the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 23 Jun 2025
Two optimized methods for the quantification of anthropogenic and biogenic markers in aerosol samples using liquid chromatography mass spectrometry and gas chromatography mass spectrometry
Abstract. In this study, we present two optimized analytical methods for the quantification of molecular markers to attribute the contribution of various Volatile Organic Compounds (VOC) oxidation products to Secondary Organic Aerosol (SOA). Those involve Ultrahigh Performance Liquid Chromatography Electrospray Ionization coupled to Ion Mobility Time of Flight Mass Spectrometry (UPLC/ESI-IMS-QTOFMS) and Gas Chromatography Mass Spectrometry (GC-MS). Liquid extraction was performed for both techniques, with an extra derivatisation step with N,O-Bis(trimethylsilyl)trifluoroacetamide (BSTFA) containing 1 % trimethylchlorosilane (TMCS) for GC-MS analysis, enhancing the compound detection capacity. Between the two techniques, 23 biogenic and anthropogenic markers were identified, with five common species detected. Recoveries > 80 % were observed for nitro-containing compounds and > 66 % for aromatic and non-aromatic acids except for 3-methyl-1,2,3-butanetricarboxylic acid. Limits of detection < 5 ng were observed by UPLC/ESI-IMS-QTOFMS analysis for 4-nitrophenol and 2-methyl-4-nitrophenol, while GC-MS (with BSTFA derivatisation) analysis allowed better detection of lower mass compounds (for example limit of detection for 2-methylerythritol was 0.10 ng). While UPLC/ESI-IMS-QTOFMS allow the analysis of high molecular weight compounds at high resolution and sensitivity, GC-MS analysis focus on compounds of lower mass and higher polarity, together, these complementary methods provide a comprehensive tool for the quantification of organic markers arising from the airborne transformation of compounds of both biogenic and anthropogenic origins.
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RC1: 'Comment on egusphere-2025-2393', Anonymous Referee #1, 19 Jul 2025
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The authors present two fully characterized complementary methods to quantify SOA marker compounds from filter samples. In this work, a number of target compounds that were previously analyzed in dedicated studies were combined and the instrument response was systematically investigated. The manuscript provides figures of merit for all investigated compounds and the instrument responses were well characterized. Such a combination of methods contributes to the better characterization of SOA composition and the comparable quantification of these marker compounds. The paper is logically structured and well written. I have, however, a few concerns about some of the numbers presented. In my opinion the paper can be suitable for publication in Atmospheric Measurement Techniques once a few issues have been addressed.
- The authors applied two previously used LC methods and combined both to test a new method. Although the authors claimed that most of the target compounds eluted after 20 min of the second method, the new method was chosen to run for 45 min with a comparable gradient, which seems quite arbitrary. Did the authors test carry-over effects for the shorter LC methods or the effect of longer flushing times on TIC and repeatability?
- More to that point, the authors describe in section 3.1.4, that the instrument signal response decreased during a continuous sequence by more that 70%. I am quite concerned about this finding, as the quantification is also depending on this response. Do the authors have an explanation for this behavior and were some parameters tested to improve on that? The authors claim that there is no carry-over effect, as none of the analytes were found in subsequent blank samples, but there seems to be some sort of matrix effect during the ionization. The authors need to provide more details here.
- In line 329 the authors describe, that for analytes with higher variability, the third replicate was not considered due to loss over time, but it seems to me from figure 2, that due to the loss of signal, the second and third replicate of a sample show lower variability. Can the authors clarify how this effected the analysis?
- The GC method applied by the authors was changed from previously used methods. Namely the SPE step was replaced by liquid extraction and direct injection, which resulted in higher LODs compared to the previous method. The authors note that in this work a wider range of compounds were analyzed, but did the authors test the markers investigated in this work with SPE injection?
- For the GC/MS method, BSTFA is used as a derivatization agent for alcohols. Perhaps the authors could briefly discuss the possibility of using other derivatization agents. This could specifically improve the detection of other compound classes, such as carbonyls.
- In the conclusion section the authors compare the LODs for the reported method with literature values. As many previously reported values are much lower, it would be worth highlighting the benefit of this combined method more, to emphasize the value from being able to analyze different compounds classes in one combined protocol.
Technical comments:
L.47 should read “nitrooxy organosulfate markers”
L.240 The authors should rephrase the last sentence of that paragraph
L.254 should read “the instrument variability between three randomly injected replicates of the mixture solution without filter extraction was less than 21% for all target compounds.”
L.274 should read “Signals were also higher than for sampled using inserts,…”
L.277 the authors should emphasize better that this was a hypothetical issue that they tested for and can decline it as a source of variability.
L.327 should read “is reported in Table 2”
L.359 unclear reference with “section 0”
L.381 ff The authors should rephrase that sentence as it is not clear which conditions are referred to
L.402 I suggest “best representation of real samples” instead of “the maximum equivalent time”
L.435 should read “ offered the advantage of detecting phenol compounds at higher sensitivity”
L.487 I would suggest “were about twice as high as”
L.502 The use of “systematically” in the context of three individual samples is a bit unclear
Citation: https://doi.org/10.5194/egusphere-2025-2393-RC1
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