The aim of this thesis work is the preparation and characterization of a new material to be used as solid phase for pre-concentration of organic pollutants. In particular, in this thesis it has been test for analytes belonging to benzenesulfonamides (BSAs), benzotriazoles (BTRs) and benzotiazoles (BTs) from environmental waters. These molecules are considered emerging organic pollutants because they have good chemical stability, high polarity and water solubility, and resistance to biodegradation [1]. Their toxicity is not yet completely known because they have been recently identified, and environmental quality standards for the water compartment have been defined only for benzotriazole (BTH) and 5-methyl-benzotriazole (5-TTR) (19 e 20 µg/L, respectively). The low concentrations of these analytes in the environment require high sensitive analytical methods based on GC-MS/MS or HPLC-MS/MS, which include a preliminary pre-concentration step usually made by solid phase extraction (SPE) with commercial cartridges. The new carbon-based sorbent phase has been prepared through the pyrolysis of humic acids (HAs) deposited on silica in N2 atmosphere at 600 °C. The obtained material (HA-C@silica) has been characterized through many techniques (TGA, SEM, EDS, BET e XPS) to evaluate its properties, and results show that the pyrolytic carbon immobilized on silica (3.5 wt% on the material prepared starting from HAs 20%) consists on a sp2 aromatic structure that conserves polar groups such as –C=O e –COOH. Basing on these results, this material can be considered a mixed-mode phase. HA-C@silica has been applied as sorbent for column-SPE using 200 mg of material packed in 3 mL cartridges.Two HA-C@silica samples were initially prepared and tested at nominal HAs concentrations, 10 and 20 wt%. The leachates of tap water samples (50 mL spiked with 50 µg/L of each analyte), showed that HA-C@silica obtained from the initial concentration of HAs 20 wt% guaranteed quantitative adsorption of all analytes, except of BSA, only partially retained. BSA is indeed the most hydrophilic compound among those analyzed (logP = 0.49), and it was no longer considered for subsequent recovery experiments. A quantitative elution from HA-C@silica was gained for all the analytes by MeOH (4 mL). To increase the enrichment factor (EF), the eluate has been evaporated under nitrogen flow until 0.25 mL before the HPLC-ESI MS/MS determination (MRM mode). The first tests have been made on different volumes (50-250 mL) of tap water enriched with concentrations between 50-5 µg/L of each analyte, obtaining recoveries higher than 70% (RSD < 12%, n=3) and reaching EF = 1000.Successively samples of river water (100 and 250 mL) enriched with two different concentrations (5 and 1 µg/L) were analyzed. Also in this matrix recoveries were quantitatives for all analytes (71-114%, RSD < 16%, n=3), and EF up to 1000.Quantification has been performed for all samples on the SPE eluate by standard additions method, carried out in the range 250-750 µg/L (R2 > 0.9962) by HPLC-ESI-MS/MS autosampler. This procedure was adopted for faster analysis, greater repeatability and good compensation of matrix effects, observed in the case of river water. HA-C@silica ensures quantitative recoveries (70-94%) for all analytes, it is easily prepared in laboratory with great reproducibility (inter-batch precision < 12%, n=3) with low costs (silica 0.1 €/g, HAs 0.6 €/g, Sigma-Aldrich prices 2018) and it is reusable (at least for two quantitative extractions). Furthermore, preparation does not involve use of organic solvents and/or hazardous reagents.
Il presente lavoro di tesi ha come obiettivo la preparazione e la caratterizzazione di un nuovo materiale a base di carbonio proveniente dalla pirolisi di acidi umici (HAs) da utilizzare come fase solida adsorbente per la pre-concentrazione in colonna SPE. di inquinanti emergenti. Dopo essere stata caratterizzata è stata testata per la pre-concentrazione di benzensolfonammidi (BSAs), benzotriazoli (BTRs) e benzotiazoli (BTs) da acque ambientali. Essi sono considerati contaminanti organici emergenti in quanto sono caratterizzati da buona stabilità chimica, elevate polarità e solubilità in acqua e resistenza alla biodegradazione [1]. La definizione della loro tossicità è ancora in fase preliminare in quanto sono inquinanti di recente individuazione nell’ambiente e solo per benzotriazolo (BTH) e 5-metil-benzotriazolo (5-TTR) sono stati definiti standard di qualità ambientali (19 e 20 µg/L, rispettivamente). Le basse concentrazioni in cui gli analiti in esame sono presenti nell’ambiente (ordine dei ng-µg/L) implicano l’utilizzo di strumenti molto sensibili (GC-MS/MS o HPLC-MS/MS) e un passaggio preliminare indispensabile di pre-concentrazione, solitamente eseguita mediante estrazione in fase solida (SPE). La procedura di preparazione prevede l’adsorbimento su silice micrometrica di acidi umici disciolti in acqua, l’eliminazione della fase liquida e la successiva pirolisi del solido (N2, 600°C). Il materiale ottenuto (HA-C@silice) è stato caratterizzato mediante diverse tecniche (TGA, SEM, EDS, BET e XPS) per valutarne le proprietà chimico-fisiche. I risultati hanno indicato che il carbonio pirolitico immobilizzato sulla silice (3.5% nel materiale con HAs 20%) è costituito da una struttura aromatica sp2 che conserva quantità apprezzabili di gruppi polari come –C=O e –COOH, pertanto può essere considerato come una fase mista (mixed-mode). HA-C@silice è stato utilizzato come SPE impaccando 200 mg di fase adsorbente in cartucce da 3 mL. Inizialmente sono stati preparati due materiali, uno a concentrazione nominale di HAs del 10% e l’altro del 20% (m/m). Analizzando i percolati di campioni di acqua di rubinetto opportunamente arricchiti con quantità note degli analiti in esame, è stato scelto il materiale a più alta percentuale di HAs perché è stato quello che ha dato un adsorbimento quantitativo per tutti i composti, ad esclusione della BSA, la quale è solo parzialmente trattenuta da HA-C@silice poiché è il composto più idrofilico tra i sette in esame (logP = 0.49) e quindi non è stata presa in considerazione nelle prove di recupero successive. La fase eluente, metanolo-acido acetico (90:10 v/v), scelta inizialmente sulla base di un precedente lavoro di tesi focalizzato sull’utilizzo di nanotubi di carbonio [41], ha dato recuperi quantitativi ma anche alcuni problemi sia a carico della fase adsorbente (rilascio di sostanza organica) sia a livello strumentale causando innalzamento del fondo dei cromatogrammi in HPLC-ESI-MS/MS. Si è quindi provato a utilizzare solo metanolo ottenendo recuperi quantitativi senza problemi del fondo eluendo le cartucce con una aliquota di 4 mL. Per aumentare il fattore di pre-concentrazione (EF) l’eluato è stato ridotto di volume sotto flusso di N2 (fino a 0.25 mL) prima della determinazione mediante HPLC-ESI-MS/MS (modalità MRM). Le prime prove di recupero sono state eseguite su differenti volumi (50-250 mL) di acqua di rubinetto arricchiti a varie concentrazioni di analiti (50-5 µg/L) ottenendo risultati superiori al 70% (RSD < 12%, n=3) per tutti gli analiti e con EF fino a 1000. Si è poi passati alla matrice acqua di fiume analizzando volumi di 100 e 250 mL arricchiti a due differenti concentrazioni (5 e 1 µg/L), ottenendo anche in questo caso recuperi quantitativi (71-114%, RSD < 16%, n=3) e EF fino a 1000. La quantificazione nell’eluato SPE è stata eseguita per entrambe le matrici media
Acidi umici pirolizzati su silice come fase solida adsorbente per inquinanti emergenti: pre-concentrzione di benzensolfonammidi, benzotriazoli e benzotiazoli da acque ambientali
PASTORE, MATTIA
2016/2017
Abstract
The aim of this thesis work is the preparation and characterization of a new material to be used as solid phase for pre-concentration of organic pollutants. In particular, in this thesis it has been test for analytes belonging to benzenesulfonamides (BSAs), benzotriazoles (BTRs) and benzotiazoles (BTs) from environmental waters. These molecules are considered emerging organic pollutants because they have good chemical stability, high polarity and water solubility, and resistance to biodegradation [1]. Their toxicity is not yet completely known because they have been recently identified, and environmental quality standards for the water compartment have been defined only for benzotriazole (BTH) and 5-methyl-benzotriazole (5-TTR) (19 e 20 µg/L, respectively). The low concentrations of these analytes in the environment require high sensitive analytical methods based on GC-MS/MS or HPLC-MS/MS, which include a preliminary pre-concentration step usually made by solid phase extraction (SPE) with commercial cartridges. The new carbon-based sorbent phase has been prepared through the pyrolysis of humic acids (HAs) deposited on silica in N2 atmosphere at 600 °C. The obtained material (HA-C@silica) has been characterized through many techniques (TGA, SEM, EDS, BET e XPS) to evaluate its properties, and results show that the pyrolytic carbon immobilized on silica (3.5 wt% on the material prepared starting from HAs 20%) consists on a sp2 aromatic structure that conserves polar groups such as –C=O e –COOH. Basing on these results, this material can be considered a mixed-mode phase. HA-C@silica has been applied as sorbent for column-SPE using 200 mg of material packed in 3 mL cartridges.Two HA-C@silica samples were initially prepared and tested at nominal HAs concentrations, 10 and 20 wt%. The leachates of tap water samples (50 mL spiked with 50 µg/L of each analyte), showed that HA-C@silica obtained from the initial concentration of HAs 20 wt% guaranteed quantitative adsorption of all analytes, except of BSA, only partially retained. BSA is indeed the most hydrophilic compound among those analyzed (logP = 0.49), and it was no longer considered for subsequent recovery experiments. A quantitative elution from HA-C@silica was gained for all the analytes by MeOH (4 mL). To increase the enrichment factor (EF), the eluate has been evaporated under nitrogen flow until 0.25 mL before the HPLC-ESI MS/MS determination (MRM mode). The first tests have been made on different volumes (50-250 mL) of tap water enriched with concentrations between 50-5 µg/L of each analyte, obtaining recoveries higher than 70% (RSD < 12%, n=3) and reaching EF = 1000.Successively samples of river water (100 and 250 mL) enriched with two different concentrations (5 and 1 µg/L) were analyzed. Also in this matrix recoveries were quantitatives for all analytes (71-114%, RSD < 16%, n=3), and EF up to 1000.Quantification has been performed for all samples on the SPE eluate by standard additions method, carried out in the range 250-750 µg/L (R2 > 0.9962) by HPLC-ESI-MS/MS autosampler. This procedure was adopted for faster analysis, greater repeatability and good compensation of matrix effects, observed in the case of river water. HA-C@silica ensures quantitative recoveries (70-94%) for all analytes, it is easily prepared in laboratory with great reproducibility (inter-batch precision < 12%, n=3) with low costs (silica 0.1 €/g, HAs 0.6 €/g, Sigma-Aldrich prices 2018) and it is reusable (at least for two quantitative extractions). Furthermore, preparation does not involve use of organic solvents and/or hazardous reagents.È consentito all'utente scaricare e condividere i documenti disponibili a testo pieno in UNITESI UNIPV nel rispetto della licenza Creative Commons del tipo CC BY NC ND.
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https://hdl.handle.net/20.500.14239/25153