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Questions tagged [analytical-chemistry]

The branch of chemistry concerned with identifying and quantifying the chemical constituents of matter.

The branch of chemistry concerned with identifying and quantifying the chemical constituents of matter. Possible subtopics include, but are not limited to:

  • Spectroscopy
  • Spectrometry
  • Calorimetry
  • Chromatography
  • Microscopy
  • Classical combustion techniques for elemental analysis
  • Numeric analysis
  • Preparative techniques such as digestion and decomposition
  • Titration techniques
  • Chemical speciation, e.g. determination of oxidation states
  • Surface tecniques, e.g. electron microscopy
1098 questions
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Manuals for a Cahn TG-171 Thermogravimetric Analyzer

Recently a Cahn TG-171 Thermogravimetric Analyzer was donated to my school. We did not get a service or user's manual with it, and some of it still needs to be put back together. I have tried to contact Thermo Fisher who bought Cahn Instruments,…
Cohen_the_Librarian
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Do electronic balance weighings still need to be corrected for buoyancy error?

Buoyancy error is a weighing error due to the difference in the buoyant force exerted by a medium (commonly air) on the object and on the standard masses. The difference in buoyant force occurs when the object and the standard masses have standard…
Acnologia
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What is the English translation of the German term "Aufschluss", a method to get insoluble analytes into solution?

In the analysis of solids, often the first step is to get the analyte into solution in some form. Sometimes, solids are heated in the presence of acids (acid digestion) or molten salts (sample decomposition through fusion according to this source).…
Karsten
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In the last step of Kjeldahl Method, is the reaction of ammonium to NaOH not taken into account?

In the last step of Kjeldahl method, the unreacted $\ce{HCl}$ in the solution is back titrated with a standard $\ce{NaOH}$ and the concentration of $\ce{HCl}$ that has been used to neutralize the ammonia is then calculated. However, other than…
Kent de los Reyes
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Strange batch of potassium nitrate with lower than expected melting point

I'm part of a rocket building team and I'm working with propellants. We use saltpeter as the oxidizer, bought as fertilizer and purified by recrystallization. Recently we bought it from another source, that identified the chemical as potassium…
Matheus Cordeiro
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LC-MS: Can a "bad" peak still be interpreted

I have done an untargeted metabolomics study using LC-MS. There is one peak that matches to a biologically relevant compound but analyte eluted at the beginning of the LC run and the peak shape is far from ideal. Do I assume the peak is an…
HarD
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Comparing wt% to at% which is normalized to 100%

I have measured the element composition of a sample using ICP-OES, and reported my results in wt%. A study which has analyzed the same sample types, but with an electron microprobe, has reported their element concentrations in at%, which in addition…
Yoda
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Is analytical imprecision normally distributed or log-normally distributed?

In textbooks and scientific litterature, analytical imprecision is often assumed to be normally distributed. I.e., theoretically, if the same chemical sample were analysed over and over again ad infinitum, the measurements would follow a normal…
Peder Holman
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Does a rotary evaporator need a draft chamber and a vacuum pump?

I am using DCM ( dichloromethane) in my research, as a solvent. At the end of the day I have to separate the salute and measure it. Up until now, I have been using a constant temperature oven, set a about 65 degree Celsius (evaporation temp of…
Ivan P.
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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: $$ LOD = {\dfrac{(3.3 \cdot {\sigma_ \mathrm{resids}})} {m}} \tag{1} $$ [see reference at bottom] where: $…
MRJ
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Easy method of analysing iodine content in supplements?

Most health-food stores carry supplements supposedly containing iodine for people with iodine deficiency. I recently bought some kelp tablets that are supposed to have iodine but as a consumer how can I be sure that there is any iodine in them at…
John Williams
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Why are acetylene and air commonly used for AAS?

I see that this fuel/oxidant combination is most commonly used, but it's never stated why.
J.P
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The sensitivity of potassium iodide starch paper

I have some questions about the sensitivity of potassium iodide starch paper. Patients with asthma caused by allergic airway inflammation have high levels of nitric oxide ($\ce{NO}$) in exhaled breath. This is usually measured with chemiluminescence…
Magnus
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Rhodizonic Acid and Silver Citrate?

I have used some of those lead check swabs from 3M. I used them on some ceramic tile and received strange results. I called the tile manufacturer who was insistent that lead had never been used in their operations. After talking with 3M they asked…
J Andrews
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(How) Does ICP-OES determine the quantity of detected elements, or just their occurance in the sample?

ICP-OES is a very common analytical method (Wikipedia page here), and I have heard a number of times (from chemists, too) that it is used for quantitative analysis. However, from the description of the process, I'm not certain if it really does give…
Hanno Fietz
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