9

You are probably mixing natural abundance (NA) and relative abundance (RA). In mass spectrometry RA is a more valuable parameter as it can be directly obtained as the $y$-coordinate of a plotted mass spectra: the most abundant ion (isotope) corresponds to the base peak, which is always $100\%.$ In other words, RA reflect isotope ratio, not NA. For the ...


6

It would indeed be $\ce{C3H3^+}$ assuming predominant isotopic species. Although there can be other isomers, the cyclic isomer, the cyclopropenyl cation is strongly stabilized by aromaticity. As PLD comments, there are really only two steps, not three, to forming this cation. The allyl cation ($\ce{C3H5^+},m/z=41)$ is first obtained by loss of the ...


4

There are a couple reasons this could be happening. The most interesting possibility: isotope effects during ion fragmentation You are performing LC-MS/MS, i.e., your mass spectrometer is chemically reacting the estradiol and estradiol-$d_5$ with gas molecules in the collision cell of the instrument. This process, known as CID or collisionally induced ...


4

The most practical approach is to identify the structure of an organic compound by combination of spectroscopic techniques. This is why you were provided with UV-Vis, IR, NMR and MS data, because it equally reflects the eventual approach in the lab after product isolation and purification, too. Hopefully you have sufficient background what theses ...


4

Thomson described the mechanical effect produced by cathodic rays on the first edition of its book Conduction of Electricity Through Gases (1903, pp. 501–502) and again later on the second edition (1906, pp. 629-630). As you mentioned it refers to the Crookes experiment with the paddle wheel in which the electron beam collides with the mill coausing it to ...


3

Lacking additional information, answers likely will be speculation-based only. To mention a few factors to consider: Stating GC-MS analysis only states, that there is technique to separate compounds by different rate of retention over a stationary phase (gas chromatography, GC) combined (a.k.a. hyphenated) with an other technique to analyze fractions ...


3

The heat of formation of a neutral molecule is important in mass spectrometry because in order to measure the characteristics of individual molecules, a mass spectrometer has to convert them to relevant ions. Once ions form, they can be moved about and manipulated by external electric and magnetic fields as depicted in following sketch of mass spectrometer (...


3

Interesting question, which originates from a major misconception related to pH in LCMS. Nowadays, there are dozens of ionization techniques so in the question always mention the ionization method. Anyway, LCMS is usually done with electrospray ionization (ESI) technique and so are amino acids. First of all nobody completely knows the exact process in ...


3

$$\frac{\ce{O}}{\ce{^16O}}=\frac{(.9976\times\ce{^16O})+(.0004\times\ce{^17O})+(.002\times\ce{^18O})}{\ce{^16O}}$$ $$=\frac{(.9976\times\ce{^16O})+(.0004\times(\ce{^16O}+1))+(.002\times(\ce{^16O}+2))}{\ce{^16O}}$$ $$=\frac{(\ce{^16O})+(.0004\times1)+(.002\times2)}{\ce{^16O}}$$ Essentially, it comes from collecting factors of $\ce{^16O}$.


3

Unfortunately I did not find a high resolution spectrum of this compound, which would have quickly answered your question. Nevertheless, ionized alcohols and even more primary alcohols have a main fragmentation pathway which is the loss of water to yield an ionized alkene. In this case, the corresponding alkene would be 4-methyl-1-pentene, at m/z 84. The ...


2

I feel you have a misconception. ESI is an ionization technique not a detection technique. The sole purpose of the electrospray ionization is to impart a charge on a molecule in the gas phase. The molecule could be neutral, anionic or cationic in the solution phase. The inventor of ESI used to say that ESI makes the elephants fly, i.e., very large molecules ...


2

The limit of detection (LOD) in these kinds of assays depends on both the noise and the signal. Usually it is defined as lowest concentration analyzed such that the signal (peak height) is three standard deviations higher than the noise. Exactly how to define "the noise" is a critical consideration -- many different sources provide different definitions ...


2

Please note that calibrating an instrument once a month is another story as compared to constructing the calibration curve from that instrument. The former is meant to check the accuracy of the instrument's output and the latter serves to determine the concentration of a substance by noting the response of the instrument to 6-7 standards. Also note that all ...


2

Extraction and GC-MS or maybe LC-MS, if you really need to measure these specific impurities I don't know a lot about this area, but you are looking for very low amounts of impurities. For ethylene oxide, for example, your desired detection limit of 0.07 mg in a 10 g sample corresponds to 7 parts per million, or 7 ppm. Your limits for the glycols ...


2

Such problems in chemistry don't work out to infinite precision like pure math problems. You have to apply some chemical knowledge to the problem too. The book formula is obviously an approximation to the exact solution. To find the exact values expected you'd need to use combinatorics. Considering the chemistry: 7 carbons have a mass of 84, so a ...


2

How to get a better turnover while maintaining a reasonably short reaction time? To speed up the reaction, you should look at changing (1) the reagents, (2) the catalysts, or (3) the reaction conditions. In particular you might be dealing with poor solubility for your alkyne substrate if you are doing the reaction in aqueous conditions. 1. Reagents You ...


1

The term "unit" probably means the size of the isolation window used in the QQQ. The term "unit" means the nominal isolation window is 1 Da (i.e. one mass "unit") wide. The "resolution" is a standard term in mass spectrometry, and here they are saying it is about 1 Da.


1

Some of the MS vendors made their software work with other vendors as well. E.g. ThermoFisher's Chromeleon, Waters' Empower seems to have Data Converters for this. If you already have software bought from your vendors it may make sense to research their cross-vendor capabilities. There are also pure software companies that build vendor-agnostic tools: As ...


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