Ernest Beinrohr

Preconcentration of palladium, platinum and rhodium by on-line sorbent extraction for graphite furnace atomic absorption spectrometry and inductively coupled plasma atomic emission spectrometry

A flow system combined with a segmentation technique was used to develop an efficient on-line sorbent extraction preconcentration system for palladium, platinum and rhodium for graphite furnace atomic absorption spectrometry (GFAAS) and inductively coupled plasma atomic emission spectrometry (ICP-AES). The investigated metals were preconcentrated as their bis(carboxylmethyl)dithiocarbamate (CMDTC) chelates on a microcolumn packed with XAD-4 after the off-line addition of solid CMDTC to the sample solution containing SnCl2 and hydrochloric acid. The sample, rinsing and eluent solutions were segmented by air to prevent dispersion. The eluate was collected on-line in a PTFE loop and was forced either into the graphite tube by nitrogen or into the ICP by using a carrier solution. The time duration of one preconcentration cycle was about 10 min. The influence of the acidity of the synthetic sample solution, the concentration of the complexing reagent and reducing agent, the flow-rate for preconcentration, the efficiency of the desorption and the influence of various matrices were also investigated. The detection limits (3σ) were 0.03, 0.1 and 0.01 ng/ml for Pd, Pt and Rh, respectively, using GFAAS detection. The method was applied for the analysis of polluted biological materials.

Determination of platinum in biotic and environmental samples by graphite furnace atomic absorption spectrometry after its electrodeposition into a graphite tube packed with reticulated vitreous carbon

SummaryTobacco, beans, slag and dust samples were digested with nitric and hydrochloric acids in high-pressure PTFE bombs. Pt in the sample solutions was electrochemically deposited at −0.9 to −1.2 V in a flow system incorporating a 3-electrode flow-through cell with a graphite counter and Ag/AgCl reference electrodes. A pyrolytically coated graphite tube packed with reticulated vitreous carbon (RVC) served as the working electrode with the RVC filling axially bored to let the light beam pass through the tube during the AAS measurements. This opening was plugged with a glass rod during the preconcentration step. After the electrodeposition the tube was placed into the graphite furnace and an atomization temperature of 2700°C was applied. The geometry of the cell, flow rate for electrodeposition, deposition potential and electrolyte composition were optimized. The absolute detection limit was found to be about 0.3 ng Pt.

On-line preconcentration of trace copper for flame atomic absorption spectrometry using a spherical cellulose sorbent with chemically bound quinolin-8-ol

Abstract Preconcentration was effected using a 50 mm × 2 mm i.d. minicolumn packed with a spherical cellulose sorbent with chemically bound quinolin-8-ol function groups (Ostorb Oxin). The column was connected to the nebulizer of the atomic absorption spectrometer and the sample solution and eluent (2 M hydrochloric acid) were sucked through it at a flow-rate of 2–3 ml min−1 by utilizing the negative pressure of the nebulizer. The experimental design was tested with the determination of traces of copper. Peak-area and peak-height measurements were compared. Owing to the simple calibration, the former method was used for quantification. The dynamic range was from 0.3 ng ml−1 (detection limit) to 5 μg ml−1 (breakthrough). The reproducibility in the concentration range 25 ng ml−1-5 μg ml−1 was better than 5%. Water-soluble inorganic salts, ammonia and sodium hydroxide were analysed. The accuracy of the results was checked by anodic-stripping voltammetry and by electrothermal AAS.

Determination of dissolved manganese in natural waters by differential pulse cathodic stripping voltammetry

A procedure based on differential pulse cathodic stripping voltammetry on the graphite electrode is described for the determination of dissolved manganese in natural waters buffered at pH about 6.5 with acetate solution. In order to avoid interference of iron(II) the addition of fluoride is used. The limit of detection is 3 μg/l for a deposition time of 6 min. Acidification and UV-irradiation are recommended for samples containing dissolved organic matter. Results of manganese determination in table mineral waters are reported and the possibility of manganese speciation is discussed.

Design and characterization of flow-through coulometric cells with porous working electrodes made of crushed vitreous carbon

SummaryThree types of flow-through, three-electrode cells with porous working electrodes made of crushed vitreous carbon were tested. The electrochemical properties of the cells were studied by hydrodynamic and cyclic voltammetry using potassium ferrocyanide test solutions. Depending on the volume of the porous working electrode, Nernstian behaviour and electrochemical yields up to 100% were observed for flow rates 1 to 7 ml/min. In the stopped-flow regime the cells exhibit thin-layer cell properties. The utility of the cells is demonstrated for on-line coulometric detection, continuous removal of impurities and dissolved oxygen and for anodic stripping coulometry of trace copper.

On-line electrochemical preconcentration of manganese for graphite furnace atomic absorption spectrometry using a flow-through electrochemical cell

A flow system incorporating a 2-electrode electrochemical microcell with a working electrode made from crushed reticulated vitreous carbon and a graphite furnace AAS instrument was used for the preconcentration and determination of trace amounts of Mn. The sample, rinsing and elution solutions were pneumatically transported through the system. Mn2+ ions can be quantitatively deposited both anodically and cathodically at a voltage of +1.5 to + 3 V and −2.5 to −4V, respectively applied to the cell. Samples of 0.1 to 1 ml volume were analyzed within 5–10 min. The limits of detection and determination were 8.7 and 29 pg, respectively. The reproducibility was 1.5 to 5%. The electrochemical behaviour of Mn in the flow system was studied by using a 3-electrode flow-through cell coupled on-line to a flame AAS instrument.

Design and evaluation of an on-line microcolumn pre-concentration technique for graphite furnace atomic absorption spectrometry

SummaryA simple method is described for trace element pre-concentration on a microcolumn of inner diameter 1 mm and 25 mm length. The column packed with methacrylate gel with bound 8-quinolinol groups (Spheron Oxin) is incorporated into the tip of the sampling arm of the autosampler. The sample solution, water, eluent and air streams are switched with an eight-port valve. The flow-rate at pre-concentration is about 0.14 ml/min. After washing out the residues of the sample matrix from the column, the collected elements are eluted with 1 mol/l HNO3 directly into the graphite tube of the atomizer. The reproducibility of the method was found to be better than 5%. The method was used for the determination of Pb in NaCl.

Electrolytic sample pretreatment in atomic spectrometry: A review

The use of electrolysis in analytical atomic spectrometry is reviewed. Topics such as electrodeposition for analyte enrichment, electrochemical sample pretreatment and hydride generation are discussed. The use of batch and flow-through electrochemical cells is compiled and critically evaluated. Flow-through cells with porous working electrodes were found to provide the best performance for analyte enrichment.

Flow-through anodic stripping coulometry and anodic stripping coulometry with collection for the simultaneous absolute determination of copper, lead, cadmium and zinc

Abstract Flow-through electrochemical cells with porous working electrodes made of crushed reticulated vitreous carbon and plated with mercury were used for the absolute determination of copper, lead, cadmium and zinc by anodic stripping coulometry and anodic stripping coulometry with collection in a flow system. The system consisted of a peristaltic pump, pneumatic pulse damper, electrochemical flow-through scrubber to remove impurities and dissolved oxygen from the flowing electrolyte, sample injection port and two serial flow-through cells with porous working electrodes. Trace metals from the injected sample volume were deposited at the working electrode of the first cell, then stripped by scanning the potential to positive values and finally collected at the second cell. Both the stripping and collection currents were registered and integrated. The conditions for a quantitative deposition, stripping and collection were investigated.

Anodic stripping coulometry with collection for absolute trace analysis of lead, using flow-through electrochemical cells with porous working electrodes

SummaryFlow-through electrochemical cells with porous working electrodes made of crushed reticulated vitreous carbon and plated with mercury were used for absolute analysis of trace amounts of lead by anodic stripping coulometry with collection (ASCWC) in a flow system. The role of mercury coating, flow rate and pH were investigated. The coulombic content of the collection peak corresponded to the theoretical values calculated by Faradays law in a concentration range from about 10−9 to 10−6 mol/l. The relative error and the relative standard deviation was +0.15% and 0.8%, respectively for 2×10−6 mol/l analyte concentration. The absolute detection limit (3 s) was 0.1 ng of Pb, the linear response range 7×104.