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mass spectrum
A mass spectrum is an intensity vs. ''m/z'' (mass-to-charge ratio) plot representing a chemical analysis. Hence, the mass spectrum of a sample is a pattern representing the distribution of ions by mass (more correctly: mass-to-charge ratio) in a sample. It is a histogram usually acquired using an instrument called a mass spectrometer. Not all mass spectra of a given substance are the same. For example some mass spectrometers break the analyte molecules into fragments; others observe the intact molecular masses with little fragmentation. A mass spectrum can represent many different types of information based on the type of mass spectrometer and the specific experiment applied; however, all plots of intensity vs. mass-to-charge are referred to as mass spectra. Common fragmentation processes for organic molecules are the McLafferty rearrangement and alpha cleavage.
Straight chain alkanes and alkyl groups produce a typical series of peaks: 29 (CH3CH2+), 43 (CH3CH2CH2+), 57 (CH3CH2CH2CH2+), 71 (CH3CH2CH2CH2CH2+) etc.
==X-axis: ''m/z'' (mass-to-charge ratio)==
The x-axis of a mass spectrum represents a relationship between the mass of a given ion and the number of elementary charges that it carries. This is written as the IUPAC standard ''m/z'' to denote the quantity formed by dividing the mass of an ion by the unified atomic mass unit and by its charge number (positive absolute value).〔(【引用サイトリンク】title=Recommendations for nomenclature and symbolism for mass spectroscopy )〕〔(【引用サイトリンク】title=TOC_cha12.html )〕 This has been referred to as a mass-to-charge ratio, although in some ways it does not fit this description. The IUPAC Gold Book gives an example:〔 "''for the ion C7H72+, m/z equals 45.5''".
Since a mass spectrum ''x''-axis represents a relationship between the ion mass and the number of elementary charges that a given ion carries it contains mass information that may be extracted by a knowledgeable mass spectrometrist. Once this is done many mass spectrometrists use dalton (Da) as the unit of mass in order to avoid the clumsy "atomic mass units".
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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