![]() We then subtract the mass of the 4 protons which made the peptide ion positively charged. The WP 532 from Wasatch Photonics is a Spectrometer with Wavelength Range 532 nm, Spectral Resolution 7 to 14 cm-1. To calculate the peptide ion’s mass we multiply the m/z for the monoisotopic peak by the charge state. Lets calculate an accurate molecular mass for both molecules using. ![]() STEP 8 Calculation of the Spectral Resolution. We can see that the m/z difference between the isotopic peaks is 0.25 and we know the mass difference between them is 1 amu therefore the charge state is +4. Now lets examine how high-resolution MS can differentiate between propane and acetaldehyde. STEP 3 Calculate the angles of incidence and diffraction of the grating. The charge state of the peptide ion can be calculated for the isotopic envelope shown below. d (slits): bandpass determined by finite spectrometer slit widths. Third and finally we know that peptide ions become positively charged by the addition of protons which have a mass of 1 amu. d (resolution): the limiting resolution of the spectrometer is governed by the limiting instrumental line profile and includes system aberrations and diffraction effects. Usually the difference between the two most abundant isotopic peaks is chosen for accuracy. Second if we have sufficient resolution we can determine the mass difference between two isotopic peaks the peptide ion. First we know that the mass difference between the isotopic peaks is 1 amu (1 Da) as isotopes differ in mass by the addition of 1 neutron which weighs 1 amu. To make this calculation we use three pieces of information. This information will allow us to calculate the monoisotopic mass (molecular weight) of the peptide being ionised. The effective resolution is the quadratic sum of the grating resolution and the spectral pixel resolution. ![]() A useful advantage of using high resolution mass analysers is the ability to determine the charge state of a peptide ion by calculating the m/z difference between its isotopic peaks. The spectrometer effective resolution for the three orders is plotted in Figure 4.13 and Figure 4.14.
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