Monika Sadowska

Thallium (III) determination in the Baltic seawater samples by ICP MS after preconcentration on SGX C18 modified with DDTC

The main difficulty of speciation analysis of thallium lies in extremely low concentrations of Tl(III) in comparison to Tl(I), which is the dominating form of thallium in environmental samples. In this study, a sensitive method is presented for separation of trace amounts of Tl(III) from Tl(I) and preconcentration of Tl(III) using octadecyl silica gel modified with diethyldithiocarbamate (DDTC). Under optimal conditions, only Tl(III) is retained on the sorbent, and then eluted with 96% ethanol. After chemical decomposition of Tl(III)-DDTC complex, thallium is determined by inductively coupled plasma mass spectrometry. High performance liquid chromatography with ICP MS detection was used to control the correctness of the obtained results. Parameters affecting solid phase extraction (SPE) such as pH, type, concentration and volume of eluent, breakthrough volume, and the impact of sample salinity (chlorides) and other interfering ions (Cd(II), Zn(II), Pb(II), Cu(II), Sn(II)) were investigated. The limit of detection (LOD), evaluated for 2 mL of sample solution, was 0.10 ng for Tl(I) and 0.43 ng for Tl(III). The method was applied to the determination of Tl(I) and Tl(III) in the Baltic seawater samples enriched in both thallium species.

TlI and TlIII presence in suspended particulate matter: speciation analysis of thallium in wastewater

Environmental context Thallium occurs in the environment in two oxidation states, with TlIII being 1000-fold more toxic than TlI. We present a fractionation and speciation study of thallium in suspended particulate matter from highly polluted wastewater samples, and elucidate the dominant forms of thallium. Abstract Thallium (Tl) is a toxic element, whose toxicity is affected by its redox state. Compared with TlIII, TlI is thermodynamically more stable and less reactive; therefore in aquatic environments, dissolved thallium is mostly present as TlI. However, TlIII could be 1000 times more toxic than TlI. A combination of a fractionation and a speciation study carried out in highly polluted wastewater samples from a mining area in southern Poland in order to characterise chemical speciation of Tl in physically defined fractions is presented here. Total, particulate and dissolved thallium was determined. A leaching experiment based on forming TlIII complexed with diethylene triamine penta-acetic acid – a TlIII–DTPA complex – was performed in filters containing suspended particulate matter after single (0.45µm) and sequential filtration (15 + 0.45µm) of wastewater samples. This is the first speciation study of Tl carried out in suspended particulate matter. The results obtained indicate that the dominant form of Tl in suspended particulate matter is TlI, but TlIII could be found in suspended particulate matter fractions larger than 0.45µm.

Selective and sensitive electrochemical device for direct VB2 determination in real products.

The developed by us electrochemical device for vitamin B2 (VB2; riboflavin) determination, without preconcentration step, in real products exhibits high sensitivity, selectivity, stability and low detection limit compared to those described in the literature. The determination procedure was based on the monitoring of the reduction current signal of VB2 bound with dsDNA anchored to the electrode surface through intermediary - carboxyphenyl layer. The application of such intermediary layer formed during electroreduction of appropriate diazonium salt at CV peak potential guarantees high efficiency of hybridization process and thus fully available places for VB2 interaction. Moreover, such intermediary layer provides good electrical contact, what is very important in the case of electrochemical sensors. The analytical range of work of the proposed VB2 sensor was between 0.08-1µM (30-377μgL-1) of riboflavin concentration. The obtained detection (LOD) and quantification limits (LOQ) were 24±2 and 55±5μgL-1, respectively. The proposed VB2 detection method was used for determination of riboflavin content in commercially available dietary supplements and yolk of hen egg samples. The accuracy of the obtained data was proved using comparison with an independent method (HPLC FLD).

The role of phytochelatins in Sinapis alba L. response to stress caused by two toxic elements As and Tl

Phytochelatins (PCs) play an important role in the detoxification and homeostasis processes in plants, since xenobiotics complexed by sulfhydryl groups are less toxic than the free ions. This paper describes studies related to PCs synthesis in Sinapis alba L. exposed to As and Tl salts, and in particular to the identification of the PC complexes that are formed in white mustard tissues. To reach the goal, two analytical methods were applied – high-performance liquid chromatography with fluorescent detection analysis after derivatisation of thiol compounds and high-performance liquid chromatography with electrospray ionization mass spectrometry (HPLC ESI MS). The study confirmed the synthesis of PCs in all plant organs under the influence of As salt. Moreover two As-PC complexes were identified: As-PC3 and As-PC4. While in the case of Tl – although that element strongly influenced the growth of Sinapis alba L. and to a great extent was transported to above-ground organs – no PC complexes or free PCs were found in plants exposed to Tl salt. Although both elements exist in mustard plant tissues at their trivalent oxidation state, showing high affinity to thiol groups, a defence mechanism associated with the synthesis of PC occurred only in case of arsenic.

Sample Pretreatment for Trace Speciation Analysis

Speciation analysis is already a challenge, and speciation analysis at trace levels is even more difficult [1]. The analytes might be of anthropogenic origin [2] (usually the concentrations are slightly increased) or naturally occurring (geochemical background) [3]. Procedures applied for speciation analysis must ensure low limits of detection as well as high selectivity, especially when the concentration of other sample compounds, potentially interfering, is much higher than the concentration of the analyte. Very often, there is no other choice but to use separation and/or preconcentration techniques. Methods applied for speciation studies should ensure isolation of the analyte from sample matrix without any changes of the original speciation and with highest possible efficiency [4–8]. The lower is the concentration of the analyte, the higher is the uncertainty of the results, because some additional steps have to be included in the analytical procedure. Deep interference in sample composition results in changes of the oxidation states and chemical compounds formed by the element of interest [9]. In case of water, soil or tissues the risk of changes in chemical speciation is created even by the sampling, not to mention chemical modifications or sample storage. Most published studies regarding speciation analysis were focused mainly on methods of separation and detection of the analytes. Determination is usually done using elemental detectors (inductively coupled plasma mass spectrometry [ICP-MS], ICP optical emission spectrometry [OES], graphite furnace atomic absorption spectroscopy [GF-AAS]) or molecular detectors (electrospray ionization [ESI] or time of flight [TOF] coupled with mass spectrometry [MS]) directly after separation on chromatographic column, or indirectly after separation using, for example, solid phase extraction (SPE). Considering how fragile are the equilibria between speciation forms, the best solution would be to determine speciation directly in the analyzed object, using techniques that can differentiate between oxidation states. In general, only a few techniques allow performing nondestructive speciation analysis of solids or water samples. For water samples, the direct voltammetry technique could be applied [10] but the limit of quantification (LOQ) is too high for trace element speciation. Voltammetric methods can be proposed for (indirect) speciation analysis of As, Tl, and Se. In water samples containing As(III) and As(V) it is possible to perform speciation analysis based on cathodic stripping voltammetry (CSV) measurements. By varying the composition of the supporting electrolyte it is possible to differentiate between As(III) and As(V). Addition of mannitol into the supporting electrolyte leads to detection of only trivalent arsenic, and then As(III) is transferred to As(V) during ultraviolet (UV) oxidation of organic matter and the total As is determined [11]. Thallium speciation can be studied when glassy carbon working electrode is modified with an ion exchange resin, which allows to selectively accumulate trivalent thallium as a chloride complex. This method was applied to determine Tl speciation in water samples modified by an addition of large amounts of chlorides [12]. Another possibility is modification of the supporting electrolyte: addition of diethylenetriaminepentaacetic acid (DTPA) to inactivate Tl(III) (electrochemically) and addition (directly to the voltammetric cell) of anion exchange resin to adsorb the organic matter. In this case, only monovalent thallium is accumulated [13, 14]. Determination of Se(IV) and selenocysteine was done simultaneously in the aqueous phase using HCl as an electrolyte, while determination of dimethyldiselenide was performed in the organic phase after extraction with CH2Cl2. Detection was done with differential pulse CSV at a hanging mercury drop electrode [15]. Also chromium speciation in water can be determined indirectly after the addition of an anion exchange resin and a chelating agent to the cell. Then, only Cr(VI) is electroactive in the supporting electrolyte [16, 17]. For solid samples, all methods of speciation analysis, which do not require sample pretreatment, are based on the use of X-rays: Mössbauer spectroscopy, X-ray photoelectron spectroscopy, and X-ray absorption nearedge structure (XANES) spectroscopy [18–21]. Unfortunately, all of them have LOQ too high for the analysis of biotic environmental samples, especially on trace levels. However, XANES was successfully applied for speciation analysis of thallium in polluted soil, and allowed to determine the kind of minerals binding Tl(I) and Tl(III)