scholarly journals Mass spectrometry analysis of polychlorinated biphenyls: Chemical ionization and selected ion chemical ionization using methane as a reagent gas

2000 ◽  
Vol 65 (5-6) ◽  
pp. 431-438 ◽  
Author(s):  
Tatjana Vasiljevic ◽  
Mila Lausevic ◽  
Raymond March
Keyword(s):  
Quantitative Analysis ◽  
Polychlorinated Biphenyls ◽  
Mass Spectrometer ◽  
Chemical Ionization ◽  
Quadrupole Ion Trap ◽  
Mass Spectrometry Analysis ◽  
Fragmentation Pattern ◽  
Gas Chromatograph ◽  
Molecular Ion ◽  
Fragment Ions

In the present paper a quadrupole ion trap mass spectrometer, coupled with a gas chromatograph, was used to compare the electron impact ionization (EI) and chemical ionization (Cl) technique, in terms of their selectivity in polychlorinated biphenyls (PCBs) quantitative analysis. The experiments were carried out with a modified Varian SATURN III quadrupole ion-storage mass spectrometer equipped with Varian waveform generator, coupled with a gas chromatograph with DB-5 capillary column. The disadvantage of using EI in the analysis of PCBs congeners is the extensive fragmentation of the molecular ion. The main fragmentation pattern recorded in the EI mass spectra of PCBs was the loss of a chlorine atom from the molecular ion. Therefore the fragment-ion signal overlapped with the molecular-ion cluster of lower mass congener. The fragmentation reactions of PCBs are suppressed if methane is used as a reagent gas for chemical ionization, but fragment ions are also present in the spectrum as an obstruction for quantitative analysis. The most selective method for PCBs quantitative analysis appears to be Cl with mass-selected C2H5 + ions from methane, which results in a mass spectrum with a negligible amount of fragment ions.

scholarly journals Coupling a gas chromatograph simultaneously to a flame ionization detector and chemical ionization mass spectrometer for isomer-resolved measurements of particle-phase organic compounds

2020 ◽  
Author(s):  
Chenyang Bi ◽  
Jordan E. Krechmer ◽  
Graham O. Frazier ◽  
Wen Xu ◽  
Andrew T. Lambe ◽  
...  
Keyword(s):  
Functional Groups ◽  
Organic Compounds ◽  
Mass Spectrometer ◽  
Chemical Ionization ◽  
Measurement Techniques ◽  
Oxidation Products ◽  
Ionization Mass ◽  
Particle Phase ◽  
Gas Chromatograph ◽  
New Instrument

Abstract. Atmospheric oxidation products of volatile organic compounds consist of thousands of unique chemicals that have distinctly different physical and chemical properties depending on their detailed structures and functional groups. Measurement techniques that can achieve molecular characterizations with details down to functional groups (i.e., isomer-resolved resolution) are consequently necessary to provide understandings of differences of fate and transport within isomers produced in the oxidation process. We demonstrate a new instrument coupling the thermal desorption aerosol gas chromatograph (TAG), which enables the separation of isomers, with the high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS), which has the capability of classifying unknown compounds by their molecular formulas, and the flame ion detector (FID), which provide a near-universal response to organic compounds. The TAG-CIMS/FID is used to provide isomer-resolved measurements of samples from liquid standard injections and particle-phase organics generated in oxidation flow reactors. By coupling a TAG to a CIMS, the CIMS is enhanced with an additional dimension of information (resolution of individual molecules) at the cost of time resolution (i.e., one sample per hour instead of per minute). We found that isomers are prevalent in sample matrix with an average number of three to five isomers per formula depending on the precursors in the oxidation experiments. Additionally, a multi-reagent ionization mode is investigated in which both zero air and iodide are introduced as reagent ions, to examine the feasibility of extending the use of an individual CIMS to a broader range of analytes with still selective reagent ions. While this approach reduces iodide-adduct ions by a factor of two, [M−H]− and [M+O2]− ions produced from lower-polarity compounds increase by a factor of five to ten, improving their detection by CIMS. The method expands the range of detected chemical species by using two chemical ionization reagents simultaneously, enabled by the pre-separation of analyte molecules before ionization.

Pesticide Confirmation by Triple Stage Quadrupole Mass Spectrometry: Etrimfos and Dimethoate

1987 ◽  
Vol 70 (5) ◽  
pp. 858-862
Author(s):  
Thomas Cairns ◽  
Emil G Siegmund
Keyword(s):  
Chemical Ionization ◽  
Organophosphorus Pesticides ◽  
Packed Column ◽  
Burden Of Proof ◽  
Sufficient Evidence ◽  
Molecular Ion ◽  
Fragment Ions ◽  
Primary Identification ◽  
Analytical Result ◽  
Ion Species

Abstract The production of a protonated molecular ion, MH+, for a pesticide under investigation is often preferred for primary identification purposes. However, the lack of fragment ions under such chemical ionization conditions can place the burden of proof on a single ion species for confirmation. Although a single ion representing the molecule at the correct retention time on a packed column or high-resolution capillary column might seem to have furnished sufficient evidence for unambiguous confirmation, in a number of cases additional specificity can improve the analytical result. With the introduction into commerce of triple stage quadrupole (TSQ) instruments, the possibility of improving the degree of specificity by chemical ionization has emerged for practical pesticide residue confirmation analysis. Use of collision-activated dissociation (CAD) experiments to form daughter ions from the protonated molecular ion of 2 representative organophosphorus pesticides has provided a second dimensional plane of characterization for confirmatory purposes at incurred residue levels

The Mass Spectra of Imidoyl Halides and Bromoiminium Bromides

1973 ◽  
Vol 51 (1) ◽  
pp. 132-138 ◽  
Author(s):  
J. Gal ◽  
B. A. Phillips ◽  
R. Smith
Keyword(s):  
Mass Spectrometer ◽  
Alkyl Group ◽  
Mass Spectra ◽  
Halogen Atom ◽  
Fragmentation Pattern ◽  
Inlet System ◽  
Molecular Ion ◽  
Major Process ◽  
Hydrogen Rearrangement

The mass spectra of imidoyl halides 1–6 and bromoiminium bromides 7–9 have been studied and their fragmentation pattern discussed. Loss of halogen atom from the molecular ion of imidoyl halides to form a N-alkylnitrilium ion is a major process. When the N-alkyl group is larger than methyl the fragmentation of N-alkylnitrilium ions with hydrogen rearrangement to give the [PhC≡NH]+ ion becomes important. Thermolysis of bromoiminium bromides in the inlet system of the mass spectrometer produces imidoyl bromides via dealkylation (or dehydrobromination) and α,α-dibromobenzylamines via addition of bromide to the C=N bond.

Letter: Hydroxide and Oxygen Atom Attachment to Dichlorophthalic Anhydride in Negative-Ion Chemical Ionization with Collisionally-Activated Dissociation in an External-Source Ion Trap Mass Spectrometer

2002 ◽  
Vol 8 (4) ◽  
pp. 329-332 ◽  
Author(s):  
Hui-Fen Wu ◽  
Chien-Hung Chen
Keyword(s):  
Mass Spectrometer ◽  
Chemical Ionization ◽  
Ion Trap ◽  
External Source ◽  
Negative Ion ◽  
Molecule Reaction ◽  
Ion Trap Mass Spectrometer ◽  
Collisionally Activated Dissociation ◽  
Fragment Ions ◽  
Negative Ion Chemical Ionization

This study reports the investigation of some unusual adduct ions of hydroxide and oxygen atoms in both negative-ion chemical ionization (NCI) and collisionally-activated dissociation (CAD) processes in an external-source ion trap mass spectrometer. The [M + OH]− and [M + OH – Cl]− adduct ions in the NCI spectrum of 4,5-dichlorophthalic anhydride are attributed to an ion/molecule reaction due to the presence of trace amounts of water. The formation of the unusual [M + O – Cl]− ions during CAD of the M− ions from 3,6-and 4,5-dichlorophthalic anhydride isomers is attributed to reactive collisions of the fragment ions with residual oxygen.

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