Combined application of Online FIGAERO-CIMS and Offline LC-Orbitrap MS to Characterize the Chemical Composition of SOA in Smog Chamber Studies

A combination of online and offline mass spectrometric techniques was used to characterize the chemical composition of secondary organic aerosol (SOA) generated from the photooxidation of α-pinene in an atmospheric simulation chamber. The filter inlet for gases and aerosols (FIGAERO) coupled with a high-resolution time-of-flight iodide chemical ionization mass spectrometer (I–ToF-CIMS) was employed to track the evolution of gaseous and particulate components. Extracts of aerosol particles sampled onto a filter at the end of each experiment were analyzed using ultra-performance liquid chromatography ultra-high-resolution tandem mass spectrometry (LC-Orbitrap MS). Each technique was used to investigate the major SOA elemental group contributions in each system. The online CIMS particle-phase measurements show that organic species containing exclusively carbon, hydrogen and oxygen (CHO group) dominate the contribution to the ion signals from the SOA products, broadly consistent with the LC-Orbitrap MS negative mode analysis which was better able to identify the sulphur-containing fraction. An increased abundance of high carbon number (nC ≥ 16) compounds additionally containing nitrogen (CHON group) was detected in the LC-Orbitrap MS positive ionisation mode, indicating a fraction missed by the negative mode and CIMS measurements. Time series of gas-phase and particle-phase oxidation products provided by online measurements allowed investigation of the gas-phase chemistry of those products by hierarchical clustering analysis to assess the phase partitioning of individual molecular compositions. The particle-phase clustering was used to inform the selection of components for targeted structural analysis of the offline samples. Saturation concentrations derived from near-simultaneous gaseous and particulate measurements of the same ions by FIGAERO-CIMS were compared with those estimated from the molecular structure based on the LC-Orbitrap MS measurements to interpret the component partitioning behaviour. This paper explores the insight brought to the interpretation of SOA chemical composition by the combined application of online FIGAERO-CIMS and offline LC-Orbitrap MS analytical techniques.

Silence as Elective Mutism in Minor Cinema

This article advances mutism as a creative mode and conceptual tool to treat silence in cinema. Whereas mutism can be a productive concept for the study of auditory and visual absence in a broader theoretical framework, my focus here is on the silence of film characters. Drawing on correspondences between the critical and the clinical in Gilles Deleuze’s writing, I argue that adopting mutism as a tool of film-philosophy permits us to supersede traditional film analysis and examine silence not as an interpretive condition at the level of the plot but as a critical-clinical mode of experimentation related to the symptomatology of life. After presenting a brief clinical history of “elective” and “selective” mutism, I then draw on the suppressed understanding of “elective mutism”. I demonstrate that “elective mutism”, which might appear to be a negative and powerless disorder in its clinical presentation, transforms itself into an affirmative and empowering (dis)order that inspires creative experimentation in cinema. In postwar films with mute protagonists, such as Ingmar Bergman’s Persona (1960), “elective mutism” engenders a negative mode of existence in its symptomatology, which can be analysed according to the tenets of Theodor W. Adorno’s philosophy of negativity. By contrast, Deleuze’s philosophy of affirmativity and the concept of minor cinema allow for a renewed positive examination of “elective mutism” in more recent films with silent characters, such as Elia Suleiman’s Palestinian quartet (1996; 2002; 2009; 2019). Approaching minor cinema as both a cinema of experimentation and minoritarian cinema, I contend that in films made by minorities mutism becomes more pronouncedly “elective” in an affirmative sense. As a mode of protest and resistance, “elective mutism” is not only a rejection of the present status quo but also an expression of futurity. Finally, I maintain that the concept of “elective mutism” can relate to and stimulate the discussion of many contemporary sociopolitical phenomena.

Surface-Induced Dissociation of Anionic vs Cationic Native-like Protein Complexes

<p>Characterizing protein-protein interactions, stoichiometries, and subunit connectivity is key to understanding how subunits assemble in biologically relevant multi-subunit protein complexes. Native mass spectrometry (nMS) has emerged as a powerful tool to study protein complexes due to its low sample requirements and tolerance for heterogeneity. For such nMS studies, positive mode ionization is routinely used and charge reduction, through the addition of solution additives, is often used, as the resulting lower charge states are often more compact and considered more native like. When studied with surface-induced dissociation, charge reduced complexes often give increased structural information over their “normal-charged” counter parts. A disadvantage of charge-reduction is that increased adduction, and hence peak broadening, is often observed when charge-reducing solution additives are present. Recent studies have shown that protein complexes ionized using negative mode generally form in lower charge states relative to positive mode. Here we demonstrate that the lower charged protein complex anions, activated by SID in an ultrahigh mass range Orbitrap mass spectrometer, fragment in a manner consistent with their solved structure, hence providing substructural information. Negative mode ionization in ammonium acetate offers the advantage of charge reduction without the peak broadening associated with solution phase charge reduction additives and provides direct structural information, when coupled with SID. </p>

Surface-Induced Dissociation of Anionic vs Cationic Native-like Protein Complexes

<p>Characterizing protein-protein interactions, stoichiometries, and subunit connectivity is key to understanding how subunits assemble in biologically relevant multi-subunit protein complexes. Native mass spectrometry (nMS) has emerged as a powerful tool to study protein complexes due to its low sample requirements and tolerance for heterogeneity. For such nMS studies, positive mode ionization is routinely used and charge reduction, through the addition of solution additives, is often used, as the resulting lower charge states are often more compact and considered more native like. When studied with surface-induced dissociation, charge reduced complexes often give increased structural information over their “normal-charged” counter parts. A disadvantage of charge-reduction is that increased adduction, and hence peak broadening, is often observed when charge-reducing solution additives are present. Recent studies have shown that protein complexes ionized using negative mode generally form in lower charge states relative to positive mode. Here we demonstrate that the lower charged protein complex anions, activated by SID in an ultrahigh mass range Orbitrap mass spectrometer, fragment in a manner consistent with their solved structure, hence providing substructural information. Negative mode ionization in ammonium acetate offers the advantage of charge reduction without the peak broadening associated with solution phase charge reduction additives and provides direct structural information, when coupled with SID. </p>

Surface-Induced Dissociation of Anionic vs Cationic Native-like Protein Complexes

<p>Characterizing protein-protein interactions, stoichiometries, and subunit connectivity is key to understanding how subunits assemble in biologically relevant multi-subunit protein complexes. Native mass spectrometry (nMS) has emerged as a powerful tool to study protein complexes due to its low sample requirements and tolerance for heterogeneity. For such nMS studies, positive mode ionization is routinely used and charge reduction, through the addition of solution additives, is often used, as the resulting lower charge states are often more compact and considered more native like. When studied with surface-induced dissociation, charge reduced complexes often give increased structural information over their “normal-charged” counter parts. A disadvantage of charge-reduction is that increased adduction, and hence peak broadening, is often observed when charge-reducing solution additives are present. Recent studies have shown that protein complexes ionized using negative mode generally form in lower charge states relative to positive mode. Here we demonstrate that the lower charged protein complex anions, activated by SID in an ultrahigh mass range Orbitrap mass spectrometer, fragment in a manner consistent with their solved structure, hence providing substructural information. Negative mode ionization in ammonium acetate offers the advantage of charge reduction without the peak broadening associated with solution phase charge reduction additives and provides direct structural information, when coupled with SID. </p>