Development and optimization of the speciation methods by using chromatographic techniques combined with mass spectrometry

The thesis consists from three individual studies in OT analysis. The first study was the development of a speciation analysis method for the simultaneous determination of inorganic (Sn) and tetramethyltin (TeMT) by headspace solid-phase microextraction and gas chromatography mass spectrometry (HS-SPME-GC-MS). A headspace solid phase microextraction (HS-SPME) method coupled to GC-MS was developed in order to determine trace levels of TeMT and Sn after ethylation to tetraethyltin (TeET) in various matrices. The derivatization of Sn and the extraction of both TeMT and Sn (as TeET) were performed in one step. Sodium tetraethylborate (NaBEt4) was used as derivatization agent and the volatile derivatives were absorbed on a PDMS-coated fused silica fiber. The conditions for the HS-SPME procedure and several critical parameters of GC-MS were optimized in order to gain in repeatability and sensitivity. The detection of TeMT and Sn as TeET peaks was performed by the selective ion monitoring mode (SIM). The precision of the proposed method is satisfactory providing RSD values below 10% for both tin species and good linearity up to 10 µg L-1. The proposed HS-SPME-GC-MS method was successfully applied to the determination of tin species in several samples like canned fish, fish tissues, aquatic plants, bottled mineral water and sea water. The method was proved suitable to monitor the concentration levels of toxic tin compounds in environmental and biological samples. The second study of the thesis was the investigation of tributyltin (TBT) stability in human urine samples using headspace solid phase microextraction and gas chromatography mass spectrometry. The HS-SPME-GC-MS method was employed in order to study the effect of storage conditions in human urine samples spiked with TBT. To render the analyte more volatile, the derivatization (ethylation) was made in situ by sodium tetraethylborate (NaBEt4) which was added directly to dilute unpreserved urine samples and buffers of similar acidity. The stability of TBT in human urine matrix was compared with the stability of TBT in buffer solutions with similar pH value by performing recovery tests of TBT in both matrices. Critical parameters of storage conditions which affect the stability of TBT in this kind of matrix such as temperature, time and microbial activity were examined extensively.The tests showed that the stability of TBT remains practically satisfactory for maximum 2 days of storage either at +4 °C or -20 °C. Higher variations were observed in the concentration of TBT in human urine samples at +4 °C and lower ones at –20 °C over a monthly storage. The freeze-thaw cycles have negative effect on the stability and should be kept to the minimum. In this study, the results from TBT recovery in spiked urine samples are also discussed in comparison to those acquired from buffer solutions of equal TBT concentration. The third study of the thesis was the speciation analysis of tripropyltin (TPrT), tributyltin (TBT), tripentyltin (TPeT) and triphenyltin (TPhT) by using liquid chromatography combined with a high resolution mass spectrometer which consisted from an octapole, an ion trap and a time of flight TOF (LCMS-IT-TOF). This unique Tandem MS construction was operated in atmospheric pressure chemical ionization (APCI) mode. In this work, the capability of a hybrid tandem technique of LCMS-ITTOF was examined for the speciation of the analytes and a relatively fast and accurate method was developed for their determination in aqueous solutions. In this context, several chromatographic parameters were studied such as chromatographic column, mobile phase, flow rate and gradient program in order to optimise the separation of the above species. Optimum separation was achieved using reverse phase C18 bonded-silica column with short length up to 3 cm. The mobile phase consisted of water and acetic acid/methanol 2% v/v and at a total flow rate was set at 0.4 mL min–1. The chromatographic peak separation of the analytes was completed in less than 8 min. The determination of the analytes was performed by exclude in the chomatograms the characteristic ions of its analyte and monitoring the isotopic profile of tin. The program of MS was set to localize a short range of ions m/z (220.0000-420.0000) in the IT. The detection limits of the set of the above four triorganotin species were ranged between 13 – 45 pg as absolute mass of Sn injected into the column and the relative standard deviation was ranged between 4.3 – 9.9 %. Finally, the performance characteristics of the method were compared to those reported in literature using similar tandem LC-MS techniquesΗ ∆ιατριβή αυτή αποτελείται από τρεις ξεχωριστές µελέτες που αφορούν τον προσδιορισµό ΟΤ. Η πρώτη µελέτη αφορούσε την ανάπτυξη αναλυτικής µεθόδου µορφοειδικού διαχωρισµού για τον ταυτόχρονο προσδιορισµό του ανόργανου κασσιτέρου (Sn) και του τετραµεθυλοκασσιτέρου (TeMT) µε την χρήση της µικροεκχύλισης στερεάς φάσης και της αέριας χρωµατογραφίας σε συνδυασµό µε φασµατοµετρία µάζας (HS-SPME-GC-MS). Με τη χρήση της τεχνικής αυτής αναπτύχθηκε µια µέθοδος για τον ιχνοπροσδιορισµό του TeMT και Sn ως τετρααιθυλοκασσίτερος (ΤeET), έπειτα από την αιθυλίωσή του, σε διάφορα υποστρώµατα. Η παραγωγοποίηση του Sn και η ταυτόχρονη εκχύλισή του ως TeET µαζί µε τον TeMT ολοκληρώθηκε σε ένα στάδιο. Το µέσο παραγωγοποίησης που χρησιµοποιήθηκε ήταν το τετρααιθυλοβορικό νάτριο (NaBEt4) το οποίο δηµιούργησε πτητικό παράγωγο το οποίο προσροφήθηκε στην επιφάνεια της ίνας που ήταν επικαλυµµένη µε PDMS υλικό. Μελετήθηκαν οι συνθήκες της HS-SPME καθώς και οι πιο κρίσιµες παράµετροι λειτουργίας του GC-MS έτσι ώστε να βελτιστοποιηθεί η επαναληψιµότητα και η ευαισθησία. Η ανίχνευση των κορυφών του TeMT και του Sn ως TeET πραγµατοποιήθηκε µε την λειτουργία της επιλεκτικής παρακολούθησης ιόντων (SIM). Η ακρίβεια της προτεινόµενης µεθόδου ήταν ικανοποιητική παρέχοντας τιµές RSD χαµηλότερες από 10% και για τους δύο αναλύτες µε καλή γραµµικότητα έως 10 µg L-1. Η προτεινόµενη µέθοδος που αναπτύχθηκε εφαρµόστηκε µε επιτυχία για τον προσδιορισµό των αναλυτών σε διάφορα είδη δειγµάτων όπως ιστό ψαριού, φύκια, µεταλλικό νερό και θαλασσινό νερό και αποδείχτηκε κατάλληλη ως µέθοδος παρακολούθησης της ρύπανσης σε περιβαλλοντικά και βιολογικά υποστρώµατα. Η δεύτερη µελέτη της ∆ιατριβής αφορούσε την αξιολόγηση της σταθερότητας του τριβουτυλοκασσίτερου (TBT) σε δείγµατα ανθρώπινων ούρων µε χρήση της µικροεκχύλισης στερεάς φάσης υπερκείµενου χώρου και της αέριας χρωµατογραφίας σε συνδυασµό µε τη φασµατοµετρία µάζας (HS-SPME-GC-MS). Η µέθοδος HSSPME-GC-MS χρησιµοποιήθηκε για τη µελέτη της επίδρασης των συνθηκών αποθήκευσης σε δείγµατα ούρων στα οποία είχε προστεθεί αρχικά ΤΒΤ. Προκειµένου να αυξηθεί η πτητικότητα του αναλύτη, πραγµατοποιήθηκε επί τόπου παραγωγοποίηση µε NaBEt4, το οποίο προστέθηκε απ’ ευθείας σε δείγµατα ούρων και σε πρότυπα ρυθµιστικά διαλύµατα όµοιας οξύτητας. Στα δείγµατα δεν προστέθηκε οποιοδήποτε συντηρητικό µέσο. Η σταθερότητα του ΤΒΤ στο υπόστρωµα των ανθρώπινων ούρων συγκρίθηκε µε τη σταθερότητα του ΤΒΤ σε ρυθµιστικά διαλύµατα µε παρόµοιο pH πραγµατοποιώντας συγκριτικούς υπολογισµούς των ανακτήσεων του ΤΒΤ στα δύο υποστρώµατα. Εξετάστηκαν ενδελεχώς οι κρίσιµες παράµετροι των συνθηκών αποθήκευσης όπως η θερµοκρασία, ο χρόνος και η µικροβιακή δραστηριότητα, οι οποίες επηρεάζουν την σταθερότητα του ΤΒΤ σε αυτού του είδους τα υποστρώµατα. Τα αποτελέσµατα υπολογισµού των ανακτήσεων έδειξαν ότι η σταθερότητα του TBT διατηρείται σε ικανοποιητικό βαθµό για µέγιστο διάστηµα αποθήκευσης 2 ηµερών είτε στους +4 °C ή στους -20 °C. Μεγαλύτερες διαφοροποιήσεις παρατηρήθηκαν στην συγκέντρωση του ΤΒΤ µεταξύ των δειγµάτων που είχαν αποθηκευτεί στους +4 °C και –20 °C για χρονικό διάστηµα αποθήκευσης έως 1 µήνα. Οι κύκλοι ψύξης και απόψυξης των δειγµάτων είχαν αρνητική επίδραση στην σταθερότητα του ΤΒΤ και για το λόγο αυτό θα πρέπει να εφαρµόζονται στο ελάχιστο δυνατό. Στη µελέτη που παρόµοιά της δεν υπάρχει στην διεθνή βιβλιογραφία, αξιολογήθηκαν συγκριτικά οι ανακτήσεις του ΤΒΤ από δείγµατα ούρων σε σχέση µε τις ανακτήσεις του ΤΒΤ από τα αντίστοιχα ρυθµιστικά διαλύµατα. Η τρίτη φάση της ∆ιατριβής αφορούσε τον µορφοειδικό διαχωρισµό των τριπροπυλοκασσίτερο (TPrT), τριβουτυλοκασσίτερο (TBT), τριπεντυλοκασσίτερο (TPeT) και τριφαινυλοκασσίτερο (TPhT) µε τη χρήση της υγρής χρωµατογραφίας σε συνδυασµό µε φασµατοµετρία µάζας υψηλής ανάλυσης η οποία αποτελούνταν από αναλυτές οκταπόλου, παγίδας ιόντων και χρόνου πτήσεως (LCMS-IT-TOF). Σε αυτόν τον καινοτόµο σχεδιασµό διαδοχικών αναλυτών MS τύπων ΙΤ και TOF, εφαρµόστηκε η λειτουργία του χηµικού ιοντισµού υπό συνθήκες ατµοσφαιρικής πίεσης (APCI). Σε αυτή την εργασία διερευνήθηκαν για πρώτη φορά οι δυνατότητες της υβριδικής τεχνικής LCMS-IT-TOF για τον µορφοειδικό διαχωρισµό των αναλυτών και αναπτύχθηκε η µέθοδος προσδιορισµού τους µε µεγάλη ακρίβεια σε υδατικά διαλύµατα. Μελετήθηκαν οι χρωµατογραφικές παράµετροι όπως στήλη, κινητή φάση, παροχή, πρόγραµµα έκλουσης σε σκοπό να βελτιστοποιηθεί ο διαχωρισµός των αναλυτών. Ο βέλτιστος διαχωρισµός επιτεύχθηκε µε τη χρήση στήλης πιρυτίας C18 αντίστροφης φάσης µε µήκος 3 cm. Η κινητή φάση αποτελούνταν από νερό και οξικό οξύ/µεθανόλη 2% v/v ρυθµίζοντας την παροχή στο 0,4 mL min–1. Ο χρωµατογραφικός διαχωρισµός των κορυφών ολοκληρώθηκε σε χρόνο µικρότερο των 8 min. Ο προσδιορισµός των αναλυτών πραγµατοποιήθηκε µε παρακολούθηση των χαρακτηριστικών ιόντων του κάθε αναλύτη στα χρωµατογραφήµατα καθώς και του ισοτοπικού προφίλ του Sn. Στο πρόγραµµα του MS ρυθµίστηκε η λειτουργία αποµόνωσης στην IT περιορισµένου εύρους ιόντων µε m/z (220,0000-420,0000). Τα όρια ανίχνευσης των τεσσάρων τριοργανοκασσιτερικών µορφών ήταν σε εύρος µεταξύ 13 – 45 pg, εκφρασµένες ως την απόλυτη ποσότητα του Sn που εγχύθηκε στη στήλη, και η σχετική τυπική απόκλιση κυµάνθηκε σε εύρος µεταξύ 4,3 – 9,9 %. Τέλος πραγµατοποιήθηκε σύγκριση των αναλυτικών χαρακτηριστικών της προτεινόµενης µεθόδου µε αναφορές παρόµοιων µεθόδων LC-M

Simultaneous Removal of Arsenate and Chromate from Ground- and Surface- Waters by Iron-Based Redox Assisted Coagulation

Arsenic (As) and chromate (Cr(VI)) contamination of ground and surface waters is a major problem worldwide. Given that a new drinking water limit is anticipated for Cr(VI) and that the limit of arsenic in drinking water is quite low (10 μg/L), there is an urgent need for evaluating technologies that could be efficient for removal of both contaminants simultaneously. In this work, the use of Fe(II) redox assisted coagulation was investigated to simultaneously remove the contaminants of interest. The basic principle of this technology is that Fe(II) could react with Cr(VI) and form Fe(III)-hydroxides and insoluble Cr(III) species, while the freshly formed Fe(III) hydroxides are very efficient adsorbents for As(V). The effect of pH, the water matrix composition, Fe(II) dose, initial contaminant concentrations, NOM presence and phosphate concentration were the examined parameters. The results revealed that with a dose of 2 mg/L Fe(II), residual As(V) and Cr(VI) concentrations were both below 10 μg/L, from initial concentrations of 50 μg/L. Though, this is effective only at circumneutral pH values. This is however not a big obstacle, since most natural waters, especially groundwaters, have near neutral pH values. At these pH values, residual iron concentration was far below 200 μg/L. The presence of phosphate anions inhibited As(V) removal but had no effect on Cr(VI) removal. Increasing Fe(II) concentrations eliminated the effect of phosphate and provided simultaneous phosphate removal. Therefore, Fe(II) coagulation can be applied, with secured results, for simultaneous As(V), Cr(VI) and phosphate removal from waters

Removal of Antimony Species, Sb(III)/Sb(V), from Water by Using Iron Coagulants

Antimony (Sb) is classified as a toxic pollutant of high priority, because its effects on human health (toxicity) are similar to those of arsenic. However, unlike arsenic, the removal of antimony from polluted waters is still not well understood. In the present study the removal of common antimony species in water, namely, Sb(III) and Sb(V), was investigated by the addition of iron-based coagulants. The applied coagulants were Fe(II), Fe(III), and equimolar mixed Fe(II)/Fe(III) salts and the experiments were performed with realistic antimony concentrations in the range 10–100 μg/L, by using artificially polluted tap water solutions. Sb(III) removal by Fe(III) provided better adsorption capacity at a residual concentration equal to the drinking water regulation limit of 5 μg/L, that is, Q5 = 4.7 μg Sb(III)/mg Fe(III) at pH 7, which was much higher than the value achieved by the addition of Fe(II) salts, that is, Q5 = 0.45 μg Sb(III)/mg Fe(II), at the same pH value. Similarly, Sb(V) was more efficiently removed by Fe(III) addition, than by the other examined coagulants. However, Fe(III) uptake capacity for Sb(V) was found to be significantly lower, that is, Q5 = 1.82 μg Sb(V)/mg Fe(III), than the corresponding value for Sb(III). The obtained results can give a realistic overview of the efficiency of conventionally used iron-based coagulants and of their mixture for achieving Sb concentrations below the respective drinking water regulation limit and therefore, they can be subsequently applied for the designing of real-scale water treatment units

Phosphate Removal Using Polyethylenimine Functionalized Silica-Based Materials

In water and wastewater, phosphate anions are considered critical contaminants because they cause algae blooms and eutrophication. The present work aims at studying the removal of phosphate anions from aqueous solutions using silica particles functionalized with polyethylenimine. The parameters affecting the adsorption process such as pH, initial concentration, adsorbent dose, and the presence of competitive anions, such as carbonate, nitrate, sulfate and chromate ions, were studied. Equilibrium studies were carried out to determine their sorption capacity and the rate of phosphate ions uptake. The adsorption isotherm data fitted well with the Langmuir and Sips model. The maximum sorption capacity was 41.1 mg/g at pH 5, which decreased slightly at pH 7. The efficiency of phosphate removal adsorption increased at lower pH values and by increasing the adsorbent dose. The maximum phosphate removal was 80% for pH 5 and decreased to 75% for pH 6, to 73% for pH 7 and to 70% for pH 8, for initial phosphate concentration at about 1 mg/L and for a dose of adsorbent 100 mg/L. The removal rate was increased with the increase of the adsorbent dose. For example, for initial phosphate concentration of 4 mg/L the removal rate increased from 40% to 80% by increasing the dose from 0.1 to 2.0 g/L at pH 7. The competitive anions adversely affected phosphate removal. Though they were also found to be removed to a certain extent. Their co-removal provided an adsorbent which might be very useful for treating waters with low-level multiple contaminant occurrence in natural or engineered aquatic systems

Use of novel composite coagulants for arsenic removal from waters : experimental insight for the application of polyferric sulfate (PFS)

In the present study, several pre-polymerized coagulants of iron and aluminum were tested for their efficiency towards As(V) and As(III) removal from water sources. The results showed that the pre-polymerized coagulants of iron, such as poly-ferric sulfate and poly-ferric silicate chloride, were very efficient for As(V) removal. With regard to As(III) removal, among all examined coagulants, including the conventional ferric chloride, only the poly-ferric sulfate (PFS) was able to reduce As(III) to concentrations below the drinking water regulation limit of 10 μg/L. In contrast, all tested composite coagulants based on aluminum were not capable of removing efficiently both species of arsenic. PFS addition in water containing 4 mM of alkalinity and 25 μg/L of As(V) and As(III) (i.e., total arsenic concentration 50 μg/L) resulted in finished water with less than 5 μg/L arsenic, only by dosing 5 mg Fe-PFS/L at pH 7, whereas, simultaneously, the residual iron concentration was found well below its drinking water regulation limit of 200 μg/L. The use of PFS could provide a viable alternative for As(III) and As(V) removal at household treatment level for application in vulnerable communities, without the need of any additional treatment, such as oxidation of As(III) to As(V).In the present study, several pre-polymerized coagulants of iron and aluminum were tested for their efficiency towards As(V) and As(III) removal from water sources. The results showed that the pre-polymerized coagulants of iron, such as poly-ferric sulfate and poly-ferric silicate chloride, were very efficient for As(V) removal. With regard to As(III) removal, among all examined coagulants, including the conventional ferric chloride, only the poly-ferric sulfate (PFS) was able to reduce As(III) to concentrations below the drinking water regulation limit of 10 μg/L. In contrast, all tested composite coagulants based on aluminum were not capable of removing efficiently both species of arsenic. PFS addition in water containing 4 mM of alkalinity and 25 μg/L of As(V) and As(III) (i.e., total arsenic concentration 50 μg/L) resulted in finished water with less than 5 μg/L arsenic, only by dosing 5 mg Fe-PFS/L at pH 7, whereas, simultaneously, the residual iron concentration was found well below its drinking water regulation limit of 200 μg/L. The use of PFS could provide a viable alternative for As(III) and As(V) removal at household treatment level for application in vulnerable communities, without the need of any additional treatment, such as oxidation of As(III) to As(V)