Studies of the response to polycyclic aromatic compounds of liquid introduction: Atmospheric pressure ionisation mass spectrometry.
Date
1999
Authors
Kolakowski, Beata Maria.
Journal Title
Journal ISSN
Volume Title
Publisher
Dalhousie University
Abstract
Description
Polycyclic aromatic compounds are ubiquitous environmental contaminants which are difficult to analyse for in real matrices and have structure-specific carcinogenic and mutagenic properties. Atmospheric pressure ionisation mass spectrometric methods provide a means of characterising PACs but poor sensitivity led to detailed studies of the methods, aimed at understanding the chemistry inside the source. Response, in this study, refers both to signal intensity and to predominant ionisation mechanism, represented as the ratio of protonated molecule to molecular ion ([M+H]+/M+•).
The instrumental parameters studied in APCI could be divided into two groups---Group 1 was associated with changes in signal but not [M+H] +/M+• and Group 2 with changes in both. Bath gas flow rate, nebuliser flow rate, probe position, data acquisition routine, source temperature, and probe temperature were all group 1 parameters. Skimmer cone orifice size, sheath gas flow rate, corona voltage, cone voltage, injection solvent, and source gas belonged to group 2. When optimising PAC detection in a new solvent, gas flow rates, source and probe temperatures, and cone and corona voltages were studied.
Of the solvents tested, organic solvents showed better results than aqueous solvents, likely the result of better nebulisation. Dichloromethane gave the highest signal, probably due to offering the best nebulisation and highest PAC solubility. The best protonation was observed in 50:50 (v/v) acetonitrile-water and hexanes. With the C5 to C9 alkanes, m/ z 59 was correlated with high signal but m/ z 43 with the highest protonation (consistent with it being the better gas phase acid of the two). These results revealed no correlation between sensitivity and ionisation mechanism. However, protonation and sensitivity were closely related to analyte structure. Ketones and carbazoles were most readily protonated and detected while partially reduced carbazoles were most poorly detected and protonated. The other PACs were of intermediate reactivity.
ESI of PACs was successful with acetic acid addition to acetonitrile (in fact, provided an order of magnitude better detection than APCI for biphenylene) and with the following chemical electron transfer reagents (CETRs): 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, chloranil and 6,7-dichloro-1,4-dihydroxyanthraquinone. The largest increase in signal intensity was for perylene with choranil. Naphthalene and pyrene derivatives differed in their reactivity to CETRs, providing a potential means of isomer discrimination.
Preliminary experiments with one, two and three gas systems indicated that Extradry(TM) air as bath gas and carbon dioxide as sheath and nebuliser gas was optimal for PAC detection in aqueous and neat acetonitrile, and dichloromethane, and nitrogen as bath gas and carbon dioxide as sheath and nebuliser gas was optimal with hexanes. Later experiments showed that an all CO2 system was best for hexanes while all Extradry(TM) air or nitrogen (bath and sheath)---carbon dioxide (nebuliser) was best for aqueous and neat acetonitrile, and dichloromethane. When applied to real world analysis of PACs in a light gas oil, the latter gas system with acetonitrile resulted in a fourfold increase in signal intensity.
Thesis (Ph.D.)--Dalhousie University (Canada), 1999.
The instrumental parameters studied in APCI could be divided into two groups---Group 1 was associated with changes in signal but not [M+H] +/M+• and Group 2 with changes in both. Bath gas flow rate, nebuliser flow rate, probe position, data acquisition routine, source temperature, and probe temperature were all group 1 parameters. Skimmer cone orifice size, sheath gas flow rate, corona voltage, cone voltage, injection solvent, and source gas belonged to group 2. When optimising PAC detection in a new solvent, gas flow rates, source and probe temperatures, and cone and corona voltages were studied.
Of the solvents tested, organic solvents showed better results than aqueous solvents, likely the result of better nebulisation. Dichloromethane gave the highest signal, probably due to offering the best nebulisation and highest PAC solubility. The best protonation was observed in 50:50 (v/v) acetonitrile-water and hexanes. With the C5 to C9 alkanes, m/ z 59 was correlated with high signal but m/ z 43 with the highest protonation (consistent with it being the better gas phase acid of the two). These results revealed no correlation between sensitivity and ionisation mechanism. However, protonation and sensitivity were closely related to analyte structure. Ketones and carbazoles were most readily protonated and detected while partially reduced carbazoles were most poorly detected and protonated. The other PACs were of intermediate reactivity.
ESI of PACs was successful with acetic acid addition to acetonitrile (in fact, provided an order of magnitude better detection than APCI for biphenylene) and with the following chemical electron transfer reagents (CETRs): 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, chloranil and 6,7-dichloro-1,4-dihydroxyanthraquinone. The largest increase in signal intensity was for perylene with choranil. Naphthalene and pyrene derivatives differed in their reactivity to CETRs, providing a potential means of isomer discrimination.
Preliminary experiments with one, two and three gas systems indicated that Extradry(TM) air as bath gas and carbon dioxide as sheath and nebuliser gas was optimal for PAC detection in aqueous and neat acetonitrile, and dichloromethane, and nitrogen as bath gas and carbon dioxide as sheath and nebuliser gas was optimal with hexanes. Later experiments showed that an all CO2 system was best for hexanes while all Extradry(TM) air or nitrogen (bath and sheath)---carbon dioxide (nebuliser) was best for aqueous and neat acetonitrile, and dichloromethane. When applied to real world analysis of PACs in a light gas oil, the latter gas system with acetonitrile resulted in a fourfold increase in signal intensity.
Thesis (Ph.D.)--Dalhousie University (Canada), 1999.
Keywords
Chemistry, Analytical.