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Amanda JameerSuperv i sor : Dr. Donald R . Hast ie
October 31 , 2014
Evaluating the Utility of an Atmospheric Pressure Chemical Ionization Mass
Spectrometer (APCI-MS/MS) at Detecting Organic Peroxides
1
2
Presentation Outline
Project goals
What are organic peroxides?
Formation in the atmosphere
Importance of organic peroxides
Previous and current detection methods
Experimental set-up
Results
Future work
3
Project Goals
To evaluate the ability of a positive-ion atmospheric pressure chemical ionization mass spectrometer ((+) APCI-MS) to detect organic peroxide formation during β-pinene ozonolysis experiments
How do organic peroxides behave in the APCI-MS/MS? What APCI-MS/MS analysis mode will be useful for organic
peroxide detection? Based on common features from mass spectra, can a
“fingerprint” analysis be developed for future applications?
4
What are Organic Peroxides?
Compounds containing at least two oxygen atoms linked together
Where:
R1 = H atom or organic substituent
R = organic substituent
Hydroperoxide Peroxy acid
Peroxy ester Peroxy hemiacetal
Dialkyl peroxide
R
O
OH O
OH
R1
O
R1
OH
O
O
RO
O
R1
O
R
R
O
O
R
5
Formation in the Atmosphere – HO Radicals
Generally formed through hydroxyl (HO) -initiated reactions
RH + HO· → R· + H2O
R· + O2 + M → ROO· + M
ROO· + HOO· → ROOH + O2
ROO· + NO· → RO· + NO2
ROO· + NO· → RONO2
ROO· + NO2· → ROONO2
6
Formation in the Atmosphere – Ozone (O3)
O3-initiated reactions with unsaturated hydrocarbons
R4
C
O
O
R3Primary
Ozonide
Criegee Biradical
Criegee Biradical
7
Criegee Biradical
+ H2OR1
R2
O
OH
OH
Formation in the Atmosphere – Ozone (O3)
Criegee biradical reacts with water vapour
R2
C
O
O
R1
8
Importance of Organic Peroxides
Play an important role in the chemistry of the troposphere
Organic peroxides are potential products from volatile organic compound oxidation with hydroxyl (HO) radicals or ozone (O3)
Organic peroxides are reservoirs for radicals
These radicals help determine the lifetime of both natural and anthropogenic hydrocarbons in the atmosphere
May contribute to secondary organic aerosol (SOA) formation
9
Contribution to SOA
Compounds with sufficiently low vapour pressure to be present in the particle phase
Organic peroxides are major components of SOA formed from alkene ozonolysis
Docherty et al., (2005) estimated that organic peroxides contributed ~ 47% and ~85% of SOA mass formed during α- and β-pinene oxidation experiments respectively
10
Previous Detection Methods
Colorimetric method for detecting hydrogen peroxide (H2O2)
Chemiluminescent method for detecting and quantifying H2O2
High performance liquid chromatography – Fluorescence method for detecting and quantifying H2O2 and organic peroxides
Tunable diode laser adsorption spectroscopy for detecting and quantifying H2O2
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Mass Spectrometry
Can provide information about the molecular weight of a species
Depending on the instrument set-up, can provide structural information of a species
On-line analysis
Does not requires sample pre-treatment
Require samples to be ionized before analysis
12
Detecting Organic Peroxides by Mass Spectrometry
Chemical ionization mass spectrometry (CIMS) analysis
Target neutral molecule is ionized through a series of collisions with a reagent ion present in the ion source
“Softer” ionization technique where ions are produced with little excess energy
For example, Crounse et al., (2006) used CF3O- reagent ions to detect H2O2 and peroxyacetic acid (PAA)
CF3O- + H2O2 CF3O-H2O2
CF3O- + PAA CF3O-PAA
13
Detecting Organic Peroxides by Mass Spectrometry
Baker et al., (2001) and Reining et al., (2009) used (H2O)H+ reagent ions to detect organic peroxide formation from linear alkene and monoterpene ozonolysis
M + (H2O)nH+ [M + H]+ + (H2O)n
Organic peroxides containing a –OOH functional group were identified based on a mass loss of 34 u (H2O2) from the [M + H] ion while performing tandem mass spectrometry (MS/MS)
14
APCI-MS/MS
Chemical ionization at atmospheric pressure conditions
q0 Q1 Q3q2
Triple quadrupole mass spectrometer
Ion source
Purified air flowIonization reagent
(H2O)nH+
(CH3OH)nH+
Detector
Mass spectrum
33 43 55
m/z
15
Ion-Molecule Reactions in the Ion Source
Most common ion-molecule reaction is proton transfer
Occurs if the proton affinity of M is greater than the proton affinity of R
If the proton affinity between M and RH+ are similar…
Adduct formation
M + RH+ [M + H]+ + R
M + RH+ [M + RH]+
16
(+) APCI-MS/MS Analysis Modes
1. Full scan mode
2. Product-ion scan mode Select Fragmen
tAnalyze
3. Neutral-loss scan mode
Fragment
Scan Scan“offset by x”
transmitScan
Q1 q2 Q3
17
ANALYSIS OF COMMERCIALLY AVAILABLE ORGANIC PEROXIDE STANDARDS
How do o rgan i c pe rox ides behave i n the APCI -MS/MS?
What APCI -MS/MS ana l ys i s mode w i l l be use fu l f o r o rgan i c pe rox ide de tec t i on?
Phase 1 of Project
18
Experimental Design for Standard Analysis
Commercially available organic peroxides were analyzed neat or by preparing a 10% v/v solution in either water or methanol
M + (H2O)nH+ [M + H]+ + (H2O)n
[M + H2O + H]+
M + (CH3OH)nH+ [M + H]+ + (CH3OH)n
[M + CH3OH + H]+
M + 1
M + 19
M + 1
M + 33
19
Organic Peroxide Standard Selection
CH3 CH3
CH3 OOH
CH3 CH3
CH3 OO
CH3
CH3 CH3CH3CH3
OOH
CH3
O
OOH
CH3
CH3
CH3
OO
O
CH3
tert-butyl hydroperoxide
di-tert-butyl hydroperoxide
tert-butyl peroxyacetate
peracetic acid
cumene hydroperoxide
20
Results for Full Scan Analysis Mode
Ionization with Protonated Water (H2O)H+
Mass spectra were dominated by fragment ion signals
[M + H]+ or [M + H2O + H]+ ion signals not found in appreciable amounts
tert-butyl hydroperoxide tert-butyl peroxyacetate
m/z 91 or 108
m/z 133 or 151
21
Results for Full Scan Analysis Mode
Ionization with Protonated Methanol (CH3OH)H+
Fragment ions were apparent in mass spectra
Four out of five standards displayed a [M + CH3OH + H]+ ion signal
tert-butyl hydroperoxide tert-butyl peroxyacetate
22
Results for Neutral-Loss Scan Analysis
Only three standards contained an –OOH functional group tert-butyl hydroperoxide, peroxyacetic acid and cumene hydroperoxide
CH3 CH3
CH3 OOH
CH3 CH3
CH3 OO
CH3
CH3 CH3CH3CH3
OOH
CH3
O
OOH
CH3
CH3
CH3
OO
O
CH3
tert-butyl hydroperoxide
di-tert-butyl hydroperoxide
tert-butyl peroxyacetate
peracetic acid
cumene hydroperoxide
23
Neutral-Loss Scan AnalysisIonization with Protonated Water
m/z m/z
m/z
tert-butyl hydroperoxide peroxyacetic acid
cumene hydroperoxide
[M + H]+
[M + H]+
[M + H]+
24
Neutral-Loss Scan AnalysisIonization with Protonated Methanol
tert-butyl hydroperoxide peroxyacetic acid
[M + H]+
[M + H]+
25
Water versus Methanol Results
Enthalpy of the Overall Gas-phase Protonation Reaction ( ΔH°reaction )
CompoundPA
(kJ/mol)
Water as Ionization Reagent
Methanol as Ionization Reagent
tert-butyl hydroperoxide 803 -107 -37
di-tert-butyl peroxide 790 -94 -24cumene
hydroperoxide >696 peracetic acid 783 -87 -17peroxyacetate 791 -95 -25
M + (H2O)H+ [M + H]+ + H2O
M + (CH3OH)H+ [M + H]+ + CH3OH
ΔPA = PAionization reagent – PAstandard = - ΔH°reaction
26
Summary of Standard Analysis
How do organic peroxides behave in the APCI-MS/MS?
Organic peroxides fragment or decompose after the ionization process
Excess energy owing to the large ΔPA values, inducing fragmentation
Intact adduct ion only found when using methanol as an ionization reagent (i.e. [M + CH3OH + H]+)
Less energy available to facilitate fragmentation since ΔPA values are small
27
Summary of Standard Analysis
What APCI-MS/MS analysis mode was useful for organic peroxide detection?
Full scan analysis mode provided a qualitative overview of the ions produced in the ion source
Nothing “selective” about this analysis mode
Neutral-loss scan analysis mode was useful at detecting ion signals that represented a hydroperoxide or peroxy acid
A mass loss of 34 u was characteristic for organic peroxides containing a –OOH functional group
28
SMOG CHAMBER EXPERIMENTS
App ly knowledge ga ined f rom s tandard ana l ys i s
Are the re add i t i ona l common mass l o ss c r i t e r i a tha t can be used to se l ec t i ve l y de tec t
o rgan i c pe rox ides?
Phase 2 of Project
29
Smog Chamber Experiments
Ozonolysis experiments using β-pinene as the precursor hydrocarbon
Naturally emitted hydrocarbon Monoterpene with the formula C10H16
Is a significant source of SOA
30
Experimental Design for β-pinene Ozonolysis
MFC Purified
Airflow
β-pinene injection
Ozone Generator
Compressed Air
Smog Chamber Input
Pump(+) APCI-MS/MS
Ozone Analyzer
8 m3 Smog chamber
Smog Chamber Output
MFM
31
(+) APCI-MS/MS Analysis Modes
1. Full scan mode
2. Product-ion scan mode Select Fragmen
tAnalyze
3. Neutral-loss scan mode
Fragment
Scan Scan“offset by 34 u”
transmitScan
Q1 q2 Q3
32
Results for Ozonolysis Experiments
Ionization using Protonated Water
Full Scan Mass Spectrum Odd number m/z values Nothing selective about this analysis mode
m/z
33
Results for Ozonolysis Experiments
Ionization with Protonated Water
Neutral-loss Scan Mass Spectrum m/z values that lost 34 u during collision events Reduced complexity to a handful of m/z values
m/z
m/z values
171173187201203
34
Ionization with Protonated Methanol
Chemical ionization using protonated water caused excessive fragmentation during standard analysis
Intact ions were observed during full scan analysis while using protonated methanol as an ionization reagent
M + (CH3OH)H+ [M + CH3OH + H]+
M + 33
Can additional m/z values be observed in full scan mass spectrum if protonated methanol is used as an ionization
reagent?
35
Results for Ozonolysis Experiments
Ionization with Protonated Methanol
Full scan mass spectrum Odd number m/z values Appears similar to previous full scan mass spectrum using protonated water
m/z m/z
Ionization with protonated waterIonization with protonated methanol
36
Results for Ozonolysis Experiments
Ionization with Protonated Methanol
Neutral-loss mass spectrum m/z value capable of losing 34 u No additional m/z values observed
m/z
Ionization with protonated methanol
m/z
Ionization with protonated water
37
Results for Ozonolysis Experiments
No new information was obtained by using protonated methanol as an ionization reagent
Ozonolysis experiments continued using protonated water as an ionization reagent
Can additional m/z values be observed in full scan mass spectrum if protonated methanol is used as an ionization
reagent?
38
Product-Ion Scan Analysis
m/z values 171, 173, 187, 201, and 203 were investigated further using product-ion scan analysis mode
Validate mass losses of 34 u and determine additional common mass losses
Propose plausible structures based on observed losses and ozonolysis mechanism
39
Product-Ion Mass Spectrum for m/z 187
m/z
Losses observed
18 u (H2O) 32 u (O2) 34 u (H2O2) 62 u (H2O2 and CO)
40
Product-Ion Scan Analysis Summary
Neutral Loss Mass (u)
m/z 18 32 34 62
171 Yes Yes Yes Yes
173 Yes YesYes
(minor)Yes
(minor)
187 Yes Yes Yes Yes
201 YesYes
(minor)Yes
(minor) Yes
203 YesYes
(minor) Yes Yes
41
Investigating Losses of 62 u
Combined mass losses totaling 62 u Loss of H2O2 and CO Peroxy acids can explain these losses
3-chloroperbenzoic acid
Hydroperoxide Peroxy acid
Peroxy ester Peroxy hemiacetal
Dialkyl peroxide
R
O
OH O
OH
R1
O
R1
OH
O
O
RO
O
R1
O
R
R
O
O
R
42
3-chloroperbenzoic acid
[M + H]+ and [M + CH3OH + H]+ were apparent in full scan mass spectrum
Product-ion mass spectrum for m/z 173 showed major losses of 62 u
Possible for peroxy acids to exhibit this mass loss during collision events
m/z m/z
Full Scan Mass Spectrum Product-ion Mass Spectrum for m/z 173
43
Proposed Structures
O
OOH
CH3
CH3
CH3
CH3O
O
OOH
CH3
CH3
O OHOH
CH3
CH3O
O
O
O
OH
CH3CH3
O
OH
OO
OH
CH3
CH3
OOOH
O
MW 170 MW 172 (a)
MW 172 (b)
MW 186 MW 200 MW 202
44
Summary for Smog Chamber Experiments
Are there additional common mass loss criteria that can be used to selectively detect organic peroxides?
Yes, product-ion mass spectra for organic peroxide candidates showed common mass losses
Aside from mass losses of 34 u, mass losses of 32 and 62 u can be used to selectively enhance the detection organic peroxides containing a –OOH functional group
45
Project Summary
(+) APCI-MS/MS can be used to selectively detect organic peroxides
Required little to no sample treatment before analysis
Tandem mass spectrometry analysis was useful to for selectively detecting organic peroxides
Neutral-loss analysis for 32, 34, and 62 u can be used as a criteria to observe m/z values that were organic peroxide candidates
46
What a re the fu tu re d i r ec t i ons f o r th i s p ro jec tknowing tha t o rgan i c pe rox ides can be
se l ec t i ve l y de tec ted by the APCI -MS/MS?
Future Work
47
Future Work
Factors that influence organic peroxide formation
Additional experiments under high and low NOx (NO + NO2) conditions
Relative humidity experiments
Quantitative studies
Need standards that are representative of products formed in the smog chamber
48
Acknowledgements
Supervisor: Dr. Donald HastieGroup members: Mehrnaz Sarrafzadeh and Zoya Dobrusin
Supervisory and exam committee members: Dr. R. McLaren, Dr. J. Rudolph, and Dr. M. Gordon
CAC graduate students and postdocsCarol Weldon from CAC
Greg Koyanagi from CRMS IACPES
Charles Hantho and Harold Schiff Foundations