Automated charge state determination of complex isotope-resolved mass spectra by peak-target Fourier transform.
This study describes a new algorithm for charge state determination of complex isotope-resolved mass spectra. This algorithm is based on peak-target Fourier transform (PTFT) of isotope packets. It is modified from the widely used Fourier transform method because Fourier transform may give ambiguous charge state assignment for low signal-to-noise ratio (S/N) or overlapping isotopic clusters. The PTFT algorithm applies a novel "folding" strategy to enhance peaks that are symmetrically spaced about the targeted peak before applying the FT. The "folding" strategy multiplies each point to the high-m/z side of the targeted peak by its counterpart on the low-m/z side. A Fourier transform of this "folded" spectrum is thus simplified, emphasizing the charge state of the "chosen" ion, whereas ions of other charge states contribute less to the transformed data. An intensity-dependent technique is also proposed for charge state determination from frequency signals. The performance of PTFT is demonstrated using experimental electrospray ionization Fourier transform ion cyclotron resonance mass spectra. The results show that PTFT is robust for charge state determination of low S/N and overlapping isotopic clusters, and also useful for manual verification of potential hidden isotopic clusters that may be missed by the current analysis algorithms, i.e., AID-MS or THRASH.
Chen
Li
L
Bioinformatics Institute, Singapore. chenli@bii.a-star.edu.sg
Yap
Yee Leng
YL
D000465:Algorithms; D002256:Carbonic Anhydrases / Q000737:chemistry; D005583:Fourier Analysis; D006657:Histones / Q000737:chemistry; D007554:Isotopes; D011506:Proteins / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods*; D013816:Thermodynamics; D025801:Ubiquitin / Q000737:chemistry
D006657:Histones; D007554:Isotopes; D011506:Proteins; D025801:Ubiquitin; D002256:Carbonic Anhydrases