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
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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. ...
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1answer
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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 ...
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1answer
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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 ...
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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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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 ...
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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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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 $\...
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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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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-...
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1answer
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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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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. ...
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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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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 ...
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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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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, ...
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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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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
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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?
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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 ...
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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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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 ...
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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 ...
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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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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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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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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. ...
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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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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 ...
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1answer
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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 ...
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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 ...
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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 ...
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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 ...
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1answer
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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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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
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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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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 ...
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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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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 ...

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