• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 23
  • 4
  • 4
  • 2
  • 2
  • 2
  • 2
  • Tagged with
  • 42
  • 42
  • 9
  • 6
  • 6
  • 5
  • 4
  • 4
  • 4
  • 3
  • 3
  • 3
  • 3
  • 3
  • 3
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Application of Relative Response Factors in Solid-Phase Micro Extraction GC/MS for the Determination of Polycyclic Aromatic Hydrocarbons in Water

Schebywolok, Tomi 13 July 2018 (has links)
Solid-phase microextraction (SPME) coupled with gas chromatography/mass spectrometry (GC/MS) is routinely used to analyze polycyclic aromatic hydrocarbons (PAHs) in water. A common SPME-GC/MS approach quantifies target analytes using isotopically labeled standards (IISs); one IIS is needed for each target analyte. This approach is challenging, even prohibitive since IISs are often expensive; moreover, they are generally not available for each analyte of interest. This study developed a novel SPME-GC/MS approach for the quantification of PAHs in water. The new method, which employs only a small number of IISs, uses relative response factor (RRF) (i.e., analyte corresponding to IIS) to quantify PAHs in water. Possible matrix dependency of RRFs values was examined using water that was modified concerning different physical-chemical characteristics (i.e., ionic strength, pH, suspended solids, humic acid, and biological organic carbon represented by hemoglobin). The results revealed that RRFs are not noticeably affected by changing ionic strength and pH; the other three parameters did affect the RRFs. However, the results also showed that the effect is minimal when the solution is dilute (i.e., low concentrations of suspended solids, humic acid or hemoglobin). Relatively stable RRFs for dilute water solutions indicates that this approach can be used for routine quantification of water that does not contain prohibitive amounts of suspended solids, humic acid, and biological organic matter. The developed method was employed to quantify trace levels of PAHs in three different types of water, namely river water, well water, and bottled water. PAH levels in every kind of water were less than 100 ng/L level (i.e., 0.1 ppb). Analyses of spiked water samples containing 2 ng PAHs revealed correlations between calculated RRFs and the physical-chemical properties of the PAHs investigated (i.e., vapor pressure, boiling point, octanol/water partition coefficient, octanol/air partition coefficient, GC retention time). This implies that RRFs for PAHs not examined in this study can be predicted. Overall, the results presented herein constitute a meaningful contribution to the development of SPME-GC/MS methods for quantitative analysis of PAHs and other chemicals in dilute aqueous solutions. Moreover, the development of methods that alleviate the need for IISs corresponding to each target analyte.
42

Étude des interactions PET - Eau minérale dans les eaux embouteillées au Liban et approches analytiques des risques sanitaires / Study of PET interaction with mineral water in lebanese bottled water and analytical approaches of health risks

Al Rayes, Layal 13 June 2013 (has links)
L'évaluation de l'inertie des matières plastiques au contact de denrées alimentaires est régie par le règlement européen N°10/2011. Au Liban, l'absence de législations relatives à l'usage des matières en plastiques a conduit à des emballages non contrôlés au niveau de la production et du stockage, ce qui peut induire un risque sanitaire pour le consommateur. L'objectif de ce travail a été d'apprécier les phénomènes de migration des contaminants du PET vers l'eau. Pour cela, l'analyse de certains migrants potentiels a été initiée tels que des COV et des SV afin de vérifier la conformité de leur teneur par rapport aux LMA dans les règlementations internationales. Le dosage des aldéhydes dans l'eau a été effectué par dérivation avec la 2,4-DNPH, suivie d'une étape de préconcentration sur une cartouche en C18, puis séparation et quantification par HPLC-UV. L'analyse des composés SV a été réalisée par SPME-GC-FID sur une fibre en PDMS/DVB. L'analyse des BTEX et du styrène a été réalisée par HS-Trap-GC-FID. Ces méthodes ont été validées conformément à la norme NF T 90-210 avec des LQ inférieures aux LMA. L'analyse des COV dans l'eau embouteillée et dans le PET a été réalisée par HSTrap- GC-MS. La présence de FA, d'AA, de DEP et des BTEX dans l'eau embouteillée en PET a été confirmée. Il a été mis en évidence que la température et l'exposition solaire influencent la migration des aldéhydes. Les concentrations d'AA trouvées après incubation à 40ºC ne sont pas négligeables et peuvent modifier les propriétés organoleptiques de l'eau. L'analyse du PET montre la présence des hydrocarbures, des aldéhydes, des alcools, et des cétones / The inertness’ value of plastics that are on contact with foodstuffs is governed by the European rule N°10/2011. In Lebanon, the lack of the Rules and Regulations of plastics’ usage led for a non-controlled packing in production as in storage, which will cause a sanitary risk to the consumer and to the population. The purpose of this research was to appreciate the migration’s phenomena of contaminants from the PET to the water. For this, there was an analysis of potential migrants such as VOC and SV to verify their tenor’s conformity relative to the MCL in international regulations. The aldehydes’ dosage in the water was performed by the derivation with the 2,4-DNPH, followed by a concentration on a C18 cartridge, then separation and quantification was done by HPLC-UV. The SV compounds’ analysis was realized by SPME-GC-FID method on a PDMS / DVB fiber. The BTEX and the styrene’s analysis was done by HS-trap-GC-FID method. These methods were validated in accordance with standard NF T 90-210 with a LQ less than the MCL. The volatile compounds in the bottled water and in the PET were analyzed by HS-trap-GC-MS method. The presence of FA, AA, DEP and BTEX in the bottled water with the PET was confirmed. It was highlighted that temperature and sun exposition influence the aldehydes’ migration. The acetaldehyde’s concentration after incubation at 40ºC wasn’t negligible and can modify the water’s organoleptic properties. The PET’s analyze reveals the presence of hydrocarbons, aldehydes, alcohols and ketones

Page generated in 0.0633 seconds