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Studio della caratterizzazione chimica di composti organici polari nel particolato atmosferico
No full textIn recent years there has been increasing interest in the public and in the authorities
on properties and origin of atmospheric particulate matter (PM) because of it has
been established its negative influence on environment and human health¹. In
particular, it is becoming more important to understand the mechanisms that lead to
the formation and distribution of atmospheric aerosol. It is a critical problem for
analytical chemistry, because the particles consists of more than thousands of
substances, both organic and inorganic, so it has not yet been realized a total
speciation². Moreover, the processes of atmospheric transport of air masses and the
transformation of compounds, which are subjected to oxidizing agents and chemical
reactions, make it essential to identify the sources even when they are very distant
from the point of collection of PM. For this reason, rather than characterizing all the
substances, the modern approaches tend to identify specific substances (markers) that
are characteristic of specific sources, in order to distinguish between biogenic and
anthropogenic sources and estimate the oxidation level of the substances produced
from primary sources (SOA: Secondary Organic Aerosol)³-⁵.
The aim of this work was to develop an innovative multi-residue method for the
analysis of a complex system like the atmospheric aerosol in order to obtain
information about the sources, the anthropogenic contribution and the oxidation level
(SOA), identifying and quantifying a wide range of compounds.
This work had focused on a group of substances present in the PM that could provide
relevant information: the soluble organic fraction (WSOC) in PM, that is the most
bioavailable, may be useful in order to estimate the risk on human health. The main
components of this fraction are the dicarboxylic acids and sugars³, ⁶.
These compounds are present at very low concentrations (average few ng/m3 of air
sampled), for this reason there is critical need for efficient and sensitive analytical
techniques; gas chromatography coupled with mass spectrometry (GC-MS) is the
mostly used because of its great sensitivity and excellent separation and
identification capabilities on highly complex matrices such as PM. Moreover, it is
necessary a preliminary process of derivatization in order to raise the volatility of
polar compounds for GC analysis.
Therefore, this work started considering and comparing the most used derivatization
techniques, the silylation and esterification, in order to choose the one that would
reach the level of sensitivity, specificity and applicability necessary for
environmental analysis⁷-⁹. From the results, the best technique is silylation with N,
O-bis (trimethylsilyl)-trifluoroacetammide (BSTFA): the developed method permits
to analyze 15 carboxylic acids with detection limits lower than 3ng/m3.
The study was extended in order to analyze other compuonds present in WSOC: in
particular sugars, that are specific molecular markers that provide important
information on sources of organic compounds in PM.
The derivatization reaction was optimized, in particular the parameters that affect the
yield and the sensitivity of the analytical method, such as time and reaction
temperature and the amount or composition of the reagents. We used a mathematical/statistical approach to assess simultaneously the effect of these factors
with a small number of experimental tests. We used an experimental design model: a
central composite design¹⁰. This allowed the development of a method for the
simultaneous determination of 15 acids and 7 sugars present in atmospheric particles
in concentration level less than 10ng/m3 in most cases.
The procedure was successfully applied to a series of samples of atmospheric
particles, both fine (PM2.5) and ultrafine (PM1), within an integrated environmental
monitoring of a local area around Bologna (Project Moniter , developed by ARPAER):
consisted of two sampling campaigns, one on summer and one on winter, over
8 sites with urban, rural or intermediate characteristics. The analytical data obtained
have provided significant information on the contribution from anthropogenic urban
transport and domestic heating, the contribution due to agriculture and the state of
formation of organic substances originating from processes in the atmosphere (SOA).
In the development of innovative methods applicable to environmental monitoring, it
has also studied a new method for analysis of PM samples, based on direct thermal
desorption, with in situ derivatization and gas chromatography coupled with mass
spectrometry time of flight (IDTD-GC-TOFMS)¹¹-¹³. This study was conducted in
collaboration with Prof. Ralf Zimmermann and his research group at the Helmholtz
Zentrum in Munich (Germany). This technique enables the analysis of environmental
samples avoiding the most common extraction treatments because the analytes are
thermally directly desorbed from filter and can enter the chromatographic column.
The addition of the silylating agent on the filter permits a gas-phase reaction of polar
compounds. The application of IDTD-GC-TOFMS in PM2.5 samples simultaneously
led to the identification of both polar (such as sugars) and apolar species (e.g. alkanes
and polycyclic aromatic hydrocarbons), with great advantage in terms of time
consuming and loss of analytes during sample pretreatment.
In conclusion, it had been developed analytical methods suitable for environmental
monitoring in order to obtain information on chemical composition that can be
integrated with other information, i.e. physical, meteorological, environmental, for an
enhanced approach to the study of particulate air pollution and its impact on the
environment and human health.
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2005
Determination of low-molecular-weight dicarboxylic acids in atmospheric aerosols: comparison between silylation and esterification derivatization procedures for GC-MS analysis
No full textThis paper is focused on the determination of LMW dicarboxylic acids (C3-C10): the most widely used procedures, i.e., esterification with butyl alcohol and BF3 like catalyst and a silylation with N,O-bis-(Trimethylsilyl)trifluoroacetamide (BSTFA) and trimethylchlorosilane (TMCS), were investigated. For each method, the effect of various experimental parameters on the reaction yield has been investigated and optimized: time and temperature, or amount of reagents. The better procedure was searched for the faster one-step derivatization to determine C3-C10 dicarboxylic acids as target compounds.
The advantages and drawbacks of the methods are investigated and compared in terms of precision and accuracy of the obtained results, sensitivity and detection limit of the procedure.
The obtained results show that the silylation procedure is the method more compatible with application to chemical analysis in PM samples: satisfactory precision and accuracy are obtained for all the studied acids at the sub-nmol level at which the dicarboxylic acids are expected to be present in trace levels. Butyl esters of low molecular weight dicarboxylic acids are too volatile to yield evaporative losses and too unstable to be accurately quantified so that quantification was possible for the dicarboxylic acids.
The precision and accuracy were investigated by comparing results obtained by the two procedures from the simultaneous analysis of dicarboxylic acids in the same PM2.5 and PM10 samples
GC/MS analysis of water-soluble organics in atmospheric aerosol: Optimization of a solvent extraction procedure for simultaneous analysis of carboxylic acids and sugars
No full textThe main goal of the present study was to develop a procedure for the simultaneous GC/MS analysis of a wide range of water-soluble organic compounds (WSOCs, mainly dicarboxylic acids and sugars) in atmospheric aerosol as chemical markers of atmospheric processes. The response surface methodology, including central composite design, was applied to systematically investigate and optimize the operating conditions of a solvent extraction method as the most widely used procedure for determining WSOCs in particulate matter (PM) samples. A solvent mixture of methanol/dichloromethane (90:10) and a volume of 10 ml were the optimum conditions that permit the simultaneous analysis of 30 target WSOCs, including dicarboxylic acids and sugars. Recoveries and limits of detection were determined for a standard mixture containing target analytes, and they varied from 79 to 103 % and 0.3 to 1 ng m−3, respectively. The optimized procedure was used for the analysis of field PM filters and demonstrated its feasibility in detecting several important environmental WSOCs
Chemical characterization of polar organic markers in aerosols in a local area around Bologna, Italy
No full textThe composition and seasonal variations of water-soluble organic compounds,
including 18 dicarboxylic acids and 7 sugars, were determined in the atmospheric aerosol during
intensive summer and winter campaigns. This study is a part of the MONITER project developed
by ARPAER (Environment Agency of Emilia Romagna region) with the aim to evaluate the
potential impact of the emissions from a municipal waste incineration plant on air quality of the
surrounding area.
In both the seasons the most abundant compound is levoglucosan, as the major by-product from
biomass burning. The abundances of dicarboxylic acids exhibit a seasonal pattern with higher
winter concentrations: the distribution profiles and the diagnostic ratios of the markers suggest
that the particulate organics are mainly emitted by primary sources (power plants, vehicular
2
circulation, biomass burning) in winter and produced by photochemical reactions from both
biogenic and anthropogenic precursors in summer. The spatial variations of the concentration of
the target compounds show a homogenous composition, reflecting the regional nature of the PM
composition, weakly impacted by emissions of local sources, including the incinerator
Studio di tecniche di analisi GC-MS per la caratterizzazione chimica della frazione idrosolubile del particolato atmosferico
No full textVengono descritte tecniche di analisi GC-MS per la caratterizzazione chimica della frazione idrosolubile del particolato atmosferico, in particolare acidi carbossilici e zuccheri
GC–MS analysis of low-molecular-weight dicarboxylic acids in atmospheric aerosol: comparison between silylation and esterification derivatization procedures
No full textThe paper describes methods for the determination
of low-molecular-weight (LMW) dicarboxylic acids in
atmospheric aerosols as important chemical tracers for
source apportionment of aerosol organics and for studying
atmospheric processes leading to secondary organic aerosol
formation. The two derivatization procedures most widely
used in GC analysis of dicarboxylic acids were compared:
esterification using BF3/alcohol reagent and silylation using
N,O-bis(trimethylsilyl)-trifluoroacetamide (BSTFA). The
advantages and drawbacks of the two methods are
investigated and compared in terms of (1) precision and
accuracy of the results and (2) sensitivity and detection
limit of the procedure. The comparative investigation was
performed on standard solutions containing target C3–C9
dicarboxylic acids and on experimental particulate matter
(PM) samples. Attention was focused on low-volume
sampling devices that collect small amounts of sample for
organic speciation. The results show that, overall, both the
techniques appear suitable for the analysis of LMW
dicarboxylic acids in atmospheric aerosols since they
provide low detection limits (≤4 ng m−3) and satisfactory
reproducibility (RSD%≤15%). Between them, BSTFA
should be the reagent of choice under the most limiting
conditions of PM filters collected by low-volume air
samplers: It provides determination of all the target C3–C9
dicarboxylic acids with lower detection limits (≤2 ng m−3)
and higher reproducibility (RSD%≤10%
OPTIMIZATION OF THE SILYL-DERIVATION PROCEDURE FOR SIMULTANEOUS DETERMINATION OF CARBOXYLIC ACIDS AND SUGARS IN PM SAMPLES
No full textThis paper describes the development of a derivatization procedure — silylation using BSTFA (N,O-bis(trimethylsilyl)-trifluoroacetamide) — for the simultaneous GC-MS analysis of a wide range of water-soluble organics in atmospheric aerosols. The reaction operating conditions were optimized in order to achieve the highest response for a large number of dicarboxylic acids and sugars. Optimization was carried out using the response surface methodology (RSM) including central composite design (CCD). The factors considered were: (i) reaction temperature (50°C-90°C), (ii) the reaction duration (60 min-90 min), (iii) reagent concentrations (10%-100% of the total solution volume) and (iv) pyridine concentration (0%-50% of the derivatization reagent). In addition, the optimum derivatization conditions were determined by considering the experimental limitations of the operative constrains and verified on real samples extracted from PM filters.
The optimized procedure was extended to a broader range of 25 target analytes that are relevant chemical markers, i.e., 18 carboxylic acids and 7 sugars. In addition, the applicability of the optimized procedure was verified in environmental matrices from PM filters collected under different conditions, i.e. different seasons (summer vs. winter), different sampling sites (urban vs. rural), different particle size dimensions (PM2.5 vs. PM1)
GC–MS analysis of water-soluble organics in atmospheric aerosol: Response surface methodology for optimizing silyl-derivatization for simultaneous analysis of carboxylic acids and sugars
No full textThis paper describes the development of a derivatization procedure - silylation using N,O-bis(trimethylsilyl)-trifluoroacetamide (BSTFA) - for the simultaneous GC-MS analysis of a wide range of water-soluble organics in atmospheric aerosols. The reaction operating conditions were optimized using the response surface methodology (RSM) including central composite design (CCD) in order to achieve the highest response for a large number of dicarboxylic acids and sugars. The factors considered were: (i) reaction temperature (50-90°C), (ii) the reaction duration (60-120min), (iii) reagent concentrations (10-100% of the total solution volume) and (iv) pyridine concentration (0-50% of the derivatization reagent). On the basis of RSM and experimental evidence, the optimum derivatization conditions were defined as reaction temperature of 75°C, reaction duration of 70min, BSTFA reagent concentration of 55% and pyridine concentration of 35%. The optimized protocol was extended to a broader range of 22 target analytes that are relevant chemical markers, i.e., 15 carboxylic acids and 7 sugars. In addition, the applicability of the optimized procedure was verified in environmental matrices from PM filters collected under different conditions, i.e., different seasons (summer vs. winter), different sampling sites (urban vs. rural), different particle size dimensions (PM2.5 vs. PM1). © 2011 Elsevier B.V
Metallacrowns of Ni(II) with α-aminohydroxamic acids in aqueous solution: beyond a 12-MC-4, an unexpected (vacant?) 15-MC-5
No full textContribution of wood combustion to wintertime atmospheric aerosol in Emilia Romagna region
No full textCurrently, numerous studies demonstrate the increasing relevance of biomass combustion emissions as a source of atmospheric particles in urban environments in Europe, especially during winter, when the domestic burning of wood logs, briquettes, chips and pellet represents an important renewable energy source. Biomass burning activities are significant emission sources for particulate matter (PM), contributing for a relevant share to the total PM2.5 and PM10 emitted, which may contain numerous toxic/carcinogenic components with a potentially high impact on human health. Therefore, a quantitative understanding of the contributions from biomass burning (BB) to fine organic aerosol is essential for the planning of efficient PM abatement strategies.
This work investigates the contribution of residential wood combustion in urban and rural sites in Emilia Romagna (Northern Italy) during five intensive experimental campaigns held in fall/winter through the 2011-2014 years, as a part of the of the “Supersito” project.
A comprehensive study was conducted on daily samples to investigate the concentrations of several individual polar and apolar organic compounds related to emissions from wood combustion. Of these individual compounds, levoglucosan, mannosan and galactosan were found to be the dominant species as the most specific tracers. Other abundant compounds included low-molecular-weight carboxylic acids, polycyclic aromatic hydrocarbons and methoxylated phenols. In addition, elemental and organic carbon (EC/OC) were investigated.
The diagnostic ratios between anhydrosugars and methoxylated phenols were computed to characterize the type of wood burnt, in particular to discriminate between hardwood and softwood. The obtained values indicate the concomitant contribution of both the wood type, with an increased contribution of hardwood in some periods.
The ambient mono-tracer approach using ambient levoglucosan concentrations was applied to compute the relative contribution of wood burning emissions to the Organic Carbon (OC) and Organic Matter (OM) in atmospheric aerosol. Wood burning is an important contributor to as it accounted on average for 36% of OC and 29% of OM.
No substantial spatial variability was found in concentrations of the investigated markers at urban and the rural background sites, which indicate homogeneous impact of wood combustion within the study areas
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