Composti Organici geochimica in sistemi naturali ed analisi

Composti Organici: geochimica in sistemi naturali ed analisi

L’approccio classico prevede… Types of analytical instruments • Personal Monitors – Light weight monitors – Can be conveniently carried or worn by a person • Portable monitors – Can be moved during sampling • Stationary monitors – Have to be operated from a fixed location Volatile Organic Compounds

Types of Sampling • Active Sampling – Contaminated air is directly drawn into a sensor or collector – Provides a real time analysis of the sample • Passive Sampling – Air diffuses into the collector – Longer period of time must be allowed for accurate results Volatile Organic Compounds

Sampling methods • Principles of Sampling Collectors 1. Air displacement 2. Condensation 3. Gas washing or absorption 4. Adsorption Volatile Organic Compounds

Air Displacement Sampling Method – Evacuated flasks or plastic bags are used – Samples are collected by opening the inlet to the contaminant-laden air – Sample is subsequently analyzed using a suitable analytical method Volatile Organic Compounds

Condensation Sampling Method – Air is passed through a U-tube or a suitable container – Sample is subsequently cooled to below the boiling point of the pollutant – In most cases a liquid nitrogen cryogenic trap is used. Volatile Organic Compounds

Gas washers/ Absorbers Sampling Method – Air containing the pollutants is bubbled through a liquid contained in an impinger – An aliquot of the liquid is analyzed to determine the characteristics and concentrations of the pollutants – Distilled water is commonly used for readily soluble gases – A liquid medium that reacts with the pollutants should be avoided Volatile Organic Compounds

Gas washers/ Absorbers Sampling Method – This method is suitable only for a few specific pollutants such as Formaldehyde, Phenol and Ethylene Oxide – Collection Efficiency can be increased by: • Decreasing the flow rate • Improving the distribution of gas phase in the liquid medium • Increasing the residence time • Using two or more collectors in series Volatile Organic Compounds

Adsorption Sampling Method – Used for measurement of emissions from materials. – Emissions are measured either in an environmental chamber or through “head space” analysis – Environmental Chamber Studies: • Material is placed in a chamber • Environmental parameters of the chamber (temperature, humidity, air exchange rates) are controlled precisely • Air samples are collected in solid adsorbent tubes for later analysis with a gas chromatograph Volatile Organic Compounds

Adsorption Sampling Method – “Head-Space” analysis • Small samples of the material are placed in a container • Head space gases are collected analyzed by a gas chromatograph • Sampling time depends on the emission rate from the material – Solid adsorption media are more popular • Pollutants are allowed to adsorb for a predetermined period of time on a solid • Most frequently used solid adsorbent is activated carbon and silica gel Volatile Organic Compounds

Adsorption Sampling Method – Factors for successful use of adsorbent cartridges • Careful cleaning of the sorbent tube to remove background contamination • Accurate determination of sampling rate – Cleaning of cartridges • Heat them at a high temperature under vacuum or by flowing inert gas through the cartridge • Flow of inert gas should also continue during cooling • Another method is to wash the cartridge with a solvent and dry it at a temp. of 100 -150 o. C Volatile Organic Compounds

Analysis Methodologies • Colorimeters and Spectrophotometers – Used to quantify a specific pollutant – Utilize liquid reagents, chemically treated papers and glass indicating tubes – Chromotropic acid method • Most frequently used to determine the concentration of Formaldehyde • Measured volume of sample air is drawn through distilled water into an absorber • Collection efficiency greater than 95% is achieved by using two absorbers in series Volatile Organic Compounds

Nella pratica…. La miglior qualità dell’homo analyticus è la capacità d’adattamentto

Campionamento da emissione puntuale di alta temperatura

Polle gorgoglianti

Fumarole

temperature fino a 700°C !!! condensatore pompa Linea pirex Tubo titanio Campionamento di fumarole in trappole solide trappola

ALOGENATI - ST Trappola Solida (ST): Carboxen B - Carboxen C – Carbapack 111 FUMAROLE ARIA Organici <C 4 analizzati tramite GC-MS con TD Composti <C 4 e maggiori analizzati tramite GC (FID e TCD)

Gas del suolo

Combinazione delle due tecniche ria (ST) Emissione puntuale (SPME+ ST) Emissione diffusa (SPME)

campionamento in aria Condizioni operative • Basso flusso (250 cc/min) • elevati tempi prelievo (fino a 12 ore) • no filtri • stoccaggio immediato • Possibilità flussaggio in laboratorio su capione prelevato in sacca (campionamento aereo)

campionamento gas disciolti Campionamento classico Testa ampolla pre-evacuata (legge Henry) Condizioni operative • No reagenti • quantità ridotte (12 -20 cc acqua) • stoccaggio immediato • No bolle aria

Le fasi analitiche Iniezione Separazione cromatografica Frammentazione con pennello elettronico Rilevazione frammenti molecolari con quadrupolo

Protocollo analitico Solid trap (ST) Purge & Trap thermal desorber SPME column headspace GC-MS

Gas massa

ANALYSIS • ANALYSIS OF INORGANIC COMPOUNDS AND CH 4 • Gaschromatography GC • Ionic Chromatography IC • (Montegrossi et al. , 2001) • ANALYSIS OF VOCs • Gas Chromatography coupled with Gas-Mass GCMS • Thermo Trace GC Ultra with mass spectromrtry (MS) Thermo DSQ

iniezione

Desorbimento COV da trappole solide Condizioni operative • Gas carrier elio • tempo desorbimento ST 20 min (230 °C) • trappola focalizzatrice trifase (-5 °C) • tempo desorbimento 2 min (250 °C) • Iniezione in testa colonna tramite transfer line (termostata 230 °C)

Tecnica SPME Desorbimento COV da fibra SPME (Solid Phase Micro Extraction)

Trasferimento campione da ampolla con fibra SPME • Iniezione da fibra SPME • Spessore 30/50 μm; lunghezza 2 cm 3 fase Di. Vynil. Benzene (DVB)-Carboxen. Poli. Di. Methyl. Xyloxane (PDMX) su supporto (siringa) • Esposizione alla fibra = 15 min. • Desobimento in testa colonna: T= 230 °C, tempo 2 minuti

Analysis by mass spectrometry Solid phase microextraction (SPME) Carboxen polymethylsiloxane Thermal desorbtion Selective capillary chromatography GS gas-pro column coupled with Quadrupole mass spectrometry

Tecnica Purge and Trap Estrazione fasi gassose da campioni liquidi

Tecnica Purge and Trap Estrazione fasi gassose da campioni liquidi Condizioni operative • Gas carrier elio • tempo purge 20 min • trappola focalizzatrice trifase • tempo desorbimento 2 min • Iniezione in testa colonna

Restituzione dato: ü Cromatogrammi ü Spettri di massa ü Determinazione qualitativa ü Determinazione quantitativa

Analisi qualitativa: la separazione cromatografica

Analisi qualitativa: la colonne capillari

CROMATOGRAMMA TEMPO DI RITENZIONE AREA PICCO SPETTRO MS

Analisi qualitativa

Analisi quantitativa

Restituzione dato Concentrazioni per gas da emissioni puntali: frazione molare (permil, ppm, ppb) Il dato di concentrazione di COV si raccorda/compara con quello delle altre specie gassose

Restituzione dato Concentrazioni gas disciolti: frazioni molari e/o moli su litro Concentrazioni in aria: mol/m 3 (rapporti stechiometrici) e/o g/m 3 (limiti legge) Il dato di concentrazione di COV si rapporta ai limiti di legge