Questions tagged [analytical-chemistry]
The branch of chemistry concerned with identifying and quantifying the chemical constituents of matter.
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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'...
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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, ...
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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 ...
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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 ...
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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....
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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. ...
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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 ...
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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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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 ...
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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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Are all salts completely dissociated in solution when put in smaller amounts than their molar solubility?
From what I understand, the solubility is given in terms of molar solubility (or $\pu{K_{sp}}$), from which it can be easily calculated). Indeed, the saturation point represents the maximum amount of ...
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How to effectively replace DMSO with LC–MS-compatible solvent for the samples from a well plate?
I want to do LC–MS analysis of the samples from a 384-well plate where each compound (at around 1–10 μM) is dissolved in 10–15 μL of DMSO. I am worried about the DMSO dwarfing the analyte’s signal, as ...
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Ways and ideas to study ym rough surfaces with scanning tunneling microscopy
We want to study porous carbon (with nanoparticles, e.g., FeO, Ni, Au, La, Ir, Ag ...) via STM. But we run into the problem that the surface is very rough. As seen in Figure 1.
Thus there is an ...
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Why isn't residual standard deviation used in FQY analysis?
I've been measuring relative fluorescence quantum yield (hereafter FQY) for a photosensitive pigment. Most analytical articles and standard operating procedures (SOPs) I've read suggest taking the ...
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Equipment recommendation for atomic absorption spectroscopy (AAS) testing for mercury, lead, and cadmium
I work in a public health laboratory in a small mining town and we have the chance to buy equipment to test for lead and cadmium in wastewater, and mercury in not just wastewater, but also in blood, ...
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Chemical Test for Hydrogen
I know that to perform a chemical test for $\ce{H2}$ we have to take a burning candle flame near to the mouth of the test tube and a blue flame with a characteristic pop sound confirms the presence of ...
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Prepration of standards for analysis of chromium using AAS
I have conducted experiments to study specific adsorption of chromium in various soils and I made my all solutions of cr with using 0.01M NaNO3 as background electrolyte. (I made solutions of 5 ...
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How to interpret gas chromatography results?
I am having trouble interpreting gas chromatography (GC) results for the production of ethyl acetate from acetic acid and ethanol. I am trying to find the reaction order from these results, as well as ...
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In a flame test, what is being excited? [duplicate]
I have done a flame test with $\ce{NaCl}$ and got the yellow characteristic flame of sodium. I am trying to understand exactly how this yellow color is being produced and when I searched for it, I got ...
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How to proceed with iodometric titration to determine caffeine concentration in liquid coffee?
Context
I'm a high school student who decided to investigate the relationship between caffeine concentration and brewing temperature of coffee out of their love for the substance. For my method, I ...
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What is alkalimetry?
I've found two answers. One says its the determination of concentration of unknown alkali solution with the help of standard acid solution.
The other says it as the determination of concentration of ...
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Silver Nitrate Test for Acetylene gas qualification; looking for an appropriate instruction
Phosphine and Hydrogen sulfide along with some other hazardous gases are of impurities of acetylene plants witch are based on the reaction between water and calcium carbide. One of the simple and fast ...
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How to calculate pH of a 0.1 M solution of ammonium bicarbonate considering simultaneous equilibrium along with hydrolysis?
We need to calculate the $\ce{[H+]}$ of 0.1M $\ce{(NH4+)(HCO3^-)}$ given the $\ce{k_b(NH4OH), k_{a_1}(H2CO3), k_{a_2}(HCO3^-)}$
The hint tells me to directly use the result $\ce{[H+]=\sqrt{k_{a_1}(\...
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What could be the origin of a persisting distorted water NMR signal?
I am currently running some solvent suppression experiment on water samples. I first run a one scan 1H experiment to get the ''O1P'' and then implement it in the solvent suppression experiment (''...
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Mechanism of Denigés' test?
According to Wikipedia, Denigés' test detects tertiary alcohols through their dehydration, marked with a colored precipitate. The reagent itself is some form of aqueous mercury(II) sulfate. My ...
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What causes HPLC peaks to look like gauss curves?
I was wondering how the form and curvature of HPLC peaks come to be. As I understand it, the mobile phase which contains the analyte, runs through the column. Many times, the distribution equilibrium ...
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How to choose the solvent gradient for the flash column chromatography of a complex mixture?
When performing a flash column chromatography, it is advised to select an eluent in which the desired compound has an $R_\mathrm{F}$ of about $0.25$ in TLC.
However, if I want to separate and isolate ...
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Trouble analyzing amine using GC-FID
I am trying to analyze a sample containing hexamethylenediamine (HMD) dissolved in ethanol using GC-FID for an undergraduate chemical engineering project. The column used is Agilent DB-FFAP (high ...
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Are there TLC stains for organo fluor compounds or anorg. fluoride that are useful for selecting the product containing fractions post purification
Are there TLC stains that work with fluoride or with organofluor compounds? I have a fluorinated phosphonic acid that does not stain with conventional means. I did research in many of the known and ...
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Dynamic equilibrium of Girard T-derivatized oxysterols
This is a question relating to organic chemistry, moreso than chromatography.
I am running LC-MS on various hydroxycholesterols (HC) and dihydroxycholesterols (diHC). To increase ionization efficiency ...
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What is the equivalence point in the context of a redox titration? [closed]
We know the standard reduction potential of the species: $\ce{Fe^{3+}}/\ce{Fe^{2+}}$, $\varepsilon_1$ and the standard reduction potential of the species: $\ce{MnO_4}^{-}/\ce{Mn^{2+}}$, $\varepsilon_2$...
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The extinction coefficients of oxymyoglobin and ferryl myoglobin
I want to know what the extinction coefficients of oxymyoglobin and ferryl myoglobin are. I was able to find the one for the oxymyoglobin in this pretty old article (it says that it equals $121 \text{...
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Number of significant figures to use in reporting the concentration of the titrand in acid-base titration [closed]
If you perform an acid-base titration yourself, how do you determine the number of significant figures to use when reporting on the concentration of the titrand?
Assume you perform seven titration ...
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Why are fluorine-19 NMR spectra less affected by paramagnetic centers than other common nuclei?
I know that 19F NMR spectra are less sensitive to paramagnetic centers as an empirical fact: it’s my experience and that’s what people in my lab have always been saying.
For instance, some of my ...
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What is the correct way to specify the weight fraction from bulk compositional data with a listed total % (e.g. from XRF, ICP)?
TL;DR = With bulk composition results, such as from X-Ray Fluorescence (XRF) testing, is the mass fraction of a given analyte that analyte given as a % or the analyte divided by the given total mass %?...
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What is the correct unit of a RI detector used for HPLC analysis?
I analyze sugar compounds in soft drinks with HPLC using refractive index detection (RID) on Agilent 1260 Infinity Binary LC (System User Guide (PDF)). I am not sure which unit to put next to the $y$-...
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Find the w/w percentage nitrogen in an ammonium nitrate solution
MCQ Question:
What is the w/w percentage of nitrogen (N) in an ammonium nitrate solution with a density of 1.05 g/cm3 and a molar concentration of 2.1 mol dm-3?
(a) 2.8 %
(b) 11.2 %
(c) 16.0 %
(d) 5.6 ...
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Finding unknown concentration using HPLC standard curve
I calculated a standard curve equation from a given concentration and peak area, which gave me $y=1994.6x+218.4$. I made the graph with the $x$-axis μg/mL and $y$-axis peak area.
The question is, a ...
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What is the inconsistency in calculating the differences in Na2O and NaOH in solids (v2)?
(Note that this question has been fully edited for clarity, SE help advised not to delete the question and post another).
Background:
I have a computer model in which I feed it input data from various ...
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Calculate volume of hydrogen gas evolved
MCQ Question:
Ammonia borane in water can release hydrogen upon hydrolysis while forming NH4BO2 as the other
product.
The volume (cm3) of hydrogen gas which will be evolved from the hydrolysis of 309 ...
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Chromatography and Height Equivalent to a Theoretical Plate (HETP)
HETP can be expressed in two ways:
HETP = L/N
HETP = A + B/u + Cu
where:
L: lenght of the coloumn
N: Number of theoretical plates
A: Eddy-diffusion parameter, related to channeling through a non-...
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Do formed galvanic cells counteract electrolysis?
I was wondering about the following:
Suppose we carry out an electrolysis with constant applied voltage. During the process, a galvanic cell should be formed by the reactants which are formed during ...
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Differentiating Ca2+ and Sr2+ ion
$\ce{Ca^{+2}}$ and $\ce{Sr^{+2}}$ both give a bit similar red color in flame test. What is the easiest way (chemical test) to distinguish $\ce{Ca^{+2}}$ and $\ce{Sr^{+2}}$?
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