Questions tagged [analytical-chemistry]
The branch of chemistry concerned with identifying and quantifying the chemical constituents of matter.
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Procedure to buffer 1L with pH=6 from 21.2g of sodium carbonate?
I need the procedure to buffer 1L with pH=6 from 21.2g of sodium carbonate. Are available solutions of NaOH and HCl 2,0mol/L. Also, what would be the concentrations of H2CO3, HCO3 and CO3 in that ...
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How is the selective titration testing equation simplified?
When there is Mn+ and Nm+ metal ions in a solution, to perform a selective complexometric titration this condition need to be satisfied,
K''MYn-4 = KMYn-4 αMn+...
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1answer
20 views
Disparity between LeChatelier's Principle and Solutions
Let's say that there is a solution
$\ce{Na+(aq) + Cl-(aq) <=> NaCl(s)}$
If the above solution is at equilibrium we can say that it is saturated and hence no more Sodium Chloride will dissolve. ...
2
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1answer
26 views
How do I interpret the results of this chromatogram and does it tell me about the compounds' polarities?
I am reading this journal article which discusses using high-performance liquid chromatography (HPLC) to separate dyes from wine. Here are the relevant facts about the experimental setup:
Two mobile ...
2
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1answer
41 views
Slope ≠ 1 in Henderson-Hasselbalch graph for determination of pKa
The $\mathrm{p}K_\mathrm{a}$ of indicators can be determined via plotting a graph of $\log \left(\frac{\ce{In-}}{\ce{HIn}}\right)$ vs $\mathrm{pH}$ with the help of a spectrophotometer, from the ...
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42 views
Finding rate constant from a change in pressure experiment
I measured the change in pressure for the decomposition of hydrogen peroxide in the presence of a manganese(IV) oxide catalyst at 5 different temperatures:
$$\ce{2 H2O2 (l) ->[MnO2 (s)] O2 (g) + 2 ...
2
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0answers
23 views
How can DI water inhibit peroxidase activity?
I'm troubleshooting an IHC staining issue, and according to Thermo-Fischer's website, "Deionized water can sometimes contain peroxidase inhibitors that can significantly impair enzyme activity.&...
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1answer
97 views
HCN, or my nose says I'm dead [closed]
As you see, I still post...
I studied chemisty decades ago (and when I was through with all the compulsory practica, I was sent to a computer chemistry workgroup and politely suggested to never touch ...
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25 views
Which fluorescence indicators can differentiate between the usual surface of steel and the different kinds of its impurities?
Corrosion sensing with fluorescence indicators (metal indicators, pH-indicators, redox indicators) is already known.
But which fluorescence dyes (fluorescence indicators) can differentiate between the ...
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26 views
Total Chloride Vs Organic/Inorganic Chloride
I am currently running a project to detect chloride level in crude palm oil. On most lab service websites, some offer total chloride detection and others offer organic chloride detection. What are the ...
2
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1answer
27 views
Copolymer purity, what does AN / MA / MS mean?
I would like to buy some polyacrylonitrile (PAN) powder from GoodFellow and I have the choice between these two products:
AN316010, quality : Copolymer (99.5% AN / 0.5% MA)
AN316020, quality : ...
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1answer
48 views
what is the concentration of EDTA after titration with Zinc Metal?
I take $\pu{1g}$ of zinc metal and after dissolving, diluting it to $\pu{500 ml}$ and adjust the $\mathrm{pH}$ of $\pu{50 ml}$ of it to make titration with an unknown concentration of EDTA.
I found $\...
4
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1answer
129 views
ELSD detection principle
While documenting myself on the detectors used in HPLC, I came across one that I did not know: ELSD.
I understood that the sample with the mobile phase was nebulized at the column outlet but I do not ...
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3answers
247 views
How to assign overlapping multiplets in 1H NMR spectra?
In the above $\ce{^1H}$ NMR spectrum ($\pu{400 MHz}$, $\ce{CDCl3}$) the methyl, alkene, and $\ce{CCl3CH2}$ protons are fairly easy to assign however, the protons in the cyclohexene ring show overlap ...
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1answer
42 views
What are the benefits of using zero capillary voltage for discarding fractions in LC–ESI–MS/MS?
In the second episode of The Association for
Mass Spectrometry & Advances in the Clinical Lab (MSACL) podcast, namely Getting going with mass spectrometry : Josh learns chromatography (aired 2021-...
2
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1answer
34 views
How can over grinding lead to reduced API extraction in HPLC analysis?
I am looking for some advice regarding particle size distribution (PSD) & how this can be affected by grinding a tablet.
During an assay by HPLC, the method requires grinding of a tablet before ...
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30 views
What reaction is used for calculating pH of the solution obtained after ethanol oxidation with potassium permanganate?
If $\pu{30.0 ml}$ of $\pu{0.20 M}$ ethanol solution reacts with $\pu{1.80 g}$ potassium permanganate, what will be the final $\mathrm{pH}$ of the solution? Assume a complete reaction and that only the ...
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1answer
82 views
Question About Sig Figs
I had this question:
Naturally occurring europium consists of two isotopes with a mass of 151 and 153. Europium-151 has an abundance of 48.030 and, and europium-153 has a natural abundance of 51.970. ...
4
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2answers
234 views
HPLC: Peak height calculation
I am trying to implement a small python script to detect peaks and calculate the corresponding area. The y-values are in mAU and x-values in minutes but there are some unit conversions in most HPLC ...
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0answers
45 views
How to measure purity of nitrogen gas in a “homemade” way?
Is there any indicator or a way of measuring purity of nitrogen? The lab-way of doing things is out of my reach and I was thinking about a DIY way. I want to decrease oxidising atmosphere in a ...
5
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1answer
64 views
How are the toxic components in a mixture identified?
I was doing research on buckwheat sprouts (as to whether I should include them in my diet) and I came across a website that said eating too much can cause fagopyrism, which is caused by compounds ...
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0answers
25 views
Iodometric titration
When you carry out iodometric titration for determining the Peroxide value of a phospholipid mixture, the end point is the solution turning colourless. But, after some time the colour reappears. Do ...
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1answer
27 views
Acid-Base Titration of ammonium dihydrogenphosphate?
How can I determine the concentration of ammonium dihydrogenphosphate solution?
In this compound, the ammonium cation and the dihydrogen anion are both weak acids.
I have a weak solution of this salt, ...
3
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0answers
36 views
Volume of sample for quantitative NMR
I’m interested in quantitating lithium via NMR using a Magritek Spinsolve 60MHz bench top NMR spectrometer. Is there any evidence that suggests the volume of the liquid sample used in the NMR tube has ...
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0answers
19 views
Sensitivity vs. Limit of Detection of rapid antigen tests
I'm comparing a bunch of SARS-CoV2 rapid antigen tests:
Columns 4 and 6 list the values for sensitivity and limit of detection (LOD). How come that a test with a several times lower limit of ...
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1answer
32 views
What would be the identification reactions of selenate(IV) ion? [closed]
I have not been able to find any $\ce{SeO3^2-}$ identification reactions anywhere. Are there any?
10
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3answers
2k views
Is it better to use a smaller, more accurate measuring cylinder several times or a larger, less accurate one for the same volume?
I need to measure out 70 ml of liquid.
I have a 10 ml measuring cylinder with a maximum uncertainty of 0.1 ml and a 100 ml measuring cylinder with a maximum uncertainty of 1 ml.
I've calculated that ...
2
votes
1answer
57 views
The algebraic problem in the equilibrium of weak acids and bases
I have had some trouble verifying the systematic treatment in a weak acid base weak balance. The great equation I must arrive at is this:
and I just can't see clearly how to get that equation from ...
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0answers
21 views
What is the best way to clean Lovibond tintometer quartz cuvette used for oil?
I work in a laboratory where we regularly check edible oil color by using a Lovibond colorimeter. Some people suggested me to wash the quartz cuvette using soap solution.
But I am thinking about ...
1
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0answers
20 views
isotopic composition database for carbon isotopes
I am seeking an isotopic composition database for carbon isotopes, since I would like to make a figure showing the different isotopic compositions of different materials. The best woudl be if the ...
2
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0answers
24 views
Milk digestion procedure for AAS analysis
I am working on a project of analyzing heavy metals in milk samples using flame AAS. So far I have only analyzed cadmium and the results of spiked and unspiked have large differences. I was wondering ...
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40 views
Problem in the calculation of ionic strength of a solution
Recently I've been trying to answer the question 10-13 (c) of 9th edition of Fundamentals of Analytical Chemistry of Skoog et al. Comparing my answers with the student manual , I realized that my ...
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0answers
38 views
Concentration of sulfur in turbid solution
I recently participated in an experiment where I need to calculated the reaction orders and the reaction constant of the reaction:
$$\ce{8 Na2S2O3(aq) + 16 HCl(aq) -> S8(s) + 8 SO2(g) + 16 NaCl(aq) ...
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2answers
666 views
How to identify a blow-out pipette?
Is my pipette a blow-out pipette?
I suspect that it is a blow-out pipette, though the double lines aren't rings. My guess is it is a TC blow-out pipette. It's a big 50 mL pipette, longer than my arm.
...
4
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0answers
45 views
How to determine the source of sub-nm periodic error in NIR spectra
I've run into an issue collecting measurements on deionized water in the $1050-\pu{1200 nm}$ range. To determine the sensitivity of my spectrophotometer in this range, I've acquired measurements on ...
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1answer
41 views
What is a common cause of peak tailing? [closed]
What is a common cause of peak tailing?
a. The distribution constant decreases as analyte concentration increases.
b. The distribution constant increases as analyte concentration increases.
c. The ...
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0answers
32 views
Best pH indicator for titration
Which substance is best suited as a pH indicator for titration of $\pu{15 mL}$ of $\pu{0.1 M}$ ascorbic acid $(K_\mathrm{a} = \pu{7.9E-5})$ with $\pu{1.0 M}$ sodium hydroxide solution?
Using the image ...
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1answer
53 views
Does using same calibration curve for chemical analysis introduce correlation in sample error/uncertainty values?
I am using a hypothetical case to explain my question
Let us consider a chemical analysis method A (using a certain instrument), which is used to quantify the value of a particular species b. ...
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1answer
39 views
Whatman 41 filter uses for? [closed]
I was reading a research article related to winter fog, so the researcher collected aerosols on Whatman 41 filters every 12h, and we know that Whatman 41 filters are usually used for Qualitative ...
4
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1answer
189 views
Why diethyl ether does not absorb in UV region?
Explain why diethyl ether does not have a UV spectrum, even though it has lone-pair electrons.
Can we say that π* molecular orbital does not exist because there are no π-bonded electrons in diethyl ...
0
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1answer
35 views
When titrating to find the concentration of a dissolved acid, does the volume of solvent matter?
I am conducting a titration to find the mass of aspirin present in tablets. I will be dissolving the aspirin tablet into a solution of ethanol and distilled water to dissolve it. But, does the volume ...
2
votes
1answer
66 views
Why burn methane to CO2 for isotopic analyis?
I am wondering why mathane is burned to CO$_2$ for isotopic analysis, e.g with a mass spec?
I have looked into several text books, they all describe how to do it but not why.
Is it because of a ...
3
votes
1answer
47 views
Difference in titration curves
In my titration curve for HCl being titrated with NaOH, the initial pH-value was plotted as 2.1 according to a pH-meter. When I found the equivalence point and calculated the concentration of HCl, it ...
0
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1answer
44 views
Chemical analysis of soapstone
Soapstone is a metamorphic mineral with a number of constituent compounds including principally:
silicon dioxide
magnesium oxide
iron oxide
aluminum oxide
calcium oxide
water/carbon dioxide
What ...
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1answer
40 views
Devarda's alloy procedure
Hello dear I have a small question
I want to do kjeldahl distillation for a 100 mL sample of water after reduction with devarda's alloy to measure the concentration of nitrate nitrogen... I want to ...
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Is it OK to dispose of potassium hydrogen phthalate into the sewer system?
I have been using potassium hydrogen phthalate (KHP) for creating primary standards. I have looked into the Flinn catalog, and the disposal consideration is classified as "organic acids, must be ...
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2answers
70 views
Unusual Titration Curve Explanation
From Costanzo's Physiology book in Acid-Base Physiology chapter, this titration curve of a weak acid ($\ce{HA}$), in the context of discussing buffers is provided:
What confused me is that in this ...
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0answers
18 views
Alkalinity measured by titration after degassing of CO2
I recently received some lab results from a sample which contained a lot of CO2, which degassed before the total alkalinity was measured by titration to a pH 4.5 end point. The best analogue for this ...
4
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1answer
229 views
Detection limit for log-log calibration curves
The limit of detection ($LOD$) for an analytical method can be derived from its calibration curve using the following equation:
$$ LOD = {\dfrac{(3.3 \cdot {\sigma_
\mathrm{resids}})} {m}} \tag{1} $$ [...
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0answers
23 views
Using the method of differential absorption to determine the ethanol content of an unknown sample [closed]
I have completed a whole set of FITR-ATR spectra analysing 6 solutions of ethanol-water mixtures, all at different concentrations of each.
I have now been instructed to use the method of differential ...
