Walter Lund

Speciation analysis : why and how ?

SummaryThe different aspects of speciation analysis are reviewed. Species-specific instrumental techniques as well as various speciation schemes are considered for the determination of species of metals and metalloids, including organometallic compounds. The application of the methods are discussed in some detail for the analysis of natural waters, air, soil, sediment and biological samples. The relationship between metal species and bioavailability is also briefly dealt with.

Multi-element speciation of tea infusion using cation-exchange separation and size-exclusion chromatography in combination with inductively coupled plasma mass spectrometry

The speciation of metals in tea infusion was studied using ICP-MS. Twenty-four elements were studied in tea leaves and tea infusion, and the extraction efficiency of the infusion process was calculated. Cation-exchange separation based on solid-phase extraction cartridges was used for studying the charge of the dissolved species. Size-exclusion chromatography was used to obtain information about the molecular size of the metal–organic complexes. The organic material eluted from the column was detected by UV spectrometry at 227 nm. The results indicate that Mg, Mn and Rb are present in tea infusion as cations, which are probably not associated with organic material. Also, Ca, Fe, Co, Ni, Cu, Zn, Sr and Ba appear to be present mainly in cationic form, but there is in addition a certain non-cationic fraction. For Fe, Ni, Cu and Zn, the non-cationic species may be metal–organic complexes in the size range 4000–6000 Da, whereas Sr, Ba and Pb are associated with even larger molecules. Al is the metal with the most marked non-cationic behaviour in tea infusion; it is associated with molecules in two size ranges, viz ., 4000–6000 and 6500–8500 Da, respectively.

Use of thiourea in the determination of arsenic, antimony, bismuth, selenium and tellurium by hydride generation inductively coupled plasma atomic emission spectrometry

A study was made of thiourea as an agent for the pre-reduction and masking of interferences in the multi-element determination of arsenic, antimony, bismuth, selenium and tellurium by hydride generation inductively coupled plasma atomic emission spectrometry. Thiourea reduces arsenic and antimony from the pentavalent to the trivalent state, without preventing the determination of tetravalent selenium and tellurium. Thiourea also eliminates the interference from a number of metals in the determination of arsenic, antimony and bismuth, but it is not effective for selenium and tellurium.

Trace metal analysis by anodic-stripping voltammetry Effect of surface-active substances

The presence of cationic, anionic, and neutral surfactants and humic substances is shown to affect the peak heights of copper, lead and cadmium in synthetic sea-water analysed by differential pulse anodic-stripping voltammetry. At surfactant concentrations below 0.1 mg/l. the effect is insignificant, but at higher concentrations the peak heights usually decrease, although for copper an increase in the peak height was also observed. The peak heights do not depend to any great extent on the pH of the solution, except in alkaline solution and in the presence of humic substances. Adsorption and complex formation may account for the observed dependences.

Evaluation of amperometric detectors for high-performance liquid chromatography: analysis of benzodiazepines

Abstract The design of amperometric detectors for high-performance liquid chromatography is discussed. A simple flow cell with interchangeable working electrodes made from glassy carbon, carbon paste and mercury is described, and its performance is compared with commercially available cells, using both constant-potential and pulse-measuring techniques. The analysis of nitrazepam, diazepam and chlordiazepoxide was used as a model system; the detectors were used in the reduction mode and the mobile phase was methanol—water (60:40) containing 0.05 M ammonium acetate. The effects of various experimental parameters are reported. The detection limit was found to depend strongly on the reduction potential: at −0.93 V vs. Ag, ng of nitrazepam could be detected, whereas at −1.30 V the detection limit was 30 ng, owing to the high background current at this potential. A potential more negative than −1.1 V must be used for the detection of diazepam and chlordiazepoxide; at −1.30 V the detection limit was 300 ng for these compounds.

Speciation of Cu, Fe and Mn in beer using ion exchange separation and size-exclusion chromatography in combination with electrothermal atomic absorption spectrometry

Methods were developed for studying the speciation of Cu, Fe and Mn in beer. The charge of the metal species was determined using cation and anion exchange separation based on solid-phase extraction cartridges, and the molecular weight of the metal complexes was studied by size-exclusion chromatography. Electrothermal atomic absorption spectrometry was used off-line for the quantitative determination of the metals. It was found that the beer contained ligands that released Cu and Fe from the separation columns; therefore, special procedures for cleaning the columns (with EDTA) had to be developed. The speciation analysis indicated that Mn was probably present as Mn2+ in beer, whereas Fe was found as negatively charged complexes and Cu as both negative and positive species. Using globular proteins for calibration of the size-exclusion column, the complexes were found to be of the order of 4–12 kDa. The ligands responsible for the complexation of Fe and Cu may be compounds such as polymeric phenols or phytic acid. When the beer was spiked with Cu2+ and Fe3+, the added metal ions were recovered as negatively charged species, indicating that the beer contained free metal-complexing ligands. It was found that the total metal concentrations in beer could be determined by direct analysis of 1 + 9 diluted beer; the results agreed with those obtained after decomposition of the beer with HNO3–H2O2.

Anodic stripping voltammetry with the florence mercury film electrode. determination of copper, lead and cadmium in sea water

Abstract The use of the rotating glassy carbon electrode mercury plated in situ for anodic stripping voltammetry has been investigated. The choice of electrode material is discussed. The effect of instrumental parameters on the stripping response for copper, lead and cadmium in sea water is studied, the results being in accordance with the theory of thin film electrodes. The variation in the observed sensitivity for the three metals in sea water is discussed in terms of complex-forming ligands. Lastly the performance of the film electrode is compared to that of the hanging mercury drop electrode.

The determination of copper, lead, cadmium and zinc in human teeth by anodic stripping voltammetry

Abstract Differential pulse anodic stripping voltamrnetry and a hanging mercury drop electrode are used for the determination of copper, lead, cadmium and zinc in Norwegian teeth and pure hydroxyapatite. Special attention is given to the choice of decomposition procedure and the determination of the blank values. A complete dissolution of the tooth material and satisfactory blank values can be obtained by using decomposition with nitric acid in a Teflon bomb.

The application of electrodeposition techniques to flameless atomic absorption spectrometry : Part I. The determination of cadmium with a tungsten filament

The use of controlled-potential electrolysis-as a separation and preconcentration technique for metal wire flameless atomic absorption analysis has been studied. The metal to be determined is electrolyzed onto a thin tungsten wire, and then atomized by electrical heating of the filament in an inert atmosphere within an absorption cell. A detailed study of the effect of various experimental parameters on the determination of cadmium is presented. The detection limit was found to be 0.1 p.p.b. cadmium, for a 2-min electrolysis period. The absolute detection limit was 4·10-11 g. The method appears to be well suited for the determination of cadmium in samples with a complex matrix.

The application of electrodeposition techniques to flameless atomic absorption spectrometry : Part III. The determination of cadmium in urine

Abstract Cadmium in urine can be determined by a simple flameless atomic absorption technique, in which the metal is electrolyzed onto a thin platinum wire, followed by electrical heating of the wire. The technique is compared with the well-established flame procedure, involving extraction with APDC into MIBK. The data obtained by the two techniques are in good agreement. Large individual variations occur in the urinary concentration of cadmium for workers suspected of cadmium exposure. The group mean values for these workers lie in the range 4–5 p.p.b.; mean values for unexposed control groups are around 1 p.p.b. On a group basis, the results indicate a significantly higher urinary excretion of cadmium for the workers than for the control groups.