mzvärdet

mzvärdet, or the m/z value, is the fundamental observable in mass spectrometry. It represents the mass-to-charge ratio of an ion detected by the instrument and is used to identify ions and infer their molecular weights. The m/z value is typically expressed in units of Daltons per elementary charge (Da/e), commonly referred to as a Thomson (Th).

In practice, an ion with mass M and charge z is detected at a value m/z = (M + z·H+)/z, where H+ is the mass of a proton. For singly charged ions (z = 1), the m/z value closely corresponds to the molecular mass plus the mass of one proton. For multiply charged ions (z > 1), the same neutral molecule can appear at multiple m/z values, each corresponding to a different charge state. Adduct formation and isotope composition can also shift the observed m/z.

mz-values are central to identifying compounds and determining molecular masses. They are used in qualitative analysis to match observed spectra against databases, and in quantitative workflows to monitor ion abundances. The accuracy and resolution of the mass spectrometer determine how precisely m/z values can be measured and how well close or overlapping peaks can be distinguished. High-resolution instruments allow accurate mass measurements with parts-per-million (ppm) precision and enable isotopic pattern analysis.

A common challenge is the ambiguity introduced by multiple charge states for large molecules. Deconvolution methods are often employed to convert a spectrum with several m/z peaks into a single neutral mass. Widely used mass analyzers include time-of-flight (TOF), Orbitrap, Fourier transform ion cyclotron resonance (FT-ICR), and quadrupole systems, each with different strengths for resolving and measuring m/z.