Chemical ionization positive

An ion containing unpaired electrons in its ground state Electron impact ionization Positive chemical ionization Negative chemical ionization... 

Charrois JW, Arend MW, Froese KL, Hrudey SE (2004) Detecting N-nitrosamines in drinking water at nanogram per liter levels using ammonia positive chemical ionization. Environ Sci Technol 38 4835-4841... 

The Finnegan single stage quadrupole powers a very flexible system for several analytical problems. The user has a choice of electron ionization positive chemical ionization or negative chemical ionization. The Quadrupole can be Hnked to gas or Hquid chromatography and several direct insertion probes. The data features powerful, multilayered software using high performance workstations, that make data analysis and instrument control easy. 

For the confirmation of PMFs in Valencia orange peel oil and juice, an HPLC method coupled with a thermospray mass spectrometry (HPLC-TSP-MS) detection system was utilized (112). A C 8 column (/zBondapak, 300 X 6-mm ID) was used with a mobile phase of H20-ACN (60 40, v/v) at a flow rate of 1.0 ml/min. Extract (20 fi1) was injected into the HPLC-TSP-MS system, and positive-ion spectra from m/z 100 to 700 were recorded at 1360 ms. Mass spectro-metric identification was done using positive chemical ionization (ICP). This technique allowed confirmation of the presence of eight flavones in the peel oils and seven flavones in the juice. 

Rostad, C., W. Pereira, and T. Leiker (1989). Determination of herbicides and their degradation products in surface waters by gas chro-matrography/positive chemical ionization/tandem mass spectrometry. Bio. Mass Spec., 18(9) 820-827. 

By the negative chemical ionization (NCI) mass spectral method the negative ions of 2-nitroimidazole are obtained [1305], This method is much more sensitive than the positive chemical ionization one. The analytical potential of the NCI mass spectrometry for the analysis of different classes of nitro compounds has been discussed [1305], Mass spectra of 1,4-dinitro-, 2,4-dinitro-, and 4,5-dinitroimidazoles have been studied [1306], Comparisons of mass spectra (70 eV) of these compounds have shown that the fragment product ions have the same m/z values, but differ in their relative abundance and in the ion appearing the main peak. It seems that this difference is due to the nitramine functionality of 1,4-dinitroimidazole [1306]. 

The particle beam-liquid chromatography-mass spectrometry (PB-L0-M8) of phenols (phenol, 4-nitrophenol, and 1—naphthol) and their glucuronide and sulfate conjugates in electron impact (El) and positive chemical ionization (PCI) is described. 

Table V. PB Positive Chemical Ionization Mass Spectra of Phenols...

In a recent controlled cannabinoid administration study of THC-containing hemp oils and dronabinol, the pharmacokinetics and pharmacodynamics of oral THC were evaluated. Up to 14.8 mg of THC was ingested by six volunteers each day in three divided doses with meals for five consecutive days (Nebro et al. 2004). There was a 10-day washout phase between each of the five dosing sessions. THC was quantified in plasma by solid-phase extraction followed by positive chemical ionization GC/MS. THC and 11-OH-THC were rarely detected in plasma following the two lowest doses of 0.39 and 0.47 mg/day THC, while peak plasma... 

Fig. 3. Plasma zl -tetrahydrocannabinol (THC), H-hydroxy-zl -tetrahydrocannabinol (11-OH-THC) and 11-nor-9-carboxy-zl -tetrahydrocannabinol (THCCOOH) concentrations in one participant over 24 h following administration of two 2.5-mgdronabinol(syntheticTHC) doses. Time zero is the time ofthefirst blood draw at 0730 hours. The 2.5-mg doses were administered with food at 1200 and 1800 (4.5 and 10.5 h after time zero). (Reprinted from Journal of Chromatography B, 789, Gustafson et al.. Validated method for the simultaneous determination of delta-9-tetrahydrocannabinol (THC), 1 Thydroxy-THC and 1 Tnor-9-carboxy-THC in human plasma using solid phase extraction and gas chromotography-mass spectrometry with positive chemical ionization, pp. 145, Fig. 2 therein. Copyright (2003) with permission from Elsevier)...

Gustafson RA, Moolchan ET, Barnes A, Levine B, Huestis MA (2003) Validated method for the simultaneous determination of delta-9-tetrahydrocannabinol (THC), 11-hydroxy-THC and 1 l-nor-9-carboxy-THC in human plasma using solid phase extraction and gas chromatography-mass spectrometry with positive chemical ionization. J Chromatogr B Analyt Technol Biomed Life Sci 798 145-154... 

Another product of esterase cleavage is p-nitrophenol (PNP), which is generated in the human body by the degradation of parathion, parathion-methyl and parathion-ethyl. Some methods for the determination of PNP in urine are summarized in Table 9.5. PNP can, for example, be determined in the urine of occupationally exposed subjects by means of GC-ECD. Sample preparation involves acid hydrolysis, extraction with diethyl ether, derivatization with diazoethane and purification on silica gel columns. The LOD was 20 pg L with a recovery of 85-98%. This method has also been used in a study on selected pesticide residues and metabolites in urine from a survey of the US general population.In the context of another survey study, a more complicated technique to detect PNP in urine has recently been used by Hill et involving GC-MS-MS with positive chemical ionization after derivatization with l-chloro-3-iodopropane. The authors also used this method for the determination of the metabolite TCP and 10 other analytes in urine.Sample preparation involved hydrolysis with p-glucuronidase, several extraction steps using different solvents and purification by SPE (silica gel column). The LOD was 1 pg L with an inter-assay RSD... 

The GC-MS of PFBOA derivatives of these three compounds also was performed by positive chemical ionization (PICI) using methane as the reagent gas. Abundant formation of the [M+H]+ ion of acetaldehyde derivatives at m/z 240, diacetyl-mono derivatives at m/z 282 and of the internal standard o-chlorobenzaldehyde derivatives at m/z 336, and abundant formation of the [M+H-18]+ ion of acetoin derivatives at m/z 282, were observed. Figure 5.8 shows the mass spectra of acetaldehyde, diacetyl monooxime, acetoin, and o-chlorobenzaldehyde PFBOA derivatives. The analytical conditions are reported in Table 5.12. 

Several gases are used in Cl ionization methane, propane, isobutane, hydrogen, ammonia, water, tetramethyl silane, or dimethyl amine. The Cl ion source is similar to the El source but is designed to have an ionization chamber. In positive chemical ionization, the ion source is filled with a reagent gas which is ionized to create a species of the proton donator type that can form a... 

Riahi, K. and Sellier, N., Separation of isomeric polycyclic aromatic hydrocarbons by GC-MS differentiation between isomers by positive chemical ionization with ammonia and dimethyl ether as reagent gases, Chromatographia, Al, 309-312, 1998. 

Technique Electron Impact Positive Chemical Ionization Negative Chemical Ionization... 

In the collision-activated dissociation MS of thiophenic ions, the ions formed due to the loss of the SH radical are prominent in polythiophenes but not in the case of alkylthiophenes <82ANC574>. The ions are generated under positive chemical ionization conditions. 

Depending on the chemical properties of the analyte, reactions other than proton transfer and electrophilic addition can be used to produce analyte molecular or quasimolecular ions. Equations 1.6 through 1.9 exemplify these alternatives with specific reactant ions, which are particularly effective for the given reactions. Overall, negative chemical ionization (Eqs. 1.8 and 1.9) is used less frequently than positive chemical ionization (Eqs. 1.4 through 1.7). 

Chemical ionization is an ionization mechanism that allows the formation of protonated or deprotonated molecules via a gas-phase ion—molecule reaction. It exists under two different forms one under vacuum (Cl) and the second one at atmospheric pressure referenced as atmospheric pressure chemical ionization (APCI). The principal difference between Cl and El mode is the presence of reagent gas, which is typically methane, isobutene, or ammonia (Mimson, 2000). The electrons ionize the gas to form the radical cations (in the case of methane, CH4 -I- e CH4 -I- 2e ). In positive chemical ionization (PCI), the radical cations undergo various ion—molecule reactions to form CHs and finally lead to the formation, after proton transfer (CHs + M [M + H] ), of protonated molecules. Negative chemical ionization (NCI) (Budzikiewicz, 1986), after proton abstraction, leads to the formation of deprotonated molecules [M — H] . Negative ions can be produced by different processes such as by capture of low-energy electrons present in the chemical ionization... 

Perr, J.M., et al. (2005) Gas chromatography positive chemical ionization and tandem mass spectrometry for the analysis of organic high explosives. Talanta, 67, 430 36. 

---