Negative ion chemical ionization NICI

Note When a positive ion results from Cl, the term may be used without qualification nonetheless positive-ion chemical ionization (PICI) is frequently found in the literature. When negative ions are formed, the term negative-ion chemical ionization (NICI) should be used. [8]... 

This book is based on the study of reactions of thermal electrons with molecules using the ECD, negative ion chemical ionization (NICI) mass spectrometry in the gas phase and polarographic reduction in aprotic solvents [18]. Only the complementary studies related to our research are considered here. 

This book is based on the reactions of thermal electrons with molecules. The ECD, negative-ion chemical ionization (NICI) mass spectrometry, and polaro-graphic reduction in aprotic solvents methods are used to determine the kinetic and thermodynamic parameters of these reactions. The chromatograph gives a small pure sample of the molecule. The temperature dependence of the response of the ECD and NIMS is measured to determine fundamental properties. The ECD measurements are verified and extended by correlations with half-wave reduction potentials in aprotic solvents, absorption spectra of aromatic hydrocarbons and donor acceptor complexes, electronegativities, and simple molecular orbital theory. 

The negative ion chemical ionization (NICI) of some barbiturates is also described.145-148 The molecular ion MT (42) is formed by electron capture, and this is followed by the elimination of the H atom or R radical, yielding stable anions 43-45 (Scheme 5). Anion 46, present in low abundance, may arise from a McLafferty rearrangement. Ring cleavage is manifested by the presence... 

Becker et al. determined PASHs in airborne particulate by GC-AED and GC-MSD. For mass spectrometric ionization, electron impact (El) and negative ion chemical ionization (NICI) were used, the latter proving to be the most sensitive (Figure 10.10). 

Careful selection of the derivatization technique may also be employed to enhance the detection limit of an analyte. The conversion of amphetamines to tetrafluorophthaloyl derivatives yields compounds possessing high electron capture cross-sections and the sensitivity toward such compounds, using negative ion chemical ionization (NICI) can be better than that achieved using positive ion formation by two orders of magnitude. Employing NICI in conjunction with SIM, the detection of amphetamine derivatives in quantities as small as 10 fg (SOamol) may be effected. 

The most widespread abuse of cannabis is by smoking. It occasionally may be abused orally. When smoked, initial metabolism occurs in the lungs, whereas this takes place in the liver when marijuana is taken orally. The identification of 9-carboxy-tetrahydrocannabinol (THC) in urine is considered to be the best indication of previous cannabis consumption. Before SPE, alkaline hydrolysis of the sample is necessary to free the metabolite 9-carboxy-THC. Afterward, M,0-bis-trimethylsilyl-trifluoroacetamide (BSTFA) and trimethylchlorodilsne (TMCS) are added for derivatization the product is analyzed by GC-MS in El or negative-ion chemical ionization (NICI) mode. ... 

Negative ion chemical ionization (NICI) may also be used for the analysis of TATP, although El or PICI are more commonly used. The major ions observed in NICI spectra of TAIP are fragment ions at m/z 57, 56, 59, and 41. The choice of reagent gas (ammonia or methane) produces some effect on the spectra, with ammonia giving a greater abundance of m/z 106 and 107 ions (Figure 16.4C,E) [30].The LOD determined by ammonia NICI were 1 ng for both linear quadrupole and ion trap mass analyzers, with quantitation of extracted ions m/z 57,56, and 59. The LOD by methane NICI was 0.5 ng for both mass analyzers, with quantitation of extracted ions m/z 57,56,59 and 41. 

In any Cl plasma, ions of both polarities, positive and negative, are formed simultaneously, e.g., [M-j-H]" and [M-H]" ions, and it is just a matter of the polarity of the acceleration voltage which ions are extracted from the ion source [71]. Thus, negative-ion chemical ionization (NICI) [72] mass spectra are readily obtained when one of the following processes occurs i) dissociation (deprotonation) of acidic analytes such as carboxylic acids, diimides, or phenols, ii) nucleophilic addition (anion attachment), or Hi) ion-pair formation [73-76] ... 

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