Tiernan T O, Chang C, Cheng C C
Environ Health Perspect. 1980 Jun;36:47-62. doi: 10.1289/ehp.803647.
A systematic study of the negative-ion chemical ionization mass spectra produced by the reaction of F(-) with a wide variety of organic compounds has been accomplished. A time-of-flight mass spectrometer fitted with a modified high pressure ion source was employed for these experiments. The F(-) reagent ion was generated from CF(3)H or NF(3), typically at an ion source pressure of 100 mum. In pure NF(3), F(-) is the major ion formed and constitutes more than 90% of the total ion intensity. While F(-) is also the major primary ion formed in pure CF(3)H, it undergoes rapid ion-molecule reactions at elevated source pressures, yielding (HF)(n)F(-) (n = 1-3) ions, which makes CF(3)H less suitable as a chemical ionization reagent gas. Among the organic compounds investigated were carboxylic acids, ketones, aldehydes, esters, alcohols, phenols, halides, nitriles, nitrobenzene, ethers, amines and hydrocarbons. An intense (M - 1)(-) ion was observed in the F(-) chemical ionization mass spectra of carboxylic acids, ketones, aldehydes and phenols. Alcohols yield only (M + F)(-) ions upon reaction with F(-). A weaker (M + F)(-) ion was also detected in the F(-) chemical ionization spectra of carboxylic acids, aldehydes, ketones and nitriles. The F(-) chemical ionization mass spectra of esters, halides, nitriles, nitrobenzene and ethers are characterized primarily by the ions, RCOO(-), X(-), CN(-), NO(2) (-), and OR(-), respectively. In addition, esters show a very weak (M - 1)(-) ion (except formates). In the F(-) chemical ionization spectra of some aliphatic alkanes and o-xylene, a very weak (M + F)(-) ion was observed. Amines and aliphatic alkenes exhibit only insignificant fragment ions under similar conditions, while aromatic hydrocarbons, such as benzene and toluene are not reactive at all with the F(-) ion. The mechanisms of the various reactions mentioned are discussed, and several experimental complications are noted. In still other studies, the effects of varying several experimental parameters, including source pressure, relative proportions of the reagent and analyte, and other ion source parameters, on the observed chemical ionization mass spectra were also investigated. In a mixture of NF(3) and n-butanol, for example, the ratio of the intensities of the ions characteristic of the alcohol to that of the (HF)(n)F(-) ion was found to decrease with increasing sample pressure, with increasing NF(3) pressure, and with increasing electron energy. No significant effects on the spectra were observed to result from variation of the source repeller field or the source temperature. The addition of argon to the source as a potential moderator did not alter the F(-) chemical ionization spectrum significantly, but the use of oxygen appears to inhibit formation of the (HF)(n)F(-) cluster ion. The advantages of using F(-) as a chemical ionization reagent are discussed, and comparisons are made with other reagent ions.
已完成对F⁻与多种有机化合物反应产生的负离子化学电离质谱的系统研究。这些实验采用了配备改进型高压离子源的飞行时间质谱仪。F⁻试剂离子由CF₃H或NF₃产生，通常在离子源压力为100 μ m时产生。在纯NF₃中，F⁻是形成的主要离子，占总离子强度的90%以上。虽然F⁻也是纯CF₃H中形成的主要初级离子，但它在升高的源压力下会发生快速离子 - 分子反应，产生(HF)ₙF⁻（n = 1 - 3）离子，这使得CF₃H不太适合作为化学电离试剂气体。所研究的有机化合物包括羧酸、酮、醛、酯、醇、酚、卤化物、腈、硝基苯、醚、胺和烃。在羧酸、酮、醛和酚的F⁻化学电离质谱中观察到强烈的(M - 1)⁻离子。醇与F⁻反应时仅产生(M + F)⁻离子。在羧酸、醛、酮和腈的F⁻化学电离光谱中也检测到较弱的(M + F)⁻离子。酯、卤化物、腈、硝基苯和醚的F⁻化学电离质谱主要分别以RCOO⁻、X⁻、CN⁻、NO₂⁻和OR⁻离子为特征。此外，酯显示出非常弱的(M - 1)⁻离子（甲酸酯除外）。在一些脂肪族烷烃和邻二甲苯的F⁻化学电离光谱中，观察到非常弱的(M + F)⁻离子。胺和脂肪族烯烃在类似条件下仅表现出不显著的碎片离子，而芳烃，如苯和甲苯与F⁻离子根本不发生反应。讨论了上述各种反应的机理，并指出了一些实验复杂性。在其他研究中，还研究了包括源压力、试剂与分析物的相对比例以及其他离子源参数等几个实验参数的变化对观察到的化学电离质谱的影响。例如，在NF₃和正丁醇的混合物中，发现醇特征离子与(HF)ₙF⁻离子强度之比随着样品压力增加、NF₃压力增加和电子能量增加而降低。源推斥场或源温度的变化对光谱没有观察到显著影响。向源中添加氩气作为潜在的缓和剂并没有显著改变F⁻化学电离光谱，但使用氧气似乎抑制了(HF)ₙF⁻簇离子的形成。讨论了使用F⁻作为化学电离试剂的优点，并与其他试剂离子进行了比较。
