Saulius Armalis

Supported liquid membrane coupled on-line to potentiometric stripping analysis at a mercury-coated reticulated vitreous carbon electrode for trace metal determinations in urine

A method for trace metal determinations in complex matrices is presented. The method combines supported liquid membrane (SLM) sample clean-up and enrichment with potentiometric stripping analysis (PSA) in a flow system using reticulated vitreous carbon (RVC) as the electrode material. The membrane contained 40% m/m di-2-ethylhexylphosphoric acid dissolved in kerosene. Lead was used as a model substance in high-purity water and urine samples. The samples were enriched after a simple pH adjustment. The SLM enrichment time was 10 min when the last 5 min electrodeposition on the RVC electrode at -1.0 V (versus Ag/AgCl) was performed simultaneously. The influence of various experimental parameters such as deposition time, deposition potential and flow rate on the lead signal was investigated. With a 10 min SLM enrichment including a 5 min deposition time, the detection limit for lead was 0.3 microgram l-1. The relative standard deviation for lead concentrations in the range 4-20 micrograms l-1 was 0.05%. The overall SLM-PSA system was found to be stable for at least 100 urine analyses. The method was validated by running a reference urine sample. The result obtained (five replicates) was 9.7 micrograms l-1 (standard deviation 1.8 micrograms l-1) which is within the recommended range of 9.2-10.8 micrograms l-1.

Wet deposition of elemental carbon in Lithuania

Elemental carbon (EC) was measured in monthly precipitation samples at 14 rural sites in Lithuania from December 1986 to June 1990. The amount of EC in the sample was determined by the light reflectance method after a procedure including the filtration through a 0.2-micron polyamide membrane filter, the chemical digestion of biogenic material and the dispersion of the mixture in an ultrasonic bath. Monthly elemental carbon concentrations in the precipitation samples during the measurement period at the Preila site varied from 8 to 530 micrograms l-1 with a volume-weighted mean of 100 micrograms l-1. The range of EC monthly deposition fluxes was from 0.5 to 25 mg m-2 month-1 for all the sites. The wet deposition of elemental carbon is doubled during the cold season of the year. The estimated mean value of EC washout ratio for Preila site is 97 (range 5-243). An even distribution of the elemental carbon deposition is characteristic for the rural sites in Lithuania and mean monthly deposition flux can be estimated as 6.2 mg m-2 month-1. It results in the deposition of approximately 4800 t of elemental carbon to the area of Lithuania annually.

VOLTAMMETRIC DETERMINATION OF 2-AMINOFLUORENE AND 2,7-DIAMINOFLUORENE USING CARBON PASTE ELECTRODE

ABSTRACT The voltammetric determination of 2-aminofluorene and 2,7-diaminofluorene based on their oxidation on carbon paste electrode is described. Britton-Robinson buffer and pH ranges 1–3 and 10–12 are recommended for the simultaneous determination of 2-aminofluorene and 2,7-diaminofluorene. The sensitivity of the determination can be enhanced substantially by adsorptive accumulation of analytes on carbon paste electrode in the pH range 10–12. The detection limits for the accumulation time 200 s were evaluated as 2.10−7 and 1.10−7 mol L−1 for 2-aminofluorene and 2,7-diaminofluorene, respectively. Relative standard deviations for the concentration range 1−10 × 10−7 mol L−1 do not exceed 10%.

Stripping potentiometry signal enhancement using mercury film-coated reticulated vitreous carbon working electrode

The effect of enhancement of stripping potentiometry signals of trace metals by using a mercury film coated reticulated vitreous carbon flow-through electrode is described. The advantage of such a system is the possibility of the efficient in situ removal of oxygen by exhaustive electrolysis in a small electrode volume during the short stop of the flow after the main deposition time. This results in a considerable enhancement of the analytical signals and also a time saving due to elimination of the unnecessary deaeration procedure.

A study of the distribution of lead, cadmium and copper between water and kaolin, bentonite and a river sediment

Experiments were carried out to monitor the equilibrium distribution of lead, cadmium and copper between an aqueous phase modelling natural water and a solid phase modelling natural sediment, under varying conditions. The aqueous phase was analysed using ETAAS and differential pulse anodic stripping voltammetry (DPASV), whereas XRD and FTIR were used to study the solid phase. Sorption isotherms at constant pH were measured. Conditional distribution constants were calculated as functions of the pH, the time of equilibration and the amount of solid material. The results obtained stress the need for standardization of the approaches to the study of water-sediment interactions in order to be able to evaluate and compare the extensive data from field measurements and to predict these interactions.

Stripping Analysis of Trace Metals at a Flow-Through Reticulated Vitreous Carbon Electrode after the Preconcentration by Supported Liquid Membrane Technique

Abstract The performance of a flow-through mercury coated reticulated vitreous carbon (RVC) electrode in the potentiometric stripping analysis (PSA) of trace metals has been examined. A wall-jet glassy carbon cell was used for the comparative experiments. Experimental parameters influencing the stripping signals have been optimised in order to use the stripping analysis after the preconcentration and matrix isolation by supported liquid membrane (SLM) technique. The SLM with di-2-ethylhexyl-phosphoric acid (DEHPA) as the extractant in the membrane liquid for proton driven transport of trace metals across the membrane has been chosen. Results presented for lead determination in river water demonstrate the analytical advantages of coupled technique SLM-PSA.