Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The need to analyse and detect volatile organic compounds (VOCs) at trace levels has led to the
development of specialized sample preparation techniques. The requirement for trace analysis of
VOCs stems from the negative effects they have on the environmental and human health. Methods
for the analysis of non-polar VOCs commonly found as trace contaminants in water and analysis of
more polar oxygenated compounds commonly found in zero-VOC water-based paints were
developed. Solid phase micro extraction (SPME) was employed and extraction of the majority of
the target analytes could be achieved at levels below 0.3 μg.l-1. In an attempt to further improve the
detection of these two target analyte groups, novel materials based on poly(dimethyl siloxane)
(PDMS) were investigated as possible extraction phases for VOCs, with the focus specifically on
the analysis of the polar analytes in paint. Conventional free radical polymerization was used to
synthesize poly(methyl methacrylate-graft-poly(dimethyl siloxane) (PMMA-g-PDMS),
poly(methacrylic acid)-graft-poly(dimethyl siloxane) (PMAA-g-PDMS), polystyrene-graftpoly(
dimethyl siloxane) (PSty-g-PDMS) and poly(butyl acrylate)-graft–poly(dimethyl siloxane)
(PBA-g-PDMS). These polymers have a copolymer functionality which presents a series of
different polarities. The MMA-g-PDMS and MAA-g-PDMS as well as the homopolymers were
electrospun into nanofibers. The low glass transition temperature and molecular weight of the PBAg-
PDMS meant that this polymer could not be electrospun. Scanning electron microscopy (SEM)
was used to study the fiber morphology of the electrospun fibers and the non-beaded fibers were
further investigated. Polyacrylonitrile-graft-poly(dimethyl siloxane) (PAN-g-PDMS) previously synthesized and electrospun by another member of the group were also investigated for use as
possible extraction material in volatile analysis. The thermal stability of the nanofibers at 200°C
was studied using thermal gravimetric analysis (TGA). This property is important since after the
target analytes are extracted using the nanofibers, elevated temperatures are used to thermally
desorp the volatile analytes from the extraction materials prior to GC analysis. The PAN-g-PDMS,
MMA-g-PDMS and PMMA showed no significant weight loss during thermal evaluation, however,
it was observed that the PMMA and PMMA-g-PDMS nanofibers looses their nanostructure and that
the PAN-g-PDMS nanofibers changes colour from white to yellow to rust brown. The polymers
based on MAA showed weight losses of more than 10% after one hour of exposure to the elevated
temperatures, but the nanostructure remained intact. The PAN-g-PDMS, PMAA-g-PDMS and
PMAA nanofibers were evaluated as possible extraction materials for VOC analysis. The
nanofibers were evaluated using a similar approach to that of stir bar sorptive extraction (SBSE).
Headspace sorptive extraction (HSSE) using a commercially available PDMS stir bar and the novel
materials were used to evaluate the extraction efficiency of the different materials. The optimized extraction method developed using SPME were employed for the extraction using the nanofibers
and PDMS stir bar. It was noted that the nanofibers lose their extraction capabilities during the first
extraction/desorption cycle possibly due to thermal degradation therefore each of the materials can
only be used in a single extraction. The majority of the non-polar analytes were extracted using the
nanofibers at levels of 500 μg.l-1, however it was noted that the commercially available SPME
extraction materials and the PDMS stir bar had superior extraction efficiencies for the specific
target analytes. In the evaluation of the nanofibers for extraction of the more polar oxygenated
analytes it was noted that 2-Ethylhexylacrylate was the only analyte to be extracted by all of the
materials. The PAN-g-PDMS extracted three of the four analytes at levels of 100 μg.l-1. At lower
analyte concentrations of 10 μg.l-1 only two of the four acrylate compounds were detected using the
PAN-g-PDMS nanofibers. Ethyl acrylate was not extracted by any of the novel materials, whereas
in SPME using the CAR/PDMS fiber, the LOD was determined to be below 1 μg.l-1. Although
these materials were not superior to the commercially available phases, this is only the case for the
specific target analytes analyzed. / AFRIKAANSE OPSOMMING: Die behoefte vir die analiese van vlugtige organiese verbindings (VOS) op spoorvlak, het gelei tot
die ontwikkeling van gespesialiseerde monster voorbereidingstegnieke. Die vereiste vir die spoor
analiese van die VOS het ontstaan uit die negatiewe uitwerking wat hierdie stowwe het op die
omgewing en menslike gesondheid. Metodes vir die analiese van nie-polêre VOS wat algemeen
voorkom as spoorkontaminante in water en polêre suurstofryke verbindings wat algemeen voorkom
in nul-VOS water-gebaseerde verf was ontwikkel. Soliede fase mikro-ekstraksie (SFME) was
gebruik, en die ekstraksie van die meerderheid van die teikenstowwe kon gedoen word op vlakke
laer as 0,3 μg.l-1. In 'n poging om die opsporing van hierdie twee teiken analietgroepe verder te verbeter, is nuwe materiale gebaseer op polidimetielsiloksaan (PDMS), ondersoek as moontlik
ekstraksiefases vir VOS, met die fokus spesifiek op die analiese van die polêre stowwe in verf. ’n
Konvensionele vrye radikaal polimerisasieproses was gebruik om poli (metiel- metakrilaat)-entpoli(
dimetielsiloksaan) (PMMA-g-PDMS), poli(metakrilaatsuur)-ent–poli (dimetielsiloksaan)
(PMAA-g-PDMS), polistireen-ent-poli(dimetielsiloksaan) (PSty-g-PDMS) en poli(butielakrilaat)-
ent-poli(dimetielsiloksaan) (PBA-g-PDMS) te sintetiseer. Hierdie ko-polimere het 'n kopolimeer
funksionaliteit wat 'n reeks van verskillende polariteite bied. Die MMA-g-PDMS en MAA-g-PDMS
sowel as die homopolimere was ge-elektrospin in orde om nanovesels te vorm. Die lae
glasoorgangstemperatuur en molekulêre gewig van die PBA-g-PDMS het beteken dat hierdie
polimeer nie elektrospin kon word nie. Skandeerelektronmikroskopie (SEM) was gebruik om die
veselmorfologie van die ge-elektrospinde vesels te bestudeer en die nanovesels wat ’n eweredige
oppervlak gehad het, was verder ondersoek. Poliakrilonitriel-ent-poli(dimetielsiloksaan) (PAN-g-
PDMS) wat voorheen gesintetiseer en ge-elektrospin was deur 'n ander lid van die groep is ook
ondersoek vir gebruik as moontlik ekstraksiemateriaal vir die analiese van vlugtige stowwe. Die
termiese stabiliteit van die nanovesels was by 200°C bestudeer met behulp van ‘n termiese
gravimetriese analiese (TGA) instrument. Hierdie eienskap is belangrik, aangesien die
teikenstowwe by hoë temperature van die nanovesels gedesorbeer word voor die GC-analiese. Die
PAN-g-PDMS, MMA-g-PDMS en PMMA het geen beduidende gewigsverlies tydens termiese
evaluering gehad nie, alhoewel dit egter waargeneem was dat die PMMA en PMMA-g-PDMS
nanovesels hulle nanostruktuur verloor en dat die PAN-g-PDMS nanovesels se kleur verander van
wit na geel na roesbruin gedurende die termiese analiese. Die polimere wat gebaseer was op MAA
het ’n gewigs-verlies van meer as 10% getoon na 'n uur van blootstelling aan die verhoogde
temperature, maar die nanostruktuur het ongeskonde gebly. Die PAN-g-PDMS, PMAA-g-PDMS en
PMAA nanovesels was geëvalueer as moontlike ekstraksiemateriale vir VOS-analiese. Die
nanovesels was geëvalueer met 'n soortgelyke benadering tot dié van “stir bar“ sorpsie ekstraksie (SBSE). Bo-ruimte sorpsie ekstrasie is gebruik om die ekstraksie-doeltreffendheid van die
verskillende materiale (kommersiële PDMS en nanovesels) te evalueer. Die geoptimaliseerde
ekstraksiemetode ontwikkel in SFME was gebruik vir die ekstraksie van die VOS met die
nanovesels en die PDMS “stir bar“. Dit was waargeneem dat die nanovesels hul ekstraksievermoë
verloor tydens die eerste ekstraksie/desorpsie siklus, moontlik as gevolg van termiese degradasie
dus, kon die materiale slegs ‘n enkele maal gebruik word vir die ekstraksie. Die meerderheid van
die nie-polêre stowwe was ge-ëkstraeer deur gebruik te maak van die nanovesels op vlakke van 500
μg.l -1, maar die kommersieel beskikbare SFME ekstraksie materiale en die PDMS “stir bar“ se
ekstraksie-doeltreffendheid vir die spesifieke stowwe was beter. In die evaluering van die
nanovesels vir die ekstraksie van die meer polêre suurstofryke stowwe was daar waargeneem dat 2-
etielheksielakrilaat die enigste analiet was wat ge-ëkstraeer was deur al die materiale. Die PAN-g-
PDMS kon drie van die vier polêre stowwe op vlakke van 100 μg.l-1 opspoor. By laer
analietkonsentrasies van 10 μg.l-1 kon slegs twee van die vier akrilaat verbindings opgespoor word
deur gebruik te maak van hierdie nanovesels. Etielakrilaat was nie ge-ëkstraeer deur enige van die
nuwe materiale nie, terwyl in SFME met die gebruik van die CAR/ PDMS vesel, die analiet op
vlakke onder 1 μg.l-1 opgespoor kon word. Alhoewel hierdie nuwe materiale nie beter is as die
kommersieel beskikbare ekstraksiemateriale nie is dit net die geval vir die spesifieke teiken
analietgroepe wat ondersoek was in hierdie studie.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/71646 |
| Date | 12 1900 |
| Creators | Malan, Mareta |
| Contributors | Mallon, Peter Edward, De Villiers, Andre, Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 101 p. : ill. |
| Rights | Stellenbosch University |
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