Developing on-line methods for metals determination in biological and environmental samples by dispersive liquid-liquid microextraction coupled with sequential injection technique and atomic spectrometry

 
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2013 (EL)
Ανάπτυξη αυτόματων μεθόδων προσδιορισμού τοξικών μετάλλων σε βιολογικά και περιβαλλοντικά δείγματα με μικροεκχύλιση διασποράς υγρού-υγρού σε συνδυασμό με την τεχνική της διαδοχικής έγχυσης και της ατομικής φασματομετρίας
Developing on-line methods for metals determination in biological and environmental samples by dispersive liquid-liquid microextraction coupled with sequential injection technique and atomic spectrometry

Ιωάννου, Καλλιρρόη - Ιωάννα

Transportation of materials from one phase to another is the most fundamentalprocedure for the separation of a chemical species from the matrix or from other coexistingcomponents. Liquid–liquid or solvent extraction is based on the principle that a solute oranalyte can distribute itself in a certain ratio between two immiscible solvents, one of which isusually water (aqueous phase) and the other an organic solvent (organic phase). In certaincases the analyte can be more or less completed moved into the organic phase. Sample pretreatmentis often the bottleneck in a measurement process, as they tend to be slow and laborintensive.In routine analysis, liquid–liquid extraction (LLE) is the most widely used samplepreparation technique, whose goal is cleanup, enrichment and signal enhancement. However,some shortcomings like the use of extensive amounts of hazardous organic solvents andsample volumes, the generation of large amounts of pollutants make this procedure timeconsuming, expensive, environmentally unfriendly, tedious, laborious and hence potentiallyprone to sample contamination when ultra-trace determinations are required.Modern trends in analytical chemistry are towards the simplification andminiaturization of sample preparation procedures as they lead inherently to a minimumsolvent and reagent consumption and drastic reduction of laboratory wastes. Under thiscontext, unconventional LLE methodologies have been arisen like: single dropmicroextraction (SDME), wetting film extraction (WFE), cloud point extraction (CPE),homogeneous liquid–liquid extraction (HLLE), dispersive liquid–liquid microextraction(DLLME) and dispersive liquid–liquid microextraction based on solidification of a floatingorganic drop (DLLME-SFO).The aim of the present dissertation study was to develop novel, miniaturized andautomated analytical methods for metal determination coupled with atomic spectrometry. Theproposed methods combined the sequential injection technique (SIA) with atomic absorptionspectrometry meeting the requirements of Green Analytical Chemistry witch are, a minimumsolvent and reagent consumption and drastic reduction of laboratory wastes. The developedmethods were applied successfully to the analysis of environmental water samples andbiological samples.In the first part a novel on-line sequential injection (SI) dispersive liquid–liquidmicroextraction (DLLME) system coupled to electrothermal atomic absorption spectrometry(ETAAS) was developed for metal preconcentration in micro-scale, eliminating the laborious and time consuming procedure of phase separation with centrifugation. The potentials of thesystem were demonstrated for trace lead and cadmium determination in water samples. Anappropriate disperser solution which contains the extraction solvent (xylene) and the chelatingagent (ammonium pyrrolidine dithiocarbamate) in methanol is mixed on-line with the samplesolution (aqueous phase), resulting thus, a cloudy solution, which is consisted of fine dropletsof xylene, dispersed throughout the aqueous phase. Three procedures are taking placesimultaneously: cloudy solution creation, analyte complex formation and extraction fromaqueous phase into the fine droplets of xylene. Subsequently the droplets were retained on thehydrophobic surface of PTFE-turnings into the column. A part of 30 κL of the eluent (methylisobutyl ketone) was injected into furnace graphite for analyte atomization and quantification.The sampling frequency was 10 h−1, and the obtained enrichment factor was 80 for lead and34 for cadmium. The detection limit was 10 ng L−1 and 2 ng L−1, while the precisionexpressed as relative standard deviation (RSD) was 3.8% (at 0.5 κg L−1) and 4.1% (at 0.03 κgL−1) for lead and cadmium respectively. The proposed method was evaluated by analyzingcertified reference materials and was applied to the analysis of natural waters.In the second part a novel, simple and efficient sequential injection (SI) on-linedispersive liquid–liquid microextraction (DLLME) procedure was described and was demonstrated for the assay of trace silver determination by flame atomic absorptionspectrometry (FAAS). Fatty alcohols, such as 1-undecanol and 1-dodecanol, were examinedas extraction solvents at micro-litre volume, overcoming a major problem of the DLLMEmethods, the high toxicity of the extraction solvents used. Furthermore, the extractant finedroplets can be easily separated from the aqueous phase using a micro-column packed with anovel hydrophobic sorbent material, poly(etheretherketone)-turnings. In this method finedroplets of 1-dodecanol were on-line generated and dispersed into the stream of aqueoussample. By this continuous process, silver diethyldithiocarbamate (Ag-DDTC) complex wasformed and extracted into the dispersed extraction solvent. No specific conditions such as icebath for low temperature or special tools are required for extractant isolation. All significantparameters that influence the efficiency of the system such as sample acidity, concentration ofcomplexing reagent and extraction solvent, flow-rate of disperser and sample solution as wellas the preconcentration time were investigated and optimized by full factorial design. Underthe optimized conditions a detection limit of 0.15 κg L−1, a relative standard deviation (RSD)of 2.9% at 5.00 κg L−1 Ag(I) concentration level and an enhancement factor of 186 wereobtained. The developed method was evaluated by analyzing certified reference material and was applied successfully to the analysis of environmental water samples. In the last part a newly, automatic on-line sequential injection dispersive liquid–liquidmicroextraction (SI-DLLME) method, based on 1-hexyl-3-methylimidazoliumhexafluorophosphate ([Hmim][PF6]) ionic liquid as an extractant solvent was developed anddemonstrated for trace thallium determination by flame atomic absorption spectrometry. Theionic liquid was on-line fully dispersed into the aqueous solution in a continuous flow formatwhile the TlBr4− complex was easily migrated into the fine droplets of the extractant due tothe huge contact area of them with the aqueous phase. Furthermore, the extractant was simplyretained onto the surface of polyurethane foam packed into a microcolumn. No specificconditions like low temperature are required for extractant isolation. All analytical parametersof the proposed method were investigated and optimized. For 15 mL of sample solution, anenhancement factor of 290, a detection limit of 0.86 κg L−1 and a precision (RSD) of 2.7% at20.0 κg L−1 Tl(I) concentration level, was obtained. The developed method was evaluated byanalyzing certified reference materials while good recoveries from environmental andbiological samples proved that present method was competitive in practical applications.

Προσδιορισμός μετάλλων
Biological and environmental samples
Βιολογικά και περιβαλλοντικά δείγματα
On-line methods
Metals determination
Αυτόματες μέθοδοι
Μικροεκχύλιση διασποράς υγρού-υγρού
Τεχνική διαδοχικής έκχυσης
Dispersive liquid-liquid microextraction
Atomic spectrometry
Ατομική φασματομετρία
Sequential injection technique

Εθνικό Κέντρο Τεκμηρίωσης (ΕΚΤ) (EL)
National Documentation Centre (EKT) (EN)

Ελληνική γλώσσα

2013


Αριστοτέλειο Πανεπιστήμιο Θεσσαλονίκης (ΑΠΘ)
Aristotle University Of Thessaloniki (AUTH)



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