^{3+}}$, $\ce{Co^{2+}}$. I need to devise a ...
3
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2answers
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Electron Ionization and the Franck-Condon Diagram: vibrationally excited and vibrationally ground states
I am currently studying Mass Spectrometry: A Textbook, third edition, by Jürgen H. Gross. On page 41, the author says the following:
As explained by the Franck-Condon diagram, hardly any molecular ...
2
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1answer
196 views
Can 2‐chloropropane and acetyl chloride give the iodoform test?
Can $\ce{CH3-CHCl-CH3}$ and $\ce{CH3COCl}$ give the iodoform test?
I thought $\ce{CH3COCl}$ having the keto-methyl group would show the iodoform test, while $\ce{CH3-CHCl-CH3}$ will not since it's ...
