Analysis of organochloro-pesticides in Eritrean water and sediment samples

Weldegergis, Berhane Tekle (2004-12)

Thesis (MSc)--Stellenbosch University, 2004.

Thesis

ENGLISH ABSTRACT: The choice of the sample preparation technique used in combination with a chromatographic technique in environmental analysis strongly influences the performance of the method as a whole. The main aim of this work was to evaluate methods like: micro liquid-liquid extraction (цLLE)and solid phase micro extraction (SPME) in combination with gas chromatography-electron capture detector (GCECD) and a recently developed technique named stir bar sorptive extraction (SBSE) combined with thermal desorption system-programmable temperature vaporizationgas chromatography-mass spectrometer (TDS-PTV-GC-MS) for the analysis of organochloro-pesticides (OCPs) in natural water and to make a comparison between them. The most suitable method was then selected for the analysis of water samples collected from Eritrea. An additional goal was to develop a sensitive method for the analysis ofOCPs in soil and sediment samples. цLLE-GC-ECD and SPME-GC-ECD methods were evaluated for the analysis of OCPs in water. The former allowed achieving a sensitivity of less than 100 ppt and the latter was able to detect down to the 1 ppt level. Both methods were found to be repeatable with %RSD of3% to 19% and 5% to 12% as well as linear with a range of 1:103 and 1:5x103 respectivey. SBSE-TDS-GC-MS was also investigated for the analysis of OCPs in water samples. With this technique a good sensitivity down to 1 ppt was also obtained. The less sensitive nature of the MS compared to ECD was hereby compensated for by the large amount of polydimethylsiloxane (PDMS) phase on the stir bar. The method was repeatable and linear with a range of 1:5000, which is similar to the one obtained for the SPME-GC-ECD method. All three methods were also tested with real contaminated water samples and a comparison of the three techniques in terms of sensitivity, linearity, repeatability, availability and cost effectiveness was done. As a method of choice in terms of the above criteria, SPMEGC- ECD was applied to the water samples collected from Eritrea. The presence of some oePs such as a-BBC (benzenehexachloride), heptachlor, heptachlor epoxide, endosulfan I, p,p'-DDE (dichlorodiphenylchloroethylene), endosulfan II, p,p'-DDD (dichlorodiphenyldichloroethane), endosu!fan sulfate and p,p'-DDT (dichlorodiphenyltrichloroethane) in some of the Eritrean water samples was demonstrated The SPME-GC-ECD technique for the analysis OCPs in soil and sediment samples was investigated. It was shown to be able to detect down to 1 pg/g (lppt) with good linearity and repeatability. The method was also evaluated for authentic soil samples. Due to a lack of time the method could not be applied for the analysis of the soil and sediment samples collected from Eritrea.

AFRIKAANSE OPSOMMING: Die keuse van 'n gepaste monster-voorbereidingsmetode wat gebruik word tesame met 'n chromatografiese skeidingtegniek in omgewings-analise het 'n beduidende effek op die algehele metode. Die doel van hierdie werk was om metodes soos mikrovloeistof- vloeistof ekstraksie (цLLE) en soliede fase mikro ekstraksie (SPME) in kombinasie met gaschromatografie met elektronvangs deteksie (GC-ECD) te ontwikkel vir die analise van organochloor-pestisiede (OCPs) in natuurlike water. Vervolgens is hierdie metodes vergelyk met die onlangs-ontwikkelde roerstaaf sorptiewe ekstraksie tegniek (SBSE) in kombinasie met termiese desorbsie-GCmassaspektrometriese deteksie (TDS-GC-MSD). Die mees geskikte metode is vervolgens gebruik vir die analise van Eritreaanse watermonsters. Daarbenewens was die doelook om 'n sensitiewe metode te ontwikkel vir die analise van OCPs in gronden sedimentmonsters. Beide цLLE en SPME-GC-ECD metodes is gekarakteriseer deur goeie herhaalbaarheid en lineariteit. Die sensitiwiteit van bogenoemde metodes was minder as 100 dele per triljoen (ppt) en 1 ppt, respektiewelik. Ook met SBSE-TDS-GC-MSD kon 'n deteksielimiet van 1 ppt bereik word. In hierdie geval is vir die verlies van sensitiwiteit van die MSD in vergelyking met die ECD, gekompenseer deur die groter hoeveelheid PDMS op die roerstaaf in vergelyking met 'n SPME apparaat. Die herhaalbaarheid en lineariteit van die metode is vergelykbaar met dié van die SPMEGC- ECD metode. Al drie metodes is vergelyk vir die analise van gekontamineerde watermonsters in terme van sensitiwiteit, liniêre bereik, herhaalbaarheid, toeganklikheid en kosteeffektiwiteit. SPME-GC-ECD is vervolgens gekies as metode van voorkeur vir die analise van Eritreaanse watermonsters. Die teenwoordigheid van sekere OCPs soos a-BHC, heptachloor, heptachloorepoksied, endosulfan I, p,p'-DDE, endosulfan II, p,p' -DDD, endosulfan sulfaat en p,p' -DDT in die monsters is gedemonstreer. Die toepasbaarheid van die SPME-GC-ECD metode vir die analise van OCPs in grond-en sedimentmonsters is ook geëvalueer, en dit was moontlik om so min as 1 pg/g waar te neem. Weens tydbeperkings was dit nie moontlik om Eritreaanse grondmonsters met die ontwikkelde metode te analiseer nie.

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