M/Z Calculator
By Jens Allmer
I found an M/Z calculator online. The Calculator Academy Team signs responsible for the calculator.
Let’s take a look
You are supposed to enter the mass in Daltons and the charge into the calculator and it will calculate the mass-to-charge ratio. OK, but what are Daltons, and what is the charge?
Daltons
John Dalton is a famous scientist (chemist and physicist). Atomic theory was one of his subjects. The unified atomic mass unit (aka Dalton, Da, or u) was later named after him and is defined as 1/12 of the mass of an unbound, neutral, $Carbon_{12}$ which means that it does not and $C_{13}$ or $C_{14}$ isotopes.
Why use Daltons? - Regular units like grams are way too large to describe things like proteins, DNA, or atoms. - Instead of saying “this molecule weighs 0.000000000000000000001 grams,” we say it weighs “500 Daltons” (or whatever its molecular weight is).
Examples:
- A single hydrogen atom (the simplest atom) weighs about 1 Dalton.
- A water molecule (H₂O) weighs about 18 Daltons.
- Proteins, like hemoglobin, can weigh tens of thousands of Daltons, e.g., about 64,500 Daltons (or 64.5 kilodaltons, kDa).
In short, Daltons are a super tiny weight unit that help scientists describe the mass of very small things in a manageable way.
Charge
Now that we covered Daltons to some extend, let’s dive into the meaning of charge. Let’s look at the most basic example: Hydrogen ($H_{2}$). Hydrogen has one electron and when it pairs with another Hydrogen, they share two electrons. In this state they are neutral as in not charged. Alone Hydrogen would crave to pair with other molecules to share the electron. This does not mean that Hydrogen is charged, yet. However, if the Hydrogen shares its electron with a stronger atom such as Oxygen, it could later end up to become charged as in $H^{+}$ where it does not have any electron and really craves electrons. The opposite in this example would be $OH^{-}$ which represents the remained of a water molecule ($H^{+}$ + $OH^{-}$ = $H_{2}O$).
$H^{+}$ and $OH^{-}$ are charged atoms and molecules (several atoms coming together). There is more to this than the simplistic discussion but this should be sufficient for the following discussion. If you want a bit more detail jump to the end of the discussion on the m/z calculator, starting with Neutral Atoms and Molecules.
The M/Z Calculator
To understand the problem with the M/Z Calculator, we need to very briefly consider mass spectrometry. In mass spectrometry, an electromagnetic field accelerates ions, i.e., charged particles. One way of adding this charge is by adding $H^{+}$ from a solution to the molecule being measured. There are other ways. In any way, we need a charged particle.
The M/Z Calculator does not specify this. Perhaps they assume that electrons are removed (or added) from the molecular mass we are entering. That mass we could ignore in the calculation. However, there are mass spectrometers that can measure the mass of electrons (Fourier transform ion cyclotron resonance mass spectrometer, for example).
In any case, a charge needs to be added or removed from the mass of the analyte in order for it to have a mass-to-charge-ratio. Either the creators of the calculator thought that the user should know about this and do this or it is an oversight. I didn’t see a mention of this topic on the M/Z calculators site. Therefore, I assume it is an oversight.
The formula they present thus needs to be amended as well.
$$m/z = (M + Z*x)/Z $$ $m/z:$ mass-to-charge-ratio
$M:$ mass of the uncharged molecule in Dalton
$Z:$ number of charges
$x:$ mass of the charge (if deducted from the molecule, it should be negative)
I will contact the creators of the M/Z calculator so that they can improve their calculator.
Further Reading
Neutral Atoms and Molecules:
- Hydrogen (H) has one proton (positive charge) in its nucleus and one electron (negative charge) orbiting it.
- When hydrogen pairs with another hydrogen atom (as in $H_{2}$), the two atoms share their electrons equally. This sharing creates a neutral molecule because the total positive and negative charges balance out.
Becoming Charged:
- Atoms or molecules become charged when they gain or lose electrons:
- Losing an electron leaves an atom positively charged ($H^{+}$, for example).
- Gaining an electron leaves it negatively charged ($OH^{−}$, for example).
Example: Hydrogen and Water
- When hydrogen ($H$) interacts with stronger atoms like oxygen, its single electron might get pulled away. This leaves a bare proton, $H^{+}$, which is highly reactive because it “craves” an electron to regain neutrality.
- The other part of the molecule, like $OH^{−}$ (hydroxide ion), is left with an extra electron, making it negatively charged.
Charge in Context
- Positive Charge ($H^{+}$):
- A proton without an electron.
- It’s a simple example of positive charge because the single proton in hydrogen now dominates.
- Negative Charge ($OH^{−}$):
- Oxygen keeps an extra electron, resulting in a negative charge.
- It’s a slightly more complex molecule but still illustrates the concept of an atom/molecule gaining charge by holding onto extra electrons.
