lc-ms液質(zhì)聯(lián)用資料系列-資料下載頁
2024-12-07 22:04本頁面
【正文】 ty TIC vs. EIC 10000000 8000000 6000000 4000000 2022000 TIC 2 4 6 8 10 12 14 16 18 800000 600000 400000 202200 0 m/z = 522, XIC 2 4 6 8 10 12 14 16 18 5000000 4000000 3000000 2022000 1000000 0 m/z = 504, XIC 2 4 6 8 10 12 14 16 18 Time (min.) Exact Mass QTOF Trends in Analytical Chemistry, Vol. 22, No. 10, 2022, Imma Ferrer, . Post column addition MicroTee MS LC 1 ml/min ml/min waste 1% Formic acid in IPA ???Sample injection ???LC separation ???No impact on LC chromatographic pattern ???Improve ionization with either acid or base addition after LC column ???Select appropriate solution to assist ionization Nitrogen Rule This rule is derived from the fact that, perhaps coincidentally, for the most mon chemical elements in neutral anic pounds (hydrogen, carbon, nitrogen, oxygen, silicon, phosphorus, sulfur, and the halogens), elements with even numbered nominal masses form even numbers of covalent bonds, while elements with odd numbered nominal masses form odd numbers of covalent bonds, with the exception of nitrogen, which has a nominal (or integer) mass of 14, but has a valency of 3. It should be noted that the nitrogen rule is only true for neutral structures in which all of the atoms in the molecule have a number of covalent bonds equal to their standard valency (counting each sigma bond and pi bond as a separate covalent bond for the purposes of the calculation). Therefore, the rule is typically only applied to the molecular ion signal in the mass spectrum. Mass spectrometry generally operates by measuring the mass of ions. If the measured ion is generated by creating or breaking a single covalent bond (such as protonating an amine to form an ammonium center or removing a hydride from a molecule to leave a positively charged ion) then the nitrogen rule bees reversed (odd numbered masses indicate even numbers of nitrogens and vice versa). However, for each consecutive covalent bond that is broken or formed, the nitrogen rule again reverses. Therefore, a more rigorous definition of the nitrogen rule for anic pounds containing exclusively hydrogen, carbon, nitrogen, oxygen, silicon, phosphorus, sulfur, and the halogens would be as follows: An even nominal mass indicates that a even number of covalent bonds have been broken or formed and an even number of nitrogen atoms are present, or that a odd number of covalent bonds have been broken or formed and an odd number of nitrogen atoms are present. An odd nominal mass indicates that a even number of covalent bonds have been broken or formed and an odd number of nitrogen atoms are present, or that a odd number of covalent bonds have been broken or formed and an even number of nitrogen atoms are present.
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